Solar-energy-system performance evaluation: Roberts Home, Reston, Virginia, February 1982-July 1982

Abstract

The Roberts Home in Reston, Virginia is equipped with a passive space heating and cooling system. The passive solar heating system provided 82% of the equipment heating load of 19.5 million Btu for the three-month period, February 1982 through April 1982. The net electrical energy savings from the passive solar space heating system were 4512 kWh or $271 at an average electrical power cost of $0.06 per kWh. Space heating is supplied by three sections of two-story Trmbe wall and a sunspace located on the third floor. Solar energy is stored in the 12-inch Trombe wall, the hollow core north wall, and the masonry walls of two centrally located fireplaces. Four fans draw air from the space between the Trombe wall and the glazing through the north wall core. Three R-12 Thermal Technology curtains reduce nighttime losses from the Trombe wall. The house walls are insulated to R-24 and the roof to R-32. Double-glazed Pella windows are used throughout the house. Backup heat is supplied by electric baseboard heaters and three window-mounted heat pumps. The net electrical energy savings from the passive cooling system were $144 for the period May 1982 through July 1982. In the cooling season, the thermal curtain is closed during the day to avoid solar gain, and opened at night. The sunspace glazing is protected by roll-down metal decking. Two thermal chimneys, which are glazed at the top with Plexiglass to admit solar energy, assist in convecting warm air out of building. A set of cooling tubes supplies cool air to the bottom of the Trombe wall cavity. The cool air is drawn past the wall's surface, between the thermal curtain and the wall, when the curtain is down. Three heat pumps provide auxiliary cooling.