Open Loop Solar Hot Water Heating Systems

Open loop systems directly heat the water. Open-loop systems work essentially by circulating water through the solar collectors via a small pump mounted on a water storage tank. The solar pump is activated by a differential thermostat controller that senses when heat is available in the solar collectors. The solar storage tank connects to the existing hot water heater and feeds the preheated solar water into the gas or electric hot water heater as hot water is used.

In regions where pipes can freeze, the solar collectors and feed lines are usually protected from freezing by automatic drain down controls. These Drain down systems allow the water in the pipes and panels to fall safely back out of the solar collectors and feed pipes to prevent freezing. These types of systems are "open loop" since the energy collection loop is not separate from the rest of the hot water system --i.e. the loop is "open" and sharing the same water.

strengths

Regular maintenance costs are associated less with open-loop systems because they don't use any special fluids or heat exchangers used with closed-loop systems. They are usually cheaper to install than closed-loop systems. Open-loop systems are more efficient at heating water than closed-loop systems, because water is directly heated from the solar panels.

weaknesses

The main weakness is related to the Drain-Down version of these systems. An open-loop systems' "drain down" freeze protection can fail, subjecting system owners to risk of substantial repair costs from freeze damage and property damage such as flooding from broken pipes. These costs can significantly outweigh the benefits of using this kind of system. A system drained-down for protection purposes can miss opportunities for providing high-performance benefits of solar hot water heating.

system configurations

Openloop and draindown systems are configured according to energy demands, solar energy availability and other factors at the point of installation. Openloop systems generally consist of at least these parts: