DESIGN AND ECONOMIC ASSESSMENT OF AN INTEGRATED SECONDARY HEAT RECOVERY CIRCUIT WITH PCM STORAGE FOR PASSIVE DEFROSTING IN AIR TO WATER HEAT PUMPS

The thesis proposes a solution to avoid the inversion of refrigeration cycle for the defrosting process of an heat pump by integrating a phase change material (PCM) latent thermal energy storage (LTES) system. In the presented concept, the refrigerant, after the condenser, passes through an heat exchanger melting the PCM (i.e., storing heat), and, when the defrosting process happens, the heat is transferred to a secondary fluid (water-glycol mixture) which is used to melt the ice that was formed on the external finned coil. In the present work, a numerical tool present in the literature was used to design the heat exchanger immersed in the PCM. In addition, the size of the same heat exchanger is used to evaluate the economic benefit of such solution. For this purpose, a cost function was defined and analyzed in terms of fixed and variable costs. Analysis shows that eliminating the inversion of the refrigeration cycle results in a theoretical increase in COP and a significantly shorter payback period, making the system more efficient, sustainable and cost-effective.