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Batch Open-Loop Systems

Batch systems for heating water are simply open-loop systems in which the storage tank is a part of the solar collector. This is sometimes called an integrated solar collector because the tank is incorporated into the collector. They are favored, however, for their low cost, low maintenance, and simple design. In colder climates, batch systems usually need to be supplement with more traditional means of heating water to achieve desired temperatures.

In these systems, cold water is pumped into the bottom of the tank, which is usually mounted on a roof or elevated platform. As the water is warmed in the collector, it rises to the top of the tank where it can be removed, usually by gravity. Like many open-loop systems, batch heaters require preprocessed water or frequent maintenance to prevent/remove scale from hard water. Hard water can clog the system and reduce efficiency.

Batch systems are not immune to freezing and as such are only useful for warmer climates where the temperature almost never falls below freezing. The size of the collector relative to the tank is determined by the amount of sun that a given location receives. In the United States, for example, the “Sunbelt” states need about 25 square centimeters of solar collector surface area for every 8 liters of tank capacity. For more northern states, such as those in New England, the same amount of surface area is required for 3 liters of water. In essence, the colder the climate, the larger the solar collector must be in relation to the tank. The problem here is that roof mounted systems may not be feasible in certain climates without additional expense for reinforcing the roof support.
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