Performance evaluation of ejector-enhanced and gas-bearing-assisted vapor compression chilled water system

Abstract

The centrifugal compressor with gas bearings is an important research direction of chiller, but the essential additional gas cycle for bearing and motor cooling still lead to the energy waste. Using an ejector to increase this gas pressure by recovering the energy of expansion process for inter-stage replenishment is a feasible solution. In this paper, a mathematical model of EGVC system (ejector-enhanced gas-bearing-assisted vapor compression chilled water system) is established and simulated comparing to the BGVC system (basic gas-bearing-assisted vapor compression chilled water system), and the performance under variable working conditions is obtained by 4E (energy, exergy, economic, environmental) analysis method. The results indicate that the ejector can reduce power consumption for gas compression and improving system performance. The COP increases while the exergy efficiency decrease with the evaporating temperature for both systems, but they show opposite changes with condensing temperature. Comparing to BGVC, the COP of EGVC increases by 1.29 %-1.52 % and the exergy efficiency increases by 1.02 %-1.21 % when the evaporating temperature rises from 1 °C to 9 °C, while they increase by 1.41 %-1.63 % and 1.12 %-1.31 % when the condensing temperature increases from 40 °C to 48 °C. The EGVC system is more suitable to the large bearing gas condition, and the COP and exergy efficiency improve by 1.49 %-2.20 % and 1.19 %-1.67 % when the proportion of gas for bearing to the total refrigerant rises from 1 % to 2 %. The cost and carbon emission of system also be reduced by using the ejector.