Experimental analysis and numerical simulations of a heat recovery unit working with propane and R32

This thesis examines an active thermodynamic heat recovery unit for mechanical ventilation systems, which plays a key role in ensuring high indoor air quality in modern buildings. In nearly zero-energy and renovated buildings, where ventilation significantly affects overall energy demand, these units recover energy from exhaust air through a vapour compression cycle, thereby improving thermal comfort and contributing to both heating and cooling loads. In the current transition to low GWP refrigerants, this work focuses on converting the ELFO FRESH unit from R32 to the natural refrigerant R290, whose use is limited by strict charge limits. The aim of this thesis is therefore to compare the performance of the unit with both refrigerants in order to assess whether an R290 configuration can achieve performance comparable to the reference while complying with the 150 g charge limit. The work combines experimental testing with the development of a numerical simulation model under steady-state conditions in MATLAB, designed to reproduce the actual behaviour of the unit to support future optimisations. The results showed that the R290 configuration achieved similar performance to the R32 ones, with comparable and, in some cases, slightly higher COP and EER values, even with a reduced refrigerant charge. The results of the developed models were validated against the experimental measurements. In fact, the deviations between the values calculated by the models and the measured values remained within 5% for heat flow rate and within ±2°C for air temperatures, superheating and subcooling. The largest discrepancies appeared in cooling mode with R290, mainly due to greater uncertainties in the parameters used as boundary conditions in the models. In addition, the TTP method was applied to evaluate the condenser geometry, which was found to be close to the optimal length that minimises exergy losses. Overall, the study demonstrated the technical feasibility of using R290 in thermodynamic recovery units and confirmed the validity of the numerical model as a reliable tool for analysing and optimising future configurations.