Geothermal Heating and Cooling
Map of Known High Chloride Groundwater - bentonite grouts cannot be used in groundwater with chloride concentration >1,500 mg/L. To contribute to an updated map send well location, chloride concentration, and sample depth to Michael Rogers or Shristi Shrestha.
BMP Guide for Managing Water Produced During Well Drilling
Click here to access a Powerpoint poster version of the content below.
What is Geothermal Heating and Cooling?
Conventional heating and cooling systems use air to transfer heat into and out of buildings. Geothermal systems use the nearly constant temperature of the ground as a heat source in the winter and as a heat sink in the summer. Properly designed and installed, these systems can heat and cool efficiently. Because these systems are often intimately connected with underground sources of drinking water, the North Carolina Underground Injection Control (UIC) Program of the Division of Water Resources regulates the construction and operation of these systems in order to keep the ground water suitable for drinking.
What Regulations and Permits Do You Need to Know About?
Proper well construction and maintenance can protect human health and ground water quality, plus help avoid problems with heat pump system operation. As with other well types, only certified well drillers are permitted to construct wells for geothermal heating and cooling systems; please refer to the Well Contractors Certification Commission for more information. Additionally, only HVAC contractors licensed by the State Board of Examiners of Plumbing, Heating and Fire Sprinkler Contractors can install heat exchange tubing into a well or borehole. Permits are required for some types of systems in order to make sure they are operating safely. The specific type of geothermal heat pump system determines what permits or notification are required.
Four Main Types of Systems:
- Open loop heat pump systems
- Vertical closed loop heat pump systems
- "Pump and dump" heat pump systems
- Horizontal closed loop heat pump systems
Open Loop Heat Pump Systems
Open loop heat pump systems operate by withdrawing water from a well, circulating it through the heating/cooling system, and returning the water to the source well or another well. This system is often used with an existing water supply well and may use separate wells for water supply and water return or may use a single well for both supply and return. The wells used for these systems have the same grouting and casing requirements as water supply wells. A Geothermal Water Return Well Application is required to be submitted and a permit issued in order to construct and operate this type of injection well.
Following receipt of an application for a permit for this type of well, an inspector will visit your site to determine its suitability for construction of the proposed injection well. If the application is approved, a permit for construction and operation of the injection well will be issued to you. After construction of the well and heat pump system is complete, the inspector will return to your site to inspect the well and collect samples of the system’s influent and effluent. If the effluent does not meet the State’s groundwater quality standards, you will be required to take action to identify and correct the problem; otherwise, you will be allowed to continue operation of the system as long as you keep the permit valid. Permits are usually issued for five year intervals.
Vertical Closed Loop Heat Pump Systems
Vertical closed loop heat pump systems operate by recirculating a liquid within continuous piping that is enclosed in a well. The continuous piping exchanges heat with the subsurface without direct contact between the recirculating liquid and the subsurface. There are two distinct types of closed loop systems:
- “Direct Expansion” or “Direct Exchange” systems circulate refrigerant gas via copper tubing and typically have cathodic protection to prevent corrosion of the copper tubing.
- Aqueous systems circulate potable water only or water with performance-enhancing additives such as antifreeze, biocide, or corrosion inhibitor via HDPE or types of materials specified in the NC Mechanical Code.
A State permit is not required, but a well construction notification form must be submitted prior to construction. Closed-loop geothermal heat pump injection wells of either type must be grouted the entire length of the borehole. Bentonite grout or “thermally enhanced” bentonite-sand grout mixtures may be used as long as the groundwater does not contain chloride concentrations of 1500 mg/L or greater. In addition to these State requirements, your county or municipality may have additional requirements for construction and operation of geothermal heat pump systems.
"Pump and Dump" Heat Pump Systems
So-called “pump and dump” systems are heat pump wells that withdraw groundwater but do not re-inject the heat pump effluent into the aquifer. These systems do not fall under the UIC rule and, therefore, are not regulated by the UIC Program.
Horizontal Closed Loop Heat Pump Systems
Horizontal closed loop heat pump systems operate just like vertical closed loop systems except that the continuous piping is placed in trenches in the ground. A variation of this type has the piping located in a pond or lake, exchanging heat with the water body instead of the ground. A permit is not required for this type of system, but you should check with your county and municipal authorities for any other applicable rules and regulations.