Structural Optimization of a Roll-Bond Collector–Evaporator and Seasonal Performance Analysis of a Solar-Assisted Heat Pump System

The solar collector–evaporator is a pivotal component in a direct-expansion solar-assisted heat pump (DX-SAHP) system, and its structural design directly affects the heat-transfer performance and overall coefficient of performance (COP). To investigate the effects of collector–evaporator geometric parameters, a system-level DX-SAHP simulation model was developed in MATLAB (R2016b). Specifically, a roll-bond plate solar collector–evaporator was represented using a distributed-parameter model. The effects of three key geometric parameters—namely, the channel-number allocation ratio between the two flow passes, channel pitch, and equivalent channel diameter—on the system COP were examined. The results show that each parameter exhibits an optimal value that maximizes COP. Furthermore, a coupled parametric analysis was conducted to account for their interactive effects, revealing that the DX-SAHP system achieves a global optimum COP when the channel-number ratio is 1:1, the channel diameter is 2.11 mm, and the channel pitch is 43 mm. Using the climatic conditions of Shanghai as a case study, the performance improvement achieved with the optimized collector–evaporator design was evaluated. The results demonstrate that, under representative meteorological conditions in spring, summer, autumn, and winter, the optimized collector–evaporator increases the system COP by approximately 4.13%, 4.72%, 4.50%, and 3.04%, respectively. These findings provide practical guidance for the structural design and optimization of collector–evaporators in DX-SAHP systems.