HomeMy WebLinkAbout17142Passive Solar Design Strategies:
Guidelines for Horne Building
Passive Solar Industries Council
National Renewable Energy Laboratory
Charles Eley Associates
With SufrPort From:
U.S. Department of Energy
Passive Solar Design Strategies: Guidelines for HODle Builders
San Diego, California
Passive Solar Industries Council
Solar Energy Research Institute
Charles Eley Associates
This document was prepared under the sponsorship of the Solar Energy Research
Institute and produced with funds made available by the United States Department
of Energy. Neither the United States Department of Energy. the Solar Energy
Research Institute. the Passive Solar Industries Councll nor any of its member
organizations. nor any of their employees. nor any of their contractors.
subcontractors. or their employees. makes any warranty. expressed or implied. or
assumes any legalliabil1ty or responsibility for the accuracy. completeness or
usefulness of any information. apparatus, product or process disclosed. or represents
that its use would not infringe privately owned rights. The views and opinions do not
necessarily state or reflect those of the United States government. the Solar Energy
Research Institute. or any agency thereof. This document was prepared with the
assistance and participation of representatives from many organizations. but the
views and opinions expressed represent general consensus and available information.
Unanimous approval by all organizations is not implied.
PASSIVE SOLAR DESIGN STRATEGIES CONTENTS
Guidelines
Part One. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1. Introduction to the Passive Solar Design Strategies Package. . . . . . . . . . . . . . . .2
2. Passive Solar Performance Potential .............................. 5
Part Two. Basics of Passive Solar, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , 7
1. Why Passive Solar? More than a Question of Energy. . . . . . . . . . . . . . . . . . . . 8
2. Key Concepts: Energy Conservation, Suntempertng, Passive Solar ............ 9
3. Improving Conservation Performance, , , , , , , , , , , , , , , , , , , , , , , , , . , , ,10
4. Mechanical Systems. . . , . , . . , , , . . . , . , , , . , , . , , , , , . . , . , , . , , , . 13
5. South-Facing Glass. , .... , , , . , .. , . , . , . , . , .. , .. , .. , . , , .. , .. .14
6. Thennal Mass .... I • I I • I •• I ••••• I I I •••••••••••••••••••••• 15
7. Orientation.""" .. ,', ... , .. ".".,"',."."., .. " .. , .16
8. Site Planning for Solar Access, . . , . , , . . , , , . , , , , . , , , , . , . , , . , , , , , 17
9. Interior Space Planning. , ...... , . , , . , , . , , . , , . , .. , .. , .. , , . , , . 18
10. Putting it Together: The House as a System, . , . , . , , , . , . , , .. , . , .. , , . , 18
Part Three. Strategies for Improving Energy Per:formance in San Diego. California, .. , .... , . , , .. , .. , .. , .. , .. , .. , . , , .. , .. 21
1. The Example Tables, . . , . . , . , . , , , , , . , , , . . , , , , , . , , , , , . . , , . , , 22
2. Suntempering""""',.,",.".,"""', ........ ,, .. ,. ,23
3. Direct Gain. , . . , . . . . . . , . , , . , , . . , . , . . , . . , , . . , . . , . , , . , , . . 24
4. Sunspaces"...,.......,.,..,..,.,..".,....".".".,. 27
5. Thermal Storage Wall, , , , , , , . '.' . , , . , , , , . , , . , , . , ... , . , , . , , . , 30
6. Combined Systems .... , .. , . , .. , . , , . , ...................... 32
7. Natural Cooling Guidelines ............ , ...................... 32
Worksheets
Blank Worksheets, Data Tables, and Worksheet Instructions
Worked Example
DeSCription of the Example Building. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , .40
Filled in Worksheets. . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . , . . . . . . 43
Annotated Worksheet Tables. . . . . . . . . . . . . . . . . . . . , . . . . . . . . , . . . . . . . 48
Appendix
Glossary of Terms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Summary Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . , , . . . . . 54
Technical Basis for the Builder Guidelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
San Diego, CaUfomia
PASSIVE SOLAR DESIGN STRATEGIES
Acknowledgements
Passive Solar Design Strategies:
Guidelines jor Home Buaders
represents over three years of
effort by a unique group of
organizations and individuals.
The challenge of creating an
effective design tool that could
be customized for the specific
needs of builders in cities and
towns all over the U.S. called for
the talents and experience of
specialists in many different
areas of expertise.
Passive Solar Design
Strategies is based on research
sponsored by the United States
Department of Energy (DOE)
Solar Buildings Program, and
carried out primarily by the Los
Alamos National Laboratory
(LANL), the Solar Energy
Research Institute (SERI) and
the Florida Solar Energy Center
(FSEC).
The National Association of
Home Builders (NAHB) Standing
Conunittee on Energy has
provided invaluable advice and
assistance during the
development of the Guidelines.
Valuable information was
drawn from the 14-country
International Energy Agency
(lEA), Solar Heating and Cooling
program, Task VIII on Passive
and Hybrid Solar Low Energy
Buildings (see next page for
more about the international
context of Passive Solar Design
Strategies) .
PSIC expresses particular
gratitude to the following
individuals: J. Douglas
Balcomb, SERI and LANL ,
whose work is the basis of the
Guidelines; Robert McFarland,
LANL, for developing and
progranuntng the calculation
procedures; Alex Lekov, SERI,
for assistance in the analysis;
Subrato Chandra and PhlUp W.
Fairey, FSEC, whose research
has guided the natural cooling
sections of the guidelines; the
members of the NAHB Standing
Committee on Energy, especially
Barbara B. Harwood, Donald L.
Carr, James W. Leach and
Craig Eymann, for the benefit of
their long experience in building
energy-efficient homes; at U.S.
DOE, Frederick H. Morse,
Director of the Office of Solar
Heat Technologies and Mary-
Margaret Jenior, Program
Manager; Nancy CarUsle and
Paul Notari at SERI; Helen
EngUsh, Executive Director of
PSIC; Michael Bell, former
Chairman of PSIC, and Layne
Ridley and Elena Marcheso-
Moreno, former Executive
Directors of PSIC; Arthur W.
Johnson, for technical
assistance in the development of
the Guidelines and worksheets;
Michael Nicklas, who worked
on the Guidelines from their
early stages and was
instrumental in the success of
the first pilot workshop in North
Carolina; Charles Eley, for his
help in every aspect of the
production of the Guidelines
package.
Although all the members of
PSIC, especially the Technical
Conunittee, contributed to the
financial and technical support
of the Guidelines, several
contributed way beyond the call
of duty. Stephen Szoke,
National Concrete Masonry
AssOCiation, Chairman of PSIC's
Board of Directors; James Tann,
Brick Institute of America,
Region 4, Chairman of PSIC's
Technical Committee; and Blon
Howard, NAHB National
Research Center, past Chairman
of the Technical Committee, all
gave unstlntingly of their time,
their expertise, and their
enthusiasm.
San Diego, California
Solar Design
Strategies and the
International Energy
Agency
Valuable Infonnation from the
International Energy Agency's
Solar Heating and Cooling
research program has been
integrated into Solar Design
Strategies.
Under the leadership of the
U.S. Department of Energy
(Michael J. Holtz, Operating
Agent on behalf of DOE) the lEA
Task VIII is prodUCing a series of
DesIgn Information Booklets on
a number of issues related to the
design and construction of
passive solar residential
buildings. Among the booklets
will be design guidelines for each
of the 14 nations participating in
Task VIII. Solar Design
Strategies is the U.S.
contribution to this part of the
Design Information Booklet
series.
All the lEA Task VIII Design
Information Booklets will be
available from PSIC. The
booklets include:
• Booklet 1: "Energy Design
Principles in Buildings" explains
the heat transfer principles
critical to the thermal comfort of
passIve solar buildings.
• Booklet 2: "Design Context"
presents a checklist of factors to
be consIdered in the design
process.
• Booklet 3: "Design
Guidelines" specifically
developed for each nation.
"Solar Design Strategies" will
present site-specific design
San Diego, California
PASSIVE SOLAR DESIGN STRATEGIES
guidelines for Cities and towns in
the U.S.
• Booklet 4: "Design Tool
Selection and Use" provides
guidance in the selection of
design tools appropriate for each
step of the design process.
• Booklet 5: "Construction
Details" identifies solutions to
construction problems unique to
passIve solar buildings.
• Booklet 6: "Passive Solar
Homes: Case Studies" highlights
the performance of buildings
constructed and mOnitored by
Task VIII countries.
• Booklet 7: "DesIgn
Language" written primarily for
design professionals and
students, deSCribes an approach
to generating whole building
design solutions based on
climate analysis and design-
centered analysis.
• Booklet 8: "Post-
Construction Activities"
discusses aspects of passive
homes that are unique and may
require attention by the
occupants and home builders.
PSIC would like to express its
thanks to the Task VIII member
nations for the wealth of
information their long-term
commitment to international
solar research has made
possible.
Passive Solar
Design Strategies
GUIDELINES
Passive Solar Industries Council
National Renewable Energy Laboratory
Charles Eley Associates
With Support From:
U.S. Department of Energy
PASSIVE SOLAR DESIGN STRATEGIES
Part One: Introduction
1. Introduction to the Passive Solar Design
Strategies Package
2. Passive Solar Performance Potential
1
San Diego, CaUfornla
2
1. Introduction to the
Passive Solar Design
Strategies Package
The idea. of passive solar 18
simple. but applying it e1fect1vely
does IeqWre iDformation and
attention to the details of design
and construction. Some passive
solar teclmJques are modest and
low-cost. and require only small
changes in a builder's standard
practice. At the other end of the
spectrum. some passive soJar
systems can almost eJlmtnate a
house's need for purchased
energy -but probably at a
relatively high ftmt cost.
In between are a broad range
of energy-conservtng passive
solar teclmJques. Whether or
not they are cost-effective,
practical and attractive enough
to offer a market advantage to
any individual builder depends
on very specific factors such as
local costs. cllmate and market
characteristics.
Passive Solar Design
Strategies: GUidellnesJor Home
BuUders 18 written to help give
builders the information they
need to make these decisions.
GUiDEUNES PART ONE: INTRODUCTION
Passive Solar Design Strategies
is a package in three basic parts:
• The GuideUnes contain
information abou~ passive solar
techniques and how they work.
and provides specific examples
of systems which will save
various percentages of energy:
• The Worksheeta o1l"er a
simple.fill-in-the-blank method
to pre-evaluate the performance
of a specific design.
• The Worked Example
demonstrates how to complete
the worksheets for a typical
residence.
BuilderGuide
A special builder-friendly
computer program called
BuUderGuld.e has been developed
to automate the calculations
involved in ftll1ng out the four
worksheets. The program
opemtes like a spreadsheet: the
user fiDs in values for the
building. and the computer
completes the calculations,
including all table lookups. and
prints out the answers. The
results are the same as if you
completed the worksheets
manually but it is much faster.
more cODVienient. and less prone
to arithmetic error. Many design
variations can be· evaluated very
quickly.
BuUderGuld.e Is available from
the Passive Solar Industries
Council. See page 53 for the
address. Computer data files
contain1ng the information on
pages 48-49 are available for
205 locations within the United
States. The user can then adjust
for local conditions so
performance can be evaluated
virtually anywhere.
PASSIVE SOLAR DESIGN STRATEGIES
The Guidelines
Some principles of passive solar
design remain the same in every
climate. But the important
thing about passive solar is that
it makes better use of the
opportunities in a house's
surroundings. So, many
fundamental aspects of the
passive solar house's design will
depend on the conditions in a
small local area, and even on the
features of the building site
itself. Many of the suggestions
in this section apply specifically
to San Diego, CalifOrnia, but
there is also information in each
section of the booklet which will
be useful in any climate.
Part One introduces Passive
Solar Design Strategies, and
presents the performance
potential of several different
passive solar systems in the San
Diego climate. Although in
practice many factors will affect
actual energy performance, this
information wUl give you a
general idea of how various
systems will perform in your
area.
Part Two discusses the basic
concepts of passive solar design
and construction: what the
advantages of passive solar are,
how passive solar relates to
other kinds of energy
conservation measures, how the
primary passive solar systems
work, and what the builder's
most important considerations
should be when evaluating and
using different passive solar
strategies.
Part Three gives more
specific advice about techniques
for suntempering, direct gain
systems, thermal storage mass
walls and sunspaces, and for
natural cooling strategies to help
offset air-conditioning needs.
The Example Tables in Part
Three are also related to
Worksheet numbers, so that you
can compare them to the
designs you are evaluating. For
example, the Passive Solar
Sunspace Example Case which
uses 40% less energy than the
Base Case House (page 29) has:
• a Conservation Performance
Level of approximately 16,688
Btu/yr-sf,
• an Auxiliary Heat
Performance Level of
approximately 7,799 Btu/yr-sf,
and
• a Sununer Cooling
Performance Level of 4,379
Btu/yr-sf.
(In this example, the energy
savings are achieved by no
increase in insulation over the
Base Case, adding a sunspace
with south glazing area equal to
7% of the house's floor area, and
using a ceUing fan to cut some of
the air conditioning load.)
A Base Case house is
compared with a series of
Example cases to Ulustrate
exactly how these increased
levels of energy-efficiency might
be achieved.
3
The Base Case House is a
reasonably energy-efficient
house based on a 1987 National
Association of Home Builders
study of housing characteristics,
divided into seven different
regions. The Base Case used for
San Diego, California is from the
1,000-2,500 heating degree days
region. The floor construction
is assumed to be slab-on-grade.
because this is typical in
CalifOrnia.
The examples show how to
achieve 20. 40 and 600Al energy-
use reductions using three basic
strategies:
• Added Insulation:
increasing insulation levels
without adding solar features.
• 8untemperiDg: increasing
south-facing glazing to a
maximum of 7% of the house's
total floor area. but without
adding thermal mass (energy
storage) beyond what is already
in the framing, standard floor
coverings and gypsum wall-
board and ceUing surfaces.
Insulation levels are also
increased.
San Diego. CaUfomla
4
• Passive Solar: using three
different design approaches:
Direct Gain, Sunspace, and
Thermal Storage Wall, and
increased levels of insulation.
For all strategies, the energy
savings indicated are based on
the assumption that the energy-
effiCient design and construction
guidelines have been followed. so
the houses are properly sited
and tightly built with high-
quality windows and doors.
The GUidelines section has
been kept as brief and
straightforward as possible, but
more detailed information is
available if needed. Some
references are indicated in the
text, and a list of other
information sources can be
found in the References. Also
included at the end of this book
are a brief Glossary, a summary
of the Example Tables for San
Diego, CalifOrnia, and two pages
explaining some of the
background and assumptions
behind the Guidelines and
Worksheets called Technical
BaSis for the Builder Guidelines.
San Diego, California
GUIDELINES PART ONE: INTRODUCTION
The Worksheets
The Worksheets are specifically
tailored for San Diego,
California, and are a very
important part of this package
because they allow you to
compare on paper different
passive solar strategies or
combinations of strategies, and
the effect that changes will have
on the overall performance of the
house.
The most effective way to use
the Worksheets is to make
multiple copies before you fill
them out the first time. You can
then use the Worksheets to
calculate several different
designs. For instance, you could
first calculate the performance of
the basic house you build now,
then fill out Worksheets for that
house plus added insulation
plus a sunspace, and then for a
third possibll1ty such as a
Thermal Storage Wall.
The Worksheets provide a
way to calculate quickly and
with reasonable accuracy how
well a design is likely to perform
in four key ways: how well it will
conserve heat energy; how much
the solar features will contribute
to its total heating energy needs;
how comfortable the house will
be; and how much the house's
annual cooling load (need for air
conditionf.ng) will be.
The Worksheets are
supported by "look-up" tables
containing pre-calculated factors
and numbers for the local area.
Some of the blanks in the
Worksheets call for information
about the house -for example,
floor area, prOjected area of
passive solar glazing, and so
forth. Other blanks require a
number from one of the tables -
for example, from the Solar
System Savings Fraction table or
from the Heat Gain Factor table.
The Worksheets allow
calculation of the following
performance indicators:
• Worksheet I: Conservation
Performance Level: determines
how well the house's basic
energy conservation measures
(insulation, sealing, caulking,
etc.) are working to prevent
unwanted heat loss in the
winter. The bottom line of this
Worksheet is a number
measuring heat loss in British
thermal units per square foot
per year (Btu/sf-yr) -the lower
the heat loss, the better.
• Worksheet D: Auxiliary
Heat Performance Level:
determines how much heat has
to be supplied (that is, provided
by the heating system) after
taking into account the heat
contributed by passive solar.
This worksheet arrives at a
number estimating the amount
of heating energy the house's
non-solar heating system has to
provide in Btu/yr-sf. Again. the
lower, the better.
• Worksheet m: Thermal
Mass/Comfort: determines
whether the house has adequate
thermal mass to assure comfort
and good thermal performance.
Worksheet III calculates the
number of degrees the
temperature inside the house is
likely to vary, or "swing", during
a sunny winter day without the
heating system operating. A
well-designed house should have
a temperature swing of no more
than 13 degrees, and the less
the better.
PASSIVE SOLAR DESIGN STRATEGIES
• Worksheet IV: Summer
CooUng Performance Level:
indicates how much air
conditioning the house will need
in the sununer (it is not.
however. intended for use in
sizing equipment. but as an
indication of the reductions in
arulUal cooling load made
possible by the use of natural
cooling). The natural cooling
guidelines should make the
house's total cooling load -the
bottom line of this Worksheet. in
Btu/yr-sf -smaller than in a
"conventional" house.
So. the Worksheets provide
you with four key numbers
indicating the projected
performance of the various
designs you are evaluating.
• The Worked Example: To
assist in understanding how the
design strategies outlined in the
Guidelines affect the overall
performance of a house. a
worked example is included.
The example house. constructed
of materials and design elements
typical of the area. is a one
story. single-family 1500 sf
passive solar design. Various
design features. such as direct
gain spaces. sunspaces.
increased levels of insulation
and thermal mass. are included
to illustrate the effects combined
systems have on the
performance of a house. Also.
many features are covered to
demonstrate how various
conditions and Situations are
addressed in the worksheets. A
description of the design
features. along with the house
plans. elevations and sections.
are included for additional
support information.
2. Passive Solar
Performance
Potential
The energy performance of
passive solar strategies varies
Significantly. depending on
climate. the specifiC design of
the system. and the way it is
built and operated. Of course.
energy performance is not the
orily consideration. A system
which will give excellent energy
performance may not be as
marketable in your area or as
easily adaptable to your designs
as a system which saves less
energy but fits your other needs.
In the following table. several
different passive solar systems
are presented along with two
numbers which indicate their
performance. The Percent Solar
Savings is a measure of how
much the passive solar system is
reducing the house's need for
purchased energy. For example.
the Percent Solar Savings for the
B~se Case is 21.6%. because
even in a non-solar house. the
south-facing windows are
contributing some heat energy.
The Yield is the annual net
heating energy benefit of adding
the passive solar system.
measured in Btu saved per year
per square foot of additional
south glazing.
The figures given are for a
1.500 sf. single-story house with
a slab floor. The Base Case has
45 sf of south-faCing glazing.
For the purposes of this
example. the Suntempered
house has 100 sf of south-facing
glass. and each passive solar
system has 145 sf.
5
The energy savings
presented in this example
assume that all the systems are
designed and built according to
the suggestions in these
Guidelines. It's also important
to remember that the figures
below are for annual net heating
benefits. The natural cooling
section in Part Three gives
advice about shading and other
techniques which would make
sure the winter heating benefits
are not at the expense of higher
summer cooling loads.
Please note that throughout
the Guidelines and Worksheets
the glazing areas given are for
the actual net area of the glass
itself. A conunon rule of thumb
is that the net glass area is 80
percent of the rough frame
opening. For example. if a south
glass area of 100 sf is desired,
the required area of the rough
frame opening would be about
125 sf.
San Die,o. CaUfomla
6
Performance Potential of Passive Solar Strategies In San Diego, California
1,500 sf, Single Story House
GUIDELINES PART ONE: INTRODUCTION
Yield Percent Btu Saved per Solar Square Foot of Case Savings South Glass
8aseCase 21.6 not applicable (45 sf of south-facing double glass) Suntempered 42.8 87,941
(100 sf of south-facing double glass)
Direct Gain (145 sf of south glass) Double Glass 57.0 81,762 Triple or low-e glass 57.0 83,129 Double glass with R-4 night insulation 1 59.9 90,880 Double glass with R-9 night insulation 1 60.6 92,542
Sunspace (145 sf of south glass) Attached with opaque end walls2 49.9 66,899
Attached with glazed end walls2 49.2 64,998 Semi-enclosed with vertical glazing3 53.4 73,818 Semi-enclosed with 50' sloped glazing3 61.2 93,867
Thermal Storage Wall -Masonry/Concrete (145 sf of south glass) Black surface, double glazing 49.9 66,167 Selective surface, single glazing 59.7 90,371 Selective surface, double glazing 58.3 87,165
Thermal Storage Wall-Water Wall (145 sf of south glass) Selective surface, single glazing 65.2 103,580
1. Night insulation is assumed to cover the south glass each night and removed when sun is available. Experience has shown that many homeowners find this inconvenient and so the potential energy savings are often not achieved. Using low-e or other energy-efficient glazing is
more reliable.
2. The attached sunspace is assumed to have, in addition to glazed walls, roof glazing at a slope of 30 degrees from the horizontal, or a 7:12
pitch. (See diagram SSB1 in the Worksheets.)
3. The semi-enclosed sunspace has only the south wall exposed to the out-of-doors. The glazing has a slope of 50' from the horizontal, or a 14:12 pitch. The side walls are adjacent to conditioned space in the house. (See diagram SSD1 in the Worksheets.)
SaD Diego. CaUfornia
PASSIVE SOLAR DESIGN STRATEGIES
Part Two: Basics of Passive Solar
1. Why Passive Solar? More than a Question of
Energy
2. Key Concepts: Energy Conservation.
Suntempering. Passive Solar
3. Improving Conservation Performance
4. Mechanical Systems
5. South-Facing Glass
6. Thermal Mass
7. Orientation
8. Site Planning for Solar Access
9. Interior Space Planning
10. Putting it Together: The House as a System
7
San Diego. California
8
1. Why Passive Solar?
More than a Question
of Energy
Houses today are more energy-
efficient than ever before.
However, the vast ~ority of
new houses still ignore a lot of
energy saving opportunities -
opportunities available in the
sunlight falling on the house, in
the landscaping, breezes and
other natural elements of the
site, and opportunities in the
structure and materials of the
house itself, which, with
thoughtful deSign, could be used
to collect and use free energy.
Passive solar (the name
distinguishes it from "active" or
mechanical solar technologies) is
simply a way to take maximum
advantage of these
opportunities.
Home buyers are also
increasingly sophisticated about
energy issues, although the
average home buyer is probably
much more famUiar with
insulation than with passive
solar. The "energy crisis" may
be temporarily over, but vety few
people perceive their own
household energy bills as getting
smaller -quite the opposite. So
a house with Significantly lower
monthly energy costs year-round
will have a strong market
advantage over a comparable
house down the street, no
matter what international oil
prices may be.
But there are many different
ways to reduce energy bills, and
some are more marketable than
others. For instance, adding
insulation can markedly improve
San Diego, CaUfornia
GUIDELINES PART TWO: BASICS OF PASSIVE SOLAR
energy-effiCiency -but added
insulation is invisible to the
prospective home buyer. A
sunny, open living area lit by
south-facing windows, on the
other hand, may be a key selling
point. Windows in general are
popular with homebuyers, and
passive solar can make windows
energy producers instead of
energy liabilities.
Another example: high-
efficiency heating eqUipment can
account for significant energy
savings -but it won't be as
much fun on a winter morning
as breakfast in a bright.
attractive sunspace.
The point is not that a
builder should choose passive
solar instead of other energy-
conserving measures. The
important thing is that passive
solar can add not only energy-
efficiency, but also vety saleable
amenities -style, comfort,
attractive interiors, curb appeal
and resale value.
In fact, in some local
markets, builders report that
they don't even make specific
reference to "passive solar".
They just present their houses
. as the state of the art in energy-
efficiency and style, and they
use passive solar as a part of the
package
The U. S. Department of
Energy and the Solar Energy
Research Institute (SERI)
conducted extensive national
surveys of passive solar homes,
home owners and potential
buyers. Some key findings:
• passive solar homes work
-they generally require an
average of about 30% less
energy for heating than
"conventional" houses, with
some houses saving much more.
• occupants of passive solar
homes are pleased with the
performance of their homes (over
900Al ''vety satisfied"), but they
rank the comfort and pleasant
living enviromnent as just as
important (in some regions,
more important) to their
satisfaction, and in their
decision to buy the house, as
energy considerations.
• passive solar home owners
and lenders perceive the
resale value of passive solar
houses as high.
Advantages of Passive Solar
• Energy performance: Lower energy bills all year-round
• Attractive living environment: large windows and views, sunny interiors, open floor plans
• Comfort: quiet (no operating nOise), solid const~ction, warmer in winter, cooler in summer (even dunng a power failure)
• Value: high owner satisfaction, high resale value
• Low Maintenance: durable, reduced operation and repairs
• Investment: independence from future rises in fuel costs, will continue to save money long after any initial costs have been recovered
• Environmental Concerns: clean, renewable energy to combat growing concerns over global warming, acid rain and
ozone depletion
PASSIVE SOLAR DESIGN STRATEGIES
2. Key Concepts:
Energy Conservation,
Suntempering,
Passive Solar
The strategies for enhancing
energy perfonnance which are
presented here fall into three
general categories:
• Energy Conservation:
insulation levels, control of air
infiltration, glazing type and
location and mechanical
equipment.
• Suntemperlng: a limited use
of passive solar techniques;
modestly increasing south-facing
window area, usually by
relocating windows from other
sides of the house, but without
adding thennal mass.
• Passive Solar: going beyond
conservation and suntempering
to a complete system of
collection, storage and use of
solar energy: using more south
glass, adding significant thennal
mass, and taking steps to
control and distribute heat
energy throughout the house.
