1. G. Lorentzen, Trans-critical Vapor Compression Cycle Device, International Publication Number: WO90/07683, World Intellectual Property Organization, 1990.
2. Use of natural refrigerants, a complete solution to the CFC/HCFC predicament;Lorentzen,1994
3. CO2 heat pump water heater: characteristics, system design and experimental results;Neksa;Int. J. Refrig.,1998
4. Theoretical evaluation of carbon dioxide refrigeration cycle;Hwang;Int. J. HVAC&R Res.,1998
5. A basic study on CO2 heat pumps especially for hot tap water supply;Saikawa,1997