In European markets, where consumers have a sharp eye for energy-saving products, sales of heat pumps, which have a COP of 3 or higher, are steadily increasing. Two types of heat pump air conditioners are available. One is the air-to-air type, which is a traditional air convection direct expansion system for heating room air. The other is an air-to-water type using water as the heating and cooling medium. Recently arriving on the market, the latter is used for space heating/cooling and sanitary water heating. Both types use heat captured from outdoor air as their heat source and include a compressor to utilize the refrigerant’s heat cycle, producing a heat output of more than 3 with an input of 1. Thus, they are high efficiency products with a COP of 3 or higher.