Ground-source Heat Exchange Borehole Drilling

Basic Geothermal Heat Exchange (GHEX) System Information

Geothermal Heat Exchange (GHEX) Systems, also referred to as ground-source heat pump systems, GeoExchange, earth-coupled, 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.

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. A GHEX system takes advantage of the earth's temperature 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 heating and cooling system to operate at a very high efficiency using a minor amount of electricity.

Types of GHEX Systems

There are four basic types of GHEX systems used in Iowa. Three of these are closed-loop systems, which use heat exchange fluid that is circulated in a loop of piping placed in either a borehole in the earth or in a large body of water. The heat exchange fluid is used to exchange heat with the ground or a body of water.

• Horizontal closed-loop
• Vertical closed-loop
• Pond and/lake closed-loop

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 inside the building. The water that has been heat altered in the process is then placed onto the land surface for absorption and evaporation or it can be placed back into the same aquifer through one or more additional water wells.

The 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 boreholes like areas of contamination, local ordinances that limit or prohibit drilling, or easements.

Private Well Construction Permits and Separation Distances

All closed loop systems that are 20 feet or greater in depth and all open loop systems require the issuance of a private well construction permit before any loop drilling, trenching, or boring takes place. For  these GHEX systems, installation must be done by a certified well contractor and use of defined construction standards. Depending on the actual drilling location, there may be additional requirements to help manage fragile geological conditions, confine localized contamination, and protect the state's drinking water aquifers.

Closed loop boreholes require minimum separation distances (a.k.a. setbacks) from other wells and sources of contamination. The current separation distances can be found in rule 567 IAC 49.8.

Heat Transfer Fluid Requirements

All heat transfer fluids used in GHEX systems must meet the groundwater safety requirements in rule 567 IAC 49.23.

• Heat transfer fluids must be potable water or food-grade or United States Pharmacopeia (USP) grade propylene glycol or calcium chloride.
• Heat transfer fluids containing additives must be National Sanitation Foundation (NSF) certified as HT1 in the NSF White Book.
• Any other materials or additives must be NSF 60 certified.
• Additives shall be mixed in concentrations recommended by the manufacturer.
• A permanent sign must be attached to the heat pump that specifies the type and mixture ratio of fluids used. The sign must state that “only approved heat transfer fluids may be used.”

Never use ethylene glycol (common automotive radiator fluid) or other non-approved fluids or additives in a GHEX system as these constitute a groundwater hazard that must be addressed at the loop owner's expense. If you suspect your system needs fluids/antifreeze, call an authorized system service provider. Adding the wrong fluid to the system will result in the need for total system flushing and fluid replacement, and repair costs that may run as high as thousands of dollars.

Before Planning a GHEX Project and Drilling GHEX Boreholes

It's important for you, the county, the DNR, and the driller to know if the proposed GHEX borehole site can actually be drilled for the installation of GHEX loops. Even though all areas of our state have the potential for GHEX loop borehole systems to function properly, there are many sites that shouldn't be drilled because of pre-existing contamination. In certain instances, it can be difficult to find a location where existing contamination does not pose a threat to the groundwater and/or the piping used in GHEX systems.

Here are some of the situations that may limit drilling on a site:

• Location of nearby public water supply wells. If you have a public water supply well within 400 feet of your site, it may be difficult for you to install a GHEX systems due to the federally required separation distances between public water wells and private drilling activities.
• Local community covenants, ordinances, or other site restrictions.
• Liquid hydrocarbon storage tanks - leaking tank sites or areas of suspected or known spills, including gas stations, fuel storage and transfer stations, railroad switch yards, etcetera.
• Landfills and dump sites - both privately owned and community owned.
• Industrial and machine districts - even if the work no longer takes place. Includes factories, power generation, rail yards, etcetera.
• Metal works (ferrous and non-ferrous) including foundries, manufacturing, fabrication, and metal plating.
• Wastewater treatment infrastructure including lagoons, sludge storage and application areas, etcetera.
• Ag and industrial chemical manufacturing, mixing, storage and loading areas.
• Consumer service areas, including dry cleaning sites, automotive service, repair and body shops, pesticide services, etcetera.
• Any scenario where contamination may be present due to manufacturing, storage, and transport of goods.

Site Review

All proposed GHEX sites that may contain contaminants require a more thorough review and construction plan. There are even cases when drilling vertical boreholes may not be an option due to the type and extent of contamination on the property or adjoining properties near where the drilling is proposed. If detailed review is not performed in these scenarios, installation cost, inconvenience, and liabilities increase for both the property owner and the drilling contractor and can result in increased monitoring requirements, fines, and associated clean-up costs. A GHEX system may not be the most economical long-term solution on a site that requires extensive review, greatly increased construction standards, ongoing monitoring requirements, or questionable long-term durability of the system piping.

It is the responsibility of the property owner to initiate the site review process and to work with a groundwater professional and the department to determine the actual risks of drilling at the proposed location. There may be properties that will not be able to utilize GHEX systems due to pre-existing site contamination issues.

The Karst Geology Variable

One additional consideration for the construction permitting and placement of GHEX loop borehole fields is Karst geology. A site in a Karst area may be subject to additional requirements before a construction permit can be obtained. In general, Karst sites require the use of more stringent construction standards to ensure that poor quality surface water and shallow groundwater do not reach the deeper protected drinking water supplies.

The additional requirements in a Karst area can include a more detailed site analysis, geological investigation and profiling, the installation of test boreholes to collect geological and aquifer information, hydrogeological modeling, increasing separation distances between the site and sources of contamination, setting specific construction and grouting standards tailored to the geology and hydrology of the site, and the use of long term monitoring to watch for ground settling and groundwater contamination.

When looking at the overall protections that all GHEX boreholes require, full depth grouting is one of the most important steps you can take to protect the groundwater resource. It also helps your GHEX system perform with high efficiency which reduces your total operational lifecycle costs. You should only hire contractors who agree to utilize full depth grouting for your installation as they're vested in providing a quality service that helps your system work as designed and helps protect the groundwater used by your family and your neighbors.

Additional information regarding Karst geology in Iowa can be obtained by contacting the department and asking to speak with one of our geologists, or by visiting our Karst website.

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 515-725-0237.

Additional information

• Iowa Geothermal Association - An Iowa based organization of professional geothermal drillers and installers.
• Iowa Water Well Association - An Iowa based organization of professional well drillers and geothermal drillers and installers.
• GeoExchange - A national organization to promote the manufacture, design and installation of geothermal systems
• The International Ground Source 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.