Passive Solar Homes

Don’t Pass on Passive Solar

by Michael Holster

But passive solar heating has other benefits besides saving energy, saving money and saving our planet. A passive solar home has a spatially inviting environment that reconnects with nature. A solar home is the most comfortable because it is bathed in warmth and light. Studies show that, under these conditions, physical, emotional, and mental health are improved, and productivity is increased. People prefer this environment to conventional design and consider it a higher quality living space.

In order to reduce the mystery surrounding modern day passive solar heating design and construction, here are some of the most frequently asked questions and their answers:

What type of passive solar heating design is best?

There are many different design approaches that can be taken to build a successful passive solar heated home. But the following four requirements are pretty basic:

1. The house has an exterior wall that faces south or nearly south to maximize solar gain.
2. During the heating season, heat rays from sunshine are absorbed during the daytime into the structure of the house.
3. At night, the stored heat continues to be released inside the house to keep the occupants warm.
4. During the summer cooling season, sunlight is blocked to prevent excess heat from entering the house.

The degree to which all four of these requirements are met determines the effectiveness of the solar heating system. Unfortunately, there are many companies that claim to provide solar heating but really don’t care about performance. When the basic design principles are not followed, the results are poor. Based on these criteria, for example, most sunrooms would fail miserably.

Does the whole house have to be designed for passive solar heating?

No. Starting from scratch and designing the entire house to optimize passive solar heating is certainly the best idea. This option will achieve the greatest energy savings at the least cost. However, almost any standard home design can be modified to successfully incorporate passive solar heating.

Can an existing home be modified to incorporate passive solar heating design?

Yes, it can. And, if possible, it should be. But the potential for passive solar will vary widely with each application. The existing home design places some limits on what can be done and how cost effective it will be.

What should a builder or homeowner do if they are interested in passive solar heating?

The easiest approach is to hire an energy consultant who will then come up with the best design for your application. There are many different passive solar design approaches and each has its own rules of thumb. Using an energy consultant will save a great deal of money as well as time that would otherwise be spent going down blind alleys, “reinventing the wheel”, or developing designs that are too costly.

Why do homeowners find passive solar heating so comfortable and so superior to conventionally heated homes?

Heat is transferred by convection, conduction, and radiation (also known as radiant or infrared). Most conventional heating systems, such as warm air or hot water, heat primarily by convection. The air in the room is heated first which in turn heats our bodies. Passive solar systems provide much more radiant heat that directly enters our bodies via infrared rays. This heat comes from direct and reflected rays from the sun. It also comes from the floors and walls that emit more infrared heat due to their higher temperature.

Human skin, regardless of color, actually has the highest infrared absorptivity factor (0.99) of any material. This means that our skin absorbs infrared heat better and faster than brick, metal, earth, man made materials, or plants and animals. There is no other explanation for this phenomenon except that our bodies are meant to get most of their heat via infrared rather than convection or conduction methods. So, one of the reasons that passive solar heating is so enjoyable may be our own biology: Our bodies crave infrared, not convective, heat.

Does passive solar heating require exotic materials or unusual construction techniques?

No. Most passive solar designs employ the same type of construction materials and techniques that the homebuilder normally uses. However, the choice of materials, how and where they are used makes all the difference. Over the years, some exotic products and techniques have been developed but they have not been widely adopted and are not necessary.

If a house does not have concrete slab floors, can it still have passive solar heating?

Yes. Although the traditional passive solar heating design includes lots of glass windows to admit sunshine, and masonry or ceramic materials to store heat, there are many other design methods that can be followed. This means that even if you don’t have a slab floor or don’t want a whole lot of windows, there are still practical solutions available. On the other hand, if you have slab construction anyway, passive solar heating will give great results at very little additional cost.

Besides saving money on utility bills and increasing home value, are there any other financial incentives for passive solar heating?

Yes. North Carolinians who install passive solar heating between now and the end of 2010 have a special bonus waiting for them. The state offers tax incentives for passive solar heating projects equal to 35 percent of installed cost up to a maximum of $3,500. These incentives are for new construction as well as retrofitting existing homes and are the highest incentives available anywhere in the country. South Carolina has the second highest tax incentive at 25 percent of installed cost up to $3,500.

Passive solar heating is a science, a skill, and an art that has been advanced by dedicated professionals all over the world. State-of-the-art products and design innovations have been created that not only provide many more options, but can achieve superior results. Energy efficient windows and modern insulating materials enhance the effectiveness of solar designed homes. Research is also underway to manufacture construction materials that will store heat more effectively.

The ancient Greek playwright, Aeschylus, wrote in 500 B.C.: “Only primitives and barbarians lack knowledge of houses turned to face the winter sun”.

We have the knowledge. Now we need to get moving!

Michael Holster is President of Solar Vision Inc, an energy consulting and design company specializing in solar, energy and water technologies.