Contents

Introduction

Benefits of Design With Climate

Benefits to building owners
Benefits to Builders and Developers

Frequently Asked Questions (FAQ's)

How much can I save?
How much does it cost?
Do "solar homes" have to look "Unusual"?
Why don't more builders Use Design With Climate?
How does one Design With Climate?
What are the basics of Design With Climate?
How does "direct gain" design work?
How well do sunspaces work?

The Passive Solar Industries Council (PSIC)

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Introduction

What is "Design With Climate?"
In a home designed with the climate, the benefits of (the natural energy sources available from) your local climate are used to help meet the need for heating, cooling and lighting. "Passive Solar" design is another term used for "Design With Climate," however the name itself, as well as most previous applications, seem to place more of an emphasis on heating than cooling. For this reason, the term "Design With Climate" is the preferred term used here.

The Benefits

Benefits to building owners owners

More Affordable
A home designed with the climate can cost slightly less to slightly more than an average home to build, but from one third to one half as much to heat and cool!

Better Indoor Environment
Stay warm and cozy in winter, and cool and comfortable in summer, largely through natural means. These homes are generally also more spacious, and better-lit than an average home. And for people with sensitivity to indoor air pollutants, they can easily include more environmentally benign materials in their construction.

Help Save The Planet For Future Generations
Help to reduce air pollution and save limited resources for future generations.

Higher Home Quality and Resale Value
A home designed with the climate is simply a higher quality home because it has been more thoughtfully designed and built to work in harmony with the natural environment. And many of the homeowners who live in these homes enjoy heating and cooling bills half the size of the average home in their community. Resale values tend to be higher than those of comparably sized average homes, according to several studies conducted by the US Department of Energy. Here is a home that won't seem obsolete in the next century. Which isn't very far away if you think about it!

Benefits to Builders and Developers

Builders and developers are finding the benefits of a home "Designed With Climate" increase the home's appeal and marketability. New home buyers are increasingly concerned about the quality of a home, and a SunSmart home offers superior attention to quality. A home "Designed With Climate" gives the seller "the green advantage" by having their homes stand out from the competition in a highly competitive market. And because a builder or developer deals with a limited number of models, typically repeated a number of times within a subdivision, the cost to "Design With Climate" is extra low because the cost for a given model can be spread over all of the homes (of that model) built.

Frequently Asked Questions

How Much Can I Save?
How much you save depends on where you live, the final design of the home, and how well it is built. In general, cost-effective savings for heating and cooling can range from 52% to 87% (see this table for more information).

For example, assuming a typical home in Sacramento, California, you could cut home heating and cooling energy in half simply by facing most of the glass area south, shading windows from the summer sun, and using a better quality window.

A home with the predominant glass facing south is referred to as "Sun-Tempered" design, because the major window area faces south, using the Sun to help Temper the need for heating. To minimize the need for cooling in summer, the smaller window areas are faced to the north, east and west and south windows are shaded by overhangs. Figure 1 below shows the difference in performance for the Sacramento CA example.

Assumptions behind Figure 1:
1) Source: Passive Solar Design Strategies: Guidelines for Home Builders; Sacramento (example tables, page 54).
2) 1,500 s.f. single story house located in Sacramento, CA, USA. Sacramento example was used as Sacramento is a fairly "average" U.S. city in terms of climate.
3) Miscellaneous assumptions used are noted in the table below. Note that the biggest difference between the "Typical" and "Sun - Tempered" home is in window placement and R-value.

	Roof	Wall	Floor	Glass	AC/hr	West Glass	North Glass	East Glass	South Glass	Heating (Btu/yr-sf)	Cooling (Btu/yr-sf)
Typical	R-27	R-15	R-18	R-0.9	0.75	45 sf	45 sf	45 sf	45 sf	23,390	13,717
South	R-30	R-15	R-19	R-1.8	0.72	30 sf	40 sf	40 sf	100 sf	14,399	5,409

Figure 1 helps illustrate the savings possible from simple, cost-effective efficiency measures combined with (predominately) south-facing glass. But this is just a first step in "designing with climate." Further savings are possible by adding additional south-facing glass and some heat-storing "thermal mass." Figure 2 below shows the difference in performance.

