Performance Evaluation of Chiller Unit with Gas Bearings Based on Energy, Exergy, Economic, and Environmental Analyses

Abstract

Chilled water units using centrifugal compressors with gas bearings are an important research direction, but the necessary additional refrigerant circulation for gas bearings and motor cooling increases the design and operation difficulty, and therefore gas-suspended chiller units have few applications in the building sector. By establishing a system model based on energy, exergy, economic, and environmental analyses, this paper analyzes and compares the coefficient of performance (COP), exergy efficiency, power consumption, and economy of three refrigeration cycles under different operating conditions. The results showed that the system performance is insensitive to the supply pressure of gas bearings due to the relatively small mass flow rate. The enhanced gas-bearing-assisted vapor compression chilled water system (EGVC) demonstrated superior COP and exergy efficiency, and lower CO2 emissions compared with the gas-bearing-assisted vapor compression chilled water system (GVCW) and dual-economizer gas-bearing-assisted vapor compression chilled water system (DGVC) for the various evaporation temperatures and ambient temperatures. Regardless of the system, the total exergy loss of the system was mainly from the condenser, accounting for approximately 40% of the total. Both the economic cost and total equal warming impact (TEWI) values of the system decreased with the evaporation temperature but increased with the ambient temperature. Specifically, the EGVC showed slightly higher economic cost and lower TEWI values than other systems. The performance parameters of the system were sensitive to the evaporation temperature for the three systems.