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Article-Southard.jpg

©2014 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 56, no. 9, September 2014.

By L.E. Southard, P.E., Member ASHRAE, Xiaobing Liu, Ph.D., Member ASHRAE; and J.D. Spitler, Ph.D., P.E., Fellow ASHRAE

About the Authors
L.E. Southard, P.E., is a lecturer and J.D. Spitler, Ph.D., P.E., is regents professor and OG&E energy technology chair in the School of Mechanical and Aerospace Engineering at Oklahoma State University in Stillwater, Okla. Xiaobing Liu, Ph.D., is a staff scientist in the Building Technology Research and Integration Center at Oak Ridge National Laboratory in Oak Ridge, Tenn.

When ASHRAE headquarters in Atlanta was renovated in 2008, one goal was to create a living lab that could be accessed by members to learn about commercial building performance and state-of-the-art sustainable technology. As a part of this living lab concept, the building uses three separate HVAC systems: 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.

Another important aspect of the living lab is the extensive array of sensors that monitor the operation of the HVAC equipment and the conditions in each zone in the building. Both historical and current data from these sensors have been trended via the building automation system and are available to interested parties through the ASHRAE website.

The authors have been researching the relative performance of the VRF and GSHP systems that control temperature in the spaces. This has involved determining the energy consumption of each system (described here) and determining the amount of heating and cooling required by the building (described in a future article.)

The VRF system that provides cooling and heating to the first floor includes two multi-zone inverter driven heat-recovery units. The multi-zone heat-recovery units are connected to a total of 22 fan coil units (FCU) with two speed fans. The cooling capacity of the heat-recovery units is 28 tons (98 kW). Several zones on the first floor are served by three dedicated split systems.

The GSHP system that serves the second floor includes 14 individual water-to-air heat pumps (two 0.75 ton [2.6 kW] units, six 2 ton [7 kW] units and six 3 ton [10.5 kW] units) connected to a ground loop consisting of 12,400 ft (122 m) deep vertical boreholes, for a total of 31.5 tons (111 kW) of cooling capacity. The heat pumps have variable speed fans (driven with electronically commutated motors) with three selected speeds.

The DOAS includes six staged air-cooled condensing units to provide cooling and two heat recovery wheels to precool or preheat the outdoor air. The total cooling capacity of the condensing units is 28.6 tons (100.6 kW).

Two years of data relating to the operation of the different HVAC systems have been collected and analyzed in an attempt to evaluate the performance of the systems. These data cover the time span from July 1, 2011 through June 30, 2013. Data points that have been collected include operating mode (off/heat/cool), zone temperature and discharge air temperature for each individual FCU or heat pump. Ground loop supply and return water temperatures and flow rate were also collected for the GSHP system. For the DOAS, the flow rate of the supply air to each floor and the supply and return air temperatures and humidity levels were collected.

 

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