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Boring Thoughts by Todd Tannehill Owner, Mud & More, LLC The Economics of Geothermal Grout I started focusing in on geothermal loop installations in 2005. Back then, our geothermal grouting class started with slides selling drilling contractors on why they should go after the loop business; we talked about system payback and quoted those times in years based on state and federal subsidies. Today, we have accept- ed lower sales in absence of the federal subsidies, wait for subsidies to return, and for the ground source heat loop segment to pick back up. As a side note, I always hated the term “ground source heat loop systems” and would rather something like “constant comfort ground loop systems.” This would be market inclusive for our southern neighbors and the great cooling these systems provide. Many have tried to reinvent better mouse traps for installing the loops. We have dedicated rigs, manifold design, direct burial systems, and yes, even the bentonite folks have joined in the innovation craze. For the bentonite producers it has been about finding a better additive to boost the thermal conductivity (TC) of the grout they already make. In my own past, we have tried many additives to grout to enhance the TC values. Some didn’t work at all, some a little, and some were rock stars. Of the rock stars, some couldn’t pass National Safety Foundation (NSF) certification, some were too hard to work with, and many worked great but cost prohibitive. A carbon composition called graphite (chemical formula C) was introduced some years back as an alternative to silica sand for geothermal grout mixes. What are the most obvious pros and cons of using graphite to boost TC? Some of the pros are: • Easy to mix in the field • Lower batch weights (less pump needed to install grout) • Not killing your crews with heavy sand sacks • Less transportation cost (can ride on same truck with grout) • Smaller material footprint on job-site • Perceived lower cost per batch. The biggest con, or “elephant in the room,” is that graphite is messy to work with. Since this is a fact, let’s discuss what in my opinion is a possible con - lower batch yields with graphite vs. silica sand. Using the manufacturers’ mixes, which includes 400 pounds of silica sand to reach a 1.2 Btu/hr (British thermal unit per hour) TC value, each batch of grout will yield about 42 gallons. To achieve the same TC value with graphite, your mix will yield you about 18-19 gallons. If you are grouting a 200-foot x 6-inch borehole with a ¾-inch loop, you would need 14 batches of graphite mix vs. 7 batches of sand mix to fill the 276-gallon need. Is this a true con for graphite? It depends on local material cost and availability, freight, labor savings, site storage cost, available jobsite footprint, and the ability to use less pump - to name a few considerations. In other words, you will have to fig- ure out if the benefits of graphite outweigh the lesser yields based on the jobsite. Some drilling contractors are using a hybrid of grout, sand, and graphite to even out the economics and hit higher TC values. The good news is manufacturers and drill crews are always working to improve the geothermal mousetrap. Graphite has been out there for some years now, and I am sure we will see new variations and different products vie to knock the current additives off the TC throne. Todd Todd Tannehill may be contacted via e-mail to michele@worldwidedrillingresource.com Atlantis Vault • Self-Contained • Simple installation • Trouble-free operation For more information call: (270) 786-3010 or visit us online: www.geothermalsupply.com 16 FEBRUARY 2018 WorldWide Drilling Resource ®