Your home's windows, walls, and floors can be designed to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design or climatic design because, unlike active solar heating systems, it doesn't involve the use of mechanical and electrical devices, such as pumps, fans or electrical controls to move the solar heat.
The thermal mass that can be used include a masonry floor, a masonry wall bordering the house, or water containers. The distribution of heat to the house can be accomplished through ceiling and floor level vents, windows, doors, or fans. Most homeowners and builders also separate the sunspace from the home with doors and/or windows so that home comfort isn't overly affected by the sunspace's temperature variations.
Sunspaces may often be called and look a lot like "greenhouses." However, a greenhouse is designed to grow plants while a sunspace is designed to provide heat and aesthetics to a home. Many elements of a greenhouse design, such as overhead and sloped glazing, which are optimized for growing plants, are counterproductive to an efficient sunspace. Moisture-related mold and mildew, insects, and dust inherent to gardening in a greenhouse are not especially compatible with a comfortable and healthy living space. Also, to avoid overheating, it is difficult to shade sloped glass, while vertical glass can be shaded by a properly sized overhang.
Design for Summer Comfort - It makes little sense to save money on winter heating just to spend it on summer cooling. So in most climates, a passive solar home design must provide summer comfort as well. The solar heat in the summer must be blocked by a roof overhang or other devices, such as awnings, shutters, and trellises.
The physical dimensions of an overhang are an important element because overheating will occur unless the overhang provides enough shade. Many variables—including latitude, climate, solar radiation transmittance, illuminance levels, and window size and type—need to be considered for properly sizing an overhang in a specific locale. Therefore, it's best to have an experienced solar designer or builder calculate the proper overhang dimensions. (The Solar Radiation Data Manual, listed below under "Further Reading," has appropriate overhang lengths for many U.S. locations.)
Design, Options, and Cost A passive solar home is an exceptional home, differing from standard construction in the thermal integrity of its shell and its well-considered design. The design options, employing the principles and methods described here, are endless. However, workmanship is always extremely important when installing insulation, air sealing the building envelope, and installing the windows.
Most successful passive solar homes are very airtight. As a result, they may require mechanical ventilation systems to maintain good indoor air quality. A heat-recovery ventilator (HRV) is often the best choice to conserve the home's hard-won solar heat. An HRV takes heat from the departing indoor air and transfers this heat to the entering outdoor air.
Passive solar technology may still be new to many designers and builders. So you're sometimes required to pay extra for them to master unfamiliar design and construction details. But if you're lucky enough to be working with an experienced solar designer and builder who are committed to excellence, a passive solar home may cost no more than a conventional one or even less in some situations. Also, properly sized heating equipment, which are typically smaller in passive solar homes, will sometimes offset the cost of the passive solar features.
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