Recycling cooling waste heat into cooling with an adsorption heat pump in data centers: A new concept of heat recovery

The rapid increase in computing density and power demand of information technology equipment (ITE) in modern data centers has intensified cooling energy consumption and waste-heat discharge to the ambient environment. This study introduces a novel “cooling-from-cooling” concept that recycles waste heat from immersion cooling back into cooling through an adsorption heat pump (AHP), thereby improving overall energy efficiency without additional compressor power. A prototype-scale system with a total ITE load of 200 kW was designed, in which 50 kW of waste heat recovered from immersion cooling is utilized as the regeneration source of the AHP to produce 20 kW of chilled-water cooling for a rear-door heat exchanger (RDHx). A theoretical model of the AHP was developed using the Linear Driving Force (LDF) equation, and the performance of two adsorbents (Silica gel and MIL101Cr) was compared. Results show that the Silica-gel/water pair achieves a high coefficient of performance (COP ≈ 0.77) at 53°C, while the MIL101Cr/water pair demonstrates a satisfactory COP ≈ 0.4 at lower bed temperatures. The integrated energy analysis based on Mechanical Load Component (MLC) and Power Usage Effectiveness (PUE) yields PUE cooling values between 1.031 and 1.065 (MLC = 0.031–0.065), well below the ASHRAE maximum annualized limits (0.22–0.31) across all climate zones. These results verify the thermodynamic feasibility and practical efficiency of using data-center waste heat as a direct cooling resource and provide a foundation for the ongoing pilot-scale validation of this self-sustaining, low-exergy cooling cycle.