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Open-Loop Direct Solar Hot Water

In direct systems, the water that is heated in the solar collector is the same water that is consumed throughout the home. There is only a single working fluid in these systems, which is pumped in and used when needed, making the system open. Like any direct system, open-loop systems are susceptible to freezing and overheating. Freezing tends to be the major problem in these systems and so their use in cooler climates is often limited.

Open-loop systems are simple, lightweight, and unobtrusive. Because the tank and solar collector are separate (unlike in batch systems), there is no concern over roof mounting of the solar collector in these systems. Another advantage over batch design is the size of the solar collector relative to the tank. A 4 meter square solar collector is enough to heat 200 liters of water in an open-loop direct system. In a batch system, the same amount of water would require a solar collector of roughly twice the size.

Direct systems are usually designed to supplement standard hot water heating. Rather than the hot water tank drawing cold water from a well, it draws already warm water from the solar storage tank. This greatly reduces the costs of heating hot water.
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