Experimental characterization of a transcritical CO2 direct expansion ground source heat pump for heating applications

Abstract

Space heating and domestic hot water account for a large portion of energy consumption in buildings. Direct expansion ground source heat pump (DX-GSHP) is a promising renewable energy technology to provide heat efficiently in a wide range of applications in buildings. Moreover, there is a renewed interest on CO2, which is a viable option to replace synthetic refrigerants with an environmentally friendly alternative, yet limited studies have examined the performance of a CO2 DX-GSHP for different heating applications in buildings. A transcritical DX-CO2 GSHP had been built, and a number of tests were carried out to evaluate the performance of such a system and the associated ground heat exchanger (GHE) for three heating applications in buildings. Those applications represent low to high water temperature demand. DX-CO2 GSHP demonstrated a better performance and a higher heating capacity in applications with lower temperature demand. The highest COP was around 4 when DX_GSHP provides heat to radiant floor heating systems. Moreover, the performance of the system was examined with different number of active boreholes. The results implied that there could be an optimum number of boreholes to provide the highest heating capacity.