A bored geothermal heat exchanger must be constructed according to the construction standards in this part and the general construction standards in parts 4725.2010 to 4725.3875.
Bored geothermal heat exchanger piping must be high-density polyethylene or cross-linked polyethylene that meets the following requirements:
for high-density polyethylene:
socket fusion and butt fusion connections must be made in accordance with ASTM Standard F2620-19, and electrofusion connections must be made in accordance with ASTM Standard F1055-16; and
for cross-linked polyethylene:
a fitting for a PEXa system must not be buried in a pipe loop boring or between a pipe loop boring and the heat pump unit, unless the fitting is located in a vault or other structure accessible from the ground surface or floor of the building; and
fittings must meet ASTM Standard F1807-19b, ASTM Standard F1960-19a, or ASTM Standard F2080-16, and ASTM Standard F877-20; and
high-density polyethylene and cross-linked polyethylene pipe must have a minimum pressure rating of 160 psi at 73 degrees Fahrenheit.
The licensee must complete a successful pressure test of the bored geothermal heat exchanger piping after the piping is installed in the bore holes. Pipe must be pressure tested with potable water at a pressure of 1.5 times the system operating pressure or 100 psi, whichever is greater. The pressure must remain constant for 30 minutes without adding additional water.
The annular space between the bored geothermal heat exchanger piping and a bore hole must be filled with grout according to the procedures in part 4725.3050, subpart 2, and according to the procedures in part 4725.3450 for a bored geothermal heat exchanger boring from which groundwater flows above the established ground surface. The annular space must be filled with:
neat-cement grout or cement-sand grout in a boring from which groundwater flows above the established ground surface; or
neat-cement grout, cement-sand grout, bentonite grout, or thermally enhanced bentonite grout in unconsolidated materials. Thermally enhanced bentonite grout must consist of:
thermal enhancement material, including:
a maximum of 200 pounds of sand per 50 pounds of bentonite, with 80 percent or more of the sand smaller than 0.0117 inch (passing U.S. Sieve #50); and
a maximum of 20 pounds of graphite that meets the ANSI/NSF Standard 60-2016 requirements per 50 pounds of bentonite.
Heat transfer fluids must be propylene glycol or ethanol that meets the following requirements:
a propylene glycol with additives, including corrosion inhibitors and dyes, must be certified as meeting the NSF Category Code HT1 for heat transfer fluids;
ethanol products must be designed by the manufacturer for use in bored geothermal heat exchanger systems. Ethanol products must not be used unless approved in writing by the commissioner. A complete list of product ingredients and concentrations must be submitted for review;
ethanol may be used in an ethanol-water solution of not more than 20 percent ethanol by volume. Ethanol concentrates used to prepare heat transfer fluid must be diluted to not more than 20 percent ethanol by volume before being brought into a building where the heat transfer fluid is to be used;
storing, handling, and using ethanol is subject to the safety precautions and procedures specified by the ethanol manufacturer, the applicable requirements of chapters 1305 and 7511, and NFPA Standard 30: Flammable and Combustible Liquids Code, 2015 Edition; and
A permanent sign must be attached to the heat pump identifying the heat transfer fluid in the bored geothermal heat exchanger and specifying that only heat transfer fluids approved in this part may be used.
The locations of all buried bored geothermal heat exchanger piping from the point where the pipe loop exits the bore hole to the point where the pipe is exposed above the ground surface or floor of a building must be marked by:
a ferromagnetic metal marker, detectable from the ground surface, located above the point where the pipe loop exits the bore hole.
A bored geothermal heat exchanger boring installed using directional drilling technology that extends under a building or within three feet horizontally of the farthest exterior projection of the building must be located at least ten feet below the lowest part of the building, including the foundation and footings. Supply-return piping that is plumbed through the building wall or floor is exempt from this requirement.
The point where the drill bit penetrates the ground surface for a geothermal heat exchanger boring must be located at least ten feet horizontally from a contaminant source that has contaminants directly entering the soil, including:
Bored geothermal heat exchanger piping must not be installed on or under property other than the property identified in the approved permit without the affected property owner's written consent or other legal authority.
The ends of each pipe loop must be accessible within a building or buried no deeper than ten feet below the ground surface. The buried ends of a pipe loop must not be built over or otherwise made inaccessible.
A pipe loop that is not connected to a geothermal heat exchanger system, such as a loop installed for thermal conductivity testing, must be protected by:
encasing the ends of the pipe loop in an ASTM Schedule 40 steel or plastic outer protective pipe that is at least four inches in diameter and extends at least one foot above and two feet below the ground surface; and
When sealing all or part of a bored geothermal heat exchanger:
all heat transfer fluid must be removed from the bored geothermal heat exchanger piping that is to be sealed;
the heat transfer fluid must be contained and recycled or disposed of according to applicable federal, state, and local requirements;
the ends of each pipe loop must be accessed and grouted by pumping grout through a tremie pipe inserted to within ten feet of the bottom of the loop, or by pumping grout into one end of the loop until grout flowing from the other end of the loop meets the minimum specifications and densities in part 4725.0100, subpart 21d, 22b, or 30n;
the portion of the piping in unconsolidated geologic materials must be filled with bentonite grout, neat-cement grout, or cement-sand grout; and
the portion of the piping in bedrock must be filled with cement-sand grout or neat-cement grout.
MS s 103I.101; 103I.111; 103I.205; 103I.221; 103I.301; 103I.401; 103I.451; 103I.501; 103I.525; 103I.531; 103I.535; 103I.541; 103I.621; 144.05; 144.12; 144.383; 157.04; 157.08; 157.09; 157.13
17 SR 2773; 33 SR 211; L 2013 c 108 art 12 s 108; L 2014 c 275 art 1 s 136; 45 SR 986
April 30, 2021
Official Publication of the State of Minnesota
Revisor of Statutes