Extreme
weather conditions, such as the harsh deep freeze we endured this past winter
or the stifling record heat that blanketed the United States this summer,
should be enough to convince any business or homeowner about the benefits of
geothermal heating and cooling systems, not to mention the accompanying federal
and state tax credits that are available. Although vertical drilling is the
most common method of geothermal loop installation, horizontal directional
drilling offers additional benefits, options and flexibility for loop
installation, along with the installation of header pipes that connect the
loops to geothermal heating and cooling systems. The benefits of horizontal
directional drilling can be fully appreciated in ground source heat pump (GSHP)
retrofit applications where well-established landscaping and structures present
a problem. Benefits of horizontal directional drilling were realized on a
recently completed residential retrofit project in Rock Hill, S.C.
Harold Peeples, owner of Tarheel Contractors Supply, needed to upgrade his
residential heating and cooling system. As a supplier to both the geothermal
heating and cooling industry and the HDD market, Peeples is well aware of the
benefits these two converging technologies have to offer. A vertical drill
would have severely damaged the extensive backyard landscaping, and installing
loops in the front yard just was not an option; therefore, horizontal
directional drilling was the only logical choice.
Utilizing a Ditch Witch 1220 horizontal directional drill, Lee Electric from
Aberdeen, N.C., set up and drilled from the side of the road, under the fence
and landscaping, and punched out into an exit pit just beyond the end of the
driveway. Once the drill punched out into the exit pit, 1-inch geothermal
loops, along with a 11⁄4-inch grout tremie line, were pulled behind the drill
bit, back toward the drill entry point. Mule tape was utilized as a spacer
between the u-bend and the bit, so that when the bit was out of the ground, and
the mule tape was cut loose, the u-bend of the loop was in the desired
position/depth. Additional depth (35-ft. deep) was added to the bore profile to
compensate for the lack of linear footage, and six 250-foot-long,
1-inch-diameter loops were installed.
After the installation of each loop, a thermally enhanced grout mixture of 16
gallons of water, a 150-pound bag of geothermal grout, and 200 pounds of sized
silica sand (provided by U.S. Silica), was pumped through the tremie line via a
ChemGrout grout mixing and pumping unit to fill the void area between the loops
and the borehole. This recipe was used to achieve a thermal conductivity of
0.90 Btu/hr/ft/F. Thermally enhanced grout increases the efficiency of the
ground loop system by providing better heat transfer from heat loops to the
earth, and the grout provides a low permeability seal in the annular space of
the borehole.
After all of the loops were installed and grouted, the drill was repositioned
behind the exit pit where Lee Electric drilled from the exit pit, under the
driveway, and punched out into a small exit pit below a crawl space under the
house. Once they punched out under the crawl space, two 11⁄4-inch header pipes,
which connected the loops to the geothermal heating and cooling system in the
house, were pulled back. Panther Heating and Cooling of Rock Hill, S.C.,
installed the WaterFurnace heating and cooling system, purged the loops, and
got the system up and running in time for the Christmas holiday
season.
Horizontal directional drilling provided a means of installing the geothermal
loops and header pipes without damaging the picturesque backyard. Today, there
are no visible signs outside of the home to indicate that such a system was
installed and operating – other than the lack of a noisy air-conditioning unit
and an electrical meter that now turns quite a bit slower. Peeples and his wife
have been enjoying the comfort and savings provided by the WaterFurnace ground
source heating and cooling system, which immediately was put to the test by
starting up in the harsh winter of 2010-2011 before going up against
record-high temperatures of the summer of 2011.
ND
Drilling Fluids: HDD Geothermal Loop Installation
![George Dugan](http://www.thedriller.com/ext/resources/Default_Images/Dugan.jpg?1434387398)