Direct Gain Solar Designs

Direct gain systems (Fig. 23-3) collect heat directly ¿( within the interior space. The surface area of the storage mass, which is built into the space, accounts for 50 to 60 percent of the total surface area of the space, including interior partitions. Surfaces are constructed of concrete, concrete block, brick, stone, adobe, or other thick, massive materials. Brick veneer or clay tile over a bed of grout is an effective finish. Floors are typically slab-on-grade without carpets or rugs. The sun should strike directly or be reflected onto the massive surfaces as soon as possible after entering the space. During the winter, the warm surfaces raise the mean radiant temperature (MRT) in the room higher than the air temperature, allowing comfortable conditions at 3°C-6°C (5°F-10°F) below normal. The mass also keeps room temperatures from becoming too hot in the summer. When additional cooling is needed, ventilation is provided with operable windows and walls.

Direct gain systems are simple, and offer daylight

and views to the south. Site conditions and window treatments must prevent bright winter sun from creating glare. Too much heat may enter the space on sunny days. Operable window insulation at night keeps the heat inside the space. Glass filters out much of the sun's UV, but enough gets through to the interior to bleach paints, interior furnishings, and other building materials. You should select fade-resistant colors and materials if they will be exposed directly to the sun for a long time.

Daily temperatures in direct gain passive solar spaces typically fluctuate 6°C-17°C (10°F-30°F). A well-designed system can be 30 to 70 percent efficient in capturing and using the solar energy that strikes the building. Direct gain design demands skillful and total integration of all architectural elements within the space, including walls, floor, ceiling, and interior surface finishes. The patterns of sun and shade create texture and rhythm, and the shadows cast on the exterior have a strong impact on the appearance of the building facade.

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