In HP157, Karim Wingedheart asked how to keep his solar-powered hot tub water at a constant 103°F. We had this same challenge with our open-loop, solar-heated, 550-gallon cedar hot tub. We live in Arizona, and without regulation of such a heating system, the water would often be too hot for comfort.
To regulate water temperature, we purchased a differential temperature controller from Art-Tec Solar. The controller compares the temperature set point to the water temperature of the hot tub and the temperature in the solar collector, turning the circulation pump on only if the water temperature in the collector is higher than the tub water’s temperature, and the hot tub water is lower than the temperature setpoint.
The controller remains the brains of our solar-heating system. Without it, we were faced with the same challenges as Karim. We hope this helps.
Dominick McCutcheon • San Tan Valley, Arizona