Assumptions behind Figure 2:
1) Source: Passive Solar Design Strategies: Guidelines for Home Builders; Sacramento (example tables, page 54).
2) 1,500 s.f. single story house located in Sacramento, CA, USA. Sacramento example was used as Sacramento is a fairly "average" U.S. city in terms of climate.
3) Miscellaneous assumptions used are noted in the table below. Basically, the south facing windows, insulation and air-tightness are increased, and thermal mass is added. Their are a variety of ways to add "Thermal Mass" to a home, including plaster walls, tiled surfaces, double sheetrock, and interior concrete walls (low height walls are typically used to avoid the high cost of tall walls due to structural requirements in earthquake zones).

Roof

Wall

Floor

Glass

AC/hr

West Glass

North Glass

East Glass

South Glass

Thermal Mass

Heating (Btu/yr-sf)

Cooling (Btu/yr-sf)

Typical

R-27

R-15

R-18

R-0.9

0.75

45 sf

45 sf

45 sf

45 sf

0 sf

23,390

13,717

South

R-35

R-19

R-23

R-1.8

0.72

30 sf

40 sf

40 sf

180 sf

450 sf

9,671

2,678

How Much Does It Cost?

Assigning an "added cost" price tag to home designed with climate is not always easy. They can cost much less to much more than a "comparable home" in the same area - it all depends on the (original or base) home design, the climate, and the available materials, expertise, and cost of same. The available data show that most design elements are low-cost and require only small changes in a builder's design. The modest increase can be attributed to higher quality windows, shading, additional tiled floor or some other heat storage material such as plaster, and a ventilation system. Energy design services for a $150,000 home can range from $100 for a few hours of professional consulting time to $1,000 (less than 1% of contracted construction cost), or more, for complete energy services. "Complete services" might include, for example, consultation with your designer, an energy and economic analysis of your energy alternatives and the design and specification of the heating, cooling, and water heating systems. Always ask around and shop around for the best services.

Maintenance and operation costs for a home designed with the climate are negligible. On the cost savings side, they will generally have a smaller heating and cooling system, which helps pay for other improvements. In some cases, the cooling system can be completely eliminated with the cost savings going to pay for the necessary efficiency improvements (to "make it so"). It all depends on the particular home design you begin with, the location, and how much the homeowner must "interact" with the home (such as opening and closing windows instead of purchasing a fan).



Do "Solar Homes" Have To Look "Unusual"?

Design with climate lends itself to virtually all types of design and has been practiced for centuries in many cultures. For example the ancient Anazazi Indians in New Mexico built their homes facing south, and New England "Salt Boxes" were oriented south to help families stay warm in winter. It was the advent of inexpensive (seemingly unlimited) fossil fuel heating and refrigeration cooling that caused interest in "design with climate" to largely disappear.

Many of the "solar homes" you have seen may appear "Unusual" because of the shape of the home and arrangement of windows used, but it doesn't need to be that way. All types of design can benefit from design with climate without sacrificing appearance - it's the designer that determines how the building will look. For example the "sun-tempered" design, whose energy performance is shown in figure 1, has it's window area distributed similar to many average tract homes. With a tract home, a 60/20/10/10 percent breakdown of window is used on exterior wall "facets" (back/front/left side/right side respectively) whereas the "sun-tempered" home example is 40/24/12/24. In either case, the appearance of the windows on these homes can accomodate just about any architectural style.

"When I am working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong."
--R. Buckminster Fuller

How the "Thermal Mass" is designed into the home can also be an appearance issue, but it doesn't need to be that way. There are a wide variety of "thermal storage mass" wall and floor materials commonly available, such as "hard-wall" plaster. In the case of plaster, it can be used on walls or ceilings with no visible impact and can even save on wall finishing time compared to conventional sheetrock in some locations.