What is immediately clear is
that these categories overlap.
For instance, a good energy-
conservation package is the
necessary starting point of all
well-designed suntempered and
passive solar houses. There's no
use collecting solar energy if it is
immediately lost through leaky
windows or poorly insulated
walls.
In the same way, many of
the measures that are often
considered part of suntempering
or passive solar -such as
orienting to take advantage of
summer breezes, or landscaping
for natural cooling, or faCing a
long wall of the house south -
can help a house conserve
energy even if no "solar" features
are planned.
The essential elements in a
passive solar house are south-
facing glass and thermal mass.
In the simplest tenns, a
passive solar system collects
solar energy through south-
facing glass and stores solar
energy in thermal mass -
materials with a high capacity
for storing heat (e.g., brick,
concrete masonry, concrete slab,
tile, water). The more south-
facing glass is used in the
house. the more thennal mass
must be provided, or the house
will overheat and the solar
system will not perfonn as
expected.
With too much glass and/ or
insuffiCient mass, solar energy
can work too well, and the house
can be uncomfortably hot even
on a winter day.
9
Although the concept is
simple, in practice the
relationship between the amount
of glazing and the amount of
mass is complicated by many
factors, and has been a subject
of conSiderable study and
experiment. From a comfort and
energy standpOint, it would be
difficult to add too much mass.
Thennal mass will hold warmth
longer in winter and keep
houses cooler in summer. But
thennal mass has a cost, and so
adding too much mass for just
thennal storage purposes can be
unnecessarily expensive.
The following sections of the
Guidelines discuss the size and
location of glass and mass, as
well as other considerations
which are basic to both
suntempered and full passive
solar houses: improving
conservation perfonnance;
mechanical systems: orientation:
site planning for solar access:
interior space planning: and
taking an integrated approach to
the house as a total system.
San Diego, CaIlfol'Dia
10
3. Improving
Conservation
Performance
The techniques described in this
section relate to Worksheet I:
Conservation Performance
Level. which measures the
house's heat loss. The energy
conselVation measures that
reduce heat loss also tend to
reduce the house's need for air
conditioning.
The most important
measures for improving the
house's basic ability to conselVe
the heat generated either by the
sun or by the house's
conventional heating system are
in the following areas:
• Insulation
• Air lnfiItration
• Non-solar glazing
Insulation
Adding insulation to walls,
floors, ceilings, roof and
foundation improves their
thermal reSistance (R-value) -
their resistance to heat flowing
out of the house.
A quality job of installing the
insulation can have almost as
much effect on energy
performance as the R-value, so
careful construction supelVision
is important. An inspection just
before the drywall is hung
identifies improvements which
are easy at that time but wUl
make a big difference in the
energy use of the home for years
to come.
San Diego, CaUforDia
GUIDELINES PART TWO: BASICS OF PASSIVE SOLAR
The thermal resistance of
ceiling/roof assembUes. walls
and floors is affected not only by
the R-value of the insulation
itself. but also the resistance of
other elements in the
construction assembly -
framing effects, sheathing.
interior drywall, and so on. The
Worksheets include tables that
show Equivalent Construction
R-Values which account for
these and other effects. For
instance, ventUated crawlspaces
and unheated basements
provide a buffering effect which
is accounted for in the
Worksheet tables.
With attics, framing effects
are m.in1mized if the insulation
covers the ceiling trusses, either
by using blown-in insulation or
by running an additional layer of
batts in the opposite direction of
the ceiling jOists. Ridge and/or
eave vents are needed for
ventUation.
Insulation In an Attic Insulation should extend over the top ceiling joists and ventilation should be provided at
the eaves.
In framed ceiling/roof
assemblies, an insulating
sheathing over the top decking
wUl increase the R-value.
Slab edge insulation should
be at least two feet deep.
extending from the surface of the
floor. Materials for slab edge
insulation should be selected for
underground durability. One
material with a proven track
record is extruded polystyrene.
Exposed insulation should be
protected from physical damage
by attaching a protection board,
for instance, or by covering the
insulation with a protective
surface.
Heated basement walls
should be fully insulated to at
least four feet below grade, but
the portion of the wall below that
depth only needs to be insulated
to about half the R-value of the
upper portion. Insulation can be
placed on the outside surface of
the Wall, or on the inside surface
of the wall. or in the cores of the
masonry units.
If the basement walls are
insulated on the outside, the
materials should be durable
underground, and exposed
insulation should be protected
from damage. In the case of a
finished basement or walk-out
basement, placing insulation on
the interior may be less costly
than insulating the exterior
foundation.
PASSIVE SOLAR DESIGN STRATEGIES 11
Air Illfiltration
Sealing the house carefully to
reduce air infiltration -air
leakage -is as necessary to
energy conseIVation as adding
insulation. Air will flow rapidly
through cracks and crevices in
the wall, in the same way water
flows through the drain in a
bathtub, so even a small
opening can allow heat to
bypass the insulation and lead
to big energy losses.
The tightness of houses is
generally measured in the
number of air changes per hour
(ACH). A good, comfortable,
energy-efficient house, built
along the gUidelines in the tabl~
on this page, will have
apprOximately 0.35 to 0.50 air
changes per hour under normal
winter conditions.
Increasing the tightness of
the house beyond that may
improve the energy performance,
but it may also create problems
with indoor air quality, moisture
build-up, and inadequately
vented fireplaces and furnaces.
The use of house sealing
subcontractors to do the
tightening and check it with a
blower door can often save the
builder time and problems,
especially when trying to achieve
particularly high levels of
infiltration control.
Checklist for Minimizing Air Leakage
./ Tighten seals around windows and doors, and weatherstripping
around all openings to the outside or to unconditioned rooms;
./ Caulk around all windows and doors before drywall is hung; seal all penetrations (plumbing, electrical, etc.);
./ Insulate behind wall outlets and/or plumbing lines in exterior walls;
./ Caulk under headers and sills;
./ Chink spaces between rough openings and millwork with insulation, or for a better seal, fill with foam;
./ Seal larger openings ~uch as ducts into attics or crawlspaces with taped polyethylene covered with insulation;
./ Locate continuous vapor retardants located on the warm side of the insulation (building wrap, continuous interior polyethylene, etc.);
./ Install dampers and/or glass doors on fireplaces; combined with outside combustion air intake;
./ Install backdraft dampers on all exhaust fan openings;
./ Caulk and seal the joint between the basement slab (or the slab on grade) and the basement wall;
./ Remove wood grade stakes from slabs and seal;
./ Cover and seal sump cracks;
./ Close core voids in top of block foundation walls;
./ Control concrete and masonry cracking;
./ Use of air tight drywall methods are also acceptable (see Reference 11);
./ Employ appropriate radon mitigation techniques (see References 13 and 14).
San Diego, CaBfomia
12
Non-Bolar Glazing
South-facing windows are
considered solar glazing. The
south windows in any house are
contributing some solar heat
energy to the house's heating
needs -whether it's a
significant, usable amount or
hardly worth measuring will
depend on design, location and
other factors which are dealt
with later under the discussions
of suntempertng and passive
solar systems.
North windows in almost
every climate lose significant
heat energy and gain very little
useful sunlight in the winter.
East and west windows are likely
to Increase air conditioning
needs unless heat gain is
minimized with careful attention
to shading.
But most of the reasons
people want windows have very
little to do with energy. so the
best design will probably be a
good working compromise
between efficiency and other
benefits. such as bright living
spaces and views.
San Diego. CaUfOJ'oia
GUIDELINES PART TWO: BASICS OF PASSIVE SOLAR
Double-glazing of all non-
solar glazing is advisable. Low-e
glazing on all non-solar windows
may be an especially useful
solution because some low-e
coatings can insulate in winter
and shield against unwanted
heat gain in sununer.
Manufacturers will provide
actual R-values for their
windows (the thermal
performance of glazing can be
expressed either as an R-value
or its reCiprocal. U-value; here
all thermal performance values
are given in terms of R-value). A
chart is also provided with the
Worksheets to show
approximate window R-values
for various types. (the
Equivalent Glazing R-Value
pertains to the entire rough
frame opening of the window.)
North windows should be
used with care. Sometimes
views or the diffuse northern
light are desirable. but in
general north-facing windows
should not be large. Very large
north -facing windows should
have high insulation value. or
R-value. Since north windows
receive relatively little direct sun
in sununer. they do not present
much of a shading problem. So
if the choice were between an
average-sized north -facing
window and an east or west-
facing window. north would
actually be a better chOice.
considering both sununer and
winter performance.
East windows catch the
morning sun. Not enough to
provide significant energy. but.
unfortunately. usually enough to
cause potential overheating
problems in summer. If the
views or other elements in the
house's design dictate east
windows. shading should be
done with particular care.
West windows may be the
most problematic. and there are
few shading systems that will be
effective enough to offset the
potential for overheating from a
large west-facing window. Glass
with a low shading coeffiCient
may be one effective approach -
for example. tinted glass or some
types of low-e glass which
provide some shading while
allowing almost clear views. The
cost of properly shading both
east and west windows should
be balanced against the benefits.
As many windows as
possible should be kept operable
for easy natural ventilation in
sununer. (See also Orientation.
page 1~. Reconunended Non-
South Glass GUidelines. page
34. and Shading. page 3'$')
PASSIVE SOLAR DESIGN STRATEGIES
4. Mechanical
Systems
The passive solar features in the
house and the mechanical
heating, ventilating and air
conditioning systems (HVAC) will
interact all year round and so
the most effective approach will
be to design the system as an
integrated whole. HV AC design
is, of course, a complex SUbject,
but the three areas below are
particularly worth noting in
passive solar houses:
• System Sizing. Mechanical
systems are often oversized for
the relatively low heating loads
in well-insulated passive solar
houses. Oversized systems wUl
cost more in the first place, and
will cycle on and off more often,
wasting energy. The back-up
systems in passive solar houses
should be sized to provide 100%
of the heating or cooling load on
the design day, but no larger.
Comparing estimates on system
sizes from more than one
contractor is probably a good
idea.
• Night Setback. Clock
thermostats for automatic night
setback are usually very effective
-but in passive solar systems
with large amounts of thermal
mass (and thus a large capacity
for storing energy and releasing
it during the night), night
setback of the thermostat may
not save very much energy.
• Ducts. One area often
neglected but of key importance
to the house's energy
performance is the design and
location of the ducts. Both the
supply and return ducts should
be located within insulated
areas, or well insulated if they
run in cold areas of the house,
and well sealed at the jOints.
The joints where the ducts tum
up into exterior walls or
penetrate the ceiling should be
particularly tight and caulked.
13
In the National AsSOCiation of
Home Builders' Energy-Efficient
House Project, all the rooms
were fed with low, central air
supplies, as opposed to the
usual placement of registers
under windows at the end of
long runs. This resulted in good
comfort and energy performance.
The performance of even the
most beautifully designed
passive solar house can easily be
undermined by details like
uninsulated ducts, or by
overlooking other basic energy
conservation measures.
San Diego, CaUfomia
14
5. South-Facing Glass
South-facing solar glass is a key
component of any passive solar
system. The system must
include enough solar glazing for
good performance in winter, but
not so much that cooling
performance in summer will be
compromised. The amount of
solar glazing must also be
carefully related to the amount
of thermal mass. Suntempered
houses require no additional
thermal mass beyond that
already in the wallboard,
framtng and furnishings of a
typical house. Passive solar
Iwuses must have additional
thermal mass.
There are three types of
limits on the amount of south-
facing glass that can be used
effectively in a house. The first
is a limit on the amount of
glazing for suntempered houses.
This limit (without adding
thermal mass) is 7% of the
house's total floor area.
For direct gain systems in
passive solar houses, the
maximum amount of south-
facing glazing is 12% of total
floor area, regardless of how
much additional thermal mass is
provided. Further details about
the most effective sizing of south
glass and thermal mass for
direct gain systems are provided
in Part Three.
San Diego, CaUfornia
GUIDELINES PART TWO: BASICS OF PASSIVE SOLAR
The third limit on south-
facing glass is the total of all
passive solar systems combined,
which should not exceed 12% of
total floor area. Using more
south glass than this limit could
lead to overheating even in
winter.
For example, a passive solar
system for a 1,500 sf house
might combine 93 sf of direct
gain glazing with 74 sf of
sunspace glazing for a total of
168 sf of solar glazing, or 11% of
the total floor area, well within
the direct gain limit of 12% and
the overall limit of 12%. For a
design like this, thermal mass
would be required both in the
house and within the sunspace.
The Natural Cooling
guidelines in Part Three include
recommendations on the window
area that should be operable to
allow for natural ventilation.
When the solar glazing is
tilted, its winter effectiveness as
a solar collector usually
increases. However, tilted
glazing can cause serious
overheating in the summer if it
is not shaded very carefully.
Ordinary vertical glazing is
easIer to shade, less likely to
overheat, less susceptible to
damage and leaking, and so is
almost always a better year-
round solution.
PASSIVE SOLAR DESIGN STRATEGIES
6. Thermal Mass
Some heat storage capacity, or
thermal mass, is present in all
houses, in the framing, gypsum
wall and ceiling board, typical
furnishings and floor coverings.
In suntempered houses, this
modest amount of mass is
sufficient for the modest amount
of south-faCing glass. But more
thermal mass Is required in
passive solar houses, and the
question is not only how much,
but what kind and where it
should be located.
The thermal storage
capabilities of a given material
depend on the material's
conductivity, specific heat and
density. Most of the concrete
and masonry materials typically
used in passive solar have
simUar specific heats.
Conductivity tends to increase
with increasing density. So the
major factor affecting
performance is density.
Generally, the higher the density
the better.
15
The design issues related to
thermal mass depend on the
passive system type. For
sunspaces and thermal storage
wall systems, the required mass
of the system is included in the
design itself. For direct gain, the
added mass must be within the
rooms receiving the sunlight.
The sections on Direct Gain
Systems, Sunspaces and
Thermal Storage Walls contain
more information on techniques
for sizing and locating thermal
mass in those systems.
The thermal mass in a
passive solar system is usually a
conventional construction
material such as brick, cast
concrete, concrete masonry,
concrete slabs, or tile, and is
usually placed in the floor or
interior walls. Other materials
can also be used for thermal
mass, such as "phase change"
materials, which store and
release heat through a chemical
reaction. Water actually has a
higher unit thermal storage
capacity than concrete or
masonry. Water tubes and units
called "water walls" are
commercially available (general
recommendations for these
systems are included in the
section on Thermal Storage Wall
systems).
Heat Storage Properties of Materials
Density Heat Capacity Material (lb/ft3) (Btu/in-sf-OF)
Poured Concrete 120 -150 2.0 -2.5
Clay Masonry
Molded Brick 120 -130 2.0 -2.2 Extruded Brick 125 -135 2.1 -2.3 Pavers 130 -135 2.2 -2.3
Concrete Masonry
Block 80 -140 1.3 -2.3 Brick 115 -140 1.9 -2.3 Pavers 130 -150 2.2 -2.5
Gypsum Wallboard 50 0.83
Water 62.4 5.2
San Diego, California
16
7. Orientation
The ideal orientation for solar
glazing is within 5 degrees of
true south. This orientation will
provide maxJmum perfonnance.
Glazing oriented to within 15
degrees of true south will
perform almost as well. and
orientations up to 30 degrees off
-although less effective -will
still provide a substantial level of
solar contribution.
In San Diego. magnetic north
as indicated on the compass is
actually 15 degrees east of true
north. and this should be
corrected for when planning for
orientation of south glazing.
San Diego. California
GUIDELINES PART TWO: BASICS OF PASSIVE SOLAR
When glazing is oriented
more than 15 degrees off true
south. not only is winter solar
performance reduced. but
summer air conditioning loads
also significantly increase.
especially as the orientation goes
west. The warmer the climate,
the more east-and west-facing
glass will tend to cause
overheating problems. In
general. southeast orientations
present less of a problem than
southwest.
In the ideal situation. the
house should be oriented east-
west and so have its longest wall
facing south. But as a practical
matter. if the house's short side
has good southern exposure it
will usually accommodate
suffiCient glazing for an effective
passive solar system. provided
the heat can be transferred to
the northern zones of the house.
PASSIVE SOLAR DESIGN STRATEGIES
8. Site Planning for
Solar Access
The basic objective of site
planning for maximum energy
performance is to allow the
south side as much unshaded
exposure as possible during the
winter months.
As discussed above, a good
solar orientation is possible
within a relatively large southern
arc, so the flexibility exists to
achieve a workable balance
between energy performance and
other important factors such as
the slope of the sUe, the
individual house plan, the
direction of prevailing breezes for
summer cooling, the views, the
street lay-out, and so on.
But planning for solar access
does place some restrictions
even on an individual site, and
presents even more challenges
when planning a complete
subdivision. Over the years,
developers and builders of many
different kinds of projects all
over the country have come up
with flexible ways to provide
adequate solar access.
Once again, there is an ideal
situation and then some degree
of flexibility to address practical
concerns. Ideally, the glazing on
the house should be exposed to
sunlight with no obstructions
within an arc of 60 degrees on
either side of true south, but
reasonably good solar access will
still be guaranteed if the glazing
is unshaded within an arc of 45
degrees. The figure on this page
shows the optimum situation for
providing unshaded southern
exposure during the winter. See
also the figure on page 35
showing landscaping for
summer shade.
~ 2 Story Buildings Allowed
Ideal Solar Access Buildings, trees or other obstructions should not be located so as to shade the south wall of solar buildings. At this latitude, A = 9 ft., B = 15 ft., and C = 35 ft.
Of course, not all lots are large
enough to accommodate this
kind of optimum solar access, so
it's important to carefully assess
shading patterns on smaller lots
to make the best compromise.
Protecting solar access is
easiest in subdivisions with
streets that run within 25
degrees of east-west, because all
lots will either face or back up to
south. Where the streets run
north-south, creation of east-
west cul-de-sacs will help ensure
solar access.
17
~Ji L
~.I
Solar Subdivision Layouts Solar access may be provided to the rear yard, the side yard or the front yard of solar homes.
Solar Subdivision Layouts Short east-west cul-de-sacs tied into north-south collectors is a good street pattern for solar access.
Two excellent references for
ideas about subdivision lay-out
to protect solar access are
BuUder's Guide to Passive Solar
Home Design and Land
Development and Site Planning
jar Solar Access. (See References
1 Sand 16)
San Diego, California
18
9. Interior Space
Planning
Planning room lay-out by
consIdering how the rooms will
be used in different seasons, and
at different times of day, can
save energy and increase
comfort. In houses with passive
solar features, the lay-out of
rooms -and Interior zones
which may include more than
one room -is particularly
important.
In general, living areas and
other high-activity rooms should
be located on the south sIde to
benefit from the solar heat. The
closets, storage areas, garage
and other less-used rooms can
act as buffers along the north
sIde, but entry-ways should be
located away from the wind.
Clustering baths, kitchens and
laundry-rooms near the water
heater will save the heat that
would be lost from longer water
lines.
In.t~rlor Spa~" Planning Livmg and high activity spaces should be located on the south.
Sao Diego, California
GUIDELINES PART TWO: BASICS OF PASSIVE SOLAR
Another general princIple is
that an open floor plan will allow
the collected solar heat to
circulate freely through natural
convection.
Other Ideas from effective
passive solar houses:
• Orienting internal mass
walls as north-south partitions
that can be "charged" on both
sIdes thus making maximum
use of the mass.
• Using an east-west partition
wall for thermal mass, but make
sure the interior space isn't
divided into a south zone which
may get too warm and a north
zone which may get too cold.
• Using thermal storage walls
(see page 30); the walls store
energy all day and slowly release
it at rught, and can be a good
alternative to ensure privacy and
to buffer noise when the south
side faces the street;
• Collecting the solar energy in
one zone of the house and
transporting it to another by'
fans or natural convection
through an open floor plan.
• Providing south-facing
clerestOries to "charge" north
zones.
10. Putting it
Together: The House
as a System
Many different factors will affect
a house's overall performance,
and these factors all interact:
the mechanical system, the
insulation. the house's
tightness, the effects of the
passive solar features, the
appliances, and, very
importantly, the actions of the
people who live in the house. In
each of these areas, changes are
possible which would improve
the house's energy performance.
Some energy savings are
relatively easy to get. Others
can be more expensive and more
diftlcult to achieve. but may
provide benefits over and above
good energy performance.
A sensible energy-efficient
house uses a combination of
techniques.
In fact, probably the most
important thing to remember
about designing for energy
performance in a way that will
also enhance the comfort and
value of the house is to take an
integrated approach, keeping in
mind the house as a total
system. On the the following
page is a basic checklist for
energy-efficient design. These
techniques are dealt with in
more detail, including their
impact In your location, In Part
Three.
PASSIVE SOLAR DESIGN STRATEGIES 19
Checklist for Good Design
./ 1. Building orientation: A number of innovative techniques can be used for obtaining good solar access on less-than-ideal sites (see References 17 and 18). No matter what the house's design, and no matter what the site, some options for orientation will be more energy-efficient than others. and even a very simple review of the site will probably help you choose the best option available .
./ 2. Upgraded levels of Insulation: It is possible. of course. to achi~ve very high.en~rgy-efficiency wi~h. a "superinsulated" design. But in many cases. one advantage of passive solar deSign IS that energy-effICiency
can be achieved with more modest increases in insulation. On the other hand. if very high energy performance is a priority -for example. in areas where the cost of
fuel is high -the most cost-effective way to achieve it is generally through a combination of high levels of
insulation and passive solar features .
./ 3. Reduced air Infiltration: Air tightness is not only critical to energy performance. but it also makes the
house more comfortable. Indoor air quality is an important issue, and too complex for a complete discussion here. but in general. the suntempered and passive solar houses built according to the guidelines provide an alternative approach to achieving improved energy efficiency without requiring air quality controls such as air to air heat exchangers. which would be needed if the house were made extremely airtight.
./ 4. Proper window sizing and location: Even if the total amount of glazing is not changed. rearranging the location alone can often lead to significant energy savings at little or no added cost. Some energy-conserving designs minimize window area on all sides of the house -but it's a fact of human nature that people like windows. and windows can be energy producers if located correctly .
./ 5. Selection of glazing: Low-emissivity (low-e) glazing types went from revolutionary to commonplace in a very short time. and they can be highly energy-efficient choices. But the range of glazing possibilities is broader than that. and the choice will have a significant impact on energy performance. Using different types of glazing for windows with different orientations is worth considering for maximum energy performance; for example, using heat-rejecting glazing on west windows, high R-value glazing for north and east windows, and clear double-glazing on solar glazing .
./ 6. Proper shading of windows: If windows are not properly shaded in summer -either with shading
devices. or by high-performance glazing with a low shading coefficient -the air conditioner will have to work overtime and the energy savings of the winter may be canceled out. Even more important. unwanted solar gain is uncomfortable .
./ 7. Interior design for easy air distribution: If the rooms in the house are planned carefully. the flow of heat in the winter will make the passive solar features more effective. and the air movement will also enhance ventilation and comfort during the summer. Often this means the kind of open floor plan which is highly marketable in most areas. Planning the rooms with attention to use patterns and energy needs can save energy in other ways, too -for instance, using less-lived-in areas like storage rooms as buffers on the north side .
./ 8. Addition of thermal mass: Adding effective thermal mass -for example. tiled or paved concrete slab.
masonry walls. brick fireplaces, tile floors. etc. -can greatly improve the comfort in the house. holding heat better in winter and keeping rooms cooler in summer. In a passive solar system. of course. properly sized and located thermal mass is essential.
./ 9. Selection and proper sizing of mechanical systems, and selection of energy-efficient appliances: High-performance heating. cooling and hot water systems are extremely energy-efficient. and almost always a good investment. Mechanical equipment should have at least a 0.80 Annual Fuel Utilization Efficiency (AFUE). Well-insulated passive solar homes will have much lower energy loads than conventional homes. and should be sized accordingly. Oversized systems will cost more and reduce the house's performance. For guides to the selection of energy-efficient appliances. see References 13 and 14.
San Diego, CaUfomia
20 GUIDELINES PART TWO: BASICS OF PASSIVE SOLAR
San Diego. CaUforoia
PASSIVE SOLAR DESIGN STRA TEGIES 21
Part Three: Strategies for Improving Energy Performance in San Diego, California
1. The Example Tables
2. Suntempering
3. Direct Gain
4. Sunspaces
5. Thermal Storage Wall
6. Combined Systems
7. Natural Cooling GuideUnes
San Diego. CaUfomla
22 GUIDELINES PART THREE: STRATEGIES FOR IMPROVING ENERGY PERFORMANCE
1. The Example
Tables
In the following sections of the
Guidelines, the primary passive
solar systems -Suntempering,
Direct Gain, Thennal Storage
Walls and Sunspaces -are
described in more detail.
As part of the explanation of
each system, an Example table
is provided. The Examples
present the following infonnation
about a Base Case house, based
on a National AsSOCiation of
Home Builders study of a typical
construction:
• Insulation levels (ceilings
and walls);
• Insulation added to the
perimeter of slab-on-grade
construction. :
• Tightness (measured in air
changes per hour, ACH);
• The amount of glass area on
each side (measured as a
percentage of floor area; the
actual square footage for a 1,500
sf house is also given as a
reference point);
• The "percent solar savings"
(the part of a house's heating
energy saved by the solar
features); and
San Diego, CaUfornla
• Three numbers
corresponding to those on the
Worksheets: ConselVation,
AuxilIary Heat, and Cooling
Perfonnance (see page 4)
The Example tables then show
how the house design could be
changed to reduce winter
heating energy by 20, 40 and
60%, compared to this Base
Case.
There are, of course, other
ways to achieve energy savings
than those shown in the
Examples. The Examples are
designed to show an effective
integration of strategies, and a
useful approach to the design of
the house as a total system.
Using any of these combinations
would result in excellent
perfonnance in your area.
However, they are general
indications only, and using the
Worksheets will give you more
infonnation about your speciflc
design.
