A system and method to retrofit a building structure having a forced air cooling system with a thermal storage system. The method typically includes the steps of: installing a coolant loop that is free of a compressor, and a condenser, where the coolant loop comprises a refrigerant fluid pump and refrigerant fluid conduits that deliver coolant loop refrigerant fluid to a coolant loop evaporator spaced within a building air cooling passageway that delivers air to at least a portion of the interior volume of the a building structure and in thermal communication with air passing through the passageway and where the coolant loop is in thermal communication with a thermal energy storage material within a thermal energy thermal storage fluid tank; and activating the coolant loop pump to provide cooling to the coolant loop evaporator thereby cooling air moving in the building air passageway of a building structure.