I recently read in the geo outlook magazine about people that were experimenting with foundation heat exchangers in Nebraska.
Because the house had a basement they were putting 2-3 tons of loop about 3-4 feet away from the foundation and from 5-9 feet deep. So at 5' deep they would run a 3/4" circuit around the outside of the trench that was used to pour the basement foundation wall, then another at 6' deep etc.

On a standard 40X50 house you can in theory, get close to 900' of pipe in the ground at an average depth of 7.5' or about 1.5 tons worth of capacity depending on the area soil etc. In the article, the other 1.5 or 2.5 tons was put in a standard horizontal trench loop field on the property but they were saying that this saved excavation and looping costs to help make GSHP's more affordable.

My main question to people here, is are there any negative impacts of this? Could this cause damage to the foundation? Knowing that we are obviously pulling heat out of the ground would this affect the basement temperature and thus negate any savings effect? What if it was not a heated space under ground and was instead something like a garage so it was not negating the effects?

Now before you bring up other options I am trying to think about the feasibility of this because in my area a horizontally bored loop is $2,500 per ton and a vertical loop is $5,000 per ton. I am building my personal home soon and thinking I might at the very least experiment with this and install this type of loop because my house will have almost a 40X55 footprint and will be a garage underground. If it doesn't work then I drill like I plan on doing anyway. If it does work then I save thousands on the 3 ton needed for my home. I just want to make sure I am not missing something else like harming my foundation.

I'd avoid letting the loop go much below freezing to avoid soil expansion problems. Increased heat loss from the house is a matter of using more insulation (a rough calc says more than double) to compensate. That has a $ cost.

I could see stapling tubing to the walls of the excavation. Perhaps use the basement floor area too.

AFAIK, unheated underground space should be insulated and I would expect that adding geo loops would upset the calculated balance between heat loss to the air and heat gain from the soil. So I don't think this one works without causing soil to freeze.

I think my original post is not clear, when I said keeping the pipe 3-4 feet away from the foundation I meant stapling to the wall of the excavation in a vertical racetrack formation.

So, let me understand this. They want to chill the basement in order to heat the home?

You mean horizontal don't you?

I think you might wind up recycling the basement heat. You would increase the delta and therefore increase the heat loss. I suppose you could put 4 to 6 inches of eps against the wall but at what cost.

Another thing to consider is that you will be going to great lengths to make sure the area adjacent to the basement drains well and therefore have less soils heat conductivity.

I don't think there is a free lunch to be had here.

The article did stress that the application was likely not a good one for heating dominated applications.

A fairly decent operator will bring his machine and dig and backfill 3 trenches for hundreds, not thousands of dollars, so I didn't see this as a particular breakthrough.

$2,500/ton is significant for horizontal loops (we pay much less). You may want to shop your loop contractor, or shop the parts (get a seperate digger and do the loops yourself).

I think foundation or even under-slab geo loops make sense as a cheap way to pre-heat and pre-cool (and dehumidify) the air for an ERV. The load will be smaller, and is a simple flow with just a basic air-water heat exchanger (no heat pump) so the water temperature won't have crazy extremes.

I would be leery about using it for primary heating because of the reasons mentioned above - it will cool the soil around the house which increases the delta, although perhaps it will be negligible. Worst case it causes the frost line to go lower which could be bad if you have a shallow foundation.

You can add insulation such that the soil cooling is more than offset - ie, the basement could have less heat loss to the soil than a basement with no geo loops around it. The question is "at what cost"?

If digging is expensive, I'd consider saving it for the geo loops and build the house without a basement (using a FPSF of course). Or perhaps insulate the whole thing so well that geo isn't needed.

I don't think you guys understand my market.
First this house is on a 75x100 lot so trenching is out. Second in my area a 3 ton trench from a "cheap" excavator is $2500 and a 4 to 5 ton trench is $3300 and that is shopping around. The first horizontal drill we did with the only geo driller in the area was $9,900 for 900' of drilling, no pipe no headers and no flush and fill... Just drilling. We finally found a plumbing service driller and helped them learn how and they are $4250 for 800' of drilling, anchors are extra and we have to buy pipe, header and flush and fill, so almost $7,000 when it's all said and do e for three tos. I am asking about the foundation because in my area there is a reason for it if it can cut a loops cost in half it will save the average homeowner $3,500 unless they have room to excavate a giant trench but 50% of our customers are on a small lot that requires drilling.

Wouldn't an air source heat pump be a consideration there?

