Solar Passive Buildings

The Allanson Laboratory and Dormitories are heated by sunlight that enters through south-facing windows in the living areas and two rows of roof windows (clerestories) in the main residence.

In the winter, the sun remains low in the sky throughout the day and sunlight shines through the windows. Ninety-five percent of the transmitted solar energy is absorbed by interior concrete surfaces and converted to heat. Some of the solar heat remains stored in the layers of concrete in the walls and slab floor. At night, as the indoor air cools, the stored heat is gradually released into the room.

In the summer, the sun rises high in the sky and sunlight is blocked from entering the buildings by the overhanging roof. Inside, the shaded concrete surfaces are cool, having lost their daytime heat to the cool night air. The concrete masses act as heat sinks, absorbing warm air temperatures and cooling the living areas.

The effectiveness of the year-round heat flux is dependent on good insulation and tight doors and windows that minimize heat loss. The walls are built from manufactured panels composed of a 4-inch-thick polyisocyanurate insulation (styrofoam) imbedded in a mesh of steel wire. After the panels were erected, they were sprayed with high-density concrete that was trapped by the wire mesh and accumulated to a 1.5-in thickness on the exterior and interior surfaces. The windows are high-quality double-pane glass. Low-emittance glass and the argon-filled space between the panes maximize solar heat gain and minimize heat loss.

Researchers at Arizona State University and University of California, Los Angeles monitored  how these solar passive buildings performed for many years. Thermocouples embedded in the walls and floors or hanging from the ceiling were connected to a datalogger that recorded building temperatures every 20 seconds. These data were then compared to outside temperatures, wind speed, and solar gain from the automated sensors outside the buildings. Experimental buildings such as these are rare and provide researchers with some of the first quantitative data on how solar passive buildings function.

How to use these buildings


To increase solar gain and retain heat, make sure that the south-facing windows are not shaded (e.g., by window screens, or outside patio furniture) and that windows and doors are closed. The reversible ceiling fans in the main residences may be used in their “winter mode.” Fan blades should rotate clockwise to pull the air from the floor upward and uniformly mix the solar heated air in the building.

On typical sunny winter days, the amount of solar radiation entering the buildings should be adequate for indoor comfort. Occasionally, during cloudy or exceptionally cold weather, it may be necessary to use the propane space heaters. Please contact the Reserve Director before turning on or setting the controls for the propane heaters. Experiments with the buildings may be in progress.

Spring and Fall

During the spring and fall, the weather is typically mild and very little activity is needed to maintain comfort in the buildings. Open doors and windows to make use of breezes and cool outdoor air when the buildings are too warm, or close doors and windows to maintain indoor heat when it is cool outdoors.


The strategy in the summer is to “trap” the nighttime low temperature inside the building during the day. Once the sun has set, open the doors and windows, including the clerestories, and let cool outdoor air flow inside to replace warm indoor air. Breezes make this process very rapid and effective and fans are not needed. Even during still nights, cool air will flow in through low windows and doors and replace warm air that rises and flows out through the clerestories. The key to this process is to remember to close the doors and windows as early as possible in the morning and keep them closed during the day to keep warm air out. The concrete surfaces in the buildings are cooled sufficiently during the night to absorb much of the heat gains during the following day.

Any reduction of sunlight and other sources of heat will also aid in maintaining cool temperatures during the summer. Use shades wherever they are available to block sunlight from entering the buildings. Keep cooking to a minimum or cook outdoors to minimize generation of heat inside the buildings. To add to indoor comfort during the day, turn on the ceiling fans which move air past your skin and increase evaporative cooling of your body. Fans should be in their “summer mode,” with the fan blades rotating counter-clockwise, pushing the air downward against your skin.