Abstract: Non-potable, utility water is circulated by a pump in a closed loop. The utility water is heated by a heat pump. Heat exchange from the utility water heats domestic hot water on demand, eliminating or reducing the need for domestic hot water storage tanks and storage of large quantities of water. In the present invention, fluctuations in condenser water temperature are dampened internally in a condenser water buffer and a control system.

Abstract: An instantaneous hot water appliance uses three loops. The first loop is an open loop that receives source water. Heat is extracted from the source water by a heat pump. The heat is supplied to a utility liquid, such as water, that is circulated within the closed loop. The resulting cooled source water may be used for other purposes. Heat exchange between the utility water in the closed loop and a second open loop heats domestic hot water within the second open loop. Domestic hot water is available on demand, eliminating or reducing the need for domestic hot water storage tanks and storage of large quantities of domestic hot water. In the present invention, fluctuations in condenser water temperature are dampened internally by a compressor control system as described herein that may be supplemented by a condenser water buffer.