Switchable multistage absorption chiller for ultra-low-grade waste heat driven cooling in data centers

Data centers (DCs) are energy-intensive facilities that generate substantial low-grade waste heat, highlighting the need for improved energy efficiency and heat recovery. This paper proposes a waste heat driven cooling scheme for DCs that enables the on-site utilization of recovered heat, wherein waste heat from the liquid-cooling loop powers absorption chillers to cool air-cooled components. Multistage absorption cooling cycles for low driving temperatures are thermodynamically analyzed and screened. A triple-stage LiBr-H2O absorption chiller is then developed for this application, capable of delivering 50 kW of chilled water at 18 °C with hot/cooling water inlet temperatures of 50 °C/32 °C. Additionally, stage switching is enabled in the chiller for continuous cooling capacity enhancement as the cooling water temperature decreases under constrained waste heat availability. Finally, the energy-saving performance of the proposed cooling scheme is evaluated across major DC locations in China, with a case study on a DC having 200 kW liquid-cooling and 100 kW air-cooling loads. This scheme is well-suited for deployment in high-temperature, high-humidity environments where free cooling is less effective. In Guangzhou, it achieves an 80.5 % reduction in mechanical cooling load and an annual electricity saving of 78.0 MWh. This work provides a novel approach for enhancing energy efficiency and recovering waste heat in DC cooling systems.