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ABSTRACT

The dynamic performance of a direct-expansion solar heat pump water heater (DX-SHPWH) system, for domestic water heating application, is analyzed by means of an in-house numerical model considering typical environmental conditions in Colombia. The DX-SHPWH system uses a thermodynamic collector as an evaporator and a condenser submerged in an accumulation tank for water heating. Natural refrigerant R290 is selected as a working fluid due to its low global warming potential, compared to more common refrigerants, and its zero ozone depletion potential. Also, a photovoltaic system is included as a power source to harness a renewable source of energy. A basic design for the system is obtained via thermodynamic analysis at nominal operational parameters and time-averaged environmental conditions. The dynamic behavior of the basic design is simulated considering a transient energy balance equation for the water accumulation tank and pseudo-stationary energy balance equations for the components in the thermodynamic cycle. Time varying solar radiation and ambient temperature meteorological data from Medellin, Colombia are specified as inputs to the numerical model to assess the transient behavior of: water temperature, cycle working pressures, compressor power consumption and system coefficient of performance. From simulation results, relevant insights are obtained to improve basic component sizing and selection, including thermodynamic collector and a photovoltaic array for the system.