JENNIFER RENNICK ARCHITECT 740 VISTA GRANDE LOS ALTOS CA An easy way to think of passive solar as a concept, is the use of natural warming sunlight to help in the heating of the home in the winter. The rear of the house faces south to taking maximum advantage of the winter sun. To function efficiently, a passive solar home also needs excellent insulation as well as thermal mass. This home is well insulated with R-38 ceiling insulation, approximately R-50 straw-bale wall insulation and two inch rigid foam insulation barrier around the perimeter of the slab floor. Thermal mass is provided by 2-inch thick plastered interior walls, by some cinder block walls (primarily used for structural support) and by the concrete slab floor. In this particular home, most of the slab floor is covered by limestone that provides additional thermal mass. Although we live in a mild climate, winter can be cold and cloudy. Therefore a heating system is necessary for the house. The primary heating system uses three gas fireplaces with inserts that are equivalent to modern gas furnaces used in homes with forced air heating systems. All fireplace inserts are controlled by their own thermostat. The location of the thermostat has been selected in order to activate the heat source thus ensuring a relatively uniform temperature within a given zone. Our experience has taught us to set the thermostats at a comfortable temperature and not change them. This has proven to be comfortable and energy efficient. Additionally, the strategic location of the fireplaces allows for optimal heating of different zones in the home. We prefer a cooler master bedroom for sleeping, so we set that thermostat between 65 and 68 degrees. The thermostats in the other living areas are set at 70 degrees. This maintains an even temperature throughout these spaces. A secondary heating system is a thermostatically controlled hydronic system that warms the upstairs bedrooms, the master bathroom and the library. This system works by circulating hot water from one of the house hot water heaters through insulated copper pipes into each unit. A fan in each unit blows warm air into the space being heated. We have learned that this system is almost never needed. A passive solar home also functions very well in the summer. Potential heat gain from direct sunlight is minimized by the length of the roof overhang, by window coverings and shades for the large skylights. A tree provides shade on the west side. Thermal mass provides year around benefit by modulating the interior temperature. In the winter, thermal mass absorbs heat from solar gain or the heating system and then releasing it back into the environment to provide an even temperature. This results in a nearly imperceptible difference in temperature within any zone, or between zones of the same thermostat setting (see above). In the summer, as heat gain occurs during the day, it is absorbed by the thermal mass maintaining a feeling that the living space remains cool. Then at night, windows and the operable skylights can be opened to cool the house. The thermal mass releases the stored heat during this ventilation time. This works well because of the cool nights we enjoy living in the Bay area. This passive solar home is comfortable and offers secondary benefits by not having air ducts that accumulate dust, allergens and potentially molds. Additionally, one does not have to endure super heated dry air being blown around the house as is the case in most forced air heating systems. Having lived in this home for 10 years, we are convinced that it really does work. Of course this was the intended result of the design by San Luis Passive Solar Group. We hope you enjoy living in this home as much as we have.