The use of graphite in thermally-conductive grouting applications has exploded in recent years with more and more drillers abandoning the use of sand either completely or partially. Some of this greater interest has been due to economics and some to labor reduction or worker safety issues. In this article, I will discuss the benefits and some of the potential trade-offs between using graphite versus sand in geothermal heat-loop grouting.
For those who may not be familiar with graphite or its use in ground-source heat pumps, here is a quick primer. We most commonly find graphite in standard pencils. The “lead” is actually graphite mixed with clay to harden it. The pencil mark is composed of thin layers of graphite laid down on the paper when we press down. It may at first seem strange that such a material can be used to increase thermal conductivity in grouts. However, crystalline-carbons conduct both heat and electricity and, of these, graphite is the softest type and is economical.