THERMODYNAMIC LIMITS OF STANDING COLUMN HEAT PUMPS IN COLD CLIMATES

This paper aims at determining if standing column heat pump systems without bleed are feasible for cold climate homes. The designed laboratory prototype includes two 150-mm diameter boreholes, 25% and 60% shallower, respectively, than typical depths of vertical ground-source heat exchangers. Critical thermodynamic parameters and energy performances at full and partial heat pump capacities were determined for both heating and cooling modes, as well as for the free cooling regime. The results show that, in the heating mode without bleed, the heat pump shuts-down on its low pressure limit after 8 to 29 hours of continuous operation, depending on the borehole depth and the water extraction level. On the other hand, system performance is high in the mechanical (with heat pump) cooling mode. However, the system is unable to provide enough dehumidification and efficient air cooling in the free (direct) cooling mode.