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

Facilitating the design, installation, and market acceptance of low-cost ground heat exchangers.

Regents of University of California, Davis

Recipient

Davis, CA

Recipient Location

3rd

Senate District

4th

Assembly District

beenhere

$1,137,234

Amount Spent

closed

Completed

Project Status

Project Result

The project is complete. Current GCHP model is improved by enabling better prediction of fluid temperatures in the bore. The simulated results show good agreement with field and laboratory data. This provides more accurate estimates of energy use for the system. The model was shared at ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) conferences. ASHRAE's guidelines on heat pumps and other measures were considered a primary reference in the industry. The recipient presented its model to the CEC's Building Standards Office and discussed updating Title 24's models. The Building Standards Office will include improved performance maps which could accommodate ground couple heat pumps in future versions of the Residential ACM Reference Manual. The project team intents to submit a Statewide Utility Codes and Standards Enhancement Report in the next Title 24 update.

The Issue

Ground-coupled heat pumps (GCHPs) have been proven to deliver heating and cooling at higher levels of efficiency than air-source air conditioners and heat pumps. However, their application in mild climates, like California, is limited by the high cost of conventional ground heat exchangers (GHE), a component of GCHP systems.

Project Innovation

This project is researching shallow (20-30 feet deep) and large diameter (2-3 feet diameter) helical coil, ground heat exchanger designs for ground source heat pumps. This project seeks to fill the current informational void with the materials and tools needed to eliminate the risks involved with engineering this new technology into homes. To this end, the project analyzed the performance of different designs of large diameter shallow bore GHEs, produced a calibrated model that can predict the performance of these GHEs and incorporate them into industry-standard design tools, and produced the materials that the industry needs to confidently move forward with the deployment of this technology. Also, a draft compliance option was prepared to facilitate this technology's incorporation into the California Energy Commission's residential energy compliance process. Determining a path of compliance of this technology will allow it to receive proper credit for incentives under the California Advanced Home Program, and will give policymakers the information they need to make policy decisions that will encourage the adoption of this technology

Project Goals

The goals of this Agreement are to:

Improve market conditions for GCHPs in California;

Develop and disseminate tools

Project Benefits

The project spurs the market for high efficiency GCHPs by evaluating and testing an innovative method to reduce the cost, which has been a barrier to more installations. The current method requires costly, specialized deep drilling rigs, that often must be transported from out of state. Using common, locally available drilling equipment for shallow bores, GHE bore drilling can be done at lower cost. This technology will be made ready for commercialization by developing modeling tools needed to properly design, size, and evaluate energy savings and to facilitate use with Title 24 compliance tools . The team plans to submit a Statewide Utility Codes and Standards Enhancement (CASE) report to the CEC as a pathway to add to their model to future Title 24 models. The project team was able to successfully integrate their model to the Department of Energy's EnergyPlus simulation program.

Consumer Appeal

Consumer Appeal

Increased use of GCHPs would eliminate noisy and visually unappealing outdoor condensing units. Also, GCHPs could improve comfort for residents compared to forced air systems.

Lower Costs

Affordability

This project seeks to reduce the cost of GHEs for heat pumps. Affordable GCHPs may result in lower utility costs for heating and cooling, lower maintenance costs, and improved system reliability compared to forced air systems. Estimated annual energy savings is over 67 billion BTU, assuming 40,000 single family homes built annually and 10% of new homes equipped with GCHPs. Annual electric savings from cooling efficiency in new homes is roughly 1.2 million kWh. For a 2100 sq ft home and a 2 ton system, and comparing the incremental cost for a GCHP system with conventional HVAC system, the annual cost savings per home is $173, when amortized over 30 years with tax credits.

Environmental & Public Health

Environmental Sustainability

If ground coupled heat pump systems were installed on all new single-family homes built in 2019, 110,000 homes a year, there would be an 8500 MTCO2e GHG reduction.

Key Project Members

Project Member

Curtis Harrington

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