A techno-economic comparison of a direct expansion ground-source and a secondary loop ground-coupled heat pump system for cooling in a residential building

This paper reports a techno-economic comparison between a direct expansion ground-source heat pump system (DX-GSHP) and a secondary loop ground-coupled heat pump system (SL-GCHP). For this purpose, a DX-GSHP and an SL-GCHP system are designed and installed in parallel for same space cooling load in a demonstrating building in Hunan province, China. The structures of the two systems are described. The performances of the two systems were experimentally determined from June to September in cooling season of 2009. The average cooling performance coefficients (PFsys) of the DX-GSHP system was obtained to be 6.03 and that of the SL-GCHP system was determined to be 5.64. The average input power values for the DX-GSHP system and the SL-GCHP system are found to be 1.39 and 1.715 kWh, respectively, which means that DX-GSHP has a 23.8% higher efficiency than SL-GCHP in cooling mode. The paper studied the initial investment, the annual cost (AC) and the present worth (PW) of the two systems. It is concluded that the DX-GSHP is more economic than the SL-GCHP. Further more, the advantage and disadvantage of the DX-GSHP are analyzed. The minimal refrigerant velocity in order to ensure oil return is derived. It is shown that DX-GSHP could be vigorously pushed when oil return problem is solved satisfactorily.