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Drilling well in yard

The Problem

The cost of installing a ground loop for a Ground Source Heat Pump (GSHP) system is as much or more than the cost of the remainder of the hardware and labor to install a complete GSHP system. This high cost, considered the main barrier to greater adoption, is driven by labor and equipment amortization costs associated with drilling wells/boreholes or excavating large area horizontal loop fields.

Ground source heat pumps (GSHP) offer great energy savings to consumers and hold the potential to significantly improve energy efficiency in the U.S. While technically proven and presently a part of the heating and cooling market, the capital and labor costs for installing the ground source heat exchanger remains the largest barrier to greater market adoption.  Reports for the DOE’s Office of Energy Efficiency and Renewable Energy[1][2][3] state that the high costs of ground coupling and ground space requirements are the most significant barriers to wider adoption of ground source heat pumps.

Presently there are several methods to extract heat from the ground (for heating) or reject heat (for cooling) to the ground in a GSHP system. The two predominant methods that account for 93% of installations[4] are drilling boreholes (deep wells – 72%), inserting a plastic pipe heat exchanger then filling it with grout and horizontal, near surface trenches (15%) using long “slinky” rolls or straight lengths of plastic pipe.

Drilling boreholes requires large well drilling equipment and is costly.  In a 2011 DOE commissioned study by the Energy Center of Wisconsin titled “Hybrid Ground-Source Heat Pump Installations: Experiences, Improvements and Tools”, it notes the average nationwide cost for drilling a borehole ground heat exchanger is about $13 per foot. Using an example of 175 feet of heat exchanger per ton of heating, a typical 4 ton residential borehole system would cost $9,100.  A horizontal trench high density polyethylene (HDPE) heat exchanger would be of similar or somewhat less cost.

The existing methodologies for creating a ground loop are costly and in the case of the horizontal trench heat exchanger, require a large area (2000 ft2 to 3500 ft2 per ton – ASHRAE 1995) and the land to be trenched to a depth of 5-8 feet.  Many home and commercial lot sizes cannot accommodate this large area and the landscape disruption can be significant.  In addition, maneuvering large drilling rigs or backhoes into residential areas can be problematic.

 

[1] Cherian, A; Konkana, K.; Gamble, R., Frost & Sullivan, Analysis of the North American Geothermal Heating and Cooling Market – Market Rising in Non-residential Applications, 2013

[2] Navigant Consulting, Inc., Ground-Source Heat Pumps: Overview of Market Status, Barriers to Adoption, and Option for Overcoming Barriers,  EERE Geothermal Technologies Program, US Dept. of Energy,  2009

[3] Hughes, Patrick J., Geothermal (Ground-Source) Heat Pumps: Market Status, Barriers to Adoption, and Actions to Overcome Barriers, Oak Ridge National Laboratory, EERE Geothermal Technologies Program, US Dept. of Energy,  2008

[4] Battocletti, E., Glassley, W., Proc. International Ground Source Heat Pump Association Conference, Indianapolis, IN (2012)