Long time readers will recall that we installed a geothermal heating system to replace our old heating oil furnace.
Here are a few more details about the geothermal thermal system and the installation process.
A geothermal heating and cooling system is essentially a heat pump system that uses the relatively constant temperature underground to move heat from one place to another. The systems are also sometimes called ground source heat pumps. In the winter, the system pulls heat from the ground and moves it into the house. In the summer, such a system can move heat from the house to the ground. Because our house does not have air ducts and instead relies on baseboard hot water radiators, our system is currently set up only for heating, though the ground loops and the heat pump can be used for cooling in the future if we make a few changes inside the house.
Our system is a closed loop system – meaning water (plus a type of antifreeze) is circulated in a loop of piping from the house to wells underground and then back up to the house to start the loop over.
Our installers used a specialized German drilling rig that can fit in tighter spaces compared to some truck based drilling rigs. It was able to move right into place in the backyard for drilling.
Our system was initially designed for 6 wells at a depth of 150 feet per well. However, once they started drilling, they hit sand at about 75 feet down on the first well. Sand is easy to drill through. However, to install the geothermal piping, the well needs to stay open long enough to insert the piping. As soon as they removed the drill, sand would flow back into the hole, preventing the insertion of the piping.
They tried a couple of different things. They tried lining the well hole with well casing – basically a series of metal tubes holding the sides of the well in place with the drill in the middle. They also tried bringing in a more powerful air compressor to push the sand down the well.
The more powerful air compressor was pretty loud and really caused a lot of sand and gravel to shoot out of the well. Here is a video of the geothermal drill with sand shooting out of the well.
Neither worked – when they removed the well casing or turned off the compressor, sand would flood into the empty space and push the piping back out of the well. Instead, they redesigned the loop system to be 10 wells at a depth of 75 feet to avoid the sand.
After drilling the wells, they needed to create a path for the loop piping to get from the basement where the heat pump is to the wells – and it needed to be deep enough to not lose too much heat before getting to the house. That process required a large pit that looked like a bit like a moat.
There was also a big pile of sand in the backyard after the attempt to drill through the sand – enough sand to create a sandbox for our chickens.
Stay tuned for more details about our geothermal heating system.