Final Report: Greener and More Energy Efficient Renewable Energy Resource – Geothermal Heat Pumps

EPA Contract Number: EPD11034
Title: Greener and More Energy Efficient Renewable Energy Resource – Geothermal Heat Pumps
Investigators: Clancy, Edward Vincent
Small Business: ACTA Technology Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2011 through August 31, 2011
Project Amount: $80,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2011) RFA Text |  Recipients Lists
Research Category: SBIR - Green Buildings , Small Business Innovation Research (SBIR)


Given the need to rein in the Nation’s energy consumption and carbon emissions, there is a need for increased nationwide deployment of geothermal heat pumps (GHPs). GHP systems are a proven renewable energy resource that provide significant energy savings in the range of 30 to 60 percent as compared to conventional heating and air conditioning units used today.
GHPs have the potential to reduce our dependence on foreign oil because of their lower energy requirements and high efficiency. GHPs could have a significant impact on the building environment, which accounts for nearly 40 percent of U.S. energy consumption and greenhouse gas emissions. The National Earth Comfort Program identified installation cost as the primary barrier to GHPs acceptance in the U.S. marketplace. Their long payback periods are the problem. In summary, GHPs are a renewable energy source with high energy efficiency, but their high initial cost causes a drag on their acceptance into the U.S. marketplace. Today's GHP systems use utility, federal and state subsidies to be accepted by the public. However, subsides are never a good long-term solution for any green technology, especially in this era of budget cuts. This project addresses the largest barrier to acceptance:  high initial cost.

Summary/Accomplishments (Outputs/Outcomes):

Today’s GHP systems use either propylene or ethylene glycol water mixtures in their ground loop, but ethylene glycol presents an environmental risk and a disposal problem. In Phase 1, ACTA Technology, Inc. (ACTA) developed novel nanofluids that increase the heat transfer in the cooling loop of GHP systems. These new fluids significantly improve the heat transfer efficiency over both propylene and ethylene glycol and reduce the need for federal and state subsidies to be used as an incentive to install GHPs. Nanofluids increase the heat transfer rate of the ground source loop, thereby reducing the life cycle cost, need for subsidies and the initial cost of these systems. This improved heat transfer lowers the installation cost because the ground loop can be smaller and thus less fluid is required to be pumped. Our new nanofluids were developed from a food-grade heat transfer fluid and from propylene glycol. Nanofluids are a new type of fluid containing nanometer-sized particles, usually below 100 nanometers in size. These nanofluids are engineered colloidal suspensions with improved heat transfer efficiency over both propylene and ethylene glycol water mixtures, thereby reducing the life-cycle cost of GHPs by 17 percent. This improved heat transfer lowers the installation cost.
The significance of ACTA's project is the need to develop new circulating fluids for GHPs that do not possess the harmful effects of ethylene glycol (CAS 107-21-1). A 5-ton residential GHP can produce 660 to 880 gallons of ethylene glycol waste over its 40-year lifetime. Ethylene glycol is extremely hazardous to pets and children and is water soluble. There is a potential risk of ethylene glycol entering the water supply via leaks in fixtures and pipes when used as the ground loop heat transfer fluid. Therefore, ethylene glycol represents both a disposal and environmental risk.
Food-grade heat transfer oils (CAS 8042-47-5) are not water soluble and are being used in many heat transfer applications today. These heat-transfer oils are not being used in GHPs because of their lower heat transfer properties as compared to glycols. Our research identified a food-grade oil nanofluid with significantly improved heat transfer efficiency compared to both propylene and ethylene glycol water-based fluids; the improved propylene glycol nanofluid had superior heat transfer properties, even to water. The nanoparticles used will be able to be removed from the fluid and reused.
The typical nanofluids use a base fluid plus a surfactant plus nanoparticles to make up the nanofluid. ACTA was able to develop nanofluids that are stable with and without a surfactant, which is a significant result. ACTA has applied for a non-provisional patent for its technology.


ACTA's propylene glycol nanofluid has heat transfer properties that were improved by 48 percent over the propylene glycol water mixture (50:50 mixture). This fluid has heat-transfer properties that are 20 percent better than water as a heat-transfer fluid. This improvement is very significant. Our food-grade heat transfer nanofluid was improved by 29 percent over the base fluid and has better heat-transfer properties than both propylene and ethylene glycols.
ACTA’s nanofluid will result in a greener and more energy efficient GHP system with a reduced payback period; this will reduce the need for subsidies for this green technology.
Table 1 below summarizes ACTA's results and compares two of the company's new nanofluids to water as a heat transfer fluid.
 Table 1 – Summary of Results for New Nanofluids
Heat Transfer Nanofluid
Heat Transfer Improvement Over the Base Fluid
Heat Transfer Capability Compared to Water (Water = 100)
Long-term Stability
Propylene glycol water nanofluid
Not required
Food Grade Heat Transfer Nanofluid
Bio-degradable surfactant

Supplemental Keywords:

geothermal heat pump, nanofluid, green building, energy consumption, greenhouse gas emissions, heat transfer, propylene, ethylene glycol, SBIR, nanotechnology, sustainable energy, renewable energy