A water based thermal storage system is designed to reclaim the building waste heat, provide suitable capacity for off-peak electric resistance heat and permit off-peak cooling during summer. The two-tank system provides a method of positive anti-blending using a flexible diaphragm to separate supply and return water in each tank.

The system configuration provides a unique opportunity to increase solar collection by 57% using typical flat plate collectors. Integration of the solar system with large thermal storage allows the capital investment for solar to be life cycled within a 20-y period.