Waste heat recovery in a data center with an adsorption chiller: Technical and economic analysis

Computing load of data centers and high-performance clusters have increased significantly over the past decade, resulting in higher energy consumption and a larger carbon footprint. We provide a method to utilize the waste heat from a data center room that contains both air- and water-cooled racks. Heat dissipated by the water-cooled racks drives a silica gel-H2O adsorption chiller, which produces chilled water required for in-row cooling units installed in the air-cooled racks. Hence, the cooling load of the existing vapor-compression chiller is either partially or fully eliminated, offering significant energy savings. Thermodynamic, economic, and environmental benefits of the proposed strategy are compared against a baseline infrastructure without waste heat utilization. Parametric sensitivity analyses reveal that the load sharing factor, inlet temperature of water-cooled racks, chilled water setpoint, airflow of the in-row cooling units, and the re-cooled water temperature all influence the energy savings efficiency, annual variable costs, CO2 emission reduction, and cost payback period. In this manner, energy savings efficiency is enhanced by 22.5% and annual CO2 emissions reduced by 104 tons. The cost payback periods with 30 and 90 kW adsorption chiller retrofits are as low as 379 and 285 days. Raising the water-cooled rack inlet temperature from 40 °C to 65 °C enhances the energy savings efficiency by as much as 16% but that also degrades computing performance per watt by 6%.