Question

Is my home well-suited to geothermal?

Asked by Ric, Chicago

I have a proposal from a contractor to install geothermal at my home in Chicago. In doing my own research, I'm getting conflicting information on the suitability for my homesite. The house is on a "typical" Chicago lot, approximately 25 feet wide with limited access for drilling. My understanding is that the bore holes need to be at least 15 feet apart in order to get the efficiency geothermal provides. Because we are going 350 feet deep or more, does that offset the minimal bore spacing?

Answer

Mick Dalrymple

Answered by Mick Dalrymple

Scottsdale, AZ

Eco-Friendly Building Center

February 28, 2008

Confession alert: I love geothermal! Quiet… Energy efficiency numbers through the roof (ground, actually)… It is such a smart idea!

That said, I am not a geothermal technical expert, so I consulted with some people who are and got some interesting responses. The idea is that you need adequate separation between the bores in order to provide sufficient soil to adsorb and supply heat. Trying to fit them in close quarters is analogous to cramming solar planels on a roof that is shaded a good portion of the day because of nearby trees – you aren’t going to get the performance for which you paid.

A David Meyers, an International Ground Source Heat Pump Association Accredited Installer with Verde Sol-air Services in Arizona, said that he would not go less than 15 feet on center, no matter what the soil conditions.

Jerry Moore, an IGSHPA Certified GeoExchange Designer with Design Mechanical Inc. in Illinois, says he does not go less than 20 feet on commercial system design. However, residential load demands are lower than commercial and he knows residential installers who go as little as 10 feet on center.

The key is to utilize an Accredited Installer or a Certified GeoExchange Designer who has at least 10 years of experience and has done multiple houses in your area, as soil types vary considerably. Jerry also recommends doing a test bore hole to verify soil type. With correct inputs, they can use software to calculate the minimum system needs.

You can find accredited professionals through the International Ground Source Heat Pump Association.

You can get additional information through the Geothermal Heat Pump Consortium, which has an online forum.

Tagged In: geothermal

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