DEFROST MODE FOR HVAC HEAT PUMP SYSTEMS

摘要

A heat pump (22, 32, 38, 40), and in particular a heat pump for heating a hot water supply (34) is provided with an improved defrost mode. The defrost mode is actuated to remove frost from an outdoor evaporator (40) that may accumulate during cold weather operation. When the heat pump is utilized to heat hot water, methods are provided to prevent the water that remains in the heat exchanger from becoming unduly heated. In one method, the water pump (36) may be periodically operated to move the water. In a second method, a control ensures that discharge pressure of the refrigerant leaving the compressor is reduced, and that the water pump (36) is not stopped until that reduced temperature falls below a predetermined maximum.