PERFORMANCE ASSESSMENT OF INSTALLED GEOTHERMAL HEAT PUMP SYSTEMS IN THE NORTHEAST

Geothermal heat pump (GHP) systems are recognized as one of the most efficient technologies for heating and cooling buildings and offer a potentially attractive alternative to heating oil and propane throughout the Northeast US. However, several significant barriers are limiting the widespread adoption of the technology, including: low consumer awareness, weak consumer confidence, and high up-front costs. Each of these barriers can be addressed with the collection and analysis of actual system performance data. Using a web-based monitoring system, we have collected and analyzed high-resolution data from over 40 GHP systems in the Northeastern United States spanning a three year period. We have found that system performance is related to both above-ground factors (including the heat pump equipment, the building envelope, and usage patterns) and below-ground factors (ground loop type, installation, and thermal conductivity). We also present a novel and cost-effective method of using inverse modeling to infer subsurface thermal properties from observed heat flux rates and the corresponding ground loop temperature fluctuations, and we demonstrate how detailed knowledge of the ground thermal characteristics at the scale of individual systems provides an opportunity to improve system design, reducing uncertainty and system cost. When properly designed and installed, GHP systems provide a reliable and cost-effective means for space heating and cooling.