Thermodynamic analysis and evaluation of a sub-ambient synergistic Carnot battery for external waste heat recovery and data-center cooling: A preliminary investigation

Abstract

The rapid development of data centers has led to significant increases in cooling energy consumption and operational costs. While waste heat recovery from data center has proven effective in improving system efficiency, existing solutions primarily operate in a 24/7 mode, limiting the ability to capture economic benefits from peak-valley electricity price differences. To maximize peak-valley electricity price benefits in data center cooling operations, this study proposes a novel Carnot battery system that synergistically integrates data center cooling, waste heat recovery, and thermal energy storage. The coupling approach allows operation mode switching between peak and valley periods while maintaining continuous cooling supply. Thermodynamic and exergy analysis models are developed to investigate the effects of different working fluid combinations and operating parameters on system performance. Results show that the R717-R1233zd(E) working fluid pair achieves optimal performance with a maximum round-trip efficiency (η_rt) of 58.78 % while meeting continuous cooling demands. The optimal operating conditions were identified at hot and cold reservoir temperatures of 293.15 K and 283.15 K respectively, with system performance significantly degrading as conditions deviate from these points up to 48.28 % reduction in heat pump COP and 66.67 % reduction in ORC efficiency. Furthermore, when implemented in Hangzhou, the system demonstrates substantial economic benefits, reducing daily operational costs by up to 14,000 CNY compared to conventional cooling methods. This study provides a reference case for innovative cooling system design in data center applications.