Solar Hot Water Heater Augmented with PV-TEM Heat Pump

Abstract

Solar assisted heat pumps (SAHPs) can provide higher collector efficiencies and solar fractions when compared against standard solar hot water heaters. Vapour compression (VC) heat pumps require environmentally hazardous refrigerants and moving parts which increase maintenance costs and place limits on operating conditions. Thermoelectric modules (TEMs) use solid state electronics to pump heat without moving parts or refrigerants. This study investigated the performance of a SAHP system utilizing an array of thermoelectric modules as the heat pump. A component model was developed to simulate the TEM heat pump performance using TRNSYS software and results were compared against those determined experimentally. A simplified model was unable to accurately predict TEM performance. The model was therefore refined to incorporate empirically determined parameters. An apparatus was constructed to measure the performance of a small photovoltaic array driven TEM heat pump and simulation results using the component model were found to be in agreement. Several SAHP configurations were simulated using TRNSYS and compared with vapour compression SAHPs previously studied at the QSCL. The TEM ISAHP provided a Free Energy Ratio (FER) of 46% and a collector efficiency of 36% whereas the VC ISAHP provided 54% and 76% respectively. The photovoltaic (PV) driven ISAHP system was able to achieve a higher FER of 50% with the use of a 2 module PV array and a reduced thermal collector area. Further optimization is required to improve TEM heat pump performance in this configuration and reduce the photovoltaic array size. The use of a maximum power point tracker into the PV/TEM system should be investigated as panel efficiency losses reached up to 30% in the configuration studied. The possibility of incorporating combined PV/T modules could decrease costs and also warrants further study. Critical factors in the success of a TEM driven solar assisted heat pump will include the improvement of thermoelectric materials performance, the optimization of TEM modules for efficient heat pumping applications, and the design of high performance heat exchangers for the TEM heat pump hot and cold faces.