Ground-source Heat Exchange (GHEX) Borehole Drilling
Geothermal heat pumps systems (sometimes referred to as GHEX, GeoExchange, earth-coupled, ground-source, or water-source heat pumps) have been used for several decades in Iowa to help Iowans’ utilize the natural thermal properties that exist under their property.
Ground-source Heat Exchange Systems (GHEX systems) use the constant temperature of the earth as the exchange medium instead of the outside air or well water source to maintain a constant temperature. The GHEX system takes advantage of this by exchanging heat between the home or business and the ground through the use of a series of ground heat exchanger loops. This allows the system to operate at a very high efficiency using only a minor amount of electricity.
There are four basic types of geothermal heat exchange systems found in Iowa.
Three of these — horizontal loop, vertical loop, and pond/lake loop — are closed-loop systems where the heat exchange fluid is circulated in a loop of piping placed in either a borehole in the earth or in a large body of water. The fourth type of system is actually a water-source heat exchange system and is called an open-loop system. This option uses one or more water supply wells to pump groundwater out of the earth and run the water through a heat exchanger in the building. The water that has been heat altered in the process is then placed onto the land surface or back into the aquifer through one or more additional water wells. Which type of system you install will depend on the contractor, the size of the application, the soil and geological conditions of the site, available land to place a system, and local site specific conditions that may limit the site for drilling operations like areas of contamination, local ordinances, or easement boundaries.
All closed loop systems placed 20 feet or greater in the ground and all open loop systems require the issuance of a private well construction permit before any loop drilling, trenching, or boring takes place. These systems also require the use of a certified well contractor and the use of construction standards.
Currently, GHEX loop borehole systems make up 33% of the private well construction permits issued in Iowa.
Closed loop boreholes require minimum setbacks from sources of contamination. The current setbacks can be found at the following web link: GHEX borehole setbacks.
Before You Plan Your GHEX Project and Drill GHEX Boreholes
It is important to know if the proposed GHEX borehole site can be drilled for the installation of GHEX loops.
Iowa has a long history of growth and progress. One of the issues that we encounter is the scenario where the existing site contains some form of contamination that may be limited to the footprint of the site or extend beyond the current property lines.
Some of the common contamination issues that may limit drilling on your site include:
Liquid hydrocarbon storage tanks - leaking tank sites or areas of spills
Industrial and machine districts where manufacturing processes may have placed contamination on-site in the soils and groundwater.
One additional consideration is for the placement of GHEX loop borehole fields is Karst geology. Karst areas may be subject to additional requirements before the site can obtain construction permitting and the use of higher standards for GHEX loop borehole construction. In general, these areas include locations near sources of contamination, older industrialized areas of our communities where manufacturing or chemical handling has taken place, railway yards and spur lines, and any place where Karst bedrock conditions place the top of the bedrock very close to the surface of the ground.
The additional requirements may include a more detailed site survey and site analysis, geological investigation and profiling, the installation of test boreholes and the interpretation of test borehole data, hydrogeological modeling, and setting specific minimum construction and grouting standards tailored to the geology and hydrology present under the construction site.
Grouting of all boreholes is they key to protecting the groundwater resource for future generations and provide your geothermal system with loop boreholes that perform with high efficiency for the life of your system. Karst conditions can make loop borehole construction and grouting difficult due to the large voids, fractures, and caverns that may be encountered during drilling operations. Improper grouting can render your system inefficient and subject the groundwater in your area to surface and shallow water contamination. Additional information regarding Karst geology in Iowa can be obtained from the Iowa Geological and Water Survey.
For more information about how to determine if your property is suitable for GHEX or water supply well drilling please contact the Iowa DNR Private Well Program at 515-725-0462.
For additional information on GHEX systems please consider viewing the following pages:
IGSHPA - The International Groundsource Heat Pump Association - A national trade organization to develop, refine, and promote heat pump installations worldwide.
ASHRAE - The American Society of Heating, Refrigerating, and Air-Conditioning Engineers. A national trade organization to promote all heating and cooling systems including geothermal and ground source heating and cooling systems.
GeoExchange - A national organization to promote the manufacture, design and installation of GeoExchange® systems
- For more information contact -
Russell Tell, Environmental Specialist Senior