Lubricant Investigation for High Temperature Heat Pump Application

Lubricant plays crucial role in safe and efficient compressor operation especially for high temperature application. Lubricant and refrigerant mixture viscosity analysis and behaviour during heat pump operation requires careful investigation. As a part of European funded CHESTER project, lubricant (oil) behaviour was investigated (visual) experimentally using a high temperature (100°C to 135°C) heat
pump test rig developed at Ulster University. In addition, a separate test rig was developed to investigate lubricant oil (POE) and refrigerant (R1233zd(E)) viscosity analysis at source temperature in a range of 50°C to 110°C.

The results from HTHP test rig showed that oil temperature increased with source temperature and in order to protect compressor components and maintain suitable lubricity, additional cooling was required along with a comprehensive start-up, operation and shut-down strategy. The viscosity results of R1233zd(E) and POE mixtures were obtained in terms of a Daniel chart (w% of refrigerant in the oil) in a temperature range of 40°C to 100°C. The viscosity variation showed a range of 80 cSt to 8 cSt between 60°C to 90°C suction temperatures. The analysis also calls for further investigation with other oils and a development of high viscosity grade lubricant suitable for R1233zd(E) and other refrigerants suitable in high temperature heat pump application.