Keeping Solar Simple

When somebody says “solar house,” what do you see? Is it acres of glass and tons of masonry? Most people, builders and designers included, think solar is an all or nothing proposition. Going all the way involves large areas of south facing windows to capture solar heat. The idea is to grab more solar energy than the house needs and save some to use later. Storage requires thermal mass, which means masonry floors and walls, or huge containers of water. Properly designed and built, these all-out solar houses work well.

But for those who may not want to go all the way, there’s an option. Sun tempering provides many of solar heating’s benefits without any special construction requirements or additional costs. You get bright, airy living spaces, with heating costs 10 to 30 percent lower than in non-solar designs.

Sun tempering doesn’t require additional thermal storage mass. It simply balances the amount of heat gain through windows with the amount of thermal mass already present in the house. That prevents overheating.

Sun tempering is a part of the house design. It won’t change the way the house is built. Almost any plan can be modified to take advantage of sun tempering. Sun tempering adds intelligence to the house instead of mass, glass and extra cost. You can go as far as you want, no solar contribution is too small.
—John Raabe, Cooperative Design

Click for larger image

Site and building orientation
You have to be able to see the sun during the heating season to take advantage of its heat. That means finding a site with direct sun even during short winter days. Ideally, that would include December 21, the shortest day of the year. One wall of the house should face within 30 degrees either side of true south. (See the last issue for more details on solar site design.)

Glass
Sun tempered designs don’t generally have more glass than a normal house, it’s just been moved to the south side, By shifting living spaces to the south wall, you also move the windows. As a rule of thumb, south facing glass area should equal between eight and ten percent of the floor area of the house. That amount of glass should capture enough solar energy to heat the living spaces during the day. To be effective in capturing heat in winter, the glass should be vertical. Overhead glass, in sun rooms and skylights, catches more sun in summer, when you don’t want it. Skylights are perfect for bringing daylight into areas without exterior walls, but don’t use them for solar heating.

Living space arrangement
Most sun tempered designs give maximum exposure to the south facing wall by stretching to floor plan out along the east-west axis. Prime living areas go on the south side. Bedrooms, stairs, storage, utility rooms and garages go on the north.

Mini-mass
Full blown passive solar homes require large amounts of thermal storage mass to maintain even indoor temperatures. Although it’s not requires, sun tempered homes can also benefit from extra mass. There are two methods you might consider for adding mass in south facing rooms. First, hang two layers of drywall. Second, install clay tile in mud or on concrete board underlayment. Both techniques add thermal mass without changing the house design.

Insulation
High efficiency windows, ample insulation and extra air sealing help keep the solar heat in the house longer. During days with clear skies or even bright overcast, the heating systems may not be needed at all.

This article appeared in Energy Source Builder Vol. III No. 3, June 1991,
©Copyright 2008 Iris Communications, Inc.