Optimum design for thermoelectric in a sub-cooled trans-critical CO<sub>2</sub> heat pump for data center cooling

Abstract

We present an analysis and optimization of a thermoelectric (TE) assisted air-cooling vapor compression (VC) cycle heat pump chiller for datacenter cooling. The technology provides enhancement of cooling performance for a trans-critical R744 (CO2) VC cycle, especially in hot climates that have air temperatures of more than 30 °C, which exceeds the critical point of the refrigerant. Absorbing a larger enthalpy from the evaporator by subcooling with TE, the VC cycle's cooling capacity is enhanced. While a TE heat pump works effectively for a small temperature difference, the system coefficient-of-performance (COP) is significantly enhanced at a lower pressure operation condition in particular. Hence, this TE subcooling approach could provide pressure reduction while maintaining cooling capacity and COP. At the optimum in TE cooler design and operating conditions, a 12-13% improvement of maximum cooling performance is expected with the currently available TE material on the market (ZT~1.5). Since the power consumption of TE is small due to the low temperature heat pumping required, the maximum system COP also gains. The cost performance optimization of the thermoelectric subcooler is also considered. System energy performance is calculated based on an example data center for the mathematically high performance computation at Purdue University.