Although the advantage of an air source heat pump (ASHP) is self evident, all kinds of ASHPs available on the market have a deadly shortcoming that prevents their application in wider areas. They cannot run smoothly where the ambient temperature is very high in summer or extremely low in winter. The capacity of the ASHP decreases sharply when the outdoor temperature deviates badly from that of mild working conditions. Therefore, in extremely atrocious climates, when heat or cold is most needed, heat pumps are always least able to supply. Still worse, the conventional ASHP cannot work reliably for a long time under atrocious weather conditions because the coefficient of performance of the ASHP becomes so small that it is pointless to keep the unit running, and the discharge temperature of the refrigerant continues increasing, which will lead to destruction of the compressor unless the ASHP is stopped. In this paper, the authors propose a new subcooling system employing a scroll compressor with supplementary injections that can effectively solve the above problems. The prototype ASHP was validated, and the relevant dynamic performance was tested. The outcomes show that this new kind of ASHP can work very well either when the ambient temperature is very high or very cold in the winter. In addition, the efficiency of the improved ASHP under all circumstances was well addressed, and a great amount of energy can be saved through the increased efficiency of the improved system. In this way, the applications of ASHPs were greatly enlarged, which is very conducive to the whole energy conservation and environment protection business! (C) 2003 Elsevier Ltd. All rights reserved.