The Example assumes a
1,500 sf house, but the
percentages apply to a house of
any size or configuration.
The R-values indicated in the
Example tables are, of course,
approximate and are intended to
show how incremental
improvements can be achieved.
All R-values in the Examples
and Worksheets are equivalent
R-values for the entire
construction assembly. not just
for the cavity insulation itself,
and take into account framing
and buffering effects.
Other assumptions are noted
for each Example. However, one
more general assumption is
important to note here. When
the Examples were calculated, it
was assumed that natural
cooling strategies such as those
described in these Guidelines
were used. particularly in the
very high-perfonnance systems.
The greater the percentage
reduction in heating energy
needs using passive solar
design, the more shading and
natural cooling were assumed.
The Examples show passive
solar strategies, but an
Insulation Only Example table
(achieving energy savings only
by increasing insulation levels,
without solar features) is
provided in the Summary
beginning on page 42, for
comparison.
PASSIVE SOLAR DESIGN STRA TEGIES 23
2. Suntempering
Suntempered and passive solar
houses both:
• begIn with good basIc
energy-conservation,
• take maximum advantage of
the building sIte through the
right orientation for year-round
energy savings, and
• have increased south-facing
glass to collect solar energy.
SuntemperIng is the simplest
passive solar system, and refers
to modest increases in windows
on the south side.
No addItional thermal mass
is necessary, only the "free
mass" in the house -the
framing, gypsum wall-board and
furnishings.
In a "conventional" house,
about 25% of the windows face
south, which amounts to about
3% of the house's total floor
area. In a suntempered house,
the percentage is increased to a
maximum of about 7%.
The energy savings are more
modest with thIs system, but
suntempering is a very low-cost
strategy.
Of course, even though the
necessIty for precIse sizing of
glazing and thermal mass does
not apply to suntemperIng (as
long as the total south-facing
glass does not exceed 7% of the
total house floor area), all other
recommendations about energy-
effiCient design such as the basic
energy conseIVation measures,
room lay-out, siting, glazing type
and so on are still important for
penonnanceandcomfortin
suntempered homes.
Examples of Heat Energy Savings
Suntempered
1 ,500 sf Single Story House
Base
Case 20% 40% 60%
R-Values
Ceiling/Roof 26 24 26 32
Walls 14 12 13 17
Slab Edge 0 0 0 0
Glass .9 1.8 1.8 1.8
Air Changes/Hour 0.75 0.69 0.51 0.73
Glass Area (percent of total floor area)
West 3.0% 2.0% 2.0% 2.0% North 3.0% 4.0% 4.0% 4.0% East 3.0% 4.0% 4.0% 4.0% South 3.0% 5.6% 6.7% 6.7%
Solar System Size (square feet)
South Glass 45 84 100 100
Percent Solar Savings
22% 37% 46% 55%
Performance (Btu/yr-sf)
Conservation 16,145 16,455 14,659 11,730 Auxiliary Heat 12,649 10,362 7,801 5,271 Cooling 8,309 5,927 3,557 3,074
Summary: The window area has been Slightly decreased on the west,
increased slightly on the east and north, and increased significantly on the south.
San Diego, CaBfomia
24 GUIDELINES PART THREE: STRATEGIES FOR IMPROVING ENERGY PERFORMANCE
3. Direct Gain
The most common passive solar
system is called direct gain:
sunlight through south-facing
glazing falls directly into the
space to be heated. and is stored
in thermal mass incorporated
into the floor or interior walls.
Direct Gsln Direct gain is the most common passive solar system in residential applications
Sizing Limit
Total direct gain glass area
should not exceed about 12% of
the house's floor area. Beyond
that, problems with glare or
fading of fabriCS are more likely
to occur. and It becomes more
dUIlcult to provide enough
thermal mass for year-round
comfort.
So the total south-facing
glass area in a direct gain
system should be between 7%
(the maximum for suntempered
houses) and 12%. depending on
how much thermal mass will be
used in the design. as discussed
below.
San Diego. caUfornla
Glazing
Double glazing is recommended
for direct gain glazing in San
Diego. The Performance
Potential table on page 6 shows
the relative performance of
different types of direct gain
glazing. You will note from this
table that yield increases by 1%
between double and triple or
low-e glazing. Night insulation
also improves energy
performance dramatically. In
fact. as the Performance
Potential table shows. covering
the windows at night or on
cloudy days with the equivalent
of R-4 shades or other material
w1ll save almost as much energy
as with R-9 material. But
studies have shown that only
relatively few homeowners will
be diligent enough about
operating their night insulation
to achieve those savings.
Energy-eIDcient glazing. on the
other hand. needs no operation.
and therefore is a more
convenient and reliable option.
Thermal Mass
Thermal mass can be
incorporated easily into slab-on-
grade type buildings as either
floor covering. walls or veneers
over interior walls. If the mass
is placed in the floor. it will be
much more effective if sunlight
falls directly on it.
Effective materials for floors
include painted. colored or vinyl-
covered. concrete. brick (face
brick or pavers have even ,higher
density than ordinary building
brick). quarry tile. and dark-
colored ceramic tile.
For houses built with
crawlspaces or basements. the
incorporation of significant
amounts of heavy thermal mass
is a little more difficult. Thermal
mass floor coverings over
basements. crawlspaces and
lower stories would generally be
limited to thin set tile or other
thin mass floors.
When more mass is required.
the next best option is for
interior walls or interior masoruy
fireplaces. When evaluating
costs. the dual function of mass
walls should be remembered.
They often selVe as structural
elements or for fire protection as
well as for thermal storage.
Another option is to switch to
another passive solar system
type such as attached slab-on-
grade sunspaces or thermal
storage walls built directly on
exterior foundation walls.
Sunlit thermal mass floors
should be relatively dark in
color. to absorb and store energy
more effectively. However. mass
walls and ceilings should be
light in color to help distribute
both heat and light more evenly.
PASSIVE SOLAR DESIGN STRATEGIES
Ratio of Glass to Mass. The
following procedure can be used
to detenn1ne the maximum
amount of direct-gain glazing for
a given amount of thermal mass.
If the amount of direct-gain
glazing to be used is already
known, thermal mass can be
added until this procedure
produces the desired
proportions:
• Start with a direct gain glass
area equal to 7% of the house's
total floor area. As noted above,
the "free mass" in the house will
be able to accommodate this
much solar energy.
• An additional 1.0 sf of direct
gain glazing may be added for
every 5.5 sf of uncovered, sunlit
mass floor. Carpet or area rugs
will seriously reduce the
effectiveness of the mass. The
maximum floor mass that can be
considered as "sunlit" may be
estimated as about 1.5 times the
south window area.
• An additional 1.0 square foot
of direct gain glazing may be
added for every 40 sf of thermal
mass in the floor of the room,
but not in the sun.
• An additional 1.0 square foot
of direct gain glazing may be
added for each 8.3 sf of thermal
mass placed in the wall or
ceiling of the room. Mass in the
wall or ceiling does not have to
be located dIrectly in the
sunUght, as long as it is in the
same room, with no other walls
between the mass and the area
where the SUnlight is falling.
More south-facing glazing
than the maximum as
determined here would tend to
overheat the room, and to
reduce energy performance as
well.
1:40 for Floor
notinSu-l
Mass Location and Effectiveness Additional mass must be provided for south facing glass over 7% of the floor area. The ratio of mass area to additional glass area depends on its location within the direct gain space.
25
Thickness. For most materials,
the effectiveness of the thermal
mass in the floor or interior wall
Increases proportionally with
thickness up to about 4 Inches.
After that, the effectiveness
doesn't increase as Significantly.
,g
ttl a:
A two-inch mass floor will be
about two-thirds as effective in a
direct gain system as a four-inch
mass floor. But a six-inch mass
floor will only perform about
eight percent better than a four-
inch floor.
The following figure shows
the effectiveness of thermal
mass in relation to density and
thickness. The vertical axis
shows how many square feet of
mass area are needed for each
added square foot of direct gain.
As you can see, performance
Increases start leveling off after a
few Inches of thermal mass.
4O~~~-----------------+
5O#/cf
:330 < gj .!!! "20 75#/cf
~ 100#/cf
:3 <10 125#/cf
15O#/cf '" '" ~
O~------~----~~----~ o 5 10 15
Thckness (nchesJ
Mass Thickness The effectiveness of thermal mass depends on the density of the material and thickness. This graph is for wall or ceiling mass in the direct gain space.
Worksheet m: Thermal
Mass/Comfort should be used
to make sure the house has
adequate thermal mass.
San Diego, Califomia
26 GUIDELINES PART THREE: STRATEGIES FOR IMPROVING ENERGY PERFORMANCE
Examples of Heat Energy Savings Passive Solar-Dlrect Gain 1,500 sf Single Story House
Base Case 20% 40% 60% R-values Ceiling/Roof 26 24 24 24
Walls 14 12 12 12
Slab Edge 0 0 0 0 Glass .9 1.8 1.8 1.8
Air Changes/Hour 0.75 0.69 0.64 0.59
Glass Area (percent ot total floor area) West 3.0% 2.0% 2.0% 2.0% North 3.0% 4.0% 4.0% 4.0% East 3.0% 4.0% 4.0% 4.0% South 3.0% 5.6% 8.4% 12.0%
Added Thermal Mass Percent of Floor Area 0.0% 0.0% 8.7% 30.0%
Solar System Size (square feet)
South Glass 45 84 126 180
Added Thermal Mass 0 0 130 450
Percent Solar Savings 22% 37% 52% 67%
Performance (Btu/yr-sf) Conservation 16,145 16,455 16,265 16,035
Auxiliary Heat 12.649 10,362 7,814 5,242
Cooling 8,309 5,927 4,388 5,652
Summary: South-facing glazing has been substantially increased. For
these examples, added mass area is assumed to be six times the excess south glass area.
SaD Diego, Callforma
PASSIVE SOLAR DESIGN STRATEGIES
4. Sunspaces
The sunspace is a vety popular
passive solar feature. adding an
attractive living space as well as
energy performance. There are
many variations on the basic
theme of the sunspace. and the
possibilities for sunspace design
are extraordinarily diverse
(References 19 through 22
include specific design ideas).
The sunspace concept used
in these Guidelines can be used
year-round. will provide most or
all of its own energy needs. and
will contribute to the energy
needs of the rest of the house as
well.
Sunspaces are referred to as
"isolated gain" passive solar
systems. because the SUnlight is
collected in an area which can
be closed off from the rest of the
house. During the day. the
doors or windows between the
suns pace and the house can be
opened to circulate collected
heat. and then closed at night.
and the temperature in the
sunspace allowed to drop.
The sunspace should not be
on the same heating system as
the rest of the house. A well
designed sunspace will probably
need no mechanical heating
system. but if necessaty. a small
fan or heater may be used to
protect plants on extremely cold
winter nights.
The sunspace should be just
as tightly constructed and
insulated as the rest of the
house.
Sunspaces Sunspaces provide useful passive solar heating and also provide a valuable amenity to homes.
Thennal Mass
A sunspace has extensive south-
facing glass. so sufficient
thermal mass is vety important.
Without it. the sunspace Is liable
to be uncomfortably hot dUring
the day. and too cold for plants
or people at night.
However. the temperature in
the sunspace can vaty more
than in the house itself. so
about three square feet of four
inch thick thermal mass for each
square foot of sunspace glazing
should be adequate. With this
glass-to-mass ratio. on a clear
winter day a temperature swing
of about 30'F should be
expected.
27
The sunspace floor is a good
location for thermal mass. The
mass floors should be dark in
color. No more than 15-25% of
the floor slab should be covered
with rugs or plants. The lower
edge of the south-facing
windows should be no more
than six inches from the floor or
the planter bed to make sure the
mass in the floor receives
suffiCient direct sunlight. If the
windows sills are higher than
that. additional mass will have
to be located in the wall.
Another good location for
thermal mass is the common
wall (the wall separating the
sunspace from the rest of the
house). Options for the common
wall are discussed in more detail
below.
Water in various types of
containers is another form of
energy storage often used in
sunspaces.
Glazing
Single-glazing may be used for
sunspaces. although double-
glazing will further improve
comfort. in terms of energy
savings. The performance
potential table on page 6 shows
the relative performance of
different types of glazing.
Windows on the east and
west walls should be small (no
more than lOOk of the total
sunspace floor area) but they are
useful for cross-ventilation.
Like tilted or sloped glazing.
glazed roofs can increase solar
gain. but they can also present
big overheating problems and
become counter-productive. If
either glazed roofs or tilted
glazing are used in the
SaD Diego. CaUfomla
28 GUIDELINES PART THREE: STRATEGIES FOR IMPROVING ENERGY PERFORMANCE
sunspace, special care should be
taken to make sure they can be
effectively shaded during the
summer and, if necessary, on
sunny days the rest of the year,
too. The manufacturers of
sunspaces and glazing are
developing products with better
abiUty to control both heat loss
and heat gain (for example, roof
glazing with low shading
coefficients, shading treatments
and devices, etc.).
You'Il note that in the
Performance Potential chart on
page 6. sunspaces with glazed
roofs or sloped glazing perform
very well. This analysis
assumes effective shading in the
SUIl'lIller. If such shading is not
economical or marketable in
your area, you should consider
using only vertical glazing, and
accepting somewhat less energy
performance in winter.
San Diego, CaUforDia
Common Wall
There are a number of options
for the sunspace common wall.
In mild climates, and when the
sunspace is very tightly
constructed, an uninsulated
frame wall is probably adequate.
However, insulating the common
wall to about R-I0 Is a good
idea, especially in cold climates.
An insulated common wall will
help guard against heat loss
during prolonged cold. cloudy
periods, or if the thermal storage
in the sunspace is insuffiCient.
If the common wall is a
masonry wall, it can also be
used for thermal mass, in which
case it should be solid masonry
approximately 4 to 8 inches
thick. Another option is a frame
wall with masonry veneer.
Probably the most important
factor in controlling the
temperature in the sunspace,
and thus keeping it as
comfortable and effiCient as
possible, is to make sure the
exterior walls are tightly
constructed and well-insulated.
Some solar energy may be
transferred from the sunspace to
the rest of the house by
conduction through the common
wall if it is made of thermal
mass. But energy is mainly
transferred by natural
convection through openings in
the common wall-doors,
Windows and/or vents.
• Doors are the most common
opening in the common wall. If
only doorways are used, the
open area should be at least
15% of the sunspace south -glass
area.
• Windows will also provide
light and views. The window
area in the common wall should
be no larger than about 400Al of
the entire common wall area. If
only windows are used, the
operable area should be about
25% of the sunspace's total
south glass area.
PASSIVE SOLAR DESIGN STRATEGIES 29
Summer ventilation
The sunspace must be vented to
the outside to avoid overheating
in the summer or on warm days
in spring and fall. A properly
vented and shaded sunspace
can function much like a
screened-in porch.
Operable Windows and/ or
vent openings should be located
for effective cross-ventilation.
and to take advantage of the
prevailing summer wind. Low
inlets and high outlets can be
used in a "stack effect". since
warm air will rise. These
ventilation areas should be at
least 15% of the total sunspace
south glass areas.
Where natural ventilation is
insufficIent. or access to natural
breezes is blocked. a small.
thermostat -controlled fan set at
about 76'F will probably be a
useful addition.
Examples of Heat Energy Savings
Passive Solar-Sunspace
1,500 sf Single Story House
Base
Case 20% 40% 60%
R·Values
Ceiling/Roof 26 24 24 24
Walls 14 12 12 12
Slab Edge 0 0 0 0
Glass .9 1.8 1.8 1.8
Air Changes/Hour 0.75 0.69 0.69 0.69
Glass Area (percent of total floor area)
West 3.0% 2.0% 2.0% 2.0%
North 3.0% 4.0% 4.0% 4.0%
East 3.0% 4.0% 4.0% 4.0%
South (windows) 3.0% 3.0% 3.0% 3.0%
Sunspace 0.0% 2.8% 6.7% 13.0%
Solar System Size (square feet)
South Glass 45 45 45 45 Sunspace Glass 0 41 100 194 Sunspace Thermal Mass 0 124 300 582
Percent Solar Savings
22% 37% 53% 69%
Performance (Btu/yr-sf)
Conservation 16,145 16,462 16,688 17,023 Auxiliary Heat 12,649 10,357 7,799 5,220 Cooling 8,309 5,962 4,379 5,923
Summary: Insulation and tightness (for the 60% case) have been
increased. North and east-facing glazing have been increased Slightly.
The sunspace assumed here is semi-enclosed (surrounded on three sides
by conditioned rooms of the house, as in Figure SSC1 of the worksheets),
with vertical south glazing. The common wall is a thermal mass wall made
of masonry. Sunspace glazing is assumed to be double .
. San Diego, CaUfomla
30 GUIDELINES PART THREE: STRATEGIES FOR IMPROVING ENERGY PERFORMANCE
5. Thermal Storage
Wall
The Thermal Storage Wall-
also sometimes referred to as a
Trombe wall or an indirect gain
system -is a south-faCing
glazed wall. usually built of
heavy masonry, but sometimes
using water containers or phase
change materials. The masonry
is separated from the glazing
only by a small air space.
Sunlight is absorbed directly
into the wall instead of into the
living space. The energy is then
released into the living space
over a relatively long period. The
time lag varies with different
materials. thicknesses and other
factors. but typically, energy
stored in a Thermal Storage Wall
during the day is released
during the evening and
nighttime hours.
The outside surface of a
thermal storage wall should be a
vexy dark color -an
absorptance greater than 0.92 is
recommended.
The summer heat gain from
a Thermal Storage Wall is much
less -roughly 99% less -than
from a comparable area of direct
gain glazing.
San Diego, California
Thermal Storage Wall . A thermal storage wall is an efffJ!:tive. paS.Slve solar system. especially to proVIde mghttime heating.
A masonry Thermal Storage Wall
should be solid, and there
should be no openings or vents
either to the outside or to the
living space. Although vents to
the living space were once
commonly built into Thermal
Storage Walls, experience has
demonstrated that they are
ineffective. Vents between the
Thermal Storage Wall and the
house tend to reduce the
system's nighttime heating
capability, and to increase the
temperature fluctuation in the
house. Vents to the outside are
similarly ineffective. and do little
to reduce summer heat gains.
Glazing
Double glazing is recommended
for Thermal Storage Walls unless
a selective surface is used. In
this case, single glazing performs
about the same as double
glazing.
The space between the
glazing and the thermal mass
should be one to three inches.
Selective Surfaces
A selective surface is a special
adhesive foil applied to the
exterior side of the mass of
Thermal Storage Walls.
Selective surfaces absorb a large
percentage of solar radiation but
radiate vexy little heat back to
the out-of-doors (low emittance).
To be effective, selective
surfaces must be applied
carefully for lOOOA> adhesion to
the mass surface.
In San Diego, California, a
selective surface will improve
Thermal Storage Wall
performance by about 37%.
Mass Material and
Thickness
In general, the effectiveness of
the Thermal Storage Wall will
increase as the dens1ty of the
material increases.
The optimum thickness of
the wall depends on the density
of the material chosen. The
following chart indicates the
recommended thickness of
Thermal Storage Walls made of
various materials.
PASSIVE SOLAR DESIGN STRATEGIES 31
Mass Wall Thickness
(inches)
Density Thickness
Material (Ib/cf) (inches)
Concrete 140 8-24
Concrete Block 130 7-18
Clay Brick 120 7-16
Ltwt. Concrete 110 6-12
Block Adobe 100 6-12
Water Walls
Water provides about twice the
heat storage per unit volume as
masonry, so a smaller volume of
mass can be used. In "water
walls" the water is in light, rigid
containers. The containers are
shipped empty and easily
installed. Manufacturers can
provide information about
durability, installation,
protection against leakage and
other characteristics. At least
30 pounds (3.5 gallons) of water
should be provided for each
square foot of glazing. This is
equivalent to a water container
about six inches thick, having
the same area as the glazing.
Examples of Heat Energy savings
Passive Solar-Thermal Storage Wall
1.500 sf Single Story House
Base
Case 20% 40% 60%
R·Values
Ceiling/Roof 26 24 24 24
Walls 14 12 12 12
Slab Edge 0 0 0 0 Glass .9 1.8 1.8 1.8
Air ChangeS/Hour 0.75 0.69 0.67 0.69
Glass Area (percent of total floor area)
West 3.0% 2.0% 2.0% 2.0%
North 3.0% 4.0% 4.0% 4.0%
East 3.0% 4.0% 4.0% 4.0% South 3.0% 3.0% 3.0% 3.0% Thermal Storage Wall 0.0% 2.2% 5.1% 9.5%
Solar System Size (square feet) South Glass 45 45 45 45 Thermal Storage Wall 0 33 75 141
Percent Solar Savings
22% 36% 52% 69%
Performance (Btu/yr-sf)
Conservation 16,145 16.431 16.501 16.840 Auxiliary Heat 12.649 10.360 7.803 5.227 Cooling 8.309 5.235 2.610 2.663
Summary: In the case of a Thermal Storage Wall, south-facing glazing and thermal mass are incorporated together. The estimates here assume
a 12-inch thick concrete Thermal Storage Wall with a selective surface and single glazing.
San Diego, California
32 GUIDELINES PART THREE: STRATEGIES FOR IMPROVING ENERGY PERFORMANCE
6. Combined Systems
Although the previous sections
have presented separate
discussions of four different
systems, it isn't necessary to
choose one and only one system.
In fact, passive solar features
work well in combination.
For example, direct gain
works very well in conjunction
with a sunspace or thermal
storage wall. Since thermal
storage walls release energy
more slowly than direct gain
systems, they are useful for
supplying heat in the evening
and at night, whereas the direct
gain system works best during
the day. Although using a
sunspace, thermal storage wall
and direct gain system in the
same house may result in
excellentpenormance, such
combinations do require a large
south-facing area, and careful
design to make sure the systems
are well-integrated with each
other and with the house's
mechanical system.
San Diego, California
7. Natural Cooling
Guidelines
The term "natural cooling" is
used here to deSCribe techniques
which help a house stay cool in
summer but which require little
or no energy. Natural cooling
techniques work to help reduce
air-conditioning, not replace it.
These techniques are useful
not only in passive solar houses,
but in "conventional" houses as
well. The strategies outlined
below -attention to the
location, size and shading of
glazing, using the opportunities
on the site for shading and
natural ventilation, and using
fans -can reduce air
conditioning needs and increase
comfort even if the house has no
passive solar heating features.
But shading is particularly
important in passive solar
houses, because the same
features that collect SUnlight so
effectively in winter will go right
on collecting it in summer -
resulting in uncomfortably hot
rooms and big air conditioning
bills -unless they are shaded
and the house is designed to
help cool itself.
Fortunately, many of the
features that help maintain
comfort and reduce energy
needs in winter also work well in
summer. For instance,
additional thermal mass
penorms well year-round.
Masonry materials are equally
effective in staying cool and
storing heat. If mass surfaces
can be exposed to cool night-
time temperatures - a
technique referred to as "night
ventilation" -they will help the
house stay cooler the next day.
A CalifOrnia utility found during
studies of small test buildings
that on hot summer days the
workmen at the facility always
ate lunch in the masonry test
building because it stayed much
cooler than any of the others.
(See Reference 9)
The additional insulation
that increases winter
penormance will also work to
improve summer performance by
conserving the conditioned air
inside the house. And some
low-e windows and other glazing
with high R-value can help
shield against unwanted heat
gain in summer.
PASSIVE SOLAR DESIGN STRA TEGIES 33
The potential of some
natural and low-energy cooling
strategies is shown in the
following table for San Diego.
Worksheet IV: CooHng
Performance Level indicates
the total annual cooling load,
and so can give an idea of how
the passive solar features
increase the cooling load and
how much reduction is possible
when natural cooling techniques
are used.
It should be noted that the
Cooling Performance numbers
presented in the Examples for
each passive solar strategy
assume that the design also
includes the recommended
natural cooling techniques. This
Is especially true of the higher
percentage reductions; these
assume better heating
performance, but also better
shading and other natural
cooling strategies.
Cooling Potential Basecase 8,309 Btu/yr-sf
Energy Savings Strategy (Btu/yr-sf)
No Night Ventilation 1
without ceiling fans 0
with ceiling fans 3,240
Night Ventilation 1
without ceiling fans 750
with ceiling fans 3,210
High Mass2
without ceiling fans 580 with ceiling fans 440
1 With night ventilation, the house is ventilated at night when temperature and humidity conditions are favorable.
Percent Savings
0%
39%
9% 39%
7% 5%
2 A "high mass" building is one with a thermal mass area at least equal to the house floor area.
San Diego, CaUfomia
34 GUIDELINES PART THREE: STRATEGIES FOR IMPROVING ENERGY PERFORMANCE
Glazing
As mentioned earlier, poorly
placed windows can increase air
conditioning loads dramatically.
It is generally best in terms of
energy performance to carefully
size non-solar glazing as
indicated in the following table.
Recommended Non-south Glass Guidelines
Orientation
East North West
Percent of Total Floor Area
4%
4% 2%
As mentioned earlier, west-
facing windows present
particularly difficult shading
problems. If glazing is added
above the levels indicated, the
need for shading will become
even more critical.
Cooling loads increase as
window area increases. This
relationship for San Diego is
shown in the following table for
each of the cardinal window
orientations. For instance when
a square foot of west area is
added or subtracted, the annual
cooling load increases or
decreases by 77,540 Btu/yr-sf.
San Diego, California
Added Window Cooling Load
Added Annual
Orientation
North East South West Skylights
Cooling Load (Btu/yr-sf)
31,130 86,960 57,280
77,540 150,540
These values are based on
double glass with a shading coefficient of 0.88. When glazing with a different shading coefficient is used the values may be scaled proportionally.
These numbers can be reduced
by shading as deSCribed in the
next section.
U sing special glazing or
window films that block solar
transmission Oow shading
coefficient) is an option often
used in particularly hot
climates. but the more effective
they are at blocking sunlight,
the less clear they are, as a rule,
and so they may interfere with
desirable views. It is important
to note, however, that some
types of low-e windows block
solar transmission but also
allow clear views. These
treabnents are not
recommended for south
windows.
