In this post, I thought I would address a common misconception about geothermal that has been brought up several times over the past few months. The recurring comment that I have heard goes something like this: “I heard that you can drill and drill and not reach what you need. Then you wasted all that money and you still need to install a gas or oil furnace because geothermal won’t work.”
I have installed over 200 tons of geothermal heating systems throughout New England and there has never been a situation where we haven’t “reached what we needed”. First, it starts with an understanding of how the underground components of a geothermal systems actually work.
Closed Loop Systems
Closed loop systems (antifreeze circulated through underground pipes) in New England are usually installed in 6″ vertical borings ranging from 250 to 400 feet in depth. The borehole is drilled right through bedrock which is usually encountered within 0 to 50 feet. Groundwater is typically encountered within this same depth range. During the heating season, these systems depend on heat being transferred from the bedrock and groundwater, through the pipe into the antifreeze, and then into the geothermal heat pump in the house. While groundwater improves the heat transfer properties of the underground portions of the geothermal system, the presence of copious amounts of groundwater is not absolutely critical to the operation of the system.
Open Loop Systems
Open loop systems circulate actual well water through the geothermal heat pump system. In some cases, the well doesn’t have enough capacity to support a geothermal system. This problem can be overcome by frac-ing the well or deepening the well to increase its capacity and yield. In extreme cases, systems that were originally intended to be open loop can be converted to closed loop when the well doesn’t produce enough water.
Sometimes, salty or brackish water can be encountered when drilling in close proximity to the ocean. Poor quality water can wreak havoc on geothermal system components causing corrosion and mineral deposits. Similarly, if salt water or hard water is encountered, systems originally intended to be open loop can be converted to closed loop.
I hope this post clarifies that there is almost never a situation where you can drill and drill and not be able to install a geothermal system. Usually, the problem is whether or not the drill rig fits on the property!