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

One of the best ways of making efficient use of energy in residential units is to use heat pump. Heat pump performance can be further enhanced by integrating a solar thermal unit to provide hot water and subsidize space heating. This paper presents numerically examined energy feasibility study of a solar driven heat pump system for a low energy residence, where a flat plate solar collector served as the sole low temperature heat source. A parametric study on the ambient-to-solar fluid heat transfer coefficient has been conducted to determine the required solar collector heat transfer characteristics in this system. 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. Achievement of this value with a realistic solar collector area (A-value) required an increase of the overall ambient-to-solar fluid heat transfer coefficient (U-value) with a factor of 6 to 8 compared to the base case with only natural convection heat exchange between solar collector cover and ambient.