Geothermal Idea - Any Designers Here ?

[Weedwaka]

Do we have and Geothermal designers here ?

Our shop is dug into the ground almost ten feet down at the back. The structure is 48 wide by 32 feet deep.

Why not utilize the area already way below grade for a mini geothermal loop that is built into your heated slab setup ( pre micro boiler ) ?

I could dig down a bit more in the front, then use only the portion of floor space which will be 5 or 6 feet below grade or greater. This would give me a large amount of run.

Does this make sense to you guys ? Run the tubing a few feet under the slab ( which will be about 5 - 6 feet below grade at minimum to about 12 feet at the back ) and then up through the micro boiler >> through the slab >> back below grade and back up through the micro boiler .

I figure I would have about 1000 square feet that is suitable under the slab without major digging. I could dig a bit and increase that to about 1200 ish pretty easily.

Thoughts ??

 

[Weedwaka]

I was thinking about this some more. We also have room for a couple 48 foot long slinky loops right behind the shop because of the large over dig.

Also, the slab being insulated will keep the ground heat deeper than if it was uninsulated or uncovered ground. ( from frost protected shallow foundation research ) . I could get a few more feet of loop because of this.

 

[redsky49]

I understand your thinking, and this is an interesting question.

A couple of thoughts.

First, the system, once completed will be totally inaccessible, short of demolishing your floor slab. Any leaks would not only render your heating system inoperative, but the leaking hydronic fliud could cause structural problems with your floor slab or foundation. Bear in mind though that 1000 ft. of 3/4" tubing only contains about 27 gallons of fluid. The problem might arise if a leak is undetected and the make-up water system goes into operation.

Secondly, the area available for energy recovery is far limited compared to typical installations, You state that about 1000 sq. ft. will be available for tubing installation. This appears to be too low, though I am guessing that there may be some residual benefit to be gained as the slab heats up and energy is lost back down to the soil surrounding the piping loop. In the past, for commercial installations I have used the parking lot for placement of the ground loop. Since these areas generally require the use of heavy equipment, I simply had the Contractor excavate a larger area, placed the loop, and then back-filled and graded for paving. The alternative is to dig a series of wells. I have done this for several school projects where the existing conditions precluded a horizontal loop, A lot depends on the soil and topography of your site.

There is no easy answer for you without an actual design study and heat loss calculation. If this is an approach that you want to pursue, I would definitely employ an Engineer to assist you. At the very least, you (or your Contractor) should contact the technical support of one of the many manufacturers to get their input. Technical support varies between manufacturers though, and they may be reluctant to get too involved in a non-standard installation, especially when dealing with someone other than an Engineering office.

Better to seek knowledgeable local help with this one.

Good luck with your project.

As always, offered only as opinion

 

[Weedwaka]

Thanks for the reply.

I sent out some emails . I will post what they have to say.

 

[jkeyser14]

The geothermal installer will most likely recommend drilling vertical bores outside the shop. Even if you don't have a lot of property, they can drill in your parking lot or wherever else you can fit 1-2 bores (plenty for 1000 sq ft). My house is 1200 sq ft (2000 including the the basement) and I'm having a 3 ton system installed using two 250 ft. deep bores.

 

[Weedwaka]

The guy I talked to said he would recommend 3000 feet of piping laid out in 5, 600 foot horizontal loops ( not slinky ) .

He said it was a bad idea to be next to or under the structure due to maintenance issues as Redsky mentioned as well as thermal issues.

I have been doing quite a bit more reading on the design of these fields and have learned that your system can actually pull a lot of heat out of the earth. This is enough of an issue that if not properly accounted for, you can loose your fields efficiency over a few years. I was under the impression that such a small draw as a shop would never even dent the available ground heat.

We have an acre to work with so I think I will look into horizontal trenches as was recommended.

McQuay Air Conditioning has a great geothermal design manual available online for free if anybody is interested. I did not bookmark the link but it should be an easy google away.