As the table shows. skylights
present a high potential for
overheating. and are usually
cUfilcult to shade properly. But
skylights are very popular
features, and they save
electricity by providing good
natural daylight to the house.
In some parts of the country
almost every new house has at
least one skylight. A good
working compromise can usually
be achieved if skylight area is
limited, and if careful attention
is paid to shading, either by
trees or by devices such as roller
shades or blinds. The
manufacturer can usually give
guidance on shading options for
a particular skylight design.
PASSIVE SOLAR DESIGN STRATEGIES
Shading
Shading strategies generally fall
into three categories:
landscaping, roof overhangs and
exterior or interior shading
devices.
Landscaping. The ideal site for
summer shading has deciduous
trees to shade the east and west
windows. Even small trees such
as fruit trees can help block sun
hitting the first story of a house.
Trees on the south side can
present a dilTicult choice. Even
deciduous trees will shadow the
solar glazing during the winter
and interfere with solar gain. In
fact, trees on the south side can
all but eliminate passive solar
perfonnance, unless they are
very close to the house and the
low branches can be removed,
allowing the winter sun to
penetrate under the tree canopy.
However, in many cases the
trees around the house are
bigger selling points than the
energy efficiency and the builder
must make a choice.
If a careful study of the
shading patterns is done before
construction, it should be
possible to accomodate the
south-facing glazing while
leaving in as many trees as
possible (see page 17, Site
Planning for Solar Access).
Land_cap/ng for Summfll' Shade Trees and other landscaping features may be effectively used to shade east and west windows from summer solar gains.
Other landscaping ideas for
summer shade:
• Trellises on east and west
covered with vines.
• Shrubbery or other plantings
to shade paved areas.
• Use of ground cover to
prevent glare and heat
absorption.
• Trees, fences, shrubbery or
other plantings to "channel"
summer breezes into the house.
• DeCiduous trees on the east
and west sides of the house, as
shown above, to balance solar
gains in all seasons.
35
Roof Overhangs. Fixed
overhangs are an inexpensive
feature, and require no
operation by the home owner.
They must be carefully designed,
however. Otherwise, an
overhang that blocks summer
sun may also block sun in the
spring, when solar heating is
desired, and, by the same token,
an overhang sized for maximum
solar gain in winter will allow
solar gain in the fall on hot days.
The following figure may be used
to determine the optimum
overhang size.
In San Diego, an ideal
overhang projection for a four
foot high window would be 15
inches and the bottom of the
overhang would be 12 inches
above the top of the window.
South Overhang Sizing In San Diego, an ideally sized south overhang should allow full exposure of the window when the sun has a noon altitude of 38 degrees (angle A) and fully shade the window when the sun has a noon altitude of 75 degrees (angle 8).
San Diego, California
36 GUIDELINES PART THREE: STRATEGIES FOR IMPROVING ENERGY PERFORMANCE
A combination of carefully sized
overhangs on the south windows
and shading devices on the other
windows will probably be an
effective solution. Adjustable
overhangs that can be
seasonally regulated are another
option.
Shading Devices. External
shades are the most effective
because they stop solar gain
before the sun hits the building.
A wide range of products are
available. from canvas awnings
to solar screens to roll-down
blinds to shutters to vert1cal
louvers. They are adjustable
and perform very well. but the1r
limitation is that they require
the home owner's cooperation.
Usually external screens that
can be put up and taken down
once a year like storm windows
are more acceptable to home
owners than those requiring
more frequent operation.
Interior shades must be
operated. too. and have the
further disadvantage of
permitting the sun to enter the
house and be trapped between
the window and the shading
device. But highly reflective
interior blinds and curtains are
relatively low-cost and easy to
operate.
Another shading "device" well
worth cons1dering is a porch.
Especially on the east and west
sides. porches add pleasant
spaces to houses and are
excellent for providing shade to
windows. Carports located on
the east or west are another
option.
San Diego. CaUforDia
Ceiling Fans
Ceiling fans will probably save
more energy than any other
single cooling strategy. Stud1es
show that air movement can
make people feel comfortable at
higher temperatures. As a
general rule. the thermostat can
be set 4 degrees higher without
affecting comfort if the air is
moving at 100-150 feet per
minute. This is enough air
movement to greatly improve
comfort but not enough to
disturb loose papers.
. Ceiling Fan Sizes
Largest Room
Dimension
12 feet or less
12 -16 feet
16 -17.5 feet
17.5 -18.5 feet
18.5 or more feet
Minimum Fan
Diameter
(inches)
36
48
52
56 2 fans
A ceiling fan should have a
minimum clearance of ten
inches between ceiling and fan
to provide adequate ventUatlon
in a standard room with eight-
foot ceUings. In rooms with
higher ceilings. fans should be
mounted 7.5 to 8.0 feet above
the floor.
PASSIVE SOLAR DESIGN STRATEGIES
Ventilation
When possible, the house should
be positioned on the site to take
advantage of prevailing winds.
During the cooUng season, the
prevailing wind is from the west.
Windows, stairwells, transoms
and other elements should be
located for maximum cross-
ventilation in each room. The
free vent area (unobstructed
openings like open windows)
should be between 6-7.5% of
total floor area, half located on
the leeward and half on the
windward side of the building.
Insect screens can reduce the
effective free vent area by as
much as 50%. Casement or
awning windows have a 90%
open area: double hung windows
have only 50%.
Natural ventilation can help
keep houses cool and
comfortable at the beginning and
end of the cooling season and
thus shorten the time when air
conditioning is required. But
natural ventilation can seldom
do the entire coolingjob,
especially for less than ideal
sites with little natural air
movement.
Ventilation for Summer Cooling Natural ventilation is often impaired by vegetation and topography. Ventilation fans do not depend on surroundings to be effective.
In cooling climates, a whole-
house fan is a good idea for
assisting ventilation, especially
in houses with sites or designs
that make natural ventilation
difficult. On the other hand,
when the temperature is higher
than about 76°F, a whole-house
fan will not be very effective.
Research indicates that a
whole-house fan should pull
approximately 10 ACH. A rule of
thumb: for rooms with eight foot
ceilings, total floor area
multipUed by 1.34 will equal the
necessary CFM of the fan. For
10 foot ceilings, multiply floor
area by 1.67.
37
The best possible
performance of a whole-house
fan results when a timer, a
thermostat and a "hUmidistat"
are used, so that the fan would
only operate when there Is less
than 600Al relative hUmidity and
a temperature ofless than 76°F.
Natural ventilation and
whole-house fans are effective at
removing heat. but not at
moving air. Ceiling fans. on the
other hand, can often create
enough of a breeze to maintain
comfort at higher temperatures,
and still use less power than
required by air conditioning. By
using natural cooling strategies
and low-energy fans, the days
when air-conditioning is needed
. can be reduced substantially.
San Diego, CaUfomia
38 GUIDELINES PART THREE: STRATEGIES FOR IMPROVING ENERGY PERFORMANCE
San Diego, California
Passive Solar
Design Strategies
WORKSHEETS
Passive Solar Industries Council
National Renewable Energy Laboratory
Charles Eley Associates
With Support From: .
U.S. Department of Energy
San Diego California
NOTE: Please make copies of the blank
worksheets and tables before entering
numbers so that the worksheets may be
used to evaluate several desJgn options.
Worksheets
Worksheet Reference Tables
Table A-EqulValeDt Thermal Performance of AaaembHet! R-va!uet! (hr-V..r/Btu)
Attic Construction
Framed Construction
2x6 at1S-oc 2x6 at 24"oc 2x8 at16"oc 2x8 at24"oc 2x10 at1S-oc 2x1 0 al 24·oc 2x12 at lS-oc 2x12 a124·oc
~~Ie
Framing
2x4 at16"oc 2x4 a124"oc: 2x6 at 16"oc 2x6a124"oc
Double Wall Framing
A1-ceUlngllRoofl
Insulation R-value R-30 R-38 R-49 R-eo
27.9 35.9 46.9 57.9
Insulation R-value R-19 R-22 R-30 R-38
14.7 15.8 16.3 15.3 16.5 17.1 17.0 18.9 20.6 21.1 17.6 19.6 21.6 22.2 18.1 20.1 24.6 25.7 18.4 20.7 25.6 26.8 18.8 21.0 25.6 30.1 19.0 21.4 27.3 31.4
A2-Framed Walla
Insulalion R-value R-11 R-13 R-19 R-25
12.0 13.6 12.7 13.9 14.1 15.4 17.7 19.2 14.3 15.6 18.2 19.8
Total Thickness finches) 8 10 1~ 14
25.0 31.3 37.5 43.8
The R-value of insulating sheathing should be added to the values in this table.
A3-lnaulated Flool1
Insulation R-value
Framing R-11 R-19 R-30 R-38
2x6s aUS-oc 18.2 23.8 29.9 2x6s at 24·oc 18.4 24.5 31.6 2x8s at1S-oc 18.8 24.9 31.7 36.0 2x8s al 24·oc 18.9 25.4 33.1 37.9 2x10 allS-oc 19.3 25.8 33.4 38.1 2x1 0 al 24·oc 19.3 26.1 34.4 39.8 2x12 a116·oc 19.7 26.6 34.7 39.8 2x12 at 24·oc 19.6 26.7 35.6 41.2
These R-values include the buffering effect of a ventilated crawlspace or unconditioried basement
Double
A4-Wlndowl
Metal Standard Frame wI Wood Metal Thermal Frame Frame Break
114· space 1.8 1.4 1.6 112" space 2.1 1.8 1.8 low-e 3.1 2.2 3.0 Triple 114· space 2.7 1.8 2.1 112" space 3.3 2.2 2. 7
These R-values are for the entire rough frame window opening. When storm sash is added, an additional 1.1 may be added. One half the R-value of moveable insulation may also be added, when appropriate.
Table A-cootlnued ••
A5-DooI1
Solid wood with 2.2 Weatherstripping
Metal with rigid 5.9 foam core
Table B-Perimeter Beat Lou Factora for Slaba-oo-Gracie and Buemeou (Btu/h-F-ft)
Perimeter Insulation
None R-5 R-7 R-11 R-19 R-30
Heated Unheated Insulated Siabs-on-Base-Base-Crawl-Grade ments ments spaces
0.8 1.3 1.1 1.1 0.4 0.8 0.7 0.6 0.3 0.7 0.6 0.5 0.3 0.6 0.5 0.4 0.2 0.4 0.5 0.3 0.1 0.3 0.4 0.2
Table C-Bea~ Deeree Days (F-day)
C1-Heatlng Deg .... 01)'1 (B ... 65°F)
San Diego 1,284
C2-Heatlng Degret Day Muhlpller
Passive Solar HeallDss Glazing Area per per Square ~r Square FOOl .20 Fool .00 . .10 .15
12.00 1.34 1.37 1.39 1.42 1.44 11.50 1.31 1.34 1.37 1.40 1.42 11.00 1.28 1.32 1.35 1.38 1.40 10.50 1.25 129 1.32 1.35 1.38 10.00 1.22 126 1.29 1.33 1.36 9.50 1.19 1.23 1.27 1.30 1.33 9.00 1.16 1.20 1.24 1.27 1.31 8.50 1.11 1.16 1.21 1.24 1.28 8.00 1.07 1.12 1.17 1.21 1.25 7.50 1.03 1.08 , 1.13 1.18 1.22 7.00 0.98 1.04 • 1.09 1.14 1.19 6.50 0.92 0.99 1.05 1.10 1.15 6.00 0.84 0.93 1.00 1.06 1.11 5.50 0.76 0.86 0.94 1.01 1.06 5.00 0.67 0.78 0.87 0.95 1.02 4.50 0.57 0.69 0.79 0.89 0.97 4.00 0.46 0.59 0.71 0.81 0.90 3.50 0.32 0.48 0.62 0.73 0.82 3.00 0.20 0.35 0.51 0.64 0.75 2.50 0.06 0.22 0.37 0.53 0.65 2.00 0.01 0.09 0.25 0.41 0.55
Table D-Bue Cue Conaervatioo Performance (Btu/)'!''''''
Base Case 16,145
Table E-ProJected Area Atijuatmeot Factora
~r:Off
South
o 5 10 15 20 25 30
Solar System Type 00, TW, SSA SSB, WW, sse SSD SSE
1.00 1.00 0.98 0.97 0.94 0.91 0.87
o.n 0.76 0.75 0.74 0.72 0.69 0.66
0.75 0.75 0.74 0.73 0.70 0.68 0.65
Table F-80w SYltem SavlojJ FractlODI
Load Collector Ratio
400 300 200 150 100 80 60 50 45 40 35 30 25 20 15
F1-Oirect Gain
DGC1 Double Glazing
0.19 0.24 0.34 0.44 0.60 0.69 0.80 0.85 0.87 0.90 0.92 0.94 0.96 0.97 0.97
Low-e Glazing
0.18 0.23 0.34 0.43 0.60 0.69 0.80 0.85 0.88 0.91 0.93 0.95 0.97 0.99 0.99
F2-Trombe Walla
00C3 R-9 Night InsulatlOll
0.20 0.26 0.37 0.47 0.65 0.75 0.85 0.90 0.92 0.94 0.95 0.97 0.98 0.98 0.98
TWF3 TWA3 TWJ2 TWI4 Load Unvented Vented Unvented Unvented Collector Non-Non-88lec-Night Ratio selective selective tive Insuliltion
400 0.16 0.19 0.23 0.18 300 0.20 0.24 0.31 0.24 200 0.29 0.33 0.43 0.35 150 0.36 0.40 0.53 0.45 100 0.48 0.53 0.68 0.59 80 0.56 0.60 0.75 0.67 60 0.66 0.70 0.84 o.n 50 0.72 0.75 0.89 0.83 45 0.75 0.79 0.91 0.86 40 0.79 0.82 0.93 0.89 35 0.83 0.86 0.95 0.92 30 0.87 0.89 0.97 0.94 25 0.91 0.93 0.99 0.97 20 0.95 0.96 0.99 0.99 15 0.98 0.99 1.00 1.00
San nie,o. CaUfonda
General Project Information
Project Name Floor Area
location Date
Designer
Worksheet I: Conservation Performance Level
A. Envelope Beat Lou
Construction R-value Heat Description Area [Table AJ Loss
Cei6ngslroofa + = + =
Wals + = + =
Insulated Floors + = + =
Non-solar Glazing + = + = Doors + = + =
Btu/"F-h Total
B. Foundation Perimeter Beat Loae Heat Loss Factor Heat Description Perimeter [Table BJ Loss
Slabs-on-Grade X =
Heated Basements X =
Unheated Basements X = Perimeter Insulated Crawlsoaees X =
Btu/"F-h Total
C. IDflltration Beat Lou X X .018 = BtuI"F-h
Buildng AjrChanges
Volume per Hour
D. Total Beat Loa8 per Square Foot 24 X + = BtuIOD-sf
Total Heat Loss Floor Area
(A+B+C)
E. Consel"9'Rtion Performance Level
X X = BtuIyr-sf
Total Heat Healing Degree Heating Degree Loss per Days [Table CJ Day Multiplier
Square Foot [Table CJ
F. Compar:l8OD Conaervation Performance (From Previous Calculation or from Table D) Btuiyr-sf
Compare Line E to Line F
Worksheet D: AllzJ1fary Heat Performance Level
Ii. Projected Area of Pasalve Solar GJazfng
Solar Systsm Ro~rame Net Area Adjustment P 'ected Reference Code Factor Factor [Table E] ~rea
X 0.80 X = X 0.80 X =
X 0.80 X =
X 0.80 X =
X 0.80 X =
X 0.80 X =
X 0.80 X =
sf
Total Area Total
Projected Area
+ .....
Total Roor Total Projected
Projected Area Area per Area Square Foot
B. Load Collector Ratio
24 X + =
Total Total
Heat loss Projected
[Worksheet I] Area
C. Solar SavlDga FractiOD
~l8m Solai Savings SoIarSysIBm Project8d Fraction Reference Code Area [TableF]
X =
X =
X =
X =
X =
X =
X =
+ = Total Total Solar
Projected Savings Area Fraction
D. Auxflfary Beat Performaace Level
[ 1-] X = BtuIyr-sf
Solar Conservation
Savings Performance
Fraction Level [Worksheet I,
SIBp E]
E. Comparative AuxtUary Beat Performaace (From Pravious Cala.Jlalion or from Table G) BtuIyr-cf
Compare Une D to LlBe E
PSle'. WOI'bIuIcts '01' Sa .... Bullden
Worksheet m: Thermal Mass/Comfort
A. Heat Capacity of Sheetrock and Interior Fumtshtngs
Unit Heat Roar Area Capacity
Rooms wi1h Direct Gain x 4.7
Spaces Connected to Direct Gain Spaces X 4.5
B. Heat Capacity of Mus Surfaces EDc10siDI Direct Gain Spaces
Unit Heat Mas DescriptIon (Indu~ 1hickiteas) Area ~ci~
TrombeWals X 8.8
WaterWaRl X 10.4
EXllQsed Slab in SuD X 13.4
EXllQsed Slab Not in Sun X 1.8
X
X
X
= =
= = = = = = =
Total Heat Capacity
Total
Total Heat Capacity
Total
C. Heat Capaclty of Mass Surfaces EDclosln, Spaces Connected to Direct GaIn Spaces
Mass Description (include lhickness)
TrombeWafts
Water WaRs
D. Total Heat Capaclty
E. Total Heat Capaclty per Square Foot
F. Clear Wblter Day Temperature SwIn.
Total
~Area II]
Direct Gain
Sunspaces or
Vented Trombe WaRs
X
X
Comfort Fetor [Table I]
----= =
G. Recommended Maximum Temperature SwIn.
Area
Total Heat
Capacity
Total
X
X
X
X
X
+
+
Unit Heat
C=ci~ IT Ie ]
3.8 4.2
Concitioned Floor Area
Total
Heat
Capacity
Total Heat Capacity
= = = = =
Total
(A+B+C)
=
=
Btul"F
BtuI"F
Btul"F
BtuI"F-sf
Compare Line F to LIne G
Worksheet IV: Summer Cooling Performance Level
A. Opaque Surfaces
Radiant Barrier Absorp-Heat Gain Heat Lou Factor lance Factor Description (Worksheet I] [TableJ] [Table K] [TableL) Load
CeiII!Jgslroofs X X X = X X X = X X X =
Wal. X na X = X na X =
Doors X na X =
Total kBtulyr
B. Non-solar Glum,
~rame Net Area Shade Factor Heat Gain Description Factor [Table MJ Factor [Table lJ load
North Glass X 0.80 X X =
EastGlau X 0.80 X X =
WestGlas. X 0.80 X X =
Skvf!ilhts X 0.80 X X =
kBtulyr Total
C. SOlar GlazID.
Solar System ~rame Net Area Shade Factor Heat Gain Description Factor [Table M] Factor [Table lJ Load
DIrect Gain X 0.80 X X =
StoraQ! Wal. X 0.80 X X =
Suns~ce X 0.80 X X =
X 0.80 X X =
kBtulyr Total
D. IDtemal Gain +( X ) = kBtulyr Constant Variable Number of
Component Component Bedrooms
[Table NJ [Table NJ
E. CooJlDi Load per Square I'oot 1,000 X + = BtuIyr-sf
(A+B+C+D) Floor Area
1'. AdJustment for Thermal Ma88 and Ventilation Btulyr-sf
[Table oJ
G. CooUD. Performance Level Btulyr-sf
(E -F)
B. Comparfaon eoollDi Performance (From Previous Calculation or from Table p) Btulyr-sf
Compare LIne G to LIne B
F3-Water Walil
Load WW~ WWB4 WWC2 Collector No Night Ni ht Insu~tion Selective Ratio Insulaton Surface
400 0.21 0.22 0.23 300 0.27 0.30 0.30 200 0.37 0.43 0.43 150 0.45 0.54 0.53 100 0.59 0.69 0.68 80 0.67 0.77 0.76 60 0.76 0.85 0.85 50 0.82 0.90 0.89 45 0.85 0.92 0.92 40 0.88 0.94 0.94 35 0.91 0.96 0.96 30 0.93 0.98 0.97 25 0.96 0.99 0.99 20 0.98 1.00 1.00 15 0.99 1.00 1.00
F4-Su1llp8C"
Load Collector Suns pace Type Ratio SSA1 SSB1 SSC1 SSD1 SSE1
400 0.26 0.22 0.19 0.31 0.27 300 0.32 0.27 0.24 0.38 0.33 200 0.41 0.35 0.33 0.49 0.44 150 0.49 0.43 0.41 0.58 0.52 100 0.61 0.54 0.54 0.71 0.65 80 0.68 0.61 0.61 0.78 0.72 60 0.77 0.70 0.71 0.85 0.81 50 0.82 0.76 0.77 0.90 0.86 45 0.84 0.79 0.80 0.92 0.88 40 0.87 0.82 0.84 0.94 0.91 35 0.90 0.85 0.87 0.95 0.93 30 0.93 0.89 0.91 0.97 0.95 25 0.95 0.92 0.94 0.98 0.97 20 0.98 0.96 0.97 0.99 0.99 15 0.99 0.98 0.99 1.00 1.00
Table G-Base Case AuxlHllJ"f Beat Performance (Btu/yr-af)
Base Case 12,649
SaD Diego, CaUfornla
Passive Solar Design Strategies
Table B-Unlt Beat Capacities (Btu/F-at)
H1-Ma1s Surfaces EnclOllng Direct Gain Spaces
Thickness (inches) Material 2 3 4 6 8 12
Poured Cone. 1.8 4.3 6.7 8.8 11.311.5 10.3 Conc.Masonry 1.8 4.2 6.5 8.4 10.210.0 9.0 Face Brick 2.0 4.7 7.1 9.0 10.4 9.9 9.0
F~Stone 2.1 4.8 7.1 8.5 8.6 8.0 7.6 Buider Brick 1.5 3.7 5.4 6.5 6.6 6.0 5.8 Adobe 1.3 3.2 4.8 5.5 5.4 4.9 4.8
Hardwood 0.4 1.4 1.8 1.7 1.5 1.5 1.5 Water 5.2 10.415.6 20.8 31.241.662.4
H2-Rooms with no Direct Solar Gain
Material Thickness (inches) 2 3 4 6 8 12
Poured Cone. 1.7 3.0 3.6 3.8 3.7 3.6 3.4 Cone. Masonry 1.6 2.9 3.5 3.6 3.6 3.4 3.2 Face Brick 1.8 3.1 3.6 3.7 3.5 3.4 3.2
F~Stone 1.9 3.1 3.4 3.4 3.2 3.1 3.0 Bui der Brick 1.4 2.6 3.0 3.1 2.9 2.7 2.7 Adobe 1.2 2.4 2.8 2.8 2.6 2.4 2.4 Hardwood 0.5 1.1 1.3 1.2 1.1 1.0 1.1
Table I-Comfort Factors (Btu/ef)
Direct Gain 870
Sunspac:es and 290 Venled Trombe Walls
Table J-Radlant Barrier Facton
Radianl Barrier 0.75
No Radianl Barrier 1.00
Table K-80lar Absorptances
Color Absorptance
Gloss While 0.25 Semi-gloss While 0.30 Light Green 0.47 Kelly Green 0.51 Medium Blue 0.51 Medium Yellow 0.57 Medium Orange 0.58 Medium Green 0.59 IJghl Buff Brick 0.60 Bare Conael8 0.65 Red Brick 0.70 Medium Red 0.80 Medium Brown 0.84 Dark Blue-Grey 0.88 Dark Brown 0.88
Table ~Beat Gain Facton
Ceiling/roofs 66.9 Walls and DOOIS 31.3 Nor1h Glass 31.1 EastGlas6 87.0 West Glass 77.5 Skyflghls 150.5 Direct Gain Glazing 57.3 Trombe Walls and 0.8 Water Walls
S~ 26.9 SSB1 26.9 sse1 0.8
SSD1 26.9
SSE1 26.9
Table lII-8badlng Facton
Projection FackIr South East North West
0.00 1.00 1.00 1.00 1.00 0.20 0.83 0.95 0.89 0.94
0.40 0.60 0.83 0.78 0.81
0.60 0.40 0.69 0.67 0.66
0.80 0.28 0.56 0.56 0.54
1.00 0.17 0.45 0.45 0.43
1.20 0.10 0.35 0.34 0.34
Table N-JDternal Gain Facton
Constant Component 2,040 kBtulyr
Variable Component 850 kBtulyr-BR
Table O-Tbermalllla .. and VentUatlon Adjustment (Btu/;yr-ef)
Total Heal Nighl Nighl No Nighl No Nighl Capacity Venl wI Vent wI No Venl wI Venl wI No per SF Ceil. Fan Ceil. Fan Ceil. Fan Ceil. Fan
0.0 5,970 3,510 6,000 2,760 1.0 7,310 4,810 7,330 4,060 2.0 8,020 5,560 8,050 4,810 3.0 8,400 6,000 8,430 5,240 4.0 8,610 6,250 8,640 5,500 5.0 8,720 6,390 8,740 5,640 6.0 8,780 6,480 8,800 5,730 7.0 8,810 6,520 8,840 5,770 8.0 8,820 6,550 8,850 5,800 9.0 8,830 6,570 8,860 5,820 10.0 8,840 6,580 8,870 5,830
T olal heal capacity per square fool is calculated on Works heel III Step E.
Table P-Base Case CoollDg Performance (Btu/.f-;yr)
Base Case 8,309
Worksheet Instructions
GeDeral The Worksheets provide a calculation procedure to estimate the performance level of passive solar building designs. It
is recommended that the results be compared to Worksheet calculations for the builder's typical house. Performance levels for the NAHB base case used in the guidelines are also provided for compartson. A separate worksheet is provided for the four separate performance levels and associated base cases. The worksheets are supported by a number of data tables. The tables are given a letter designation and are referenced next to each worksheet entIy, when applicable. The floor area used in the calculations should not include
sunspaces, garages or other unconditioned spaces.
