Active Solar Water Heating

There are two basic types of solar water heating systems. A passive system requires no mechanical parts -- simply gravity to circulate the heating fluid. An active solar water heating system uses pumps and valves to circulate the heating fluid.

A fluid such as antifreeze is usually used to circulate through the solar collector. This allows a solar water heating system to be used in northern climates without the danger of the circulating fluid freezing. Areas which do not have freezing temperatures -- such as Florida -- can use water instead of anti-freeze. When water is used, it is heated directly by the sun. When anti-freeze is used, a heat exchanger transfers the heat from the anti-freeze to the water.

The solar collector is an insulated box placed in an area which has direct sunlight. Pipes enter the solar collector to heat the liquid passing through them. In an active solar water heating system, the liquid is circulated with an electric pump which can be powered with regular household electricity or photovoltaic solar panels.

If the heated liquid is water, it passes into the hot water tank inside the house. As hot water is drawn from the hot water tank, it is replaced with heated water from the solar collector.

If the heated liquid is anti-freeze, it passes from the solar collector to a heat exchanger which heats the water in the hot water tank. The anti-freeze is continually circulated to maintain it at a constant temperature. Hot water is drawn from the top of the hot water tank and it is replaced by cold water which is fed to the bottom of the tank.

Anti-freeze is used within a closed system -- the liquid does not come in contact with household water. Open systems are used to directly heat the water and provide a constant supply of fresh water.

Active solar water heating systems only produce hot water during the daylight hours. A backup system such as electricity or propane is needed to heat water during the night. However, if members of the household can get used to using most of their hot water during the day, water heating expenses can be reduced to a minimum.

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