Performance enhancement of CO2 air conditioner with a controllable ejector

Abstract

This study presents performance enhancement of a transcritical CO2 air conditioner with a controllable ejector at variable operating conditions and variable compressor frequencies. The effects of ejector geometries, operating conditions and compressor frequency on the performance of an ejector expansion transcritical CO2 air conditioner were investigated. Experimental results show that the COP of a CO2 air conditioning system can be enhanced by using an ejector expansion device to replace a conventional expansion valve. This enhancement became more significant as the outdoor air temperature increased (COP increased by up to 36%), the compressor frequency decreased (COP increased by up to 147% compared to conventional cycle with compressor frequency at 50 Hz), and the motive nozzle throat diameter decreased (COP increased by up to 60%). In addition, the COP reached a maximum when the distance between motive nozzle exit and mixing section entrance was three times the mixing section diameter.