Why Don't More Home Builders Use Design With Climate?

Builders identify two barriers to orienting buildings to the south: cost and adaptability of certain building lots. However, both of these barriers are easily overcome.

Orientation is a matter of planning. Many builders and developers have found that the cost to reposition the building is really quite small. Even when home plans are changed to add more windows to the south side of a home, they are generally windows that the builder planned to include in the home anyway, so simply shifting them adds little or nothing to the overall cost.

Physical barriers to orienting a home toward the sun, such as steep slopes, conflicts with the direction of a view or existing street patterns, can frequently be overcome with proper design. Most building lots are adaptable to solar site design. The small amount of extra effort brings worthwhile benefits to both the home buyer and the builder by adding another dimension to a home's comfort, efficiency, value and marketability. With resources available to help in planning solar subdivisions, there's really no reason not to design with climate!

How Does One "Design With Climate?"

Generally speaking, the best way is to use advanced technology to find the most cost-effective mix of features. In a home designed with the climate, the home's energy and economic consequences can be evaluated, before a single nail is driven,with a "Building Simulation" computer software package. Most of the popular computer design tools have been validated against real buildings and other such tests to assure relative accuracy of results and include features like heating/cooling equipment sizing and economic analysis.

But most advanced "Building Simulation" design tools are not likely to be very useful to non-professionals. And one of the most important things these tools can't provide - an evolving knowledge of what is available locally and at what cost - may also escape most non-professionals. For these reasons and more, consider professional assistance.

What Are The Basics Of "Design With Climate?"

First, place the home on the building site in such a way that the home takes full advantage of the sun's natural heat. By facing the long side of a home to the south (north in the southern hemisphere) and the short sides to the east and west, the building can capture more solar heat in winter and more effectively block solar heat in the summer. Although it is best to face most of the windows due south, they can face up to 15 degrees away to the east or west without much loss in energy savings.

Placing most of the windows on the home's south side will expose them to the low winter sun. Carefully designed overhangs and other features can be used to shade them from the high summer sun. Window areas on the east and west should be much lower, because the wall is smaller, and they will be less of a problem in summer. Carefully balanced window locations can enhance architectural appeal, balancing natural light, view, and comfort.

There are some physical constraints, such as steep lots, shading from buildings and trees, and existing street patterns, when orienting a home on a lot. However, with fifteen degrees of flexibility it is much easier for builders to place the home on the lot in a "south-facing direction."

"Design With Climate" concepts are applied most easily in a new building where they can be incorporated into the original design. However, existing buildings can be adapted or retrofitted to passively collect and store solar heat.

How Does "Direct Gain" Design Work?

In a "Direct Gain" design, the living space is warmed - direct - with heat gain from the sun. A sunspace is a common example of "indirect gain" because heat indirectly enters the living space. There are two

Sun-Tempering
The term "sun-tempering" is applied to a house or other building that collects solar radiation through large south-facing windows but does not have additional "thermal storage mass" for longer term heat storage.

The south window area must be sized carefully, because without storage mass there is the possibility that the living space can overheat during the day. Sun-tempering is used when the goal is to reduce the use of the conventional furnace while the sun shines; the furnace will probably be needed at night. Sun-tempering may be particularly suited to buildings that are used primarily during the day.

Direct Gain Solar Design
Direct Gain solar design, in full form, uses both solar (directly gained) and additional thermal storage mass for longer term heat storage. With the thermal storage mass distributed throughout the home, it works very well for homes in climates with significant heating needs, cooling needs, or both. How it works is fairly straightforward:

Winter -
Capture the sun's energy by day - Hold onto it through the night
On a cold winter day, sunlight enters the house through a large area of south-facing windows and strikes "thermal storage mass" in walls and/or floor surfaces. Here, the solar energy is absorbed and stored for the evening (see Winter Day, below).

