When the sun shines again, the pump is activated by a differential controller. Water is pumped from the reservoir to the collectors, allowing heat to be collected. The water stored in the reservoir tank circulates in a closed loop through the collectors and a heat exchanger at the bottom of the solar tank. The heat exchanger transfers heat from the collector loop fluid to the potable water in the solar tank. Cold water flows progressively through the collector where it is heated by the sun.
Hot water is drawn from the top, which is the hottest, and replacement water flows into the bottom.
This system is simple because pumps and controllers are not required. A flush-type freeze protection valve is installed in the top plumbing near the collector. As temperatures near freezing, this valve opens to allow relatively warm water to flow through the collector to prevent freezing. In south Florida and certain areas of central Florida, the thermal mass of the large water volume within the ICS collector provides a means of freeze protection. As the sun shines on the collector, the water inside the collector flow-tubes is heated.