Condenser-side thermal resistance in heat pump water heaters: Experimental investigation and quantitative decomposition.

Comprehensive analysis of the condenser-side thermal resistance in heat pump water heaters (HPWHs) offers valuable insights for improving system efficiency and reducing energy consumption. This study presents both experimental investigations on a prototype HPWH and a numerical analysis based on a thermal resistance network model. In the model, the total thermal resistance is decomposed into three components for separate calculation and analysis, namely the refrigerant-side condensation resistance, the thermal conduction resistance of the microchannels and the thermally conductive silicone grease as thermal interface materials, and the combined resistance of cylinder wall conduction and water-side convection. A quantitative analysis of each component was conducted, and the calculated total thermal resistance deviated by only 4.9 % from experimental measurements, demonstrating the accuracy of the proposed model. The results showed that the combined resistance of cylinder wall conduction and water-side convection contributed more than 60 % of the total resistance. Therefore, reducing the combined resistance should be a primary focus to enhance overall HPWH performance. This study establishes a quantitative basis for the optimization and design of next-generation, high-efficiency HPWH systems.