Experimental investigation of a R290 domestic heat pump equipped with a thermoelectric-aided sub-cooler

The energy efficiency of heat pumps is an important factor for the sustainability and electrification of domestic heating, especially for the most common air-to-water heat pumps, which are a competitive solution to conventional heating methods. However, novel solutions for cold and moderate climate zones must be developed considering environmentally friendly natural refrigerants such as hydrocarbons. One idea is to introduce a thermoelectric-aided sub-cooler into an air-to-water heat pump to improve the coefficient of performance. Therefore, this work aims to experimentally investigate a novel propane heat pump system with a prototype thermoelectric-aided sub-cooler for domestic heating. Energy analysis was performed to evaluate the energy impact of the sub-cooler in terms of ambient conditions from -10.0∘C to 5.0∘C, different water temperatures for heating applications in existing buildings from 45.0∘C to 55.0∘C and varying operating conditions of thermoelectric modules in the sub-cooler. The performance of the sub-cooler was evaluated. The results confirm that introducing a thermoelectric-aided sub-cooler can improve the heat pump performance by up to 6.0% and the heating capacity improvement by up to 17.0% for the low ambient temperature of -10.0∘C. Furthermore, an optimal direct current voltage below 3.0 V was found for every investigated operating condition to ensure the best system coefficient of performance.