HEAT PUMP AND AIR CONDITIONER OR WATER HEATER HAVING THE SAME

A heat pump that can accurately detect a frost formation state on an evaporator without being affected by changes in an indoor environment and changes in a compressor frequency, and an air conditioner or water heater on which the heat pump is mounted are provided. In the heat pump having a refrigerant circuit in which a compressor 3, an indoor heat exchanger 8 (condenser), an expansion valve 5, and an outdoor heat exchanger 6 (evaporator) are sequentially connected, evaporator refrigerant saturation temperature detecting means 10 for detecting an evaporation temperature Te of the outdoor heat exchanger 6, evaporator sucked air temperature detecting means 11 for detecting an evaporator sucked air temperature Ta of the outdoor heat exchanger 6, compressor frequency detecting means 12 for detecting a compressor frequency f of the compressor 3, and frost formation state detecting means 103 for detecting a frost formation state on the outdoor heat exchanger 6 are provided, and the frost formation state detecting means 103 detects a drop in heat exchange performance caused by a frost formation on the outdoor heat exchanger 6 on the basis of a characteristic amount T1, which is a calculation value obtained by dividing a difference between the evaporator sucked air temperature Ta and the evaporation temperature Te by a compressor frequency f.