Open Loop Solar Water Heater.

Open loop solar water heater is common in the Southern United States and Tropical Climates. Open loop solar water heater system consists of solar collector installed on the roof and a hot water storage tank usually located in the garage or utility room. An open loop solar water heater consists of alternating current (A/C) pump that circulates the water from the tank up to the collector and back. The Open loop solar water heater system is referred to a direct because the sun’s heat is transferred through the collector directly to the potable water. No antifreeze solution or heat exchanger is required.
The Open loop solar water heater System utilizes a differential control to sense the temperature differences between water leaving the collector and the coldest water in the bottom of the storage tank. The control of an open loop solar water heater turns the pump on when the water in the collector is about 20F warmer than the water in the tank. Similarly, the pump is turned off when the temperature variation is approximately 5F. This process ensures that the water is always being heated while the pump is operating.
A thermally operated valve is in-stalled in an open loop solar water heater at the collector of an Open loop solar water heater to provide freeze protection where required. This valve will open to let warm water flow through the collector whenever temperatures approach freezing. As an alternative, the collector can be manually drained by closing the isolation valves and opening the drain valves of the Open loop solar water heater.