Research on energy saving potentials using pure and zeotropic refrigerants in data center cooling systems

Zeotropic refrigerants possess the characteristic of temperature glide during phase-change process, making them suitable for temperature matching between cold and hot sources and reducing total temperature differences. In this manuscript, the applicability of two commonly used refrigerants, zeotropic refrigerant R407C and pure refrigerant R134a in data center cooling systems are investigated. Firstly, the heat transfer and flow characteristics of R407C and R134a are studied to obtain boiling heat transfer empirical correlations. Secondly, a data center cooling model is established, and modeling calculations are conducted based on experimental results. Finally, the influence of refrigerants on the energy saving effect are calculated based on the model. Experimental results demonstrate that R134a exhibits a 48.3% higher boiling heat transfer coefficient compared to R407C at heat flux 16500 W/m2. However, when considering a data center cooling system, using R407C as working fluid shows the advantage of temperature matching as heat transfer area increases. Based on modeling results, at large heat transfer area, the annual cooling load factor using R407C at low mass flow rate is 0.5% lower than that of using R134a at low mass flow rate, and 22.5% lower than that of using R134a at large mass flow rate for typical climate city Harbin.