Topic 10.a Hybrid Geothermal Heat Pump for Single Residences

Statement of the Problem or Situation
Geothermal heat pumps have the potential to significantly reduce residential and commercial energy usage for space heating, air conditioning, and hot water. The largest barrier to wider adoption of this technology is the high installation cost and long payback periods relative to conventional air conditioners, gas furnaces, and heat pumps.
How the problem is being addressed
Our concept combines both air and ground heat transfer the so-called hybrid geothermal heat pump (HGHP). This concept combines both air and ground heat transfer. The system is split like a traditional heat pump with the proposed outdoor unit and any indoor unit (air handler). The HGHP outdoor unit consists of the compressor, an air cooled heat exchanger, the liquid coupling components (pump, heat exchanger), and the controls for the entire system. The concept of operations is that in cooling or heating mode when the air temperature is near the desired indoor temperature, the system would transfer heat to the surrounding air. In this condition the air-source and geothermal heat pumps would have similar COPs. When the temperature extremes of summer and winter increase the difference between indoor and ambient temperatures significantly, the system would transfer heat to the ground when it has a much better COP than an air source. The HGHP trades a significant fraction of the expensive borehole field with an inexpensive air-cooled heat exchanger that is used only when advantageous.
What was done in Phase I
A first-generation prototype of the outdoor unit for the hybrid geothermal system was designed and fabricated. The 3.5 tonR system was designed to reject heat to either air or the ground at the AHRI 65 rating condition for condensing units giving maximum flexibility. We fabricated the prototype using a mixture of in-house fabrication techniques, COTS part, rapid prototyping, and custom heat exchangers from outside vendors. Testing is ongoing.
What is planned for Phase II
The objective of the Phase II program will be to complete the development and commercialization of our 3.5 tonR HGRCU. Technical performance will be measured prior to the start of Phase II. Thus, the focus of the proposed effort is to make any adjustments required for thermal performance, design for manufacture, and reduce manufacturing cost as much as possible.
Commercial Applications and Other Benefits
Mainstream is reducing GHP system costs by developing a unique HGHP, where the hybrid nature reduces ground loop size and therefore cost, while the rotomolded structure reduces manufacturing costs and increase system life. We calculate that the total cost of ownership for the hybrid system will be significantly lower than a full geothermal heat pump and has a lower install cost.