WOl'ksheet I-CoD&e1'VatioD Pedormance Level This is an estimate of the amount of heat energy needed by the building each year from both the solar system and the auxtliaJy heating system. For Step A, it is necessruy to measure the net area of surfaces that enclose conditioned space. For walls, the net surface area is the gross wall area less the window and door area. Rough frame dimensions are generally used to measure window area. The R-values in Table A4 are for the rough frame window area. Heat loss from passive solar systems is excluded. The surface area of direct
gain glazing. Trombe walls, water walls and the walls that separate sunspaces from the house are ignored. Step A tncludes consideration of Insulated floors over crawlspaces, unheated basements or garages. R-values are provided in Table A3 that account for the buffering effect of these unconditioned spaces. When Insulation
is not installed in the floor assembly, but
rather around the perimeter of a crawlspace or unheated basement, Step B should be used. The perimeter method of Step B is used for slabs-on-grade, the below-grade portion of heated basements, unheated basements (when the floor Is not insulated), and perimeter insulated crawls paces (when the floor Is not Insulated). Heated basement walls that are above grade should be considered in
Step A Slab edge perimeter, unheated
basements or perimeter insulated crawlspaces adjacent to sunspaces
should not be included. The conservation performance level is
calculated as the product of the heat loss
per degree day per square foot (Step DJ and the heating degree days, adjusted for
the heat loss and solar glazing per
square fool The adjustment is taken
from Table C, based on data calculated on Woricsheet I, Step D and Worksheet H,
Step A
PSIC'. Worksheetl for Home Bullden
Should the estimated conservation performance level be greater than desired, the designer should consider additional building insulation or reducing non-south glass area.
Worksheet D-AuzIIlaJy Beat Pedormance Level This is an estimate of the amount of heat that must be provided each year from the auxlliaIy heating system. It accounts for savings due to solar energy. In Step A ,the user may enter the rough frame area of solar gIaztng. since it
is generally easier to measure the rough frame area than It is the net glazing area. The worksheet includes a net area factor of 0.80 to account for window frames and mullions. If the designer enters the net glass area. then the net area factor is 1.00. The projected area of the solar systems may be calculated using the adjustment factors in Table E or by
making a scaled elevation drawing of the building facing exactly south and
measuring the glazing area from the scaled drawing.
The projected area per square foot is calculated as the last part of Step A. This is used to determine the heating degree days adjustment used on Worksheet I, Step E. The load collector ratio is calculated in Step B. This Is used to determine the solar savings fractions in Step C. The solar systems used in Step C should be identical to those used in Step
A. The first and last columns of Step A are simply carried down.
The solar savings fraction is determined separately for each type of passive solar system by looking up values in Tables Fl through F4. The suns pace system types are shown beneath Table F4.
If the auxtliary heat performance level calculated in Step D is larger than desired, the designer should consider increasing the size o(lfue solar systems or adding additional solar systems, i.e. thermal storage walls.
Worksheet III-Comfort Performance Level This is the temperature swing expected on a clear winter day with the auxiliary heating system not operating. This worksheet requires that two sub-areas be defined within the building: those areas that receive direct solar gains and those areas that are connected to rooms that receive direct solar gains. Rooms that are separated from direct
gain spaces by more than one door should not be included in either
category.
Thermal mass elements located in
unconditioned spaces such as sunspaces
are not included.
An exposed slab is one finished with
vinyl tile, ceramic tile or other highly
conductive mater1als. Carpeted slabs should not be considered exposed. The exposed slab area should be further
reduced by about 50 percent to account for throw rugs and furnishings.
As a rule-of-thumb, exposed slab area should be considered to be in the sun only when it is located directly behind south glazing. The maximum slab area that is assumed to be in the sun should not exceed 1.5 times the adjacent south glass area. In Step F, the projected area of solar glazing calculated on Worksheet n is used to calculate the comfort performance level. The projected area of water walls and unvented Trombe walls
is excluded in this step. A high temperature swing indicates inadequate thermal mass or too much direct gain solar glazing. If the comfort performance level is greater than desired (l3°F recommended), additional thermal mass should be added to the building or direct gain glazing should be reduced.
Workabeet lV-8ummer Coollog
Pedormance Level This is an estimate of the annual cooling
load of the buil~the heat that needs to be removed from the building by an
air conditioner in order to maintain comfort during the summer. In Step A. only the envelope surfaces that are exposed to sunltght are to be included. For Instance, floors over crawlspaces and walls or doors adjacent to garages are excluded. Steps B and C of the worksheet account for solar gains. They use the rough frame area since this is easier to measure. The worksheets include a net area factor of 0.80 to account for window
frames and mullions. If the net window area is used, the net area factor is 1.00. Table M gives the shade factor for windows with overhangs based on a projection factor. The projection factor is the ratio between the horizontal projection of the overhang from the surface ofwtndow and the distance from the bottom of the window to the bottom of the overhang. When windows have sunscreens, tints or fllms, the shade factors in Table M should not be used. Instead, a shading coefficient should be determined from manufacturers'
literature.
If the cooling performance level is
greater than desired, the designer should consider reducing non-south glass, providing additional shading or increasing thermal mass.
Passive Solar
Design Strategies
EXAMPLE
Passive Solar Industries Council
National Renewable Energy Laboratory
Charles Eley Associates
With Support From:
U.S. Department ofEnerg,y
_________________________________ 39
San Diego California The Worked ExaDlple
40
The Worked Example
Description of
Example Building
A 1.504 square foot passive
solar. single-family home is used
to illustrate how to fill in the
worksheets. See sketches for
the building layout. A vartety of
design features have been
incorporated into the house to
help illustrate how to handle
different situations in the
worksheets.
The building selected has
good insulation as deSCribed on
Worksheet I.
The east portion of the house
is slab on grade. The great room
and master bedroom are
constructed over a crawlspace.
N N Garage
The house has a semi-
enclosed sunspace with vertical
glazing. The sunspace floor has
a four-inch thick slab-on-grade
with quany tile set in a mortar
bed. The sunspace is separated
from the conditioned portion of
the house by sliding glass doors
and a masonry fireplace wall.
Sunspace ventilation is provided
to the outside by awning
windows located at the top and
bottom of the south wall.
South facing windows
provide direct gain solar heating
to the dining area. kitchen and
master bedroom. The south
glazing in the kitchen and dining
area provides heat to an exposed
slab-on-grade finished with
ceramic tile to provide direct
gain heat storage.
The house faces 10 degrees
to the east of true south.
3040
4040
Great Room
WORKED EXAMPLE
The house is equipped with a
ceiling fan to help reduce the
air-conditioning load. North
windows have an overhang with
a projection factor of 0.30. East
and west windows are small and
have no effective overhang
because of the gable roof. South
windows. including the
sunspace windows. have an
overhang with a projection factor
of 0.20.
Take-offs from the house are
given in the worksheets. Refer
to the Circled values in the
worksheet tables to locate where
the various values which show
up in the worksheets come from.
Performance, is found to be
satisfactory on all four
worksheets.
3040
Bedroom
•••••.•. w ............... ~~ •• Master Bedroom
4050
8088
28'
o 2 4 8 12
Floor Plan ----
PASSIVE SOLAR DESIGN STRA TEGIES 41
•
South Elevation
I
North Elevation
:~-. "1
~
Section
Sao Diego. CaUfomla
42 WORKED EXAMPLE
Sao Diego. California
San Diego California
43
NOTE: These worksheets are completed
for the example house described on the
previous pages. Also the reference tables
are marked up showing how the numbers
are selected.
Worksheets
Sao Diego. Ca11fomla
44
General Project Information
Project Name 9A>S\~ So...A~ GcA(V).fLE. Floor Area
Location >AN "D ' ~bo j e..A Date
Designer
Worksheet I: Conservation Performance Level
A. Envelope Heat Loss
Construction Description
Ceilings/roofs 1l-16 ,N A'f"{ l(....
Walls 'R:-l\ k 9...-0 $~€A1'\;\}b)G
'0.-1\ A! &AAAGf
Insulated Floors
Doors
B. Foundation Perimeter Heat Loss
Description
Siabs-on-Grade
Heated Basements
Unheated Basements
Perimeter Insulated Crawlspaces
C. IDflltratlon Heat Loss i :l.'-HB
Building Volume
D. Total Heat Loss per Square Foot 24
E. Conservation Performance Level
1.6'-1'-\
Total Heat
Loss per
Square Foot
Area
140
51.
Lso
Perimeter
R-value [Table A]
+ ;1..1.'1 =
+ ig.1 =
+ 1~.15 =
+ i2....0 =
+
+
+
+
+
+
X
X
X
X
Heat Loss Factor [Table B]
0.80
= = = = = =
= = = =
x O.t;o X .018 = Air Changes per Hour
Heat Loss
1..1
\z...
11
Heat Loss
I 5$ BtufOF-h Total
BtufOF-h
X 4\9 + \';0'1 = ,. 6~'-t Btu/DO-sf
Total Heat Loss Floor Area (A+B+C)
X \'2.84
Heating Degree
Days [Table C)
X I. let =
Heating Degree
Day Multiplier
[Table C]
l\6S0 Btu/yr-sf
F. Comparison Conservation Performance (From Previous Calculation or from Table 0) Btu/yr-sf
Compare Line E to Line F
SaD Dlego, CallforDia
45
Worksheet II: AuxUiary Heat Performance Level
A. Projected Area of Passive Solar Glazing
Solar System R01h Frame Net Area Adjustment P~ected Reference Code rea Factor Factor [Table EI rea
]CZL ! 69 X 0.80 X O.ttS = 65
'5Sc.l ~a X 0.80 X 0.<19 = I' >
X 0.80 X =
X 0.80 X =
X 0.80 X = X 0.80 X = X 0.80 X = v:t6 2..'3 z... sf Total Area Total
Projected
Area
2.:~1... + 1504 = O. \.e;
Total Floor Total Projected Projected Area Area per Area Square Foot
B. Load Collector Ratio
24 X 41" + l..JZ-= C;O
Total Total Heat Loss Projected [Worksheet II Area
C. Solar Savlngs Fraction
System
Solar System Projected Solar Savings Fraction Reference Code Area [Table F]
]26(",,( 65 X O.g~ = 5:.8.. ~s.
~Sc..1 Uil X 0.1'1 = jlS," I
X =
X =
X =
X =
X =
lai.t·L6 + ·l.Tl.. = ().1Q
Total Total Solar Projected Savings Area Fraction
D. AuxlUary Heat Performance Level
[1 -O.ll\ X IlbSO = l~<;J Btu/yr-sf Solar Conservation Savings Performance Fraction Level [Worksheet I,
Step EI
E. Comparative AuxlUary Heat Performance (From Previous Calculation or from Table G) il.6--I ]. Btu/yr-sf
Compare Line D to Line E
San Diego. CaUfomla
46
Worksheet m: Thermal Mass/Comfort
A. Heat Capacity of Sheetrock and Interio, Furnishings
Unit Heat Floor Area Capacity
Rooms with Direct Gain 46£1 X 4.7
SQaces Connected to Direct Gain SQaces li~ 1\ X 4.5
B. Heat Capacity of Mass Surfaces Enclosing Direct Gain Spaces
Trombe Walls
Water Walls
EX!)Qsed Slab in Sun
Mass Description (include thickiless)
EX!)Qsed Slab Not in Sun
Area
1~1
Unit Heat
C~ci~ IT Ie )
X 8.8
X 10.4
X 13.4
X 1.8
X
X
X
Total Heat Capacity
= 2..H~ l
= ~~, l
6.4.~1.. Total
Total Heat Capacity
=
= = 1380
= L~I
= = =
162.J Total
C. Heat Capacity of Mass Surfaces Enclosing Spaces Connected to Direct Gain Spaces
Unit Heat Mass Description C~ci~ Total Heat (include thickiless) Area IT Ie ) Capacity
Trombe Walls X 3.8 =
Water Walls X 4.2 =
'((.\{..£ l!~~ \\l X 1'-1 = 41\
X =
X =
Yll Total
D. Total Heat Capacity (A+B+C)
E. Total Heat Capacity per Square Foot 9'1go + \~0::l = <j. (,
Total Heat Conditioned
Capacity Floor Area
F. Clear Winter Day Temperature Swing
Total Comfort PWcected Area Factor I orksheet II) [Table I)
Direct Gain 6q X 6 10 = 6ooJo
SunsQaces or 16;3 X L/1.0 = ~12..10
Vented Trombe Walls lO' ~oo + ~~,\o = \7..·6
Total Total Heat Capacity
G. Recommended Maximum Temperature Swing iJ
Btu/OF
Btu/OF
Btu/OF
Btu/OF
Btu/OF-sf
OF
of
Compare Line F to Line G
SaD Diego. California
47
Worksheet IV: Summer Cooling Performance Level
A. Opaque Surfaces
Radiant Barrier Absorp-Heat Gain Heat Loss Factor tance Factor Description [Worksheet I) [Table J) [Table K) [Table L) Load
Ceilings/roofs .3 11 X \.00 X (kG X ~b.q = 17..7..{.
·L1 X /.0& X O.~:J X ~,.tj = /1-1
X X X =
Walls !t3 X na Q.]o X :n~ = .\~ !g
X na X =
Doors ~ X na Q.]O X il.l = g~
J~~ ~ kBtulyr
Total
B. Non-solar Glazing
Rough Frame Net Area Shade Factor Heat Gain Description Area Factor [Table M) Factor [Table L) Load
North Glass 40 X· 0.80 X o,ay X 31.1. = fjJb
East Glass b X 0.80 X I 00 X Sl.O = '-T I Q,
West Glass C2 X 0.80 X l·OO X 11.~ = liz..
Sklllights X 0.80 X X = l b z., kBtu/yr
Total
C. Solar Glazlng
Solar System Rough Frame Net Area Shade Factor Heat Gain Description Area Factor [Table M) Factor [Table L) Load
Direct Gain sa X 0.80 X O·IH X ~7-J = JJ'-\a·
Storage Walls X 0.80 X X = Sunseace '2...08 X 0.80 X Q.e3 X O.S = \ 10
X 0.80 X X =
1'1~~ kBtu/yr Total
D. Intemal Gain 'Z..O"'it) +( gt;'o X 1. ) = '-1$,\0 kBtu/yr Constant Variable Number of Component Component Bedrooms [Table N) [Table N)
E. Cooling Load per Square Foot 1,000 X j'!,~Ll + \ S"oi-\ = ~C(j~ Btu/yr-sf (A+B+C+D) Floor Area
F. Adjustment for Thermal Mass and Ventilation fflB(; Btu/yr-sf
\Jo N\6Lb"l VEiJ"iLI."I<lnolJ; 'k! ,C'"AtJ [Table 0) c...€1I_"l1J6
G. Cooling Performance Level z..o8 Btu/yr-sf (E -F)
H. Comparison Cooling Performance (From Previous Calculation or from Table P) ffWt1 Btu/yr-sf
CompareLlneGtoLlneH
San Diego. CaUfomia
48
Table A-Equlvalent Thermal Performance of AaaembUea R-valuea (br-F-af/Btu)
Allic Construction
Framed Construction
2x6 al16"oc 2x6at24"oc 2x8 at 16"oc 2x8 at 24"oc 2xl0 at 16"00 2xl0 at 24"00 2x12 at 16"00 2x12 at 24"00
~~Ie
Framing
2x4 at 16"oc 2x4 at 24"oc 2x6 at 16"oc 2x6 at 24"oc
Double Wall Framing
A1-ceUlngaiRoofl
Insulation R-value R-3() R-38 R-49 R~ @ 35.9 46.9 57.9
Insulation R-value R-19 R-22 R-3O R-38
14.1 15.8 16.3 15.3 16.5 17.1 17.0 18.9 20.6 21.1 17.6 19.6 21.6 22.2
~ 20.1 24.5 25.7 .4 20.7 25.5 26.8 18.8 21.0 25.5 30.1 19.0 21.4 27.3 31.4
A2-Framed Walls
R-l1
~ 14.1 14.3
Insulation R-value R-13 R-19 R-25
13.6 13.9 15.4 17.7 19.2 15.6 18.2 19.8
Total Thickness (inches) 8 10 12 14
25.0 31.3 37.5 43.8
The R-value of insulating sheathing should be added to the values in this table.
A3-lnaulated Floors
Insulation A-value Framing R-ll R-19 R-3O A-38
2x6s at 16"00 18.2 23.8 29.9 2x6s at 24"00 18.4 24.5 31.5 2x8s at 16"00 18.8 24.9 31.7 36.0 2x8s at 24"00 18.9 25.4 33.1 37.9 2xl 0 at 16"00 19.3 25.8 33.4 38.1 2xl0 at 24"00 19.3 26.1 34.4 39.8 2x12 at 16"00 19.7 26.5 34.7 39.8 2x12 at 24"00 19.6 26.7 35.5 41.2
These R-values include the buffering effect of a ventilated crawlspace or unconditioned basement.
Double 1/4" space 112" space
LeW-8
M-Windowl
Metal Standard Frame wI Wood Metal Thermal Frame Frame Break
1.8 2.1 3.1
qp
2.2
1.5 1.8 3.0
Triple 1/4" space 2.7 1.8 2.1 112" space 3.3 2.2 2.7
These R-values are for the entire rough frame window opening. When storm sash is added, an additional 1.1 may be added. One half the R-value of moveable insulation may also be added, when appropriate.
Sao Diego. California
Table A-coDtinued ••
A5-Doors
Solid wood with Weatherstripping
Metal with rigid foam core
®
5.9
Table B-Perimetv Heat Loaa Facton for 8laba-oD-Grade and Basements (Btu/h-F-ft)
Perimeter Insulation
None R-5 R-7 R-l1 R-19 R-30
Heated Siabs-on-Base-
G~ ments (Qj) 1.3 0.4 0.8 0.3 0.7 0.3 0.6 0.2 0.4 0.1 0.3
Unheated Insulated Base-Crawl-ments spaces
1.1 1.1 0.7 0.6 0.6 0.5 0.5 0.4 0.5 0.3 0.4 0.2
Table C-Beating Degree Days (F-day)
C1-HIating Degree DaYI (B881 65°F)
San Diego 1,284
C2-HIatlng Degree Day Multiplier
Passive Solar HeatLess Glazing Area per per Square orr Square Foot Foot .00 . .10 .15 .20
12.00 1.34 1.37 1.39 1.42 1.44 11.50 1.31 1.34 1.37 1.40 1.42 11.00 1.28 1.32 1.35 1.38 1.40 10.50 1.25 1.29 1.32 1.35 1.38 10.00 1.22 1.26 1.29 1.33 1.36 9.50 1.19 1.23 1.27 1.30 1.33
9.00 1.16 1.20 1.24 1.27 1.31
8.50 1.11 1.16 1.21 ~ . ."l.1.28 800 1.07 1.12 1.17 . 1.25
1.''"'''1:50 1.03 1.08 1.13 1.22
7.00 0.98 1.04 1.09 1.14 1.19 6.50 0.92 0.99 1.05 1.10 1.15 6.00 0.84 0.93 1.00 1.06 1.11 5.50 0.76 0.86 0.94 1.01 1.06 5.00 0.67 0.78 0.87 0.95 1.02 4.50 0.57 0.69 0.79 0.89 0.97
4.00 0.46 0.59 0.71 0.81 0.90 3.50 0.32 0.48 0.62 0.73 0.82 3.00 0.20 0.35 0.51 0.64 0.75
2.50 0.06 0.22 0.37 0.53 0.65 2.00 0.01 0.09 0.25 0.41 0.55
Table D-Baae Case Conservation Performance (Btu/yr-si)
Base Case 16,145
Table E-ProJected Area Adjustment Facton
Degrees off Solar System Type True 00, TW, SSA SSB, South WW, sse SSD SSE o 1.00 0.77 0.15
5 *' 0.76 0.75 10 O. 0.75 0.74 15 .97 0.74 0.73 20 0.94 0.72 0.70 25 0.91 0.69 0.68 30 0.87 0.66 0.65
Table F--SOlar System Saving FractlODB
F1-Dlrect Gain
Load DGCl 00C3 Collector Double Low-e R-9Ni9ht Ratio Glazing Glazing Insulation
400 0.19 0.18 0.20 300 0.24 0.23 0.26 200 0.34 0.34 0.37 150 0.44 0.43 0.47 100 0.60 0.60 0.65 80 0.69 0.69 0.75 60 ~ 0.80 0.85 50 0.85 0.90 45 0.88 0.92 40 0.90 0.91 0.94 35 0.92 0.93 0.95 30 0.94 0.95 0.97 25 0.96 0.97 0.98 20 0.97 0.99 0.98 15 0.97 0.99 0.98
F2-Trombe Walls
TWF3 TWA3 TWJ2 TWI4 Load Unvented Vented Unvenled Unvented Collector Non-Non-Salec-Night Ratio selective selective tive Insulation
400 0.16 0.19 0.23 0.18 300 0.20 0.24 0.31 0.24 200 0.29 0.33 0.43 0.35 150 0.36 0.40 0.53 0.45 100 0.48 0.53 0.68 0.59 80 0.56 0.60 0.75 0.67 60 0.66 0.70 0.84 0.77 50 0.72 0.75 0.89 0.83 45 0.75 0.79 0.91 0.86 40 0.79 0.82 0.93 0.89 35 0.83 0.86 0.95 0.92 30 0.87 0.89 0.97 0.94 25 0.91 0.93 0.99 0.97 20 0.95 0.96 0.99 0.99 15 0.98 0.99 1.00 1.00
F3-Water Walls
Load WWA3 WWB4 WWC2 Collector No Night Night Selective Ratio Insulation Insulation Surface
400 0.21 0.22 0.23 300 0.27 0.30 0.30 200 0.37 0.43 0.43 150 0.45 0.54 0.53 100 0.59 0.69 0.66 80 0.67 0.77 0.76
60 0.76 0.85 0.85 50 0.82 0.90 0.89 45 0.85 0.92 0.92 40 0.88 0.94 0.94 35 0.91 0.96 0.96 30 0.93 0.98 0.97 25 0.96 0.99 0.99 20 0.98 1.00 1.00 15 0.99 1.00 1.00
F4-Sunspaces
Load Collector Sunspace Type Ratio SSAl SSBl SSCl SSDl SSEl
400 0.26 0.22 0.19 0.31 0.27 300 0.32 0.27 0.24 0.38 0.33 200 0.41 0.35 0.33 0.49 0.44 150 0.49 0.43 0.41 0.58 0.52 100 0.61 0.54 0.54 0.71 0.65 80 0.68 0.61 0.61 0.78 0.72 60 0.77 0.70 ~ 0.85 0.81 50 0.82 0.76 0.90 0.86 45 0.84 0.79 0.92 0.88 40 0.87 0.82 0.84 0.94 0.91 35 0.90 0.85 0.87 0.95 0.93 30 0.93 0.89 0.91 0.97 0.95 25 0.95 0.92 0.94 0.98 0.97 20 0.98 0.96 0.97 0.99 0.99 15 0.99 0.98 0.99 1.00 1.00
Table G-Base Case Auxillarr Heat Performance (Btu/yr-&f)
Base Case 12,649
Table H-Unit Heat Capacities (Btu/F-s1)
Hl-Mass SUrfaces Enclosing Direct Gain Spaces
Material Thickness (inches) 2 3 4 6 8 12
Poured Conc. 1.8 4.3 6.7 8.8 11.3 11.5 10.3 Conc. Masonry 1.8 4.2 6.5 8.4 10.210.0 9.0 Face Brick 2.0 4.7 7.1 9.0 10.4 9.9 9.0 2.1 4.8 7.1 8.5 8.6 8.0 7.6 FI~Stone Buider Brick 1.5 3.7 5.4 6.5 6.6 6.0 5.8 Adobe 1.3 3.2 4.8 5.5 5.4 4.9 4.8 Hardwood 0.4 1.4 1.8 1.7 1.5 1.5 1.5 Water 5.2 10.4 15.6 20.8 31.2 41.6 62.4
H2-Rooms with no Direct Solar Gain
Material Thickness (inches) 2 3 4 6 8 12
Poured Conc. 1.7 3.0 3.6 3.8 3.7 3.6 3.4 Cone. Masonry 1.6 2.9 3.~3.6 3.4 3.2 Face Brick 1.8 3.1 3. 3 3.5 3.4 3.2
FI~~ Stone 1.9 3.1 3.4 3.4 3.2 3.1 3.0 Bui der Brick 1.4 2.6 3.0 3.1 2.9 2.7 2.7 Adobe 1.2 2.4 2.8 2.8 2.6 2.4 2.4 Hardwood 0.5 1.1 1.3 1.2 1.1 1.0 1.1
Table !-Comfort Factors (Btu/s1)
Direct Gain 870
Sunspaces and 290 Vented Trombe Walls
Table J-Radlant Barrier Factors .
Radiant Barrier
No Radiant Barrier ~ QQQ.J
Table K-8olar AbSOrptaDCeB
Color Absorptance
Gloss White 0.25 Semi-gloss White 0.30 Light Green 0.47 Kelly Green 0.51 Medium Blue 0.51 Medium Yellow 0.57 Medium Orange 0.58 Medium Green 0.59 Light Buff Brick 0.60 Bare Concrete 0.65 Red Brick 0.70 Medium Red 0.80 Medium Brown 0.84 Dark Blue-Grey 0.88 Dark Brown 0.88
Ceiling/rools Walls and Doors North Glass East Glass West Glass Skylights Direct Gain Glazing Trombe Walls and Water Walls
S~
SSBl SSC1 SSDl SSEl
0.8
26.9
~ 26.9 26.9
Table M-SbacllDg Factors
49
Projection FaclOr South ~ North West
0.00 1.00 0.20 0.83 0.40 0.60 0.60 0.40 0.80 0.28 1.00 0.17 1.20 0.10
0.95 0.83 0.69 0.56 0.45 0.35
1.00 Gil
~ Bi 0.94 lQ.].aI' 0.81
0.67 0.66 0.56 0.54 0.45 0.43 0.34 0.34
Table N-lDterDal Gain Factors
Constant Component 2,040 kBtu/yr
Variable Component 850 kBtulyr-BR
Table o-Tbermal Ma .. and Ventilation Adjustment (Btu/)'l"-td)
Total Heat Night Night No Night No Night Capacity Ventwl Ventw/No Ventwl Ventw/No per SF Ceil. Fan Ceil. Fan Ceil. Fan Ceil. Fan
0.0 5,970 3,510 6,000 2,760 1.0 7,310 4,810 7,330 4,060 2.0 8,020 5,560 8,050 4,810 3.0 8,400 6,000 8,430 5,240 4.0 8,610 6,250 8 5,5 5.0 8,720 6,390 ,1 6.0 8,780 6,480 8 7.0 8,810 6,520 , 8.0 8,820 6,550 8,850 9.0 8,830 6,570 8,860 10.0 8,840 6,580 8,870
Total heat capacity per square foot is caJQJlated on Worksheet III, Step E.
