Drainback System Characteristics
The above left picture of a heat storage tank, with associated pump and controller, shows the simplicity of a drainback system. When the layout of the house allows for a drainback design to be used, the homeowner can enjoy these benefits:
- Higher efficiency; water has a a higher heat transfer/storage capacity than glycol, also, there is usually one less heat exchanger for the heat to pass through.
- Simpler plumbing design; fewer components, non-pressurized plumbing on solar collection side.
- No need to "dump excess heat" in summertime in order to protect glycol from overheating.
The picture on the right shows the collector panels (not yet plumbed) for the tank on the left. Despite the advantages of drainback, these systems do impose restrictions that cannot be ignored:
- Panels and supply/return pipes must be tilted adequately.
- Controls must be designed so as to eliminate the possibility of the drainback circulator coming on when the interior panel temperatures are below freezing.
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