Redesign a thermodynamic heat recovery unit with R290: experimental and simulation results
Proper ventilation systems are critical for providing high Indoor Air Quality standards in buildings. Concerning nearly zero energy buildings (NZEB), and in renovated buildings, the energy impact of mechanical ventilation units on the overall consumption is significant. In this context, thermodynamic heat recovery units have a great potential to decrease the electrical energy demand and contribute to improving the indoor thermal comfort and meet space heating and cooling loads. Thermodynamic heat recovery units are recuperators provided with an internal vapor compressor cycle whose function is to enhance the supply airflow temperature by exploiting the energy content of the exhaust airflow extracted from the building. In this way, the system can be used to efficiently meet a part of the heating and cooling loads, integrating the existing generation system. Towards global targets of net zero emissions, the redesign of many vapor-compression cycle units, converting them from synthetic refrigerants to natural refrigerants represents both an opportunity and a challenge for manufacturers. In particular, when it comes to the use of hydrocarbons, the main challenge for manufacturers is to provide the same performance of a synthetic refrigerant unit, with a maximum refrigerant charge of 150 g to comply with current safety regulations (IEC 60335-2-40). This paper aims to investigate the redesign of an existing R32 thermodynamic heat recovery unit to R290 refrigerant. The casing of the unit is kept the same size as the original, due to spacing requirements, and attention is given to the refrigeration cycle. Experimental tests are performed to assess the performance. A numerical model was developed in MATLAB to reproduce the steady-state behavior of the unit under different thermodynamic conditions and operating configurations. The model was then validated using experimental data, showing good accuracy.