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Designing buildings for the best passive use of solar energy involves consideration of the building's characteristics and the climate. Small buildings in cold climates are often designed for solar heating, but buildings in hot climates need to be designed to minimize solar heat gain while still taking advantage of sunlight. Commercial buildings often have high internal heat sources that require cooling loads in nearly all climates, so they are usually designed to minimize solar heat gain. The case studies presented here represent one case of passive solar heating and one case of passive cooling.
Case Study: Mountain Building Relies on Passive Solar Heating
Rocky Mountain Institute, Snowmass, Colorado
The Rocky Mountain Institute is a 4000-square-foot building that is used as a research center, a greenhouse, and a residence. The bedroom wing of the building is heated mainly by its south-facing windows. The heavily glazed greenhouse is a 900-square-foot area that sustains semitropical growing conditions year round. Plants, fish, and other creatures inhabit the area.
An arch in the greenhouse collects hot air through two stacks that rise to just below the glass. Hot air is drawn into an air-to-air heat exchanger, a device that can recover up to 75% of the heat into fresh incoming air and route it to rooms that need heat. The greenhouse stores solar heat in its floor slabs and in its arch and contents, and provides heat to the living room and the research center.
The Institute also uses the greenhouse to preheat water for the active solar hot water system. Heat stored in the mass of the arch preheats water in polybutylene piping going to the active solar system, reducing the necessary collector area by more than one-third.
Case Study: Navy Building Uses Passive Solar to Minimize Cooling Loads
Building 850, Port Hueneme, California
Building 850 is an example of a building designed to minimize solar heat gain, maximize the use of daylighting, and allow natural ventilation. The building is oriented along an east-west axis and utilizes an integrated daylighting system with continuously dimming ballasts automatically dimming lighting fixtures in reaction to available daylight. North-facing clerestory glazing is used, with shaded southern vision glazing and south-facing light shelves to minimize the heat gains from south-facing windows while maximizing daylighting in all occupied spaces. Glazing types at each window level were customized to maximize occupant comfort while viewing computer terminal screens. The result is a 100% daylit facility with a 6% daylight factor and minimized solar heat gain. In addition, the roof has a reflective white finish to minimize solar heat gain.
Building 850 is approximately 55% more efficient than California's 1995 Title 24 Energy Efficiency Standards. In addition to the passive solar features, the building features an R-19 roof and R-11 wall insulation; an efficient mechanical system that includes premium efficiency motors for pumps and fans; high SEER air conditioners with engine-driven, direct-expansion, reciprocating compressors; a gas-fired absorption chiller/heater; a solar hot water system; under-floor air distribution; and a direct digital control system linked to a building management system computer terminal. A 30-kW photovoltaic array further reduces the building's total annual energy bill by 68%.
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