Low-Cost, Large-Diameter Shallow Ground Loops for Ground-Coupled Heat Pumps

California Energy Commission

This project developed and validated modeling tools for simulating a ground heat exchanger technology that provides a less expensive method for implementing ground-source heat pumps and significantly reduces energy use in many California climate zones, furthering attainment of California’s energy goals. It is well documented that properly sized and installed ground-source heat pumps enjoy higher system efficiencies than conventional air-source systems by exchanging heat with the ground rather than with ambient air. Ambient air temperatures are hottest when cooling is most required and coldest when heating is most required. Exchanging heat with the ground reduces the temperature extremes and improves heat pump performance.

Market adoption of ground-source heat pump technology has been slow largely due to the significant cost of installing the ground heat exchangers. This technology generally requires drilling deep to place the heat exchanger. Typical California valley soil conditions require 200-foot-deep bores for each ton of heat pump capacity, so a three-ton system would require three 200-foot bores, costing at least $9,000. The large-diameter shallow bore technology studied in this project, however, costs roughly one-third the cost of the deep bore technology.

To evaluate the benefits to California ratepayers, this project performed an analysis using EnergyPlus, and considered the effect of using the large-diameter shallow bore ground-source heat pump on heating and cooling energy end uses for a prototypical single-family home located in each of California’s 16 climate zones. Simulations show a significant reduction in energy use for many California climate zones, with an average heating and cooling energy savings of 20 percent and 23 percent, respectively. Based on a general cost of $0.20 per kilowatt-hour, the annual savings for California ratepayers would be more than $100 for eight of the 16 climate zones and more than $300 for climate zone 16.

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