Enhancing Energy Efficiency in DHW System with High-Temperature Heat Pumps in a Student Campus

This study explores the potential for enhancing the energy efficiency of the domestic-hot-water (DHW) preparation system in a student campus of the Technical University of Cluj-Napoca, Romania, where DHW accounts for approximately 50 ± 10% of total thermal consumption. The current natural gas boiler system is evaluated alongside two energy-enhancing solutions: high-temperature heat pumps utilizing either CO2 (R744, transcritical cycle) or propane (R290) as refrigerant, for supply temperature scenarios of 75 °C and 55 °C, combined with rooftop photovoltaic systems. Original mathematical models based on real manufacturers’ data are introduced for the components and heat pumps. Expanding the study to eight international locations, the heat pumps cover the entire DHW demand in the simulated scenario, with the boiler retained only as backup, achieving cost reductions between 2.85% and 71.17%. Furthermore, integrating photovoltaics covers significant solar fractions ranging from 21.02% to 83.82% and reduces CO2 emissions compared to the baseline level in most of the analyzed locations. Across the analyzed locations, payback periods range from 0.4 to 174.7 years for heat pumps alone and from 1.1 to 22.4 years with photovoltaics. A parametric analysis shows that payback is inversely proportional to the price difference, while its non-linearity is driven by the price ratio relative to the break-even threshold.