Recently, many air-conditioners are utilizing high-efficiency compressors, high-efficiency heat exchangers, and microcomputers to save energy and get more comfort. In Japan, the inverterdriven heat pump is gaining popularity in the residential heat pump market. Total demand for packaged air-conditioners is estimated to be 450,000 and 80% of these are air-source heat pumps in Japan.

It is one of our main themes to improve low ambient temperature characteristice of heat pumps and also to engineer the refrigerant circuits matched to a variable-capacity heat pump with inverter or one with plural indoor units.

We have developed the electronic linear expansion valve with its refrigerant circuit to achieve high efficiency operation in wide ambient temperature range to attain 35% energy savings in the case of an inverter-driven unit. Also we obtained high performance operation with suitable refrigerant distribution to each indoor unit in inverter-driven heat pumps. The operation was controlled to get constant superheat in cooling, constant subcooling in heating and totally adequate superheat in the suction line.

Units: SI