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Space Heating and Cooling

Just as solar energy can provide hot water for a building, it can heat the air in the building, as well. By using passive solar systems or more elaborate active solar systems, solar energy can help heat or cool buildings. A solar heating system can consist of passive systems, active systems, or a combination of both.

Passive systems are typically less costly and less complex than active systems. However, when retrofitting a building, active systems might be the only solar option. Additionally, the roof-top location of active allow them to aviod shading from nearby buildings.

Passive Solar Heating

Passive solar design takes advantage of the sun's warmth and light through design features such as large, south-facing windows and materials in the floors or walls that will absorb warmth during the day and release that warmth at night, when the heat is most needed. Passive solar designs are typically oriented toward the south because the southern exposure will receive the most sunlight. Incorporating passive solar designs can reduce heating bills by as much as 50%.

Passive systems do not use mechanical devices, such as fans or blowers, to distribute solar heat from a collector. Instead, they take advantage of the natural flow of warmer air to distribute warmth. A great example of a passive system for space heating is a sunspace or greenhouse.

Although passive solar heating is best incorporated into a building during the initial design, the concepts of passive solar heating can also be used when remodeling or adding to your home or small business.

Whereas the orientation should be to the south regardless of local climate, strategies differ by climate. In cold climates, south-facing windows are designed to let the sun's heat in while insulating against the cold. In hot and moderate climates, the strategy is to admit light while rejecting heat.

There are three main passive-solar design systems. The simplest is direct gain, in which the sun shines directly into the building and warms materials, such as tile or concrete, that will store the heat energy and slowly release it. An indirect gain system will use a similar concept, except the materials that will hold, store, and release the heat are located between the sun and the living space, usually in the wall. The third system is called isolated gain, in which the system is isolated from the primary living area. An example would be a sunroom attached to the house. The warmer air from the sunroom flows naturally into the rest of the house.

Active Solar Heating

Active solar heating systems consist of collectors that collect and absorb solar radiation and electric fans or pumps to transfer and distribute the solar heat. Active systems also generally have an energy storage system to provide heat when the sun is not shining. The two basic types of active solar heating systems use either liquid or air as the heat-transfer medium in their solar energy collectors.

Liquid-based systems heat water or an antifreeze solution in a "hydronic" collector, whereas air-based systems heat air in an "air" collector. Both of these systems collect and absorb solar radiation, then transfer the solar heat directly to the interior space or to a storage system, from which the heat is distributed. If the system cannot provide adequate space heating, an auxiliary or back-up system provides the additional heat. Liquid systems are more often used when storage is included.

There are many different types of active solar heating systems:

Medium-temperature solar collectors are used for space heating and operate in much the same way as indirect solar water heating systems, but they have a larger collector array area, larger storage units, and more complex control systems. They can also be configured to provide solar water heating and typically provide 30% to 70% of the residential heating, or combined heating and hot water, requirements. Active space-heating systems require more sophisticated design, installation, and maintenance techniques.
Transpired-air collectors, mounted as an exterior cladding on a building's south-facing wall, are used for ventilation preheating. These collectors are unglazed, and a blower or fan is used to draw air through perforations in the wall to deliver ventilation air into the building. Solar ventilation air preheating systems are generally used in commercial and industrial applications that require large quantities of ventilation air, including warehouses, large manufacturing plants, and airplane maintenance hangars.
Solar process heating systems are designed to meet the need for large quantities of hot water or space heating at commercial, industrial, and institutional buildings. A typical system consists of several thousand square feet of ground-mounted collectors, combined with pumps, heat exchangers, controls, and one or more large-volume storage tanks. Solar process heating systems have successfully developed niche markets in federal and state governments, which operate facilities such as schools, military bases, office buildings, and prisons that provide hot water for bathing, cooking, laundry, and space heating.
Cooling and refrigeration using active-solar cooling systems can provide for year-round utilization of collected solar heat, thereby significantly increasing the cost effectiveness and energy contribution of solar installations. These systems are sized to provide 30% to 60% of the building's cooling requirements. Solar-driven absorption systems use an active cooling technology option that currently appears to have the greatest potential.
Solar absorption systems use the thermal energy from the solar collector to separate a binary mixture of an absorbent and a refrigerant fluid. The refrigerant is condensed, throttled, and evaporated to yield a cooling effect, after which it is re-absorbed to continue the cycle. Because of the high-temperature requirements of absorption cooling systems, evacuated-tube or concentrating collectors are typically used.