PRELIMINARY EXPERIMENTAL EVALUATIONS OF INDIRECT SOLAR ASSISTED HEAT PUMP SYSTEMS

An indirect solar assisted heat pump (ISAHP) system for heating domestic hot water has shown promise as an alternative to conventional electric or natural gas water heaters. In a previously conducted theoretical study, it was concluded that an ISAHP could operate with a lower life-cycle cost than a conventional solar domestic hot water (SDHW) system. Therefore, to further investigate the feasibility of the proposed system, an experimental study was conducted on a prototype (ISAHP) system. To undertake the study, a fully instrumented heat pump water heater was assembled in a laboratory environment and connected to a simulated “solar heat ” input. The “solar ” input was provided by an electrically heated circulation loop that delivered temperature-controlled fluid to the heat pump evaporator. This allowed repeatable test sequences to be performed in the laboratory regardless of weather conditions. Tests were conducted at various evaporator supply temperatures, ranging from 10 to 30°C. At each temperature, charging of a 270 L hot water tank was completed through a natural convection heat exchanger/condenser. Initial results indicated coefficient of performance (COP) values ranging from 2.8 to 3.3 depending on the evaporator and condenser temperatures. These results demonstrate that the numerical simulation overpredicted COP values for the system due to simulated heat exchanger effectiveness values much higher than experimentally measured. Corrections made to these effectiveness values bring the experimental and simulated data to within 3 % of each other for the 10oC test. Further testing and system optimization will be undertaken to attempt to increase the performance levels