Experiences with Application of a CO2 Reciprocating Piston Compressor for a Heat Pump Water Heater

This paper describes some of the challenges experienced in the application of a carbon dioxide reciprocating piston compressor to a water heating heat pump. Due to the characteristics of CO2 in a trans-critical cycle, including high pressures, high discharge temperatures, and high solubility in oil, particular difficulties may be experienced such as reduced bearing reliability caused by bearing wear and reduced performance caused by valve and port size limitations. These challenges were overcome using analyses from compressor simulation and component models to diagnose the problems and correct them, and experimental testing to validate models, root causes, and design improvements.