Determination of Heat Transfer Characteristics of Solar Thermal Collectors as Heat Source for a Residential Heat Pump

With reducing energy demand and required installed mechanical system power of modern residences, alternate heat pump system configurations with a possible increased economic viability emerge. Against this background, this paper presents a numerically examined energy feasibility study of a solar driven heat pump system for a low energy residence in a moderate climate, where a covered flat plate solar collector served as the sole low temperature heat source. A parametric study on the ambient-to-solarfluid heat transfer coefficient was conducted to determine the required solar collector heat transfer characteristics in this system setup. Moreover, solar collector area and storage tank volume were varied to investigate their impact on the system performance. A new performance indicator "availability" was defined to assess the contribution of the solar collector as low temperature energy source of the heat pump. Results showed that the use of a solar collector as low temperature heat source was feasible if its heat transfer rate (UA-value) was 200 W/K or higher. Achieving this value with a realistic solar collector area (A-value) required an increase of the overall ambient-to-solarfluid heat transfer coefficient (U-value) with a factor 6-8 compared to the base case with heat exchange between covered solar collector and ambient.