Tim Halweg-Larson (2001)
This project the covers the design, construction, testing and evaluation of a simple and dependable auto-draindown mechanism for use with solar water heaters to prevent frost damage.
This is considered a key link in making thermosyphoning solar water heaters economically and practically feasible for Himalayan regions lying above the snowline. Solar water heaters can make a significant contribution to reducing a household’s reliance on purchased or laboriously collected fuels.
In its simplest form, the proposed mechanism consists of two valves and a thermally controlled actuator. One valve isolates the water tank, the second drains the solar panel. Both are operated by the actuator. The actuator consists of a car thermostat whose reservoir of wax has been replaced with water. When temperatures drop to zero, the water freezes, expanding into ice and driving forward an actuator rod to operate the valves. The next day the mechanism resets itself and the water heater can continue to operate.