Facility Expansion Opts for HDD Geothermal Loop Installation

July 2012, Vol. 67, No. 7

The geothermal system for the new facility is composed of 48 vertical closed loops, each extending approximately 150-feet deep that transfer heat to and from the ground. LSI’s licensed and IGSHPA-accredited (International Ground Source Heat Pump Association) crew used the D20x22FX Series II Navigator flex-angle drill, manufactured by Vermeer, to install the loop field.

According to Bussert, the flex-angle drill allowed his crew to complete three separate bores from the same drill site location, simply by adjusting the angle of the entry points by approximately 20 degrees. The process began by digging a mud reclaiming pit, approximately 10 feet long by four-feet deep, and positioning the drill within close proximity. The flex-angle drill then completed the first three bores, was repositioned to the opposite side of the mud pit for completing three additional bores -- six total within a very narrow footprint. Bussert selected a 4 3/4-inch diameter PBC bit to navigate the heavy clay soils intermixed with narrow layers of coarse sand.

The drill was also used to complete the installation of the individual closed loops within each bore.

“The flex-angle drill also functions as a push tool for installing the loops,” Bussert says. “After each drill hole was completed and cleaned, we would trip out, then swap out the drill bit with the push tool, hook directly onto the loops and push back down into the bore. After reaching the bottom, the loop was then unlocked from the push tool and grouted securely into place.”

Bussert further explained that the mud recycling pits served a dual purpose once drilling was complete. “The pits we used for recycling the mud were then vacuumed out and cleaned up and used as header pits for consolidating the series of loops,” he says. “From there, everything was brought together, tied into the return line and taken from there to the building. It worked great.”

LSI’s drill team was able to complete between four and five loops a day, finishing the installation of all loops within a two-week period. After making some minor adjustments in response to the varying clay/sand soil conditions that required experimenting with varying bentonite/polymer mixtures, Bussert was pleased that the installation phase of the loop field went pretty much according to plan.