Thermo-economical performance analysis of a direct-expansion solar heat-pump water heater driven by a photovoltaic array and the electrical grid in Medellín Colombia

Sustainable water heating technologies with competitive costs can contribute to meet carbon reduction goals. In this study. the dynamic performance of a proposed configuration for a photovoltaic direct-expansion solar heat-pump water heater (PV-DX-SHPWH) with 110 L capacity is assessed by means of a validated numerical dynamic model at typical meteorological conditions in Medellín, Colombia. Refrigerant R1234yf is selected as the working fluid due to its low global warming potential and its zero ozone depletion potential. A photovoltaic panel system is included as the main power source for a DC variable speed compressor in order to harness a renewable source of energy, while energy backup is provided by the electric grid. After validating the numerical approach by comparison to experimental data from the literature, the behavior of the PV-DX-SHPWH is simulated for values of installed photovoltaic peak power between 200 and 1000 W during a complete typical meteorological year to estimate the average thermal performance. From these simulation results, thermal performance for three representative days is analyzed in detail in terms of water temperature and coefficient of performance (COP) evolution. Also, an economic analysis is performed for the yearlong simulations results in terms of the levelized cost of heat (LCOH), and the results for the PV-DX-SHPWH are compared with other traditional water heating systems. According to the thermo-economic analysis, the COP of the system is higher at low installed photovoltaic powers, and a photovoltaic power range is found (200 W–800 W) whereby high performance of the system (COP greater than 3.5) is achieved at a low LCOH. Also in this range, the proposed system is more competitive than traditional alternatives such as electric and natural gas water heaters.