Development of R744 Two Stage Compressor for Commercial Heat Pump Water Heater

Youhei Hotta
Yoshiyuki Kimata
Hajime Sato
Hiroyuki Kobayashi
Hisao Mizuno


A novel CO2 two stage compressor has been developed. The developed compressor equips one rotary and one scroll compression chambers as first and second stage respectively. For efficiency improvement, authors measured the cylinder pressure in each stage and conducted loss classification in the compressor. By adopting appropriate compression type in each stage, and by decreasing critical loss found by measuring the pressure, it resulted in 6% and 10% improvement of heating capacity and COP respectively on rated condition, and 25% and over 50% improvement on deep-frozen condition compared with conventional single stage compressor. The developedcompressor is installed on our newly developed commercial heat pump water heater.