Table P-Base Case Cooling Performance (Btu/sf-yr)
Base Case 8,309
San Diego. Califomia
50 WORKED EXAMPLE
San Diego. CaUforDia
PASSIVE SOLAR DESIGN STRA TEGIES
Glossary
AuzWary HeatiDg System: a term for
the system (gas, electric, oil, etc.) which
provides the non-solar portion oC the
house's heating energy needs, referred to
as the "auxilary heat."
British Thermal Unit (Btu): a unit used
to measure heat. One Btu is about equal
to the heat released from burning one
kitchen match.
CODllervation: In addition to energy
conservation In the general sense, the
term is used to refer to the non-solar,
energy-saving measures In a house
which are primarily involved with
Improving the building envelope to guard
against heat loss --the Insulation, the
air infiltration reduction measures, and
so forth.
Direct Gain: a passive solar system In
which the sunlight falls directly Into the
space where it is stored and used.
Glazing: often used interchangeably with
window or glass, the term actually refers
to specifically just to the clear material
which admits sunlight, and so can also
be plastic. Double and triple glazing
refer to two or three panes.
Indirect Gain: a passive solar system in
which the sunlight falls onto thermal
mass which Is positioned between the
glazing and the space to be heated, I.e. a
1'hermal Storage Wall or Trombe Wall.
Low-Emissivity: the term refers to a
surface's ability to absorb and re-radiate
heat. A material with a low emissivity
absorbs and re-radlates relatively small
amounts of heat. Low-emissivity or "low-
e" glass sandwiches a thin layer of
metallic film or coating between two
panes of glass. The low-e glass blocks
radiant heat, so it will tend to keep heat
energy inside the house during the
winter, and kL-ep heat energy outside the
house during the summer.
Pal.ive Solar: design and construction
techniques which help a building make
use of solar energy by non-mechanical
means, as opposed to active solar
techniques which use equipment such
as roof-top collectors.
Phaae-Cbange Material.: materials
such as salts or waxes which store and
release energy by changing "phase"; most
store energy when they turn Uquid at a
certain temperature and release energy
when they turn solid at a certain
temperature, but some remain solid but
undergo chemical changes which store
and release energy. Phase change
materials can be used as thermal mass
but few products are commercially
available at this time..
Purchaaed Energy: although the terms
are often used Interchangably, a house's
"purchased energy" is generally greater
than its "auxilary heat" because heating
systems are seldom 100% efficient, and
more energy is purchased than Is
actually delivered to the house.
R-Value: a unit that measures the
resistance to heat flow through a given
material. The higher the R-value, the
better Insulating capability the material
has. The R-value is the reciprocal of the
U-value. (see below)
Radiant Barrier: reflective material used
In hot climates to block radiant heat,
particularly in a house's roof,
Shading Coefllcient: a measure of how
much solar heat will be transmitted by a
glazing material. as compared to a single
pane of clear uncoated glass, which has
a shading coefficient (SC) of 1. For
example, clear double-pane glass might
have an SC In the range of .88.
Reflective glass might have SC's of .03-
.06. In general, lower shading
coefficients are desirable when heat gain
Is a problem.
SUDspace: passive solar system
sometimes also referred to as an isolated
gain system, where sunlight is collected
and stored In a space separate from the
living space, and must be transferred
there either by natural convection or by
fans.
51
SUDtempering: a modest form of a direct
gain passive solar system; suntempered
houses Increase south-facing glass to
about 7 percent of a total floor area. but
add no thermal mass beyond the "free"
mass already In a typical house --
gypsum board, framing, conventional
furnishings and floor coverings.
Temperature Swm,: a measure of the
number of degrees the temperature In a
space will vary during the course of a
sunny winter day without the furnace
operating; an indicator of the amount of
thermal mass In the passive solar
system.
Thermal Mau: material that stores
energy, although mass will also retain
coolness. The thermal storage capacity
of a material is a measure of the
material's ability to absorb and store
heat. Thermal mass In passive solar
buildings is usually dense material such
as brick or concrete masonry, but can
also be tile, water, phase change
materials, etc.
Thermal Storage Wall: a passive solar
system also sometimes called Trombe
Wall or indirect gain system; a south-
facing glazed wall, usually made of
masonry but can also be made of
containers of water.
Tramhe Wall: a thermal storage wall,
referred to by the name of its Inventor,
Dr. Felix: Trombe.
U-Value: a unit representing the heat
loss per square foot of surface area per
degree OF of temperature difference (see
R-value above).
San Diego, Califorula
52
References
General
1. A Sunbuilder's Primer. Solar Energy
Research Institute.
2. Passive: It's a Natural. Solar Energy
Research Institute.
3. The Passive Solar Construction
Handbook, Steven Winter
AsSOCiates/Northeast Solar Energy
Center/National Concrete Masonry
AsSOCiation/Portland Cement
Association/Brick Institute of America.
Available for $29.95 plus $3.00
handling, from Steven Winter Associates,
Attn: Publications. 6100 Empire State
Building. New York. N.Y. 10001
4. Suntempertng en the Northeast, Steven
Winter Associates. Available from them
at the address above for $9.50.
5. Passive Solar Design Handbook,
Volume I, II, III. Available from National
Technical Information Service, U.S. Dept.
of Commerce, 5285 Port Royal Road,
Springfield. Va. 22161, $32.00 each for I
and II. $12.00 for III.
6. Balcomb. J.D •• et al. Passive Solar
Heattng Anal!Jsis. This volume
supercedes and expands Volume III of
the Passive Solar Design Handbook (Ref.
5). Available from ASHRAE,
Publications, 1791 Tull1e Circle NE.
Atlanta. Ga, 30329, $30.00 for ASHRAE
members. $60.00 for non-members.
7. living With the Sun (for consumers)
and BuUding With the Sun (for builders),
PPG Industries.
8. The Passive Solar Iriformation Guide.
PSIC.
9. Passive Solar Trends. Technical briefs
from PSIC.
a. Infiltration in Passive Solar
Construction
b. The State of the Art in Passive Solar
Construction
c. Passive Solar in FactoIY-Built
Housing
d. Radiant Barriers: Top Performers in
Hot Climates
San Diego. CaUfornia
e. Glazings: The Design Considerations
Aren't As Clear As Glass
f. Ideas for Passive Solar Remodeling
g. Passive Homes in the Marketplace
(Class C Studies)
h. Daylighting in Commercial
Buildings
i. Human Comfort and Passive Solar
Design J. Passive Design for Commercial
Buildings
k. Passive Solar: Principles and
Products
1. Increasing Design Flexibility
m. Utilities and Passive: Predicting the
Pay-otT
APPENDIX
Insulation
10. NAHB Insulation Manual, National
Association of Home Builders, National
Research Center. Available from NAHB
Bookstore, 15th and M Streets N.W.,
Washington, D.C. 20005. (202) 822-
0200.
11. UschkotT. James K. The Airtight
House: Using the Airtight Drywall
Approach, Iowa State University
Research Foundation. Available for
$14.95; Attn: Sarah Terrones. EES
Building. Iowa State University. Ames.
IA. 50011
12. Spears. John. Radon Reduction in
New Construction, Interim Guide.
National Association of Home Builders,
Environmental Protection Agency OPA
87-009 •• August 1987. Available from
the EPA or the NAHB Bookstore. 15th
and M Streets N.W., Washington. D.C.
20005. (202) 822-0200.
AppUances
13. Saving Energ!J and Mone!J with Home
ApplianceS. Environmental Science
Department, Massachusetts Audobon
Society/American Council for an Energy
Efficient Economy. Available for $2.00
apiece from ACEE. 100 1 Connecticut
Ave. N.W., Suite 535, Washington D.C.
20036
14. The Most Energy E;jJU:tentAppliances.
1988 Edition, ACEEE, $2.00 apiece at
address above.
PASSIVE SOLAR DESIGN STRATEGIES
Site Planning
15. Builder's Guide to Passive Solar
Home Design and Land Development,
National Fenestration Council. Available
for $12.00 from NFC, 3310 Harrison,
White Lakes Professional Building,
Topeka, KS. 66611
16. Site Planningfor Solar Access, U.S.
Department of Housing and Urban
Development/American Planning
Association. Available for $6.60 from
Superintendent of Documents, U.S.
Government Printing Office, Washington
D.C. 20402
Sunspaces
17. Jones, Robert W. and Robert D.
McFarland. The Sunspace Primer. A
Guidefor Passive Solar Heating, available
for $32.50 from Van Nostrand Reinhold,
115 5th Avenue, New York, N.Y. 10003
18. Greenhousesfor Uvtng, from Steven
Winter Associates, Attn: Publications,
6100 Empire State Building, New York,
N.Y. 10001, $6.95.
19. Concept W, from Andersen
Corporation, Bayport, MN. 56003, $6.95.
20. Passive Solar Greenhouse Design and
Construction, Ohio Department of
Energy/John Spears, 8821 SUver Spring,
Md., 20910.
53
More Information
COWleIVadon and Renewable Energy
Inquiries and Referral Service
(CAREIRS) 1-800-523-2929, Renewable
Energy Information, Box 8900, Silver
Spring, Md. 20907
National Auoclatlon of Rome Build ....
Attention: Technical Services
15th & M Streets N.W.
Washington, D.C. 20005
Nadonal Concrete Masonry
Association
Attention: Energy Engineer
2302 Horse Pen Road
Herndon, Va. 22070
Brick Iutltute of America
Attention: Energy Engineer
11490 Commerce Park Drive
Suite 300
Reston, Va. 22091
Solar Enerll1 Research Iutitute
Attention: Solar Buildings
1617 Cole Boulevard
Golden, Co. 80401
PaBBlve Solar Industries Councll
1090 Vermont Avenue, Suite 1200
Washington, DC 20005
San Diego, California
54 SUMMARY FOR SAN DIEGO. CALIFORNIA
Example Tables
Examples of Heat Energy Savings Passive Solar-Dlrect Gain
Examples of Heat Energy Savings Added Insulation 1,500 sf Single Story House
1,500 sf Single Story House
Base Case 20% 400/0 60"10
R·values Base Case 20% 40% 60% Ceiling/Roof 26 24 24 24 Walls 14 12 12 12 R-values Ceiling/Roof 26 27 33 40 Slab Edge 0 0 0 0 Glass .9 1.8 1.8 1.8 Walls 14 13 17 22 Slab Edge 0 0 0 1
Glass .9 1.8 1.8 1.8 Air ChangealHour 0.75 0.69 0.64 0.69
Air Changea/Hour 0.75 0.44 0.69 0.55 Glass Area (percent of total floor area) West 3.0% 2.0"10 2.0% 2.0%
North 3.00/0 4.0"10 4.0% 4.0% Glass Area (percent of total floor area) East 3.0% 4.0% 4.0% 4.0% West 3.0% 2.0% 2.00/0 2.00/0 South 3.0"10 5.6"10 8.4"10 12.0% North 3.00/0 4.0% 4.0% 4.0% East 3.0% 4.0"10 4.0"10 4.0"10 Added Thermal Ma .. South 3.0"10 3.0% 3.0"10 3.0% Percent of Floor Area 0.0"10 0.00/0 8.7% 30.O"k
Percent Solar Savings Solar System Size (square feet) 22% 24% 29% 37"10 South Glass 45 84 126 180
Added Thermal Mass 0 0 130 450 Performance (Btulyr-sf)
Conservation 16,145 13,806 11,167 8,447 Percent Solar Savings Auxiliary Heat 12,649 10,364 7,823 5,281 22% 37"10 52"10 67"10
Cooling 8,309 4,987 2,094 1,815
Performance (Btu/yr-sf) Conservation 16,145 16,455 16,265 16,035
Auxiliary Heat 12,649 10,362 7,814 5,242
COOling 8,309 5,927 4,388 5,652
Examples of Heat En~y Savings
Suntempe~ 1,500 sf Single Story House
Summary: South-facing glazing has been substantially increased. For these examples, added mass area is assumed to be six times the added south glass area.
Base Case 20"10 40% 60"10
R·Values Ceiling/Roof 26 24 26 32
Walls 14 12 13 17
Slab Edge 0 0 0 0
Glass .9 1.8 1.8 1.8
Air Changea/Hour 0.75 0.69 0.51 0.73
Glass Area (percent of total floor area) West 3.0"10 2.0"10 2.0% 2.0%
North 3.0"10 4.0% 4.0"10 4.0"10
East 3.0% 4.0% 4.0% 4.0"10
South 3.0% 5.6"10 6.7"10 6.7%
Solar System Size (square feet)
South Glass 45 84 100 100
Percent Solar Savings 22"10 37"10 46% 55%
Performance (Btu/yr-sf)
Conservation 16,145 16,455 14,659 11,730
Auxiliary Heat 12,649 10,362 7,801 5,271
Cooling 8,309 5,927 3,557 3,074
Summary: The windoW area has been slightly decreased on the west, increased slightly on the east and north, and increased
significantly on the south.
PASSIVE SOLAR DESIGN STRATEGIES
Examples of Heat Energy Savings Passive Solar-5unspace
1 ,500 sf Single Story House
Base Case 20% 40% 60% R·Values Ceiling/Roof 26 24 24 24
Walls 14 12 12 12
Slab Edge 0 0 0 0
Glass .9 1.8 1.8 1.8
Air Changes/Hour 0.75 0.69 0.69 0.69
Glass Area (percent of total floor area)
West 3.0% 2.0% 2.0% 2.0%
North 3.0% 4.0% 4.0% 4.0%
East 3.0% 4.0% 4.0% 4.0% South (windows) 3.0% 3.0% 3.0% 3.0% Sunspace 0.0% 2.8% 6.7% 13.0%
Solar System Size (square feet) South Glass 45 45 45 45 Sunspace Glass 0 41 100 194 Sunspace Thermal Mass 0 124 300 582
Percent Solar Savings 22% 37% 53% 69%
Performance (Btu/yr-sf) Conservation 16,145 16,462 16,688 17,023 AuxiliarY Heat 12,649 10,357 7,799 5,220 Cooling 8,309 5,962 4,379 5,923
Summary: Insulation and tightness (for the 60% case) have been increased. North and east-facing glazing have been increased slightly. The sunspace assumed here is semi-enclosed (surrounded on three sides by conditioned rooms of the house, as in Figure SSC1 of the worksheets), with vertical south glazing. The common wall is a thermal mass wall made of masonrY. Sunspace glazing is assumed to be double.
55
Examples of Heat Energy Savings Passive Solar-Thermal Storage Wall
1 ,500 sf Single Story House
Base Case 20% 40% 60% R·Values Ceiling/Roof 26 24 24 24 Walls 14 12 12 12 Slab Edge 0 0 0 0
Glass .9 1,8 1.8 1.8
Air Changes/Hour 0.75 0.69 0.67 0.69
Glass Area (percent of total floor area)
West 3.0% 2.0% 2.0% 2.0%
North 3.0% 4.0% 4.0% 4.0% East 3.0% 4.0% 4.0% 4.0% South 3.0% 3.0% 3.0% 3.0% Thermal Storage Wall 0.0% 2.2% 5.1% 9.5%
Solar System Size (square feet) South Glass 45 45 45 45 Thermal Storage Wall 0 33 75 141
Percent Solar Savings
22% 36% 52% 69%
Performance (Btu/yr-sf) Conservation 16,145 16,431 16,501 16,840 AuxiliarY Heat 12,649 10,360 7,803 5,227 Cooling 8,309 5,235 2,610 2,663
Summary: In the case of a Thermal Storage Wall, south-facing glazing and thermal mass are incorporated together. The estimates here assume a 12-inch thick concrete Thermal Storage Wall with a selective surface and single glazing.
Cooling Potential
Basecase 8,309 Btu/yr-sf
Energy
Savings Strategy (Btulyr-sf)
No Night Ventilation 1
without ceiling fans 0 with ceiling fans 3,240
Night Ventilation 1
without ceiling fans 750 with ceiling fans 3,210
High Mass 2
without ceiling fans 580 with ceiling fans 440
Percent Savings
0% 39
9
39
7 5
With night ventilation, the house is ventilated at night when
temperature and humidity conditions are favorable.
2 A "high mass" building is one with a thermal mass area at least equal to the house floor area.
San Diego. California
56 SUMMARY FOR SAN DIEGO. CALIFORNIA
San Diego, California
56
Technical Basis for
the Bullder
Guidelines
How the Builder
Guidelines Were
Produced
The text of the Builder GuideUnes book
is generated by merging two computer
files. The first Is a word-processor file
containing the text; it does not change
from location to location. The second
contains numbers and text and is
location dependent. This second file is
produced by running a computer
program that calculates performance
numbers based on long-term monthly
weather and solar data compiled by the
National Oceanic and Atmospheric
Administration for a particular location.
The merge operation slots the numbers
and text In the second file Into their
correct locations In the first file. This Is
then laser printed to produce the
camera-ready manuscript.
More than a Decade of
Experience
The concentrated effort of research.
design. construction. monitoring. and
evaluation of actual buildings that
started at the First Passive Solar
Conference In Albuquerque In 1976 has
continued up to the present. It Is
estimated that more than 200.000
passive solar homes have been built In
the United States during this time. This
wealth of experience has been reviewed
by SERI. the Technical Committee of
PSIC. and by the Standing Committee on
Energy of the National Association of
Home Builders and is distilled into these
Guidelines.
Analysis Procedures
The analysis procedures used
throughout the Guidelines were
developed using simple. well-established
methods for estimating the performance
of passive solar heating and natural
cooling strategies. These procedures
(described below) were developed at the
Los Alamos National Laboratory with
funding from the U.S. Department of
Energy Solar Buildings Program. See the
references for more Information.
Annual Heat Loss
(Worksheet 1]
The heat-loss calculation is based on a
straightforward summation of the
traditional elements that make up the
bUilding heat-loss coefficient (excluding
the solar components). The worksheet
procedure estimates the annual heat loss
by multiplying the heat-loss coefficient
by annual degree days (times 24 to
convert from days to hours). Degree days
for each month were determined using
an appropriate base temperature that
accounts for an assumed thermostat
setting of 70 degrees. an assumed
Internal heat generation of 36 Btu/day
per sq ft of floor area, and the total
building loss coefficient. This forms the
basis of the table of heating degree day
multipliers. The result of the worksheet
is an estimate of the annual heat
required to maintain comfort. excluding
both positive and negative effects
resulting from the solar components. In
this estimate. no solar heating credit Is
given to east. west. and north windows.
because It Is assumed that these will be
protected by vegetation or other shading
in accordance with the Builder Guideline
recommendations. This Is a conservative
assumption because there w1ll always be
some solar gain through these windows.
APPENDIX
Annual Auxiliary Heat
(Worksheet Il]
The tables of passive solar savings
fractions are calculated using the solar
load ratio (SLR) method (references 1 and
2). Monthly solar savings fraction (SSF)
values are determined using correlation
fits to the results of hourly computer
simulation calculations for a variety of
climates. These 12 values are converted
Into an annual value and entered Into
worksheet Tables FI-F4. The SLR
method gives answers that agree within
about 5% of the hourly computer
simulations and within 11% of the
measured passive solar performance of
55 buildings monitored under the Solar
Buildings Program. The SSF estimates
account properly for both solar gains
and heat losses through the solar
aperture and. thus. correct for omitting
the solar components from the
calculation of annual heat loss.
Temperature Swing
(Worksheet Ill]
The temperature swing estimate on
worksheet III Is based on the diurnal
heat capacity (dhc) method (reference 3).
The method Is an analytic procedure In
which the total heat stored In the
bUilding during one day Is estimated by
summing the effective heat storage
potential of the all the various materials
In the building for a 24-hour periodic
cycle of solar Input. Rooms with direct
gain are assumed to have radiative
coupUng of the solar heat to the mass.
Rooms connected to rooms with direct
gain are assumed to have convective
coupUng. which is rather less effective.
especially for massive elements. The dhc
of the sheetrock. framing. and furniture
Is approximated as 4.5 or 4.7 Btu/"F per
sq ft of floor area. Worksheet Tables HI
and H2 list the Increased value of
diurnal heat capacity for various
conventional materials that are often
used to provide extra heat storage.
assuming these materials replace
sheetrock.
PASSIVE SOLAR DESIGN STRATEGIES
The only numbers in worksheet III
that are location d~pendent are the
comfort factors. taken from Table I. The
direct -gain comfort factor is 61% of the
solar gain transmitted through vertical.
south-facing double glazing on a clear
January day. The driving effect of
suns paces and vented Trombe walls is
assumed to result in one-third this
value. based on data from monitored
buildingS. The origin of the 61 % factor is
described in the references.
Annual Auxiliary Cooling
(Worksheet IV)
The purpose of including the summer
cooling estimates in the Builder
Guidelines is to (1) determine if design
elements added to promote pasSive solar
heating will cause excessive summer
cooling loads and (2) provide a rough
estimate of the effectiveness of solar
shading and natural cooling strategies.
The analysis method is based on a
modified monthly degree-day procedure
in which the day is divided into day and
night periods (reference 4). All estimates
are derived from correlations based on
hourly computer simulations. Solar.
conduction. and internal gains are
estimated for each half-day period in
each month. Delay factors are used to
account for heat carryover from day to
night and night to day. The results are
estimates of annual sensible cooling
delivered by the air conditioner and do
not include latent loads.
Because the the original Los Alamos
monthly procedure is too complex to be
implemented in a worksheet. a Simplified
procedure is adopted on worksheet IV.
Heat Gain Factors and Internal Gain
Factors in Tables L and N are the
calculated annual incremental cooling
loads resulting from a one-unit
incremental change in the respective
heat input parameter (that is. a one-unit
change in UA. glazing area. or number of
bedrooms). The combined heat load
resulting from all inputs is summed and
then adjusted for thermal mass and
ventilation. This correction includes a
constant required to match the
calculated cooling load of the base-case
building. This linearized procedure gives
accurate estimates for cooling loads that
are less than about 150% of the base-
case building; however. it
underestimates very large cooling loads
in poorly designed buildings.
The adjustment factors for
ventilation properly account for
maintaining comfort in hot and humid
climates. Ventilation is restricted to
times when the outside dew-point
temperature is less than 62 OF. This
restriction avoids ventilation when high
hUmidity might cause discomfort.
Notfor Sizing Equipment
All heating and cooling values given in
the Builder Guidelines Tables and
numbers calculated using the
worksheets are for annual heat delivered
or removed by the mechanical heating or
cooling system. You cannot directly use
these numbers for stztng the capacity of
this equipment The methods developed
by the American Society of Heating.
Refrigerating. and Air Conditioning
Engineers for sizing equipment are well-
established and are recommended. The
purpose of the guidance provided in
these booklets is to min1m1ze the
operating time and resources consumed
by this equipment.
Using the Worksheets in
Nearby Locations
The applicability of worksheets I and 11
can be extended somewhat by using the
base-65 OF degree-day value for a site
which is close to the location for which
the worksheet tables were generated. We
recommend limiting such applications to
sites where the annual heating degree-
days are within plus or minus 10% of the
parent location and where it is
reasonable to assume that the solar
radiation is about the same as in the
parent location. The procedure is simple:
Use the measured base-65 OF degree-day
value in worksheet I. line F. instead of
the degree-day value for the parent
location.
Worksheet III depends only slightly
on location. The only variables are the
Comfort Factors in Table I. which only
change with latitude. Thus. this
worksheet can be used anywhere within
4 degrees of latitude of the parent
location.
The cooling estimate obtained from
worksheet IV is specific to the location.
Within the same vicinity and within plus
57
or minus 20%. the result could be
adjusted. based on a ratio of cooling
degree days. However. this adjustment is
not done automatically within the
worksheet.
Getting Data
Heating and cooling degree-day data can
be obtained from the National Climatic
Center. Asheville. NC. Refer to
Climatography of the United States No.
81 which lists monthly normals for the
period 1951-1980 on a state-by-state
basis. More than 2400 locations are
listed in this data base.
San Diego, California
58
References
1. J. Douglas Balcomb. Robert W. Jones.
Robert D. McFarland. and William O.
Wray. "Expanding the SLR Method".
Passive Solar Journal. Vol. 1. No.2.
1982. pp. 67-90. Available from the
American Solar Energy Society. 2400
Central Ave. Unit B-1. Boulder. CO
80301.
2. J. Douglas Balcomb. Robert W. Jones.
Robert D. McFarland. and William O.
Wray. Pauive Solar Heatiag AnaJy.i •.
American Society of Heating.
Refrigerating. and Air-Conditioning
Engineers. 1984. Available from
ASHRAE. 1719 Tullie Circle. NE. Atlanta.
GA30329.
3. J. Douglas Balcomb and William O.
Wray. Pauive Solar Heatiag Analyai ••
SupplemeDt One. Thermal Ma ..
Effect. aDd Additional SLK
CorrelatioD •. American Society of
Heating. Refrigerating. and Air
Conditioning Engineers. 1987. See
ASHRAE address above.
4. Robert D. McFarland and Gloria
Lazarus. MODthly AuzlUary CoollDg
E.tlmatiOD for ReaideDtlal Bullcliag •.
