Water Well Journal

This allows the drilling contractor to drop the U-bend as- sembly down the borehole without having to first fuse pipes to the U-bend fitting. About 5 feet of pipe length from each pipe will remain outside the 400-foot borehole for connection to horizontal headers, in this example. Ground loops are one of the most demanding applications for pipes, so there are specific recommendations for HDPE piping components. For example, HDPE ground loop piping should have a minimum pipe material designation code of PE 3608 (higher numbers are even better) and be certified to in- dustry standard NSF/ANSI Standard 358-1. HDPE pipes and fittings are joined using various heat fu- sion methods: butt fusion, socket fusion, or electrofusion. One bad joint buried underground could create a leak that is expen- sive and difficult to find, access, and repair. With that, fusion contractors should strictly follow the guidance provided in ASTM F2620 "Standard Practice for Heat Fusion Joining of Polyethylene Pipe and Fittings" that describes proper fusion procedures for butt and socket fusion. Once installed, ground loops should be tested according to ASTM F2164 "Standard Practice for Field Leak Testing of PE and PEX Pressure Piping Systems Using Hydrostatic Pressure." Crosslinked Polyethylene (PEX) PEX is HDPE that is modified during manufacturing to crosslink the majority of molecular chains. It is a high- temperature, flexible pressure pipe material first developed in the early 1970s. The primary benefit is capability of continu- ous operation at temperatures of 180°F (82°C) or above. This higher temperature capability may be necessary in borehole thermal energy storage (BTES) systems where ther- mal solar energy is pumped into the earth to raise the ground temperature during summer, for example. PEX tubing (Figure 2) has greater resistance to chemical contact, and it is slightly more flexible than HDPE. It is also more expensive. PEX tubing cannot be joined using butt fusion or socket fu- sion. Instead, several types of mechanical compression fittings are approved for underground use with PEX tubing, as are electrofusion fittings. PEX ground loop piping should have a minimum material designation code of PEX 1206 and be certified to ASTM F876 or CSA B137.5, as well as NSF/ANSI Standard 358-3. In North America, PEX is available up to 3 inches in diam- eter and can be supplied as coils, straight lengths, or as pre- fabricated U-bends for boreholes. Polyethylene of Raised Temperature (PE-RT) PE-RT is high-density polyethylene material with enhanced capabilities to withstand higher temperatures up to 180°F. PE-RT may be joined using heat fusion processes, just like HDPE, or using mechanical compression fittings, just like PEX. PE-RT ground loop piping should have a minimum pipe material designation code of PE 3608 and be certified to ASTM F2623, ASTM F2769, or CSA B137.18, as well as NSF/ANSI Standard 358-4. Summary Geo piping materials are produced according to rigorous product standards with strict industry certification programs to ensure consistent quality control. The life expectancy of these plastic piping materials, when specified correctly and installed according to industry and manufacturers' guidelines, is typically well in excess of 50 years. In fact, many of the earliest geo ground loops installed in the 1970s using earlier generations of plastic piping are still in service today 50 years later. Several industry tools are available to assist geothermal de- signers, specifiers, and installers. For example, PPI document TN-55 "Plastic Piping Materials for Ground Source Geother- mal Heating and Cooling Applications" provides even more details about the piping loops. Designers can also use the free online Plastic Pressure Pipe Design Calculator at www.plasticpipecalculator.com to assist with calculations. Design and installation training is available through IGSHPA, and CSA/ANSI/IGSHPA C448 is the ultimate code for geo- thermal design and installation. More information is accessi- ble on Plastics Pipe Institute's geothermal webpage at www. plasticpipe.org/buildingconstruction. Become a Certified Vertical Closed Loop Driller by NGWA Advances in geothermal technologies and their usage created the need for a specific voluntary certification designation for geothermal drillers. The National Ground Water Association responded to this need with the designation of Certified Vertical Closed Loop Driller (CVCLD). The CVCLD is considered an independent designation from the CWD or CWD/PI. The designation reflects an individual who has passed a written exam administered by NGWA that evaluates an in- dividual's knowledge of the skills and competencies associated with constructing a loop well. To learn more, visit www.ngwa.org/advance-your-career/certification/ Geothermal-driller-CVCLD. WWJ All ground loop pipes must meet the requirements of standard NSF/ANSI/CAN 61 to ensure that any aquifer into which the piping system is installed is not contaminated by the pipe itself. facebook.com/WaterWellJournal WWJ July 2022 n 23 Lance MacNevin, P.Eng., is the director of engineer- ing for the Building & Construction Division at the Plastics Pipe Institute (PPI). He has been in the plastic pipe industry since 1993, involved with applications such as hydronic heating and cooling, geothermal, plumbing, and fire protection systems. MacNevin earned his IGSHPA installer accreditation in 2008 and has been closely involved with the geothermal industry ever since.

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