Understanding solar hot water. Part I. Open and closed loop systems

Open and closed loop solar collectors are discussed. The open loop system uses potable water as the heat transfer fluid and may also use a conventional tank, which can lower the cost to the consumer. Most open systems cannot be used in climates which are prone to freezing conditions. Open draindown systems use a solar controller signal to dump water from the collectors for freeze protection. Closed loop systems employ a separate loop filled with a non-freezing heat transfer fluid. This fluid is pumped through the collectors to pick up heat and then through a heat exchanger where heat is transferred to potable water. (MJF)