Innovative Ground-Source Heat Pumps: a Challenge for Cheaper and More Efficient Heat Pumps Working with New Environmental Friendly Fluids

This study has delved into critical aspects of heat pump technology, specifically concentrating on low Global Warming Potential (GWP) refrigerants, responding to the pressing need for environmentally balanced and efficient alternatives in this domain. This research scrutinized the thermophysical properties of a number of low-GWP refrigerants through extensive simulations encompassing 120 iterations across diverse temperature settings and scenarios. Notably, this study reveals significant trends and underscores the profound influence of isentropic efficiency and temperature glide on performance, emphasizing the complexity inherent in selecting suitable refrigerants. The computer simulations allowed to select isobutane (R600a) as the refrigerant to test, along with R454B selected from previous studies, on two geothermal heat pumps installed in a pilot facility within the EU GEO4CIVHIC project. Such experimental investigations led to valuable insights about the real performance of low-GWP refrigerants and geothermal heat pumps. The two refrigerants were compared under the same boundary conditions. Moreover, the monitoring system played a fundamental role in detecting eventual design and operational issues, highlighting interesting technical aspects. At the same time, this research has pursued comprehensive experimental investigations into the thermophysical properties of refrigerants, focusing on vapor-liquid equilibria, compressed liquid density, and speed of sound for specific mixtures. Despite the limited available data, particularly regarding mixtures, this study contributed by proposing tailored models based on the Helmholtz-energy-explicit equation of state, aiming to enhance understanding and accurate modeling of these new fluids and mixtures.