Performance evaluation of an ORC-based combined cooling system for data center waste heat recovery

The rapid growth of data centers has produced large amounts of low-grade waste heat, but its efficient use remains difficult. To address this problem, an HPA-ORC-VCR system was proposed to convert data center waste heat directly into useful cooling. A comprehensive framework was developed to evaluate thermodynamic, economic, and environmental performance under three server utilization conditions and 17 working fluid combinations. The results showed that lower condensing temperature, lower compressor outlet temperature, smaller intermediate heat exchanger pinch temperature difference, and higher micro-channel evaporation temperature improved overall performance. Increasing evaporation temperature increased COP all but reduced exergy efficiency. Among all working fluid combinations, R161-pentane consistently gave the best overall performance. Under low server utilization, this combination achieved the highest COP all of 1.618 at T eva = 288 K and the maximum exergy efficiency of 26.04% at T cond = 298 K, T 3 = 363 K, T mic = 358 K, and T pinch-i = 5 K. Under high utilization, it also gave the best economic and environmental performance, with a minimum payback period of 0.7118 years, a maximum annual emissions reduction of 24.720 × 10 5 kg, and a maximum annual fossil fuel savings of 22.038 × 10 4 L. These results show that the proposed HPA-ORC-VCR system has strong potential for recovering low-grade waste heat from data centers and converting it into useful cooling. The low-GWP working fluid pair R161-pentane is a promising option for sustainable waste-heat-driven cooling in data center applications.