5th Generation District Heating and Cooling (5GDHC) Systems: Improving the Efficiency of a Booster Heat Pump

Abstract This study addresses the limitations of booster heat pumps in achieving high secondary supply temperatures, which are constrained by declining Carnot efficiency. The research investigates the performance and economic feasibility of integrating booster water-to-water heat pumps into a 5th generation district heating and cooling (5GDHC) system, particularly for a newly built office building in a moderate climate zone with an average winter supply temperature of 50 °C. The methodological framework assumes idealized system behavior without part-load penalties, and models heat pump performance based on Carnot cycle efficiency corrected by a typical Carnot scaling factor (η = 0.6). Key assumptions include fixed building envelope characteristics, specific energy consumption based on energy performance certificates, and cost parameters for standard and advanced heat pumps (1.5× and 5× higher variable and fixed costs, respectively). The model incorporates pinch temperatures to reflect practical heat exchange limitations and applies a simultaneity factor for accurate heat pump sizing across multiple buildings. Results show that despite a 50 % increase in capital expenditures (CapEx), operational expenditures (OpEx) decrease significantly, resulting in an overall cost reduction of 11 %. Advanced heat pumps with 22 % higher efficiency compared to mass-market units demonstrate notable improvements in seasonal COP (SCOP) by 22 % and electricity consumption by 18 %. Maximum COPs of 6.0 in winter and 12.0 in transitional periods are observed. A peak heat demand of 12 MW is covered by 25 booster units averaging 478 kW each, activated when secondary supply temperatures exceed the network temperature. The findings support the strategic deployment of efficient, electricity-driven booster heat pumps in 5GDHC systems. Improved thermal integration and the use of renewable energy sources further reduce energy costs and carbon emissions, enhancing both the energetic and economic performance of the system.