GEO Will Compare Performance of Geothermal, VRF Systems

The Geothermal Exchange Organization (GEO) has contracted with a renowned research team to ferret out the efficiency performance differences between two heating and cooling systems at the American Society of Heating Refrigeration and Air-conditioning Engineers (ASHRAE) Head-quarters Building in Atlanta, GA. In 2008, ASHRAE performed a major renovation of their two-story, 31,000 sq. ft. building, improving some aspects of its envelope, switching to an open plan con-figuration, and adding a number of other sustain-ability features.

Of interest to GEO and the geothermal heat pump industry are the structure’s new HVAC systems, particularly a geothermal heat pump that serves the second floor, and a variable refrigerant flow (VRF) system that serves the first floor. The main objectives of the research project is to compare the performance of the two heating and cooling systems, and to explain reasons for differences with academic rigor and scientific integrity. The research team includes:

Dr. J.D. Spitler, Regents Professor of Mechanical Engineering at Oklahoma State University will lead the project. His primary focus will be data analysis and computation of experimental metrics from the data set. He will also oversee development of calibrated EnergyPlus simulation models. One graduate student will be appointed to a half-time research assistantship to work on the project.

Dr. Xiaobing Liu, Staff Scientist at Oak Ridge National Laboratory, will also participate in the project. Dr. Liu assisted in the design and energy modeling of the ground-source heat pump (GSHP) system for the ASHRAE Headquarters. Dr. Liu will lead an effort to determine the actual heating and cooling provided by both the VRF and GSHP systems.
           
GEO Members Emerson Copeland and Gulf Power/The Southern Company have also pledged financial support of the effort and will make their companies’ research capabilities available if needed. The project is organized for one year, with a concerted effort to analyze the existing ASHRAE data set and building/system design information, and to develop a simulation model. Project tasks will include:

Preliminary Processing and Analysis of Data
This step will involve checking the data for self-consistency and for consistency with previously published data. Some of this has been done for the GSHP system, but not for the VRF and DOAS systems. The task will be accomplished by comparing redundant measurements; identifying expected trends in groups of measurements; and by calculating values that can be compared with previously published data. For example, the team anticipates making a comparison of hourly cooling capacity determined with a performance map of a heat pump to hourly cooling capacity determined with a heat balance on a heat pump. Or it may have to be determined in aggregate. The project team will also make comparisons to preliminary simulation results, which often helps in identifying problems with data or with interpretation of data.

Computation of Metrics Based Solely on Experimental Measurements.
This step will involve computation of performance metrics that are determined from the experimental measurements. It is expected that the data set will support calculation of a number of metrics, including the energy consumption per square foot for different spaces; the energy efficiency ratio (EER) for different time periods; and the COP for different part loads. Sources of inefficiencies, such as heat gains to refrigerant lines, will be isolated to the extent that the data set allows.

Computation of Metrics Based on Experimental Measurements
and Computer Simulation.
Preliminary checking of the available data suggests strongly that not all needed metrics can be determined directly from the monitored data. A particular shortcoming already identified is that there is no direct way to determine the amount of heating and cooling provided by the variable refrigerant flow system. It’s likely that the first floor will require less heating and cooling than the second floor, but it does not seem possible, at present, to determine that definitively from the monitored data. Therefore, an alternate approach, using building simulation—specifically the EnergyPlus program—will be used. This will involve development of a building model (a specific description of the ASHRAE Headquarters building geometry, occupancy, lighting, office equipment, etc.) and calibration of the model based on available measurements. Sufficient detail will be included in the system models to allow calculation of outdoor air loads and coil loads.

Final Report
Project deliverables include two ASHRAE Transactions papers and a final report. Prior to publication, the papers will be submitted to ASHRAE for review. This is a requirement of using the data. The team hopes that ASHRAE will invite Daikin and ClimateMaster to review the papers prior to publication. The EnergyPlus models and data analysis programs developed during the project will also be made available to GEO for distribution to its membership. The researchers will release data in technical papers regarding: “Evaluation of System Performance in the Renovated ASHRAE Headquarters Building,” and “Calibrated Simulations of the Renovated ASHRAE Headquarters Building.” (GEO)