Going Underground: Geothermal

Geo-Exchange Technology

I’d like to draw your attention to a ‘green’ technology that has quietly been making inroads into the midwestern energy landscape. Geothermal heat pump systems are advertised by many of the HVAC companies in our region as a highly energy-efficient alternative to conventional air conditioning / heating systems. More accurately called geo-exchange technology, geothermal systems circulate a fluid through a closed (or more rarely, open) tubing loop in the ground. The relatively constant ground temperature below the frost line brings the fluid temp to between 45 and 75 degrees Fahrenheit, depending on latitude. As the fluid returns to the building, it passes through a water-to-refrigerant heat exchanger inside. Depending on whether you need heating or cooling, the heat exchanger either pulls heat out of the fluid (for heating) or dumps heat into it (for cooling).

Geothermal - heat exchanger

Advantages of Geothermal

Since you are only providing the electricity to run the pumps circulating the fluid, the compressor in the heat exchanger, and the fans to move the air through the building, your power bills will go down significantly. Apples to apples comparisons depend upon how you heat your building right now and the electricity rates. Geothermal cooling has fewer moving parts than a conventional air conditioning unit, and geothermal heating has no risk of carbon monoxide, unlike natural gas or oil-heating furnaces. Many residential installations have the ability to also heat your water. The inside components of a geothermal system can last for up to 25 years, while the buried tubing can last for 50+ years, creating long term savings.

Types of Ground Loops

The ground loop can be configured in several ways, depending upon how much space you have, the availability of a pond or well water, and how much you can pay. The most economical is laying the loops of tubing in a pond if one is available. Another water-dependent version is what is called an open loop, in which water is pulled out of and pumped back into wells drilled just for the geothermal system. The most common layout though, is the horizontal closed loop. The tubes are trenched in below the frost line in a wide horizontal array. This type is well matched to our region, due to our land availability and relatively rock free soil. If you don’t have the space for a horizontal loop, then you can choose a vertical closed loop. This has fewer loops, but they go much deeper into the ground, requiring drilling equipment for installation.

Disadvantages of Geothermal

Like every technology, there are disadvantages. Installation costs are high, mostly due to the laying of the tubing for the loop. A geothermal system works most efficiently when the building doesn’t need a high temperature to heat adequately. In other words, a poorly sealed, poorly insulated house requires the system to work harder to keep it at a comfortable temperature. No surprises there. A geothermal system requires electricity to function, and the pumps run at all times to keep the fluid flowing. The installation of the tubing will scar your landscape for a season.

It’s a big change, and it often makes the most sense for geothermal systems to be installed when a home is being built. But homeowners aren’t the only ones experimenting with geothermal. Schools and municipalities install geothermal because they see how much heating and cooling takes of their budget and they want a long-term solution. If you have had a geothermal system installed in your home or workplace, what is your take on the technology?