Geothermal Well Drilling—Demystified Part 1: Planning a Successful Well Field Installation

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By David Brown, President of Yadkin Well Co, Inc.

Most commercial HVAC professionals are familiar with the principles of geothermal heating and cooling. Some are experts in designing and installing ground source heat pumps and loop field sizing. But when it’s time to put the drill to the earth, builders and engineers generally turn to a professional well driller experienced in all aspects of vertical geothermal well installation. In this blog series, we unearth the mysteries of this critical process.

Planning is Critical

A vertical well loop field costs approximately half the equipment cost of a geothermal heating and cooling system. Drilling several hundred feet into the earth requires specialized equipment and software and meticulous precision. For example, it is critical that each well forms a perfect 90-degree angle with the earth’s surface. A single degree off, and you may encroach on the heat dissipation area of the next well. Drilling the wells too close can shorten the functional life of the field by prematurely depleting its capacity to absorb heat.

These are just a few costly drilling mistakes that can undermine a client’s desire to have one of today's most energy-efficient, eco-friendly, and low-maintenance heating and cooling systems. An experienced well driller will take every step to avoid these and other mistakes, including getting the lay of the land.

Driller’s First Visit to the Jobsite

I like to visit the job site (whether the project is a retrofit or a new construction) long before drilling commences. On this first visit, I will typically choose the location for the test well, using the building and loop field drawings as my guide. We use this initial well to conduct a thermal geothermal conductivity test (TGCT). This two-day test, which we cover in detail in Part 2, tells us if the earth formation at the proposed site has the capacity to absorb the building heat as designed.

When I visit a geothermal job site for the first time, I'm looking for a few things:

drilling location for the thermal geothermal conductivity test (TGCT), flagged at a jobsite.

  1. The test spot for the TGCT. The test spot needs to be located within the boundaries of the wellfield design, as shown on the project drawings. If all goes well, the TGCT well will become a functional part of the well field, so it needs to be thoughtfully located to save the cost of drilling an extra well.

  2. Access to the test spot. Since we will be bringing over 40 tons of drilling equipment onto the job site, we need to make sure we have a clear path on and off the site. Prior to testing, we will confirm that the ground is nice and dry.

  3. Direction of Water Runoff. Drilling creates a fair amount of runoff water, which is a major concern, especially in urban locations. Most cities have environmental impact regulations that prohibit this runoff from entering storm drains since these drains ultimately lead to creeks and rivers. If there is a storm drain, we have to make plans to capture the runoff water. We have a number of strategies at our disposal to clean the water onsite so that it meets environmental standards for release.

Although we can’t know what type of formation lies beneath the soil of a particular site, we can make a well-educated guess based on the geographical area. In the Carolinas, we know to expect a lot of sand and water if the site is no more than 75 miles from the coast. Further west, we will likely encounter less water and much more rock.

In most cases, the builder will check the density of the soil by drilling approximately 50 feet into the earth with an auger to evaluate the ground's ability to support the proposed building. I typically ask to see this report in case any unexpected surprises might impact the loop field. Ultimately, however, we will be drilling several hundred feet for a vertical geothermal well, so we won't know the whole story until then.

Next up, we’ll discuss the actual drilling of the test well!

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David Brown is the Co-owner and vice President of Yadkin Well Co, Inc. in Hamptonville, NC. He and his technicians drill water and geothermal wells throughout North and South Carolina. The business, purchased by David's father in 1964, is now owned by David, his son, Matthew, and his brother, Vaughn. The Brown family has been drilling wells for geothermal installations since 1985. David is a Certified Well Driller/Pump Installer (C.W.D./P.I.), a Certified Vertical Closed Loop Driller (Geothermal) (CVCLD), and Geothermal Accredited Installer (AI) and inspector (CGI). He is also North Carolina Level A contractor. For more information, click Yadkin Well Co.