An exergy-based analysis of the effects of rear door heat exchange systems on data center energy efficiency

A holistic system-level analysis of the energy and mass transfer in a data center cooling system is used to determine the exergy destruction by each component in the system. The analysis, performed using our in-house analysis code, allows for identification of system inefficiencies and comparison of the energy efficiency of different data center cooling strategies. In this paper, we describe a systematic analysis of the exergy destruction in a traditional air-cooled strategy and a hybrid liquid-air system containing rear door heat exchangers (RDHXs). The results show that the exergy destruction by RDHXs increases with the amount of rack heat removal. However, the removal of rack heat concurrently decreases the heat removal and exergy destruction by computer room air handling (CRAH) units. The resultant overall exergy destruction is increased when both RDHX and CRAH units are in operation, but this gain in exergy may be attributed to low heat exchanger effectiveness values. The analysis also shows that when all heat is removed by the RDHX, the exergy destruction is lower than when all heat is removed by the CRAH, suggesting that the data center energy efficiency can be increased through the use of localized hybrid liquid-air cooling schemes as compared to centralized air cooled strategies.