LA-11394-MS. Los Alamos National
Laboratory. Los Alamos. NM 87545.
1989.
5. J. Douglas Balcomb and Alexander B.
Lekov. Algorithms for Builder
GuldeUDea. SERI/TP-254-3492. Solar
Energy Research Institute. Golden CO.
Also contained in the Proceedings of the
14th Passive Solar Conference. Denver.
June 19-23. 1989. See ASES address
above.
SaD Diego. CaUforDia
APPENDIX
PASSIVE SOLAR DESIGN STRATEGIES
Any town , USA
59
Note: This is a generic example to explain how to
fill out the worksheets. For an example specific to
this book, refer to the worked example on the
prior pages. The actual house design used for both
examples is the same, but specific numerical
values will be different.
Anytown, USA
60
Introduction
Purpose
The purpose of the Any Town,
USA section is to explain how to
use the passive solar
worksheets in the Passive Solar
Design Strategies: Guidelines for
Home BUilding. Separate
Worksheets booklets are
available for specific locations
throughout the continental
USA. Each booklet contains
detailed technical data for a
specific location. Although the
example presented in this
booklet is for a moderate mid-
Atlantic climate, the procedure
is presented in a general
manner and is intended to be .
used for all locations.
General Description
of Worksheets
The Worksheets booklet for each
location provides an easy-to-use
calculation procedure, allowing
the designer to estimate the
performance level of a particular
building design and compare it
against a base-case performance
level or against the performance
of the builder's more
conventional house.
Anytown, USA
A separate worksheet is
provided for each of four
separate performance levels
perfo~ance level and
associated target. These are
deSCribed below:
Worksheet I: Conservation
Performance Level: the
estimated heat energy needed by
the building each year from both
the solar and auxiliary heating
systems. The units are
Btu/yr-sf.
Worksheet II: Auxiliary Heat
Performance Level: the
estimated heat that must be
provided each year by the
auxiliary heating system. This
worksheet accounts for the solar
savings. The units are
Btu/yr-sf.
Worksheet III: Thermal
Mass / Comfort: the temperature
swing expected on aclear winter
day with the auxiliary heating
system not operating. The units
are OF.
Worksheet N: Summer Cooling
Performance Level: the
estimated annual cooling load of
the building. The units are
Btu/yr-sf.
INTRODUCTION
The estimates from
Worksheets I and II are based on
a heating thermostat setting of
70°F. The .estimates from
Worksheet IV are based on a
cooling thermostat setting of
78°F with no ceiling fans and
82°F with ceiling fans.
The worksheets are
supported by a number of data
tables. The data tables are given
a letter deSignation and are
referenced when applicable next
to each worksheet entry.
A description and drawings
of the example building are
provided below, followed by
completed worksheets. Data
tables have also been included
when appropriate.
Each step of the worksheets
is then explained in detail.
\
( )
\
PASSIVE SOLAR DESIGN STRATEGIES
Description of
Example Building
A 1.504 square foot passive
solar. single-family home with
an 8.3 ft. average ceiling height
is used to illustrate how to use
the worksheets. A floor plan.
building elevations. building
sections and details are shown
below.
The building has an
attached sunspace. The
sunspace floor has a four-inch
thick slab-on-grade with quarry
tile set in a mortar bed. The
sunspace is separated from the
conditioned portion of the house
by sliding glass doors and a
masonry fireplace wall. Awning
windows located at the top and
bottom of the south wall provide
outside ventilation for the
sunspace.
61
South facing windows
provide direct gain solar heating
to the dining area. kitchen and
master bedroom. The south
glazing in the kitchen and
dining area provides heat to an
exposed slab-on-grade.
The east portion of the
house is slab-on-grade
construction. The great room
and master bedroom suite are
raised floor construction. The
slab-on-grade floor in the
kitchen and dining area is
finished with ceramic tile so that
the floor may function as
thermal mass.
The exterior doors are metal
with a foam core center.
~r--~2~O~' --.....;*~i ~ __ ..!:2=2-'--~r· ...... · .... · .............. g4.' ............ : ............. ..
;.. .,...
Garage
Master
Bedroom
14'
8088
4040
Bedroom
Great Room
Suns pace
8088
o 2 4 8 12
FLOOR PLAN ----
AnytOWD, USA
62
I nsulation,.---i''ti"*t:=;::::::l I . ., . .... . .. ' : .r'''<:'.:l.-m~'-'-:!
""""!1rf"'_'11IT'nl-.LA .' .' • § 1111 § III I;, : ..... : . ini~),i~, §1I11 § 1111 ., ..•• ". 1I11§1Il1t=' •.• ' :." .•• 1I11§1II" .• : .' ~'. 1111"
", • "II .~. ", 111' .... . ....
. . '" .•..... " . ",'.' . . . -... '. -.. ' ... ", .. ' ... " . ,' .
• ' II' .' II'
SLAB-ON-GRADE
Anytown, USA
SOUTH ELEVATION
NORTH ELEVATION 024 B 12 ----
' ....... .
. ........................ ::::::::::::::J
"r
ABOVE GRADE SECTION
02 4 B 12 ......
CRAWLSPACE
TYPES OF FOUNDATIONS
INTRODUCTION
FULL BASEMENT
)
\
/
~ I
PASSIVE SOLAR DESIGN STRATEGIES
General pro~ect Information
~:Area 1504 sf
Worksheet I: Conservation Performance Level
A. Envelope Heat Loss
Construction Description
Q!!iliog~L[QQt~ B-;36 io 8!liQ
B-;3Q io Qrull!!Qml Q!!iliog
WiillI~ B-l!:!± B-Z SIl!!iillIliog io BigiQ IO~!JliiI!iQO
B-1!:! io ~iilmg!!
IO~!JliiI!!!Q EIQQ[~ B-1!:! io EIQQ[ Qll!![ ~!!ois!Q Q[5nIl1~I2ii1Q!!
~Qo-~QliiI[ ~Iiili:iog OQ!Jbl!! !:aliilZ!!Q WQQQ E[iillD!! liZ' iili[ giill2
-L.QY:l-i; (!!:;;-4Q)
OQQ[~ M!!!iilllI:li!1l EQiillD QQ[!!
B. Foundation Perimeter Heat.Loss
Description
Sliilb~-QO-!:a[iilQ!! B-Z
H!!iilis!Q BiilS!!ID!!O!S
Uoll!!ru!!Q Eliil~!!ID!!O!~
E!![iID!!t!![ IO~!Jliilt!!Q Qmll:ll~I2ii1Q!!~
C. Infiltration Heat Loss
1246;3
Building
Volume
D. Total Heat Loss per Square Foot
24
E. Conservation Performance Level
H!2
Total Heat
Loss per
Square Foot
X
X
X
Area
]Q64
42Q
!:!!:!2
14Q
Z64
f22
4Q
Perimeter
62
Q f2Q
Air Changes
per Hour
2~6
Total Heat Loss
(A+B+C)
nQ;3
Heating Degree
Days [Table C]
+
+
..,...
+
+
+
+
+
+
+
X
X
X
X
X
+
X
R-value [Table A]
;3f2!:!
24f2
24Z
lZZ
2f26
16
f2!:!
Heat Loss Factor [Table B]
Q;3Q
.018
lf2Q4
Floor Area
Qn
Heating Degree
Day Multiplier
[Table C]
F. Comparison Conservation Performance (From Previous Calculation or from Table O)
63
Heat Loss
= ;3Q
= ]I
= 4Q
6 = ;3Q
=
2!:!
= Z =
1121 Btu/OF-h
Total
Heat Loss
2f2 =
=
=
2f2 Btu/oF-h
Total
112 Btu/OF-h
= 4Z!2 Btu/DD-sf
= lZQn Btu/yr-sf
2f2 ;3!2Q Btu/yr-sf
Com are Line E to Line F
Anytown, USA
64
Worksheet I: Conservation Performance Level
Worksheet I is essentially a heat
loss calculation, similar to the
type of calculation made to size
heating and cooling equipment.
The major difference is that the
calculation does not consider
heat loss through any of the
passive solar systems. The
following building corriponents
in the example building are not
considered in the calculation:
• Heat loss through direct gain
solar glazing.
• Heat loss through walls and
windows that separate the
house from the sunspace.
If the example building had
Trombe walls or water walls,
heat loss through these passive
solar systems would also be
excluded from the calculation.
Heat loss from the passive
solar energy systems is excluded
since the solar savings fractions
in Worksheet II take these losses
into account.
Anytown, USA
CONSERVATION PERFORMANCE LEVEL
Step A. Envelope Heat Loss
The first step is to calculate the
heat loss through the building
envelope. The building envelope
consists of all walls, roofs,
floors, non-solar windows and
doors that enclose the
conditioned space of the house.
Heat loss for each envelope
component is calculated by
dividing the surface area of the
component by the total R-value.
The total envelope heat loss is
the sum of the heat loss for all
of the envelope components.
Table A in the Worksheets
booklet contains R-values that
may be used in the calculation.
There are actually five separate
tables labeled AI, A2, A3, A4
and A5. A separate table is
provided fQr ceilings/roofs,
walls, floors, windows and
doors. The R-values' in these
tables include the thermal
resistance of both the insulation
and other materials that
typically make up the
construction assembly such as
exterior sheathing and
sheetrock. They also account
for framing members that
penetrate the insulation and
reduce the effectiveness.
Ceilings/Roofs
There are two types of
ceiling/roof construction in the)
example building. R-38 mineral \
insulation is located in an attic
space, and R-30 insulation is
located in the framed cathedral
ceiling. The total R-value is
selected from Table Al for each
ceiling/ roof component. The
values in Table Al account for
the buffering effect of the attic
(when applicable), the ceiling
material (sheetrock) and the
effect of framing.
A 1-Ceilings/Roofs
Attic Insulation R-value Construction R-30 I!1J R-49 R-60
27.9 35 46.9 57.9
Framed Insulation R-value Construction R-19 R-22 R-30 R-38
2x6 at 16"oc 14.7 15.8 16.3 -2x6 at 24'oc 15.3 16.5 17.1 -2x8 at 16"oc 17.0 18.9 20.6 21.1 2x8 at 24"oc 17.6 19.6~ 22.2 2x10 at 16"oc 18.1 20.1 24. 25.7 2x10 at 24"oc 18.4 20.7 . 26.8 2x12 at 16"oc 18.8 21.0 25.5 30.1
2x12 at 24 'oc 19.0 21.4 27.3 31.4
The area and R-value of the )
two different types of
construction are entered on two
lines of the table under
"ceilings/roofs" and the heat
loss is calculated by dividing the
surface area by the total .
R-value. Note that the ceiling
over the sunspace is not
included in this calculation.
'\ )
\
/
PASSIVE SOLAR DESIGN STRATEGIES
Walls
There are two types of wall
construction in the example
building. The typical exterior
wall is of 2x6 wood frame
construction with R-19 mineral
insulation in the cavity. An
insulating sheathing with an R-
7 rating is attached to the
exterior surface of the framing.
The wall is finished with 1/2
inch sheetrock on the inside
and a brick veneer on the
outside.
The second type of wall
construction separates the
house from the garage. This
wall is also of 2x6 wood frame
construction With R-19 in the
cavity, but it does not have the
insulating sheathing or the
brick veneer. Note that the
walls that separate the house
from the sunspace are not
included.
It is necessary to measure
the surface area of each type of
wall construction. The surface
area may be determined by
multiplying the length of wall by
the average height and
subtracting the area of doors
and windows.
The R-value of each wall
type is detennined from Table
A2 in the Worksheets booklet.
The R-value of both wall types is
17.7 from the table, but since
the first wall type has R-7
insulating sheathing, this is
added to the value from the
table so that 24.7 is used in the
calculations. These R-values
along with the associated areas
are entered on two lines of the
table and the heat loss is
calculated by dividing each
surface area by the
corresponding R-value.
Single Wall Framing
2x4 at 16"oc 2x4 at 24"oc 2x6 at 16"oc 2x6 at 24"oc
Double Wall Framing
A2-Framed Walls
Insulation R·value R-11 R-13 R-19 R-25
12.0 13.6
12.7 13.9 ~ -14.1 15.4 17. 19.2 14.3 15.6 . 19.8
Total Thickness (inches) 8 10 12 14
25.0 31.3 37.5 43.8
..... The R·value of insulating. sheathing should be added to the values in this table.
Floors
Only the raised floor is
considered in this step of the
heat loss calculation; heat loss
from the slab-on-grade floor is
conSidered in Step B. There is
one type of raised floor
construction in the example
building. R-19 mineral
insulation is placed between
2xlO floor joists at 16 inches on
center; the crawlspace beneath
is ventilated.
65
The total R-value is selected
from Table A3, which considers
the buffering effect of the
crawlspace as well as framing
and the floor materials. The
area and R-value is entered on
one line of the table and the
heat loss is calculated by .
dividing the area by the R-value.
A3-lnsulated Floors
Framing
2x6s at 16"oc 2x6s at 24"oc 2x8s at 16"oc 2x8s at 24"oc 2x10 at 16"oc 2x10 at 24"oc 2x12 at 16"oc 2x12 at 24"oc
Insulation R·value R-11 R-19 R-30 R-38
18.2 23.8 29.9 18.4 24.5 31.5 18.8 24.9 31.7 36.0
18.9 4W 33.1 37.9 19.3 25.8 33.4 38.1 19.3 .1 34.4 39.8 19.7 26.5 34.7 39.8 19.6 26.7 35.5 41.2
These R·values include the buffering effect of a ventilated crawlspace or unconditioned basement.
Had there been different
insulation conditions for the
raised floor, an additional line of
the table would be completed for
each condition.
If the example building had
insulated floors over a garage or
unheated basement, these
components would also be
included in this step.
As an alternative to
insulating between the floor
joists, the perimeter walls of the
crawlspace could have b~en
insulated and floor insulation
eliminated. When this
technique is used, the perimeter
heat loss method in Step B
should be used. Step A only
includes floors when insulation
is placed in the floor assembly.
Anytown, USA
66
Non-solar Glazing
Next, heat loss from the non-
solar glazing is calculated. Note
that the passive solar direct gain
glazing is not included. Also the
windows that separate the
house from the sunspace are
not included.
The rough frame opening of
each window is generally used
for the window area. This is
because the R-values presented
in Table A4 and most heat loss
data presented by window
manufacturers is for the rough
frame opening. Using the rough
frame opening also makes it
easier to estimate window areas
since windows are usually
specified on the plans in terms
of the rough frame dimensions.
A4-Windows Air Gap 1/4 in. 1/2 in. 1/2 in. argon Slandar'd Metal Frame Single .9 Double 1.1 Low-e (e<=0:40) 1.2 Metal frame with thermal break
1.2 1.3
Double 1.5 <t.!> Low-e le<=0.40} 1.6 '. Low-e e<=0.20} 1.7 Wood frame with vinyl cladding Double 2.0
Low-e (e<=0.40l 2.1 Low-e le<=0.20 2.2 Low-e e<=0.10 2.3
2.1 2.4 2.6 2.6
1.2 1.3
1.7 I.S 2.0
2.2 2.5 2.7 2.9
These R-values are based on a 3 mph wind speed and are typical for the entire rough framed opening. Manufacture's data, based on National Fenestration Rating Council procedures, should be used when available. One half the R-value of movable insulation should be added, when appropriate.
Anytown, USA
CONSERVATION PERFORMANCE LEVEL
Windows in the example
building are all double-pane
wood windows with a 1/2 inch
air space between the panes.
The R-value for this window
type is 2.1, selected from Table
A4.
The non-solar window area
is taken from the building plans.
These values are entered in the
table and the heat loss is
calculated by dividing the
window area by the window
R-value. If the example building
had more than one window type
(different R-values), then
additional lines of the table
would be completed.
Doors
The doors are the last
component of the envelope to
consider. The example building
has two exterior doors: the main
entrance and an additional door
to the garage. These have a
total surface area of 40 square
feet and an R-value is selected
from Table A5. Note that the
door that separates the garage
from the exterior is not included
since the garage is
unconditioned.
AS-Doors
Solid wood with 2.2 Weatherstripping
Metal with rigid C1i) foam core
These values are entered in
the table and the heat loss is
calculated by dividing the door
areas by the R-value. If the
example building had more than
one door type (different
R-values), then additional lines
of the table would be completed.
Total
The heat loss of all components
of the building envelope is
summed at the bottom of the
table and this completes Step A
of the worksheet.
)
PASSIVE SOLAR DESIGN STRATEGIES
Step B. Foundation
Perimeter Heat Loss .
Foundation heat loss from
slabs-on-grade. basements and
insulated crawispaces is
estimated by multiplying the
length of perimeter times an
appropriate heat loss factor
taken from Table B.
The dining area, kitchen and
secondary bedrooms in the
example house have slab-on-
grade construction. R-7
insulation is installed around
the perimeter.
The heat loss factor for the
slab edge is 0.3, selected from
Table B. The heat loss factor is
multiplied by the perimeter to
calculate the heat loss. The
units of heat loss, using the
perimeter method, are the same
as for the building envelope
calculated in the previous step.
Note that sunspace slab is not
included in this calculation.
The slab edge perimeter
adjacent to the crawlspace and
the sunspace is also excluded.
Table B-Perimeter Heat Loss Factors for Slabs·on·Grade and Unheated Basements (Btuth·F·ft)
Heated Unheated Insulated Perimeter Siabs-on-Base· Base-Crawl· Insulation Grade ments ments spaces
None 0.8 1.3 1.1 1.1
R 5 ~ 0.8 0.7 0.6 R:7 0.3 0.7 0.6 0.5
R·11 . 0.6 0.5 0.4 R-19 0.2· 0.4 0.5 0.3 R-30 0.1 0.3 0.4 0.2
When a raised floor assembly is
not insulated, for instance, over
crawlspaces insulated at the
perimeter or basements, heat
loss occurs primarily at the
perimeter.
The example house does not
have a basement or a heated
crawlspace, but if it did, the
foundation heat loss would be
calculated by multip1ying the
perimeter of these elements by a
heat loss factor selected from
Table B.
When houses have heated
basements, heat loss from ,
basement walls located above
grade would be included in
Step A.
Step C. Infiltration Heat Loss
The heat loss from infiltration or
air leakage is estimated by
multiplying the building volume
times the air changes per hour
times a heat loss factor of 0.018.
The example building is
estimated to have an infiltration
rate of 0.50 based on local
building experience.
67
The building volume is
calculated by multiplying the
average ceiling height by the
conditioned floor area. In this
example the average ceiling
height is 8.3 ft. The conditioned
floor area is 1,504 sf which does
not include the garage or the
sunspace. The resulting
building volume is 12,483 cubic
feet.
The units of infiltration heat
loss are Btu;oF-h, the same as
for the building envelope and
the foundation perimeter.
Step D. Total Heat Loss per
Square Foot
The total building heat loss is
the sum of the heat loss for the
building envelope (Step A), the
foundation perimeter (Step B)
and infiltration (Step C). For
residences this value will range
between 200 and 500. It
represents the Btu of heat loss
from the building envelope over
the period of an hour when it is
one OF colder outside than
inside. This total heat loss, of
course, does not include heat
loss from the solar systems,
including direct gain glazing.
The result of Step D,
however, is the annual heat loss
per degree day per square foot.
This value is calculated by
mUltiplying the total heat loss
by 24 hours/ day and dividing
by the conditioned floor area.
Anytown, USA
68
Step E. Conservation
Performance Level
Once the total heat loss per
square foot is calculated, the
conservation perfonnance level
may be calculated by
multiplying the total heat loss
per square foot (Step D) by the
heating degree days times the
heating degree day multiplier.
C1-Heating Degree Days ~ 65°F)
Raleigh·Durham ~
This value is from TMY weather tapes and should be used for Worksheet Calculations. It will vary from long term averages.
Anytown; USA
CONSERVATION PERFORMANCE LEVEL
The heating degree days are
selected from Table C 1 and
based on specific locations. The
heating degree day multiplier is
selected from Table C2 and is
based on the total heat loss per
square foot (Step D) and the
passive solar glazing area per
square foot of floor area
(Worksheet II, Step A).
C2-Heating Degree Day Multiplier Passive Solar Heat Loss Glazing Area per per Square per Square Foot Foot .00 .05 .10 .15 .20 8.00 1.03 1.05 1.07 1.09 1.11 7.50 1.01 1.04 1.06 1.07 1.10 7.00 0.99 1.02 1.04 1.06 1.08 6.50 0.97 1.00 1.02 1.04 1.06 6.00 0.94 0.97 1.00 1.03 1.05
~ 0.90 0.94 0.98~. 1.03 .00 0.86 0.91 0.95 . 1.01
~5 Q~ Q~ Q~ Q9 Q~
. 0 0.77 0.83 0.88 . 2 0.96 3.50 0.72 0.78 0.83 0.88 0.93
The conservation
perfonnance level for the
example building is compared to
the base case conservation
perfonnance level in the next
step.
Step F. Comparison
Conservation Performance
The conservation performance
level for the proposed design
may be compared to the base
case perfonnance level for the
area, given in Table D.
Table D-Base Case Conservation Performance (Btu/v. •
Base Case 25,38
Alternatively, the
conservation perfonnance level
may be compared to other
building designs considered by
the builder to be typical of the
area. In this case, the
worksheets would first be
completed for the typical design
and the results of these
calculations would be entered in
Step F.
If the conservation
per.(onnance level of the
proposed building (Step E) is
greater than the base case or
typical-design conservation
perfonnance level. the designer
should conSider additional
building insulation or reduced
non-solar glass area.
)
PASSIVE SOLAR DESIGN STRATEGIES 69
Worksheet II: Auxili Heat Performance Level
/ ) A. Projected Area of Passive Solar Glazing I.
Solar System Rough Frame Net Area Adjustment Projected Reference Code Area Factor Factor [Table E] Area
Q~QI ee X 0.80 X ~e fl~
SSQI 2Qe X 0.80 X ~e jfl~
X 0.80 X
X 0.80 X =
X 0.80 X =
X 0.80 X = X 0.80 X =
2~fl 2~2 sf
Total Area Total
Projected
Area
2~2 -;-jf!Q4 = jf!
Total Floor Total Projected
Projected Area Area per
Area Square Foot
B. Load Collector Ratio
24 X 2~a + 2~2 = ~Q e~
Total Total
Heat Loss Projected
[Worksheet I] Area
C. Solar Savings Fraction
) System
/ Solar Savings Solar System Projected Fraction Reference Code Area [Table F]
Q~Qj fl~ X 44 ~Q ~fl
SSQl jfl~ X 4f! = Z~~f!
X =
X =
X =
X =
X =
jQ~ Zj + 2~2 Q 4f!
Total Total Solar
Projected Savings
Area Fraction
D. Auxiliary Heat Performance Level
[1 -Q4f! jx 1ZQ~Z = ~Q4~ Btu/yr-sf
Solar Conservation
Savings Performance
Fraction Level [Worksheet I,
Step E]
E. Comparative Auxiliary Heat Performance (From Previous Calculation or from Table G) 23 Q99 Btu/yr-sf
Com are Line D to Line E
,
Anytown, USA
70
Worksheet II: Auxiliary Heat Performance Level
Worksheet II is used to estimate
the savings from passive solar
systems and to estimate the
auxiliary heat performance level..
This is the amount of heat that
must be provided to the building
each year after the solar savings
have been accounted for.
The example building has
two solar systems: direct gain
south glazing and a sunspace.
Step A. Projected Area of
Passive Solar Glazing
The first step is to calculate the
projected area of the solar
glazing. The proj ected area of
passive solar glazing is the area
projected on a plane facing true
south (the actual glazing may be
oriented slightly east or west of
true south). The projected solar
glazing also accounts for sloped
glazing in certain types of
sunspaces.
For most solar systems the
projected area may be calculated
by multiplying the actual glazing
area times an adjustment factor
taken from Table E.
Alternatively. the projected
area may be determined by
making a scaled elevation
drawing of the building. looking
exactly north. Surface areas
may then be measured from the
scaled elevation drawing. This
concept is illustrated in the
figure below.
Anytown, USA
AUXILIARY HEA T PERFORMANCE LEVEL
South Projection
Projected Area of Passive Solar Glazing
The solar savings fraction is based on the
projected area of solar glazing.
The worksheet allows the
user to enter the rough frame
area of solar glazing. since it is
generally easier to measure this.
The rough frame area is
multiplied by a net area factor of
0.80 to account for window
framing and mullions. If the net
glass area is entered. the net
area factor is 1.00.
The example building has
two separate passive solar
systems: direct gain and a
sunspace. This means that two
lines of the table must be
completed. If the example
building had other types of solar
systems. for instance Trombe
walls or water walls. additional
lines in the table would be
completed.
In the first column. the
reference code for each type of
solar system is entered along
with a description of the system.
The reference codes are shown
on Tables FI through F4 for
various types of solar systems.
More information about the
system types is provided in the
discussion under Step C of this
worksheet. The reference code
for the direct gain system is
"DGC 1" because night
insulation is not proposed. The
reference code for the sunspace
is "ssc 1" since all the sunspace
glazing is vertical.
The south wall of the
example building actually faces
10° east of south because of site
conditions. The adjustment
factor is therefore 0.98 for both
solar systems as selected from
Table E. Each solar system area
is multiplied by the net area
factor and the appropriate
adj ustment factor to calculate
the projected area. Both the
total projected area and the total .
area are summed at the bottom
of the table.
Table E-ProJected Area Adjustment Factors
Degrees off ~solar System Type True D SSA SSB, South ,S SSD SSE o 1.00 0.77 0.75
5 c$? 0.76 0.75 10 0.98 0.75 0.74 15 . 0.74 0.73 20 0.94 0.72 0.70 25 0.91 0.69 0.68 30 0.87 0.66 0.65
The last part of Step A is to
divide the total projected area by
the conditioned floor area. giving
the total projected area per
square foot. This value is used
in Worksheet I. Step E to
determine the heating degree
day multiplier.
