District Heating Integration for High-Temperature Heat Pumps: Assessing the Optimal Trade-Off between Environmental and Economic Benefits
This study presents a multi-objective optimization of a moderately high-temperature heat pump (HTHP) prototype using the low-global-warming-potential refrigerant R-450A, aiming to identify an optimal balance between energy performance and economic benefits. Building upon previous experimental work, empirical grey-box models derived from steady-state tests serve as the foundation for simulating the HTHP operation under various condensation temperatures (70, 80, 90, and 100 °C) and heat source conditions represented by different district heating networks. The optimization process utilizes a genetic algorithm to vary the evaporation temperature and compressor frequency, aiming to maximize both the coefficient of performance and the net hourly economic benefit. Results reveal a trade-off between these objectives: while higher evaporation temperatures generally improve both performance and hourly net cash-flows, reducing compressor frequency favors energy performance but can decrease profitability. The Pareto fronts derived illustrate that the real optimum operating points offer a balanced compromise, yielding significant cost savings without substantial losses in performance. An environmental assessment reveals that even under unfavorable high condensation temperatures, the real optimum point reduces carbon dioxide emissions for HTHP operation, emphasizing its environmental advantage. Conversely, maximizing economic gains slightly reduces environmental benefits, while maximizing the coefficient of performance alone is the least economically favorable solution. These findings underscore the importance of integrated optimization strategies that consider both economic and environmental dimensions in HTHP operation. The study also highlights the influence of regional electricity mix and energy market conditions on results, suggesting the need for tailored analyses in different contexts.