Controllers for solar-heated swimming pools are very similar to SHW differential thermostats. Pool systems have much higher flows than domestic solar hot water systems, and the on and off differentials are adjusted for this. The typical on-differential of a pool control is about 5°F, with the off differential being just 2°F. Pool differential thermostats usually control a three-port motorized valve that diverts the pool water to the collectors when the on-differential is reached. Pool pump timers are set to filter only in the daylight hours when the sun can heat the pool. As long as the sun-heated pool collectors can add heat to the pool, the differential will keep the valve positioned to divert water to the collectors.
