Home heating Headquarters

In a two-year study of geothermal-heat-pump (GHP) and variable-refrigerant-flow (VRF) hvac methods put in at ASHRAE Headquarters in Atlanta, the GHP system outperformed the VRF system by a broad margin, the Geothermal Exchange company (GEO) claims.

When ASHRAE contracted an important remodelling of this two-story, 31, 000-sq-ft building in 2008, it established a “living lab” for the analysis of commercial-building power and sustainability performance. In January 2013, GEO, with monetary the assistance of Southern Co., contracted a research team from Oklahoma State University and Oak Ridge nationwide Laboratory to evaluate the general overall performance regarding the VRF and GHP methods.

The VRF system serves rooms regarding the first floor, as the GHP system primarily acts spaces regarding the second floor. A dedicated outdoor-air system, at the same time, materials oxygen to both floors.

“Our research of heating and cooling performance on ASHRAE building demonstrates that over a two-year period—with all factors accounted for—energy use by the geothermal system averaged 44 % not as much as the VRF system, ” GEO President and Chief Executive Officer Doug Dougherty stated.

The VRF system includes three committed split systems and two multizone inverter-driven heat-recovery products. The heat-recovery units are connected to 22 fan-coil products (FCUs). The air conditioning ability of this heat-recovery units is 28 tons, as the three specific systems have actually an extra 10 a great deal of ability. The GHP system includes 14 water-to-air heat pumps (two 3/4-ton devices, six 2-ton units, and six 3-ton products) attached to a ground-loop temperature exchanger consisting of 12 400-ft-deep straight boreholes for a total of 31.5 a great deal of cooling capacity.

To facilitate performance studies, the building includes 1, 600 sensors that monitor HVAC businesses and conditions in each zone. Historical and current information from the detectors had been available to the research staff, led by Jeff Spitler, PhD, regents teacher of mechanical engineering at Oklahoma State University. Their colleagues included Xiaobing Liu, PhD, staff scientist at Oak Ridge National Laboratory, and Laura Southard, Oklahoma State mechanical-engineering graduate student. South Co. supplied a power engineer to help with on-site data measurements.

The researchers concentrated on determining real hvac given by the GHP and VRF systems, information evaluation, and computation of calculated and experimental metrics. They obtained couple of years of operational information (July 1, 2011, to Summer 30, 2013). Information points included operating mode (off/heat/cool), zone heat, and discharge-air temperature for each FCU or heat pump. The scientists collected data on ground-loop water supply, return heat, and movement rate for the geothermal system.

The team in addition gathered metered energy used by each system. For GHP system, that included energy for many 14 temperature pumps, along with the ground-loop water-circulation pumps. For the VRF system, energy is metered and recorded only for both heat-recovery products in addition to 22 FCUs connected to them. Energy when it comes to three specialized split systems is metered through an unusual panel that also includes energy employed for computer system computers also equipment. All these types of distinctions had been taken into account for contrast.

“Though the vitality used by each system is impacted by a few facets, including living area, heating and cooling lots, control strategies, and operating conditions/efficiencies, the efficiency ramifications of each system are obvious, ” Spitler said. “Raw information reveal the VRF system used double the amount power since the geothermal system during the two-year research period.”

Areas supported by the GHP and VRF methods have different cooling and heating lots, and so the analysis team estimated the lots provided by each predicated on individual product airflows. Figure 2 demonstrates whenever variations in space on the floor had been normalized, the vitality use (kilowatt-hours per sq ft) associated with GHP system had been a typical 44 per cent not as much as that the VRF system.

“During the two-year research duration, the GHP system utilized 29 per cent less energy in the summertime and 63 percent less energy when you look at the winter/shoulder seasons compared to the VRF system while keeping similar area temperatures, ” Spitler stated.

“The underlying difference between the geothermal system and also the air-source VRF system lays into the heat sink and origin: ground vs. ambient atmosphere, ” Spitler proceeded. “Though the control technique for the VRF system led to longer runtimes set alongside the geothermal system, it's obvious that ground-loop water supply temperatures had been more positive than ambient-air temperatures for heat-pump procedure. This Permits the geothermal equipment to use at higher efficiencies.”