A differential controller works on temperature differential and is normally a necessary accessory in split systems installations (forced circulation), where it commands the recirculation pumps that moves water between the solar collectors and the tank and in pool heating installations where, similarly, it controls the circulation of the water in the solar collectors and the pool itself.

It’s the heart of the system in split systems installations. Once the water in the solar collectors reaches a certain temperature, the controller starts the pump that pushes the water inside the collectors in the storage tank and fill them with cooler water drawn from the tank itself. The process is ongoing insuring the heating process is constantly ongoing when the sun is out and is stopped when the sun sets or simply isn’t there because of bad weather. If water would be recirculated just on timers, instead of differential temperature, we would have situations whereby we are actually cooling the water in the storage tank running it through cold collectors which aren’t heated by the sun but, to the contrary, kept cold by bad weather or the night air.

The same concept is applied to pool heating with the only difference that the water that is recirculated is the pool water instead of water contained in a storage tank.

This controllers can be integrated with heat pumps as well and control the electric boosting in solar water heating installations.