Performance and carbon emission study of composite air conditioning systems oriented toward oil-free terminal and refrigerant replacement

Baoqi Qiu, Xiuming Li, Yanqiang Di, Mengjie Song, Yiqi Zhang, Shuoquan Huang, Yishi Cheng, Fumin Tao and Zongwei Han

Energy, 2025, vol. 334, issue C

Abstract: The rack-level cooling technology adopting on-demand cooling is a promising solution for data centers. However, the multi-split supplying mode worsens the oil return problem, particularly in pump/compressor composited systems requiring substantial refrigerant charges. To solve the problem, an oil-free rack-level system with indirect double loops is proposed, utilizing a heat exchanger to separate cabinet terminals from outdoor circulation. The proposed oil-free system using two CO2 charge modes (partial/full replacement) is compared with conventional direct systems in performance and carbon emissions to validate the feasibility. Results indicate that the proposed system can solve oil return issues using an indirect heat exchanger. However, both charging modes suffer from a decreased coefficient of performance (COP) from 9.96 to 7.68 due to reduced operation time in the heat-pipe mode. In contrast, compared to conventional direct-connection systems, the proposed system reduces the R410A refrigerant charge quantity by 100 % and 18 % through full or partial CO2 replacement as an environmental-friendly refrigerant, and the full CO2 substitution brings an about 7 % decrease in carbon emission. This study provides a way to solve the oil return problem in refrigeration systems while using the system advantages to achieve the replacement of environmentally friendly refrigerants to reduce carbon emissions.

Keywords: Data centers; CO2; System performance; Refrigerant replacement; Carbon emission (search for similar items in EconPapers)
Date: 2025
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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:334:y:2025:i:c:s0360544225033572

DOI: 10.1016/j.energy.2025.137715

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