Closed-Loop Active System (Drainback System) ...continued

Drainback systems use water as the heat-transfer fluid in the collector loop. A pump circulates the water through the solar water heater. When the pump is turned off, the solar water heater drains the water, which ensures freeze protection and also allows the system to turn off if the water in the storage tank becomes too hot.

A consideration with drainback systems is that the solar water heater installation and plumbing must be carefully positioned to allow complete drainage. The pump must also have sufficient head pressure to pump the water up to the collector each time the pump starts. Electricity usage is therefore slightly higher than a other closed or open loop systems.

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