Thermosyphon systems use the lower density of the water heated by the collector to drive water circulation around the collector and tank circuit. The systems are simpler than most solar water heating systems in that the need for both a circulation pump and a controller are replaced by the thermosyphon natural circulation.
Lonnie did a very nice job on this system, and provides full construction detail. While the collector construction follows the general design of the $1K collectors, Lonnie includes some new wrinkles in the collector that should improve performance.
- The tank must be above the top of the collector. This allows the hotter water in the collector to rise upward into the tank. It also automatically shuts off the circulation when the water in the collector cools below the tank temperature.
- The plumbing between the collector and tank must slope upward toward the tank. And, since the thermosyphon forces driving the flow are relatively weak, the collector and connecting plumbing should have low flow resistance.
- This thermosyphon design does not include freeze protection, so is only for situations in which no freezing weather occurs, or the collector can be drained for the winter. There are thermosyphon designs that circulate antifreeze through the collector and use a heat exchanger to transfer the collector heat to the storage tank.
Full details on Lonnie's Thermosyphon Solar Water Heater...
Details on other DIY solar water heating systems...