Performance of HVAC systems at ASHRAE HQ

The ASHRAE headquarter building at Atlanta has a living lab, which uses three separate HVAC systems. These include a variable refrigerant flow (VRF) system for spaces on the first floor, a ground source heat pump (GSHP) system, primarily for spaces on the second floor, and a dedicated outdoor air system (DOAS), which supplies fresh air to both floors. The GSHP system serves 15,558 ft² of office and meeting space primarily on the second floor with a normal occupancy of 60 people. The VRF units for which power measurements are available serve a total of 17,213 ft² on the first floor, which includes offices, large meeting spaces and storage areas. The DOAS, which conditions outdoor air to 55°F, satisfied part of the cooling load in summer, but contributed to the heating load in winter. The average DOAS airflow rate to the first floor was 2,560 cfm, which is significantly higher than the average flow rate to the second floor of 1,480 cfm. Ground loop water supply temperatures were more favorable than ambient air temperatures for heat pump operation. This allows the GSHP equipment to operate at higher efficiencies. The control strategy of the VRF system resulted in longer runtimes than the GSHP system, especially in mild weather. These longer runtimes coincided with significant amounts of simultaneous cooling and heating in adjacent spaces.