| Abstract |
Ground-source heat pumps (GSHPs) are often touted as one of the most efficient, sustainable system choices for heating and cooling of homes. While there is much anecdotal evidence, both supporting and detracting from GSHPs, there is little data documenting the long-term installed performance of GSHPs in homes. To establish a deeper understanding of installed GSHP system performance and the associated energy savings potential, the authors worked with contractors and homeowners in Connecticut, Virginia, and Wisconsin to monitor the in-situ performance of three residential ground source heat pump systems. As market penetration for GSHPs continues to increase, partially due to greater availability of federal, state, and utility incentives that help offset the higher installation costs associated with these systems, the findings of these field evaluations are presented to assist manufacturers in identifying specific areas of opportunity for improving the technology and to support the development of more accurate methods and modeling tools to predict the energy consumption of heat pump systems. Four key objectives were identified for this research: • Develop a better understanding of the in-field performance of residential ground-source heat pump systems by measuring real-world conditions, including ancillary components. • Identify optional system components and installation methods that have an impact on the total system energy consumption, have the potential to improve system performance, and/or result in increased system reliability. • Compare measured conditions to the ground-source heat pump unit rating provided by the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) for use by others in developing a more accurate accounting method to assess system performance. • Contrast the predicted energy performance with the actual energy performance to determine the accuracy of current modeling methods. All three monitored systems have two-stage compressors to provide additional heating and cooling capacity during periods of peak demand and each system is served by a horizontal ground loop. After a minimum of one heating season of monitoring for each system, all three systems are operating at efficiency levels within the range of anticipated performance. Measured heating Coefficients of Performance (COP) typically vary from 3.0 to 4.3. Although these measured COPs fall below the rated efficiency levels for these units, the rated efficiency does not account for pressure drop in the ground loop or the duct system. It is interesting to not that the results do not show increased efficiency when the units operate at part-load capacity. The authors address the potential cause of this finding in this report, as well as some common errors observed in these GSHP installations and possible methods to avoid these issues. |