,
./
)
PASSIVE SOLAR DESIGN STRATEGIES
Step B. Load Collector Ratio
The load collector ratio is
calculated by taking the total
heat loss from Worksheet I, Step
D and multiplying this value
times 24 (hours/ day) and
dividing by the total projected
area of the solar glazing
calculated in the previous step.
Step C. Solar Savings Fraction
The next step is to calculate the
solar savings fraction for the
building. This is calculated as a
weighted average of the solar
savings fraction for the separate
passive solar systems. The
weightings are based on
projected area.
The solar systems used in
this step should be identical to
those used above in Step A. The
first two columns are simply
carried down from the first and
last columns in· Step A.
The solar savings fraction for
e9-ch individual system is taken
from Tables F1 through F4
based on the load collector ratio
calculated in Step B and the
type of solar system. Table F1 is
for direct gain systems, Table F2
for thermal storage walls, Table
F3 for water walls and Table F4
for sunspaces. There are
multiple columns in each table
that account for system design
features such as night
insulation or selective surfaces.
A reference code, for
instance "DGC 1 ", is also
provided for each solar system
variation. These references are
entered on the worksheet "Solar
System Reference Code". They
are also a key to additional
information about each solar
system as provided in Passive
Solar Heating Analysis and
other reference manuals.
F1-Direct Gain
Load DGCI DGC2 DGC3 Collector Double Low-e R-9 Night Ratio Glazing Glazing Insulation
200 0.10 0.11 0.13 155 0.13 0.14 0.17 100 0.18 0.20 0.24 80 0.22 0.25 0.30 60 0.28 0.31 0.38 50 0.32 0.36 0.44 45 0.34 0.39 0.47 40 0.37 0.43 0.51 ar 0.47 0.56 ~ 0.52 0.62 . 9 0.58 0.69 20 0.55 0.65 0.77 15 0.62 0.74 0.85
F4-Sunspaces
Load Collector sunsEace Type Ratio SSAI SSBI SCI SSDI SSEI
200 '0.17 0.14 0.11 0.19 0.15 155 0.20 0.17 0.14 0.23 0.19 100 0.26 0.22 0.19 0.30 0.26 80 0.30 0.25 0.23 0.35 0.30 60 0.35 0.30 0.28 0.42 0.36 50 0.39 0.34 0.32 0.46 0.40 45 0.42 0.36 0.35 0.49 0.43 40 0.44 0.39 0.38 0.52 0.46
~ 0.48 0.42 0.56 0.49 0.52 0.46 ~ 0.60 0.54 0.56 0.50 .0 0.65 0.59 20 0.62 0.56 0.57 0.72 0.65 15 0.70 0.64 0.65 0.79 0.73
71
The solar savings fraction for
each system is multiplied by the
projected area and totaled at the
bottom of the table. This total is
then divided by the total
projected area from Step A to
calculate the weighted average
solar savings fraction for the
whole building.
The solar savings fractions
are based on reference designs.
The assumptions made about
these reference designs are
summarized below.
Direct Gain
The direct gain reference
designs are all assumed to have
double-pane glass and sufficient
heat storage to limit the clear
day temperature swing to 13°F.
For the case with night
insulation, the thermal
resistance is assumed to be R-9.
Trombe Walls
The Trombe wall reference
designs are all assumed to have
double-pane glass. The mass
wall is assumed to be 12 inches
thick and constructed of
masonry or concrete.
Water Walls
The water wall reference designs
are all assumed to have double-
pane glass. The water tank is
assumed to be nine inches
thick, extending continuously in
front of the glazing surface. The
space between the water tank
and the glazing is assumed to be
sealed.
Anytown l USA
72
Sunspaces
Data is provided for five
sunspace reference designs as
illustrated on the following
figure. Double glazing is
assumed for all reference
designs. Reference designs
SSAl, SSB 1 and SSD 1 are
assumed to have opaque end
walls. All are assumed to have a
concrete or masonry floor about
six inches thick and a masonry
or concrete common wall
separating the sunspace from
the living areas of the house.
The glazing for designs SSAI
and SSD 1 is assumed to be
sloped at an angle of 50° from
the horizon. The sloped glazing
in designs B and E is assumed
to be at an angle of 30°.
Anytown, USA
AUXILIARY HEA T PERFORMANCE LEVEL
Sunspace Reference Designs
Data is provided for five types of sunspaces.
Step D. Auxiliary Heat
Performance Level
The auxiliary heat performance
level is calculated by multiplying
the conservation performance
level from Worksheet I, Step E,
times one minus the solar
savings fraction, calculated in
the previous step. This value
represents the amount of heat
that must be provided to the
building by the auxiliary heating
system(s).
Step E. Comparative Auxiliary
Heat Performance
The calculated auxiliary heat
performance level may be
compared to the performance
level for a typical basecase
building in the area. This may
be taken from Table G and is
23,099 Btu/yr-sf.
Alternatively, the
performance level may be
compared to a previous
worksheet calculation made for
a typical builder house.
If the auxiliary heat
performance level calculated in
Step D were larger than the base
case auxiliary heat performance,
the designer should conSider
increasing the size of the solar
systems, adding additional solar
systems or increasing insulation
levels.
\ )
I
\
/
PASSIVE SOLAR DESIGN STRATEGIES 73
Worksheet III: Thermal Mass/Comfort
( \ A. Heat Capacity of Sheetrock and Interior Furnishings '\ ) Unit Total Heat Heat Floor Area Capacity Capacity
BQQIDl! lIlli!b Qi[~Q! !:aiilie 424 X 4.7 2H~1
QRiilQ~l! QQee~Q!~g !Q Qi~Q! !:aiilie QRiilQ~l! ~4~ X 4.5 = 42Z1
2452 Btu/OF
Total B. Heat Capacity of Mass Surfaces Enclosing Direct Gain Spaces
Unit Heat Mass Description capaci~ Total Heat (include thickness) Area [Table ] Capacity
nQIDb~ WslIIl! X 8.8 , wm~[Wiillll! X 10.4 =
E~RQl!~g Qliilb ie Que lQa X 13.4 = laaQ
E~RQl!~g Qliilb IlIQ! ie Que laZ X 1.8 = 24Z
X =
X =
X =
122Z Btu/OF
Total
C. Heat Capacity of Mass Surfaces Enclosing Spaces Connected to Direct Gain Spaces
Unit Heat Mass Description Capacity Total Heat (include thickness) Area [Table H] Capacity
I[QIDb~ WslIIl! X 3.8
W~[WiillIl! . X 4.2 = ) EiilQ~ 6[iQis 4" III X 3,Z = 4ll
X =
X =
4ll Btu/OF
Total
D. Total Heat Capacity
a4~Q Btu/OF
(A+B+C)
E. Total Heat Capacity per Square Foot
a4~Q + 15Q4 = 52 Btu/OF-sf
Total Heat Conditioned
Capacity Floor Area
F. Clear Winter Day Temperature Swing
Total Comfort Projected Area Factor [Worksheet II] [Table I]
Qi~Q! !:aiilie 2~ X a22 = 5~Z54
Quel!RiilQ~l! Q[ 12a X 2~~ = 4a zaz
~e!~g nQIDb~ WslIIl! lQa 4~1 + a4~Q = 12 a OF
Total Total
Heat
Capacity G. Recommended Maximum Temperature Swing
13 OF
) Com are Line F to Line G
Anytown, USA
74
Worksheet III: Thermal Mass/Comfort
This worksheet is used to
calculate the thermal
mass/comfort performance level,
which is the temperature swing
expected on a clear winter day
with the auxiliary heating
system not operating. A high
temperature swing would
indicate that inadequate thermal
mass is provided in the building
design, which not only creates
discomfort but decreases solar
heating performance.
The general procedure of the
worksheet is to calculate the
effective heat capacity of mass
elements located within the
conditioned space of the
building. The total effective heat
capacity is then combined with
the direct gain projected area to
estimate the clear winter day
temperature swing. Note that
thermal mass elements located
within unconditioned spaces
such as the sunspace are not
included in this calculation.
Anytown, USA
Step A. Heat Capacity of
Sheetrock and Interior
Furnishings
The first step is to estimate the
effective heat capacity
associated with low-mass
construction and interior
furnishings. To complete this
step it is necessary that two
sub-areas be identified within
the building: those areas that
receive direct solar gains and
those areas that are connected
to rooms that receive direct solar
gains. This is because the mass
of sheetrock and furnishings
located in direct gain rooms is
more effective. Rooms that are
separated from direct gain
spaces by more than one door
should not be included in either
category.
COMFORT PERFORMANCE LEVEL
In the example building, the
master bedroom, dining area
and kitchen are all direct gain
space.s. The secondary
bedrooms, bathrooms and
master bedroom closet are
directly connected to the direct
gain spaces. The utility room
and entry foyer are not
conSidered in this calculation
since they are not connected to
a direct gain space. These areas
are illustrated for the example
building.
The direct gain space is
multiplied by 4.7 and the spaces
connected to direct gain spaces
are multiplied by 4.5. These
products are summed and
represent the effective heat
capacity associated with the
sheetrock and interior
furnishings.
Unconditioned
Garage
1i)))1 Direct Gain Spaces
I,l@ililm Spaces Connected to Direct Gain Spaces moo Spaces Not Connected to Direct Gain Spaces
Suns pace
Building Sub-areas for Calculating Effective Heat Capacity
Worksheet 11/ requires that the building be divided into sub-areas.
)
()
)
PASSIVE SOLAR DESIGN STRATEGIES
Step B. Heat Capacity of Mass
Surfaces Enclosing
Direct Gain Spaces
The heat capacity of thermal
mass elements (other than
sheetrock and furnishings) that
enclose the direct gain spaces is
conSidered in this step. The
surface area of each element is
measured from the building
plans and multiplied by the unit
heat capacity. The unit heat
capacity is printed directly in
the table for Trombe walls. water
walls. and exposed slabs-on-
grade. The unit heat capacity
for other mass elements is
selected from Table H 1. Note
that thermal mass located in the
sunspace is not included in this
calculation.
H1-Mass Surfaces Enclosing Direct Gain Spaces .
Material
Poured Conc. Conc. Masonry Face Brick Flag Stone Builder Brick Adobe Hardwood Water
Thickness (inches) 1 2 3' 4 6 8 12
1.8 4.3 6.7 8.8 11.311.5 10.3 1.8 4.2 6.5 8.4 10.210.0 9.0 2.0 4.7 7.1 9.0 10.49.9 9.0 2.1 4.8 7.1 8.5 8.6 8.0 7.6 1.5 3.7 5.4 6.5 6.6 6.0 5.8 1.3 3.2 4.8 5.5 5.4 4.9 4.8 0.4 1.4 1.8 1.7 1.5 1.5 1.5 5.2 10.415.6 20.8 31.241.6 62.4
Exposed slabs-on-grade
include those with a surface of
vinyl tile. ceramic tile or other
materials that are highly
conductive. Slabs that are
covered with carpet should not
be considered to be exposed.
The exposed slab area should be
further reduced. when
appropriate. to account for
throw rugs and furnishings.
The exposed slab area is
then subdivided into two areas:
that which is expected to be in
the sun and that which is not.
As a rule-of-thumb. slab area
should be considered in the sun
only when it is located directly
behind south glazing. In any
event. the slab area assumed to
be in the sun should not exceed
1.5 times the south glass area.
In the example building. the
slabs-on-grade located in the
kitchen and dining room are
located within direct gain
spaces. Some of this area is
considered to De in the sun and
the remainder not. These
surface areas are entered in the
table and multiplied by the
appropriate unit heat capacity.
The products are then summed
at the bottom of the table.
75
Step C. Heat Capacity of Mass
Surfaces Enclosing Spaces
Connected to Direct Gain
Spaces
The same type of calculation is
performed for mass surfaces
that enclose spaces connected
to direct gain spaces. The
primary difference is the unit
heat capacity figures taken from
Table H2 instead of Table H 1.
In the example building. the
fireplace wall and hearth are
considered in this category.
This area and the unit heat
capacity is entered in the table
and multiplied by each other.
This represents the total
effective heat capacity of mass
elements that enclose the
spaces connected to direct gain
spaces.
H2-Rooms with no Direct Solar Gain
Material
Poured Conc. Conc. Masonry Face Brick
Fla~Stone Builder Brick Adobe Hardwood
Thickness (inches) 1 2 ~ 4 6 8 12
1.7 3.0 3.6 3.8 3.7 3.6 3.4
1.6 2.9 3.5 ~.6 3.4 3.2 1.8 3.1 3.6 3.7 .5 3.4 3.2 1.9 3.1 3.4 . 3.2 3.1 3.0 1.4 2.6 3.0 3.1 2.9 2.7 2.7 1.2 2.4 2.8 2.8 2.6 2.4 2.4 0.5 1.1 1.3 1.2 1.1 1.0 1.1
Anytown, USA
76
Step D. Total Heat Capacity
The total heat capacity is the
sum of the heat capacity from
Steps A, B and C. This
represents the effective heat
capacity of all thermal mass
within the building.
Step E. Total Heat Capacity
per Square Foot
The total heat capacity
calculated in Step D is divided
by the total floor area of the
building to get the total heat
capacity per square foot. The
floor area used in this
calculation should not include
the sunspace or other
unconditioned spaces. This
value is calculated here for
convenience, but it is not used
until Worksheet IV is completed.
Anytown, USA
Step F. Clear Winter Day
Temperature Swing
The clear winter day
temperature swing is calculated
in Step F. The projected area of
all direct gain glazing is entered
in the first row. This includes
all direct gain systems either
with or without night insulation.
In the second row, the projected
area of sunspace glazing and
Trombe walls vented to the
indoors is entered. Unvented
Trombe walls and water walls
are not included in this
calculation since solar gain from
these systems does not
contribute to the temperature
swing of the conditioned space.
The appropriate comfort
factor is entered in the second
column, selected from Table I.
,(he projected areas are
multiplied by the appropriate
comfort factors and summed.
This sum is then divided by the
total heat capacity from Step D
to yield the clear winter day
temperature Swing.
Table I-Comfort Fact~r Btu/sf)
Direct Gain
Suns paces and 99 Vented Trombe Walls
COMFORT PERFORMANCE LEVEL
Step G. Recommended
Maximum Temperature Swing
The comfort performance target '\
for all locations is 13°F. If the )
comfort performance level
calculated in Step F had been
greater than 13°F, additional
thermal mass should be added
to the building or direct gain
glazing should be reduced.
'\ !
)
PASSIVE SOLAR DESIGN STRATEGIES 77
Worksheet IV: Summer Coolin Performance Level
'\ A. Opaque Surfaces
Radiant Barrier Absorp-Heat Gain j Heat Loss Factor tance Factor Description [Worksheet I] [Table J] [Table K] [table L] Load
Q!2i1iDg:!lrQQf:! ~Q X j QQ X Q !lZ X !lZQ = !2!2~
lZ X j QQ X Q!I:Z X !lZQ = ~Z!2
X X X =
W§II:! !lQ X na QZQ X 2!2~ = Z~!2
X na X =
OQQ[:! ~fi X na Q~Q X 2!2~ = 2a
jaQ~ kBtu/yr
Total
B. Non-solar Glazing
Rough Frame Net Area Shade Factor Heat Gain Description Area Factor [Table M] Factor [Table L] Load
t!/Q[tb !:al~:!:! !lQ X 0.80 X Q !2Z X ~ZQ = ~~fi
X 0.80 X X =
ESI:!t !:a lSi:!:! !2 X 0.80 X Q aQ X !2a ~ = ~~j
X 0.80 X X =
W!2:!t!:aI~:!:! !2 X 0.80 X QaQ X Z~2 = ~fij
X 0.80 X X =
Slsllligbt:! X 0.80 X X =
X 0.80 X X =
j!2ZZ kBtu/yr
Total
C. Solar Glazing
Solar System Rough Frame Net Area Shade Factor Heat Gain
\ Description Area Factor [Table M] Factor [Table L] Load
)
Oi[!2Qt !:a~iD aa X 0.80 X Q a~ X fifiQ = ~2g
X 0.80 X X =
StQ[~g!2 llll~lI~ X 0.80 X X
X 0.80 X X =
S!.ID:!J2~Q!2 2Qa X 0.80 X Qa~ X j22 = j!2afi
X 0.80 X X =
!la~~ kBtu/yr
Total
D. Internal Gain
22fiQ +( ~!lQ X ~ = fiQZQ kBtu/yr
Constant Variable Number of
Component Component Bedrooms
[Table N] [Table N]
E. Cooling Load per Square Foot
1,000 X j~ !I!I~ + jfiQ!I a~!l2 Btu/yr-sf
(A+B+C+D) Floor Area
F. Adjustment for Thermal Mass and Ventilation
No night vent with no ceiling fan Z~!2 Btu/yr-sf
[Table 0]
G. Cooling Performance Level
a2Q!2 Btu/yr-sf
(E -F)
H. Comparison Cooling Performance (From Previous Calculation or from Table P)
9Z!2!2 Btu/yr-sf
Com are Line G to Line H
Anytown, USA
78
Worksheet IV: Summer Cooling Performance Level
Worksheet IV is used to
calculate the summer cooling
performance level. This is the
heat that would need to be
removed from the bUilding by an
air conditioner in order to
maintain comfort during the
summer.
The worksheet accounts for
four sources of cooling load:
opaque surfaces exposed to the
sun, non-solar windows, passive
solar systems, and internal gain.
These loads are then adjusted to
account for ventilation and
thermal mass ..
Step A. Opaque Surfaces
Not all opaque surfaces
contribute to the cooling load of
the building: only those surfaces
exposed to sunlight
(ceilings/roofs and walls) are
included in the calculation. For
each ceiling and wall surface
listed on Worksheet I and
exposed to the sun, the heat
loss should be carried over to
this worksheet along with a
consistent description. This
heat loss is then multiplied by a
radiant barrier factor when
appropriate (from Table J), the
absorptance (from Table K) and
a heat gain factor (from Table L).
The end product of this
calculation is an estimate of the
annual cooling load that is
associated with each suIface in
thousands of Btu per year
(kBtu/yr).
Anytown, USA
SUMMER COOLING PERFORMANCE LEVEL
Table J-Radiant Barrier Factors
Radiant Barrier
No Radiant Barrier .0
Table K-Solar Absorptances
Color
Gloss White Semi-gloss White Light Green Kelly Green Medium Blue Medium Yellow Medium Orange Medium Green Light Buff Brick Bare Concrete Red Brick Medium Red Medium Brown Dark Blue-Grey Dark Brown
Ceiling/roofs Walls and Doors North Glass East Glass West Glass Skylights Direct Gain Glazing Trombe Walls and Water Walls Sunspaces SSAl SSBl SSCl SSDl
Absorptance I 0.51 0.57 0.5B 0.59 0.60
~ 0.B4 O.BB O.BB
39.3
.~
SSEl 39.3
In the example building, four
lines of the table are completed,
two for the ceiling/roof types,
one for the exterior walls with
brick veneer and one for the
entrance door. The wall that
separates the house from the
garage and the door in this wall
are not included, since they are
not exposed to sunlight.
The heat loss from each of
these elements is carried over
from Worksheet I. Note that the
door heat loss is reduced by half .
since one of the two doors does
not receive sunlight. The
proposed building does not have
a radiant barrier in the attic, so
the radiant barrier factor is 1.00.
Absorptances are selected based
on the exterior building colors
and the heat gain factors are
from Table L.
Step B. Non-solar Glazing
Cooling load associated with the
windows that do not face south,
i.e. those that are not part of one
of the solar systems, is
calculated by multiplying the
surface area in each orientation
times the net area factor, a
shade factor (from Table M) and
a heat gain factor (from Table L).
This calculation gives the
annual cooling load for each
non-solar glazed surface. The
total for the building is the sum
of the cooling load for each
surface.
Table M-Shading Factors Projection Factor South
0.00 ~ 0.20 . 0.40 . 3 0.60 0.49 O.BO 0.35
~st North 21 . 1.00 .
.93 ~ .93 . 4I1o,~ 0.B1 1 9' O.Bl • c;1JC7 0.71 0.7 '67 0.6B 0.60 0.6f 0.56 1.00 0.30 0.50 0.54 0.45 1.20 0.24 0.40 0.46 0.3B
-... Multiply by O.B for low-e glass, 0.7 for tinted glass and 0.6 for low-e tinted Qlass.
The rough frame area is
generally entered in the table
and adjusted by the net area
factor. If the net glazing area is
entered instead, then the net
area factor is 1.00.
)
\
PASSIVE SOLAR DESIGN STRATEGIES
Table M gives the shade
factor for overhangs. The
overhang shade factor depends
on the orientation of the window
and the projection factor. The
proj ection factor is the overhang
projection divided by the
distance from the bottom of the
window to the bottom of the
overhang. as illustrated below.
A
Overhang Projection Factor
The projection factor is the overhang
projection divided by the distance between the
bottom of the window and the bottom of the
overhang.
The north windows have a
height of four feet and the
bottom of the overhang is about
six inches above the window
head. The overhang projection
is 1.5 feet. The projection factor
is calculated by dividing the
overhang projection by the
distance from the bottom of the
window to the bottom of the
overhang. This is about 0.33. A
shade factor of 0.84 is used in
the calculations. which is
interpolated between the values
for a projection factor of 0.2 and
0.4
If the example building had
tinted glazing. glazing films or
external shading devices. the
shade factors from Table M
should not be used. Sunscreen
and glass manufacturers
usually rate the shading effect of
their devices by publishing a
shading coefficient. The
shading coefficient is a number
between zero and one that
indicates how much solar heat
makes it through the window
compared to an unshaded 1/8
inch clear pane. This shading
coefficient may be used in the
calculation instead of the value
from Table M.
The overhang on the east
and west is at the eave. well
above the window. and does not
provide any useful shading. For
these windows. the shade factor
is 1.00.
Each glazing area is
multiplied by the net area factor
and the appropriate shade
factor. The products are
summed at the bottom of the
table.
79
Step C. Solar Glazing
The solar systems addressed on
Worksheet II reduce heating
energy. but they also can
increase cooling energy. The
cooling energy impact of the
solar systems is calculated in
this step. Each solar system
listed on Worksheet II should be
carried over to this worksheet.
The cooling energy for each
system is calculated by
multiplying the total surface
area (not the projected area)
times the net area factor. the
appropriate shade factor (as
discussed above) and a heat
gain factor (from Table L). This
calculation gives the annual
cooling load for each passive
solar system.
A shade factor of 0.83 is
used because of south
overhangs. This is based on a
projection factor of about 0.2 as
discussed above.
The annual cooling load
associated with all the passive
solar systems is summed at the
bottom of the table.
Anytown, USA
80
Step D. Internal Gains
The last component of cooling
load is from internal gain.
Internal gain is heat given off by
lights, appliances and people.
Some of the cooling load
associated with internal gain is
considered to be constant for all
houses regardless of the number
of bedrooms or size. This is
because all houses have a
refrigerator and at least one
occupant. Another component
of cooling load from internal
gain is considered to be variable
and depends on the number of
bedrooms. These components
are accounted for separately in
the calculation.
Both the constant
component and the variable
component are taken from Table
N. The variable component is
multiplied by the number of
bedrooms in the house and
added to the constant
component to yield the total
cooling load from internal gain.
Constant Component
Variable Component
Step E. Cooling Load per
Square Foot
This step sums the cooling load
associated with opaque
surfaces, non-solar glazing,
passive solar systems and
internal gain (Steps A, B, C and
D). The sum is then divided by
the floor area of the building
and multiplied by 1,000 to
convert the cooling energy into
terms consistent with the base
case cooling performance.
Anytown, USA
SUMMER COOLING PERFORMANCE LEVEL
Step F. Adjustment for
Thermal Mass and Ventilation
The total cooling load calculated
in Step E is adjusted in this step
to account for the effects of
thermal mass and ventilation.
The adjustment depends on
the total heat capacity per
square foot calculated on
Worksheet III, Step E, but also
depends on whether or not the
building has night ventilation or
ceiling fans. The adjustment is
entered in the blank in Step F.
Table 0-Thermal Mass and Ventilation Adjustment (Btu/yr-sf) Total Heat Night Night No Night No Night Capacity Vent wI Vent wI No Vent wI Vent wI N per SF Ceil. Fan Ceil. Fan Ceil. Fan Ceil. Fan 0.0 4,250 400 2,320 -1,600 1.0 5,550 1,480 3,620 -520 2.0 6,240 2,080 4,310 080 3.0 6,610 2,420 4,680 410 dP 6,800 2,600 4,8 600 . 6,910 2,700 ,0 700 6.0 6,960 2,760 5,0 760 . 6,990 2,790 , 60 790 8.0 7,010 2,810 5,080 810 9.0 7,010 2,820 5,080 820 10.0 7,020 2,820 5,090 820
Total heat capacity per square foot is calculated on Worksheet III Ste E.
The example building has a
total heat capacity per square
foot of 5.6. It has neither night
ventilation nor ceiling fans.
Night ventilation is a
building operation strategy
where windows are opened at
night when the air is cooler.
The cool night air allows heat to
escape from the thermal mass
elements in the building. The
cooler thermal mass elements
help keep the building
comfortable the following day
when air temperatures rise.
Step G. Cooling
Performance Level
The summer cooling \
performance level is calculated' )
by subtracting the adjustment
in Step F from the cooling load
per square foot calculated in
Step E. This is an estimate of
the amount of heat that must be
removed from the building each
year by the air conditioner.
Step H. Comparison Cooling
Performance
The cooling performance level
for the proposed design may be
compared to the base case
cooling performance level for the
area, given in Table P.
Alternatively, the cooling
performance level may be
compared to other building
designs conSidered by the )
builder to be typical of the area.
In this case, the worksheets
would first be completed for the
typical design and the results of
these calculations would be
entered in Step H.
If the cooling performance
level of the proposed building
(Step G) is greater than the base
case or typical-design
conservation performance level,
the designer should conSider
measures to reduce the cooling
performance leveL Such
measures might include
reducing non-solar glass,
providing additional shading or
increasing thermal mass.