Geothermal heat pump install with crawlspace encapsulation

[Country Geek]

Digging has started. 7 trenches, 150 feet long, three feet wide by six feet deep.

When you say that the trenches are three feet wide, it seems like that's not that much... they shouldn't take up too much space, right? Well they don't. It's the spoil piles that take up all the space! In my case the trenches are being dug, piped, and filled one at at time, so the spoil piles won't become a major hindrance to progress.

The mainfold trench and the first geo trench are dug. The first geo trench makes a 90 degree turn to avoid areas pasture which are the result of an unfortunate decision made 15 years ago to bury stumps from clearing in a pit in the pasture. I agreed to that when we were building, and I shouldn't have.

 

[buckeyefarmer]

are they installing slinkies?

 

[Country Geek]

The first trench is done. In previous pictures there were spill piles on both sides of the trench. I talked to the installer and he explained to me that I had two layers of soil, a more sandy type of clay soil on top and more chunky clay underneath. He had made the sandy soil pile on one side and the chunky clay pile on the other side because when he filled it he wanted to reverse the soil, so the more sandy type soil is what's in contact with the tubing... that would give it better contact and therefore better thermal conductivity with the ground.

This is a two layer trench... one layer of tubes at six feet, and one at four feet. (this should answer BuckyeFarmer's question, it's not a slinky system).



Here they are filling in the trench... one Bobcat dumps the fill soil in, and the other one tamps it down.



This is the finished product. Just one trench with six more to go, look at all that grass wiped out! It's not just the width of the trench obviously, but also the spill piles, and the maneuvering that the equipment had to do. This is the first of seven trenches so when it's done there will be very little grass left in this pasture, so it will need to be reseeded, which I already knew but it's something to see the actual results

 

[cre10]

I bet that is taking forever with that mini. In good soil we've put in 14 slinkies in one day. 3/4" 700' coils at 125 feet long.

 

[Country Geek]

I bet that is taking forever with that mini. In good soil we've put in 14 slinkies in one day. 3/4" 700' coils at 125 feet long.

I suspect my North Carolina Clay wouldn't qualify as "good soil." But yeah, it's going to take several days to get all the trenches in.

 

[farmer2009]

Why did you go with a straight run over the slinky?

Looks to me the slinky system would let you use a shorter trench for the same contact area.

 

[techman]

It is interesting to read about contact area of the geo field pipes. Contact area is nearly the same in any configuration. The big variable is the amount of area between pipes. The heat flow through soil is relatively poor. For most soils it is about 1 deg F/foot/BTU. If pipes are closer together, like in a slinky, the soil around the pipes will chill (or heat) more due to the pipe density and given heat flow. This results in a lower overall efficiency due to the chilling of the soil. One or two pipes in a trench, with trenches 8' apart is ideal, but impractical in some installations. It is documented, and I have also seen up to 20 deg swing in the trench (pipe) temps over seasonal changes. Some of that is ground/depth effects and the rest is low heat flow. My system reaches its lowest efficiency around march, when the incoming water temps are in the upper 20's. Last year was interesting as we had a good layer of snow from December onwards. The snow provided some insulation from the surface temps, and even though it was a much colder winter than usual, the incoming water temps were about 5 deg F warmer than other winters.

paul

 

[nc redneck]

Very interesting post I will be following it closely as I may install the same type system. Thanks for posting.

 

[KRBrouwer]

Sent you a PM

Thanks!

 

[cre10]

Why did you go with a straight run over the slinky?

Looks to me the slinky system would let you use a shorter trench for the same contact area.

It's silly. While it is better to have the pipe spread out if you dig 7 trenches 3' wide x 150' long and you only have 600 feet of pipe?? Why not fill that trench with pipe? You can do a slinky that's 110' long with 600' of pipe and you could get by with 5 trenches in 1 day (picture your hand with 5 fingers spanning out from a header pit. That gives plenty of separation for efficiency. People overthink pipe separation. Geo wells have the supply and return pipes in the same well that touch). Pipe is dirt cheap. Them digging all week with excavation costs and labor is not cheap.

The benefit of the 2 pipe systems is doing them with a trencher for speed, not using a 3' bucket and tearing up the whole pasture.

If you calculate the degree heating days, do a manual J on the house, and know your soil thermal conductivity it's super easy deciding what loop to go with. For loops the more moist the soil the more efficient.

I have slinkies and my loop wasn't below 45 degrees last year even with a few weeks of cold weather at 0 degrees Fahrenheit.

I know a heck of a lot of slinkies that are put in up in Montana and South Dakota using only 800' per ton with a trench around 140' long.

All loops work if designed properly, 2 pipe, 4 pipe, trenching, slinkies, wells, pond loop etc. It just depends on what you want and what you have to work with. Geo wells are by far the most expensive at around $2000 per whole around here, but if you have a small yard that's what you get. You can hire an excavator to dig all day long for $2000 and do 5 tons leisurely. Some around here trench for speed and to get around obstacles better and less ground disturbance.