Novel Heat Pump Solution for Strategic Reallocation of Building Heating Demands: A Radically New Concept for Cost-Effective Data Centre Waste Heat Recovery

Abstract

Due to their high waste heat temperatures and locations inside buildings, liquid-cooled distributed/edge data centres (DCs) provide high-quality waste heat with easy access to the return lines of onsite building heating networks. However, the return water temperatures of these networks are often lower than the waste heat temperatures but not low enough for full waste heat recovery using only heat exchangers. State-of-the-art heat pump data centre waste heat recovery (DCWHR) systems can handle high return water temperatures by using waste heat directly as a heat source for heat pumps, but they come with high investment and operation costs. In this study, we introduce a novel concept using heat pumps to dynamically reallocate building heating demands, enhancing DC waste heat utilisation for heat exchangers. Based on this concept, we developed a hybrid DCWHR system that integrates a heat pump with a heat exchanger for DC waste heat recovery. In commercial buildings, district heating (DH) substations typically have space and ventilation heating networks. The heat pump in a hybrid DCWHR system transfers heat between the return lines of these two networks, reallocating their heating demands. This strategic reallocation lowers the return water temperature and increases the heating demand of one network, enabling it to capture DC waste heat more effectively via a heat exchanger. Additionally, a smaller heat pump is sufficient because the heat transfer between the networks is much smaller than the available DC waste heat, resulting in lower investment and operating costs. This innovative heat pump reallocation concept significantly advances current knowledge and literature. This study uses TRNSYS simulation and measurements to verify our proposed hybrid DCWHR system for a liquid-cooled data centre with a constant 25 kW waste heat output, located inside a DH-heated office building with an annual space and ventilation heating consumption of approximately 274 MWh. The goal is to reduce DH consumption and carbon dioxide (CO2) emissions. Using five winter months of measured mass flow rates and supply and return water temperatures, we modeled the building's space and ventilation heating networks, with 100% DH supply as the base case. The results show that the hybrid DCWHR system recovers 98.4% of DC waste heat during the winter months, increasing waste heat recovery efficiency by 16% compared to using only a heat exchanger. Due to the smaller heat pump used, the system achieves a COP of 13. A 25-year life cycle analysis indicates that the hybrid DCWHR system saves €123,005 in heating costs and reduces CO2 emissions by 167,077 kg. With a payback period of just over two years, hybrid DCWHR systems prove to be a significantly more cost-effective decarbonisation solution for recovering data centre waste heat, advancing beyond current state-of-the-art methods.

Keywords: Liquid-cooled distributed/edge data centre, District heating-heated buildings, Hybrid data centre waste heat recovery system, Heating demand reallocation by heat pump, Life cycle cost and CO2 emission analysis