In a two-year study of the geothermal-heat-pump (GHP) and variable-refrigerant-flow (VRF) heating and cooling systems installed at ASHRAE Headquarters in Atlanta, the GHP system outperformed the VRF system by a wide margin, the Geothermal Exchange Organization (GEO) says.
“During the two-year study period, the GHP system used 29 percent less energy in the summer and 63 percent less energy in the winter/shoulder seasons than the VRF system while maintaining similar zone temperatures,” Spitler said.
“The underlying difference between the geothermal system and the air-source VRF system lays in the heat sink and source: ground vs. ambient air,” Spitler continued. “Though the control strategy for the VRF system resulted in longer runtimes compared to the geothermal system, it is clear that ground-loop water supply temperatures were more favorable than ambient-air temperatures for heat-pump operation. This allows the geothermal equipment to operate at higher efficiencies.”
“Final Report, Performance of the HVAC Systems at the ASHRAE Headquarters Building” is available at https://www.geoexchange.org/library/download-info/performance-hvac-systems-ashrae-headquarters-building/.