Energy Supply Characteristics and Economic Analysis of a Coupled Heat Pump–Solar System
: Targeting the diverse and highly seasonal loads of existing residential buildings, this study develops a hybrid “solar–air-source heat pump–shower wastewater heat recovery–stratified thermal storage–fan-coil” system, and proposes a temperature-difference-threshold-driven valve–pump coordinated control strategy enabling multi-mode operation. Cross-season typical-day experiments are conducted to quantify energy balance and efficiency. Results indicate that midday during the shoulder and winter seasons forms an overlapping high-efficiency window; the maximum solar contribution ratio reaches 31.17%, and piping heat loss rates are 24%–38%. The air-source heat pump achieves a Coefficient of Performance (COP) of 1.38–3.39; wastewater heat recovery under shower conditions yields an Energy Efficiency Ratio (EER) of approximately 2.8–3.1; fan-coil space heating exhibits an EER of about 8.69–9.34. In summer, coordinated “domestic hot water + space cooling” operation is attainable. Based on local electricity tariffs, the annually normalized energy savings are approximately 2.83 × 10 4 MJ, with a cost saving of about 6363 RMB; the initial investment is about 18,060 RMB, yielding a simple payback period of roughly 2.84 years. The findings demonstrate that multi-source hybrid heat pump systems offer strong seasonal adaptability and favorable economics in existing residential applications. Further improvements in off-peak integrated efficiency can be achieved by optimizing the TC temperature-difference thresholds, enhancing solar piping insulation, and reducing fan-coil hydronic resistance with improved pump matching. The study provides a reproducible technical pathway and empirical data to support the engineering deployment of hybrid heat sources in residential buildings.