Open Loop Solar Water Heating System


Open Loop Systems are suitable for single application domestic hot water (DHW) systems, in mild and moderate climates. One or two tanks can be used in various configurations and they retrofit easily into existing systems. An Open Loop System is for climates where there is no risk of freezing. Recirculation freeze protection can be provided by the Recirculation feature in the controller. At about 42ºF. the pump will turn on for a short time, circulating the water through the loop and preventing freezing. 


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In the event of a power outage, pump or controller failure, secondary freeze protection can be provided by a freeze protection drip valve that will allow water to leak out by the collector at low temperatures; while also bringing warmer water from below. The collector does not hold water and the manifold across the top holds about one pint of water. Heat in the manifold cannot leak out through the collector because of the "Thermal Diode" one way heat transfer mechanism of the heat pipe. The supply and return loop holds about 5 pints of water so we are really more concerned about protecting the piping than the manifold, which is well insulated. Additional sensors are available for the controller to cover these areas and activate Recirculation.

It is the simplest and typically the least expensive active system to install. There is no heat exchanger, which allows efficient heat transfer directly to the water. The system operates at standard line pressure. It is simple to add capacity to the system if demand changes. The system integrates easily with existing systems.

Some stored heat can be lost when the system recirculates. It does, however recirculate from the colder bottom of the tank and supply pipes, and there are minimal losses in the loop and none through the collector. The primary freeze protection needs electricity or battery back-up.
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