Facilitating the design, installation, and market acceptance of low-cost ground heat exchangers.
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. The project team is developing models, validating them with field data from two home sites and an outdoor lab, identifying optimal designs, and developing modeling methods that can be adapted for use with code compliance tools. The project also produces design specifications that will support future Title 24 eligibility criteria. A design guide is being developed for industry as a training aid, and a position paper is being prepared for the Department of Water Resources' California Geothermal Heat Exchange Well Standards Stakeholder Advisory Group.
Project Benefits
The project spurs the market for high efficiency GCHPs by evaluating and testing an innovative method to reduce the cost of GHE, whose cost has been a barrier to more GCHP installations. The current method of drilling GHE bores requires costly, specialized deep drilling rigs, that often must be transported from out of state. Instead, by using common, locally available drilling equipment for shallow bores, GHE bore drilling can be done at lower cost. In addition, 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 California Title 24 standards compliance tools.
Lower Costs: 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 Benefits: Assuming a 10% market penetration on new homes, estimated greenhouse gas emissions would be reduced by 8 million pounds per year.
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.