Of the two types of active solar hot water systems you can install in your home, direct circulation systems are most suitable for homes in climates where the temperature rarely dips below the freezing point. That, then, is Fact #1 about direct circulation solar hot water systems.
Facts about Direct Circulation Solar Hot Water Systems
Fact #2: Direct circulation systems directly circulate the water from the cold water intake through the solar collector to be heated and back into the insulated storage tank. It differs from indirect circulation systems which pump a heat transfer fluid such as air, hydrocarbon oil or a refrigerant through the solar collector and return it to the storage tank to heat the cold water.
Fact #3: Automatic controllers installed on active direct circulation systems sense when sunlight is being collected. The valve is opened automatically, and cold water is pumped through the solar collector to heat up and flow back into the storage tank. When the system detects no further heat from the sun, the pump is turned off and the valve is closed.
Direct circulation solar hot water systems are one of two types of active solar water heaters, the other being indirect. Whereas indirect systems rely on another liquid to transfer heat to the water used in the house, direct systems heat the very water coming in from the cold water intake.