The selection of volume ratio of two-stage rotary compressor and its effects on air-to-water heat pump with flash tank cycle

► Two-stage rotary compressor was developed for vapor injection cycle. ► The effect of volume ratio of a two-stage rotary compressor on AWHP was investigated. ► Experimental investigation on vapor injection air-to-water heat pump. ► Higher COP and larger heating capacity than conventional AWHP at cold climate.