Heat exchange drilling (geothermal systems)
Heat exchange drilling in Wisconsin requires a license.
Geothermal works on the principal of using the earth's natural underground temperature and a geothermal heat pump unit to provide heating in the late fall, winter and early spring and cooling in the late spring, summer and early fall. In Wisconsin, the average underground temperatures range from about 52 degrees in the south to 42 degrees in the north. Below about 20 feet in depth, the influence of surface temperature variations begins to dissipate rapidly and becomes the average of all surface temperature values.
Four basic types of geothermal systems are allowed in Wisconsin:
- A closed loop vertical system has the loops installed in a vertical or angled drillhole.
- A closed loop horizontal systems has the loops installed in a shallow trench or angled drillhole.
- A pass-through system or "pump and dump" draws water from a well and discharges it back to a surface source.
- A direct exchange (DX) system has loops typically made of copper and are installed in a vertical or angled drillhole.
Constructing heat exchange drillholes
Any geothermal system that involves construction of one or more drillholes extending more than 25 feet below the ground surface must meet construction standards and notification or approval requirements in NR 812, Wis. Adm. Code. In addition, heat exchange drillholes may only be constructed by a licensed Heat Exchange Driller or a Registered Heat Exchange Drill Rig Operator working for a licensed driller.
Heat exchange drilling projects require a prior DNR approval if any of the following conditions apply to the project:
- Ten or more drillholes
- Drillholes greater than 400 feet deep
- Project within 400 feet of a municipal well
- Project in Outagamie County
- Project in Winnebago County
Use the Closed Loop Heat Exchange Well Application (Form 3300-255) to apply for DNR approval. If none of the above conditions apply to the project, a Heat Exchange Notification number is required prior to construction.