During a cold winter night, the energy stored during the day is naturally released, as the home begins to cool in response to dropping outdoor air temperatures, providing a portion of the energy needed to heat the home. Because the heat collected and stored in the walls and/or floor surfaces makes these surfaces warmer than in a typical home, a passive solar home is generally more comfortable as well (see Winter Night operation, below).

Summer -
Capture the cool night climate - Block the hot day-time climate
To naturally cool the home, cool night air can be vented into the home to absorb and carry away the heat gained from the day. This also helps "pre-cool" the home for the following day. The night air may be introduced either naturally, through opening windows, or by a whole house fan system. To make the most of this night cooling, a roof overhang, awning or other device is used to shade windows from the hot summer sun during the day. Other measures, such as light colored exterior surfaces, insulation, and radiant barriers may also be used to further increase the effectiveness of night cooling. In some cases, natural night cooling is so effective that no air conditioning is needed at all!

It is important to install the correct amount of thermal storage material in relation to south facing glass. If there is not a balanced amount of heat storage, large temperature swings will occur in the heated space, and problems with overheating may also occur. The ratio of thermal mass to glazing varies with the type of system, type of storage, climatic conditions, and the fraction of heat to be supplied by solar. Likewise, sufficient summer shading and other "heat source" controls are needed to maintain cool indoor temperatures through a hot summer day using natural cooling alone. Professional assistance is recommended for getting the best results.

How well does a Sunspace work?

Known by many names - solar room, greenhouse, solarium - the sunspace has been a popular approach to solar space heating. A sunspace can be built as part of a new building or as an addition to an older building. Although generally not provided with backup heating or cooling during extremely hot or cold weather, due to cost, they are used as extended living space when comfortable.

Solar heat is collected through the sunspace glazing. The distribution of heat from a sunspace can be accomplished in a variety of ways. A masonry wall between the sunspace and the living space can collect and store solar energy for night time heating. Heat can also be moved from the sunspace into the house with the help of a small fan or blower or circulated into the home by simply opening connecting windows and doors between the sunspace and the house. A sunspace also provides a "buffer zone" for the house that will help cut heat loss, and it adds another space to the home, a space that can be used for a variety of purposes, including plants.

Sunspaces are useful primarily as a passive heating device since they do not generally provide any cooling benefit; sunspaces with roof glass may actually add to a home's cooling needs. Because the heat storage in a sunspace is more concentrated (smaller area & thicker) than distributed (larger area and thinner as in Direct Gain), sunspaces are typically considered for climates where cooling is not a problem.

Other Options: The use of one approach to passive solar heating does not preclude the use of another in the same building. It is not unusual for different approaches to overlap. An attached sunspace, for instance, can be combined with direct gain windows in the south-facing wall. The variety of passive options leaves a great deal of room for the individual tastes of homeowners and for the market considerations of homebuilders.

The Passive Solar Industries Council (PSIC)

The Passive Solar Industries Council (PSIC) advances the design of residential, institutional and commercial buildings; making them more affordable, comfortable and environmentally sound. As a leading resource for passive solar design and product information, PSIC offers professional training, consumer education and analysis tools nationwide.

Formed in 1980, PSIC represents a unique partnership of the leading organizations, product manufacturers and professionals within the building industry. PSIC members are industry leaders and recognized experts in the energy efficiency and sustainable development field. From its beginning in 1980, PSIC has pursued a strong partnership with the U.S. Department of Energy's Office of Building Technology and the National Renewable Energy Laboratory (NREL). PSIC represents a uniquely successful public - private partnership for better buildings and a healthy environment. For more information, contact PSIC at:

Passive Solar Industries Council (PSIC)
1331 H. Street, NW
Suite 1000
Washington, DC 20005-4706 USA
Phone (202) 628-7400
Fax: (202) 393-5043
E-Mail: PSIC_DC@AOL.com