22 May 2008
Ground-source heat pumps with direct expansion (DX) heat exchangers provide several well-known advantages that may help increase the acceptance of geothermal technology for residential applications. This paper describes a residential ground-source heat pump prototype with vertical DX heat exchanger and improved refrigerating circuits and controls. A simplified design approach for vertical DX ground-coupled heat exchangers is proposed. The paper also investigates some operational issues in cold climates, such as oil return to the compressor and refrigerant management during system start-ups and mode switching. Initial installation errors produced undesirable phenomena, such as excessive soil freezing and the collapsing of vertical ground tubes during long continuous operating cycles in the heating mode. Methods to avoid such incidents are finally suggested.