A comparison study on direct expansion solar assisted heat pump water heater system with different channel pattern roll-bond collectors/evaporators

In this paper, three types of roll-bond collectors/evaporators for direct expansion solar assisted heat pump (DX-SAHP) water heater were designed, fabricated and tested. The roll-bond collectors/evaporators were south-faced and wall-mounted for building integration purpose during the experiment. Results show that, under the test conditions, the roll-bond collector/evaporator with honeycomb and rectangle shaped channel pattern shows significant improvement of COP and heating capacity than the conventional channel pattern. Furthermore, compared with the rectangle shaped channel pattern, the honeycomb shaped channel pattern further improved COP by 6.2%. Finally, the DX-SAHP water heater with optimized channel pattern roll-bond collector/evaporator was tested under a series of different weather conditions. With the fixed initial water temperature, the COP of DX-SAHP water heater varied from 1.76 to 5.54 when the operating condition changed. When operating during night, the sky background temperature significantly influenced the COP of the system. Under the same ambient temperature, the results of COP in cloudy and clear night are 2.82 and 1.76 respectively.