Are you saying that your vertical drilling costs are $5000/ton due to geological challenges and/or lack of available drillers at a lower cost?

An 8 ton loop, done vertically, is $40K?

Best regards,

Bill

Posted By Bill Neukranz on 31 Oct 2013 01:32 PM
Are you saying that your vertical drilling costs are $5000/ton due to geological challenges and/or lack of available drillers at a lower cost?

An 8 ton loop, done vertically, is $40K?

Best regards,

Bill

Yes thats correct, the last 5 ton vertical loop we had drilled was $24,250 for the drilling the piping and the headers. Then my company still had to flush and fill and connect to the flow center and bring the loop in through the foundation. I WISH my area was like everybody else that I read about that complains about $2,000 per ton ground loops! There is only one vertical IGSHPA certified loop driller. We hit basalt at 50 feet but I don't know anything about drilling. In 2010 there were only 408 GSHP's installed in the state of Oregon and my company is putting in 50 per year so our area has a lot of growth potential but our costs are way to high. But yes about $40k for an 8 ton vertical loop.
For horizontal loops as I stated, the first loop we had drilled with the only horizontal driller was $9,900 for 9 bore holes with anchors at 100' per bore hole and that did not include pipe or headers. I had to buy the pipe and pay my guys to custom build the headers, so you can see why I want other options.
Hell the most recent quote I got for a 5X5 trench 600' long for a 6 pipe racetrack was $3,300 and that was the cheap quotes, I had another one at $4,400 and one at $9,000 so after I put pipe in the ground and headers etc its easily $6,000-$8,000 for a 3-5 ton loop with excavation not counting flush and fill.

Posted By ICFHybrid on 31 Oct 2013 08:28 AM
Wouldn't an air source heat pump be a consideration there?

Yes but this is my personal house and I want a GSHP for my home so that customers can see them installed since it is a huge portion of my business. Will I get a payback on my personal GSHP over an air source variable capacity, probably not but thats not what its about. I WILL get a payback in the additional work that I will sell from having one at my home and second, I am one of those environmental nut jobs and I want to practice what I preach and have LED bulbs and the lowest energy bills possible to show customers what is possible. I just had a customer call me up and say they went from a 2,400 sq foot or so home to a 3,500 sq foot home at the top of a hill with a lot more windows, but the old home was gas furnace and AC and gas tanked water. The new home is WaterFurnace 7 series variable capacity with Waterfurnace NSW018 ground source water heater and all CFL lights and their bill is half of what their smaller home used to be and the new home is more comfortable. We all know thats possible but I want to be able to bring people to my home kinda like a showroom to show off the technology that is possible.

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We wrap the slinky around the house all the time, lots are 70x140, but they want in-ground pools in the back. Trying to stay away from the foundation 3-4 feet. Temp sensors indicate that at the house wall the difference in temperature is minimal compared to ground without a heat exchanger. Freezing does not occur more than 6-12" away from the pipe if you deal with good saturated ground. Keep in mind that water has to go through a phase change when it freezes, releasing a large amount of energy. Unless you really screw up your load calculations, it is very difficult to freeze the ground further away. One of the reasons horizontal loops stabilize (a better word is saturate) usually around 30F, unless you grossly undersize the loop. Something the algorithms in the loop software do not account for. Loops for 3 tons are 2400' total 1" pipes (2 slinkies of 1200'), 4' diameter, 9' and 6' depth.

doc - who wants good saturated soils that close to the foundation?

SkyHeating - call your local CAt Rental store and find out what it cost to rent a 430 rubber tired backhoe. At those rates you can make more money digging then installing ;-)

If you are putting in that many, you might seriously consider buying a hoe or mini hoe.

Posted By FBBP on 04 Nov 2013 03:25 PM
doc - who wants good saturated soils that close to the foundation?

Allright, you might be challenged with dry sand, but I was referring to the typical clay with a reasonable moisture content, implying that what works for us here in Buffalo, NY might not work that well elsewhere, where you have lousy soil to work with.

Doc - I was just inferring that we tend to go to great lengths, anywhere in the country, to drain the soils around basements with granular fill and drain pipe, to protect the basement from moisture and water ingress. This would seem counter productive to geo, right?

It might make sense if you over excavate to get the dig wall seven or eight feet away from the basement wall but then you still have the expensive of the dig.

Sky, of the 50 you install each year. How many of those on average to you vertical drill for? Have you ever looked into buyng your own drill rig?