Understanding solar hot water systems. Part two. Hybrid, phase change, thermosiphon and batch heaters
The closed loop and draindown systems were discussed in part one in the previous issue. The hybrid drainback system contains a reservoir located in the home's heated space, external piping runs, and a heat exchanger within the reservoir or in a solar tank. A pump circulates water from the reservoir or in a solar tank. A pump circulates water from the reservoir to the collectors and then to the heat exchangers. When solar energy is not available the pump is stopped and the water from the collectors and pipes fall back to the reservoir. Thermosiphoning systems depend upon the natural circulation of hot water and need no controls or pumps. The collectors must be mounted about two feet below the storage tank, and tubing in the collectors and piping runs should be of a size to minimize flow restrictions. Phase change collectors are similar in principle to thermosiphoning systems except for the heat transfer fluid. A pressure limiter is the only control needed and installation must be such as to ensure the system has only one high point and one low point to prevent traps from impeding the flow. Batch heaters consist of a storage tank heated directly by the sun. Hot water exits the top of the tank when needed and is replaced with cold water from the bottom incoming line. The surface area to volume ratio, tilt angle, insulation, overglazing, and over-extending the system's seasonal limits are discussed in general terms. (CKK)
- OSTI ID:
- 5673995
- Journal Information:
- Wood Energy; (United States), Vol. 2:10
- Country of Publication:
- United States
- Language:
- English
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