Still juggling some ideas in geo fields.  I am curious if there are any amendments or products for bedding geo loops that are worth while compared to just installing more tubing? 

I am experienced with construction and water lines and I would be looking to bed the tubing with sand which helps give uniform compaction around the tubing before backfill.  We use it for many other reasons but the thought came to mind that I might be able to amend the sand with a product to improve thermal conductivity thus making this more worth while. 

My original thought on the loop would be to dig approx a 1ft wide trench 10ft deep and allow the coiling to be vertical rather than lay flat?  I will have to run some numbers on excavation time but this should be faster than cutting a 3ft wide trench 8ft deep. 


I would just LOVE to get my hands on a trencher that could do this but they are rare at this depth. 

http://welserver.com/WEL0114/

geodean put his slinky in standing vertical.

Chris

thanks chris, fastline...you only need to protect the pipe from damage, increasing the conductivity of the backfill, is not worth the effort since the conductivity of the native ground is still low.

Dean, I reviewed your page on your installation. I am curious though, the slinky design seems to be a great way to get a lot of pipe in the ground but I was just reading where that is a specifically bad idea due to the localized heat transfers not matching the soil conductivity? IE, too much energy density per given area and soil or fluid temps would not be optimal.   I am able to easily calculate everything else but I have yet to find a way to get really good data on soil types, moisture levels, and comparable conductivities.


Did you run enough numbers to feel that you had a good match to the soil conductivity or was this mostly a design that was to match the existing conditions? IE, a small backyard?

What piece of equipment was used for that installation by the way?

I did it initially because I had a small back yard. But the results speak for themselves. My loop temp has not dropped below 45°!!

Any claims that slinkies are not a good design are not based on long term usage data. There are many systems being monitored that prove the value of slinkies.

Slinky lengths are easily calculated with a loop design program.

I dug my trenches with a rented mini excavator.

What were the specs on that field? size of loop, feet per length of trench, etc? IIRC, your page said you were 9ft deep?

1" loop, 1000' feet of pipe in a 120' trench. I have since learned that 500' of 3/4" pipe in 100' of trench works just as well. 9' was as deep as the mini would dig.

"Dean, I reviewed your page on your installation. I am curious though, the slinky design seems to be a great way to get a lot of pipe in the ground but I was just reading where that is a specifically bad idea due to the localized heat transfers not matching the soil conductivity? IE, too much energy density per given area and soil or fluid temps would not be optimal. "

Heat moves to cold. Extracting heat from surrounding soil means adjacent heat moves in. the bigger the delta T (temp difference) the faster the heat moves. slinkies work great (if designed correctly) as do 2, 4 and 6 pipe trenches.
A six pipe race track has 6 feet/ft of pipe in a trench where a 4'/ft slinky has only 4.
It's a numbers game, but whoever tells you that one kind of loop doesn't work needs to do more homework.

Remember average depth is also a key so a vertical slinky that is say 6'/ft will only have an average depth of 7' in a 10' trench making an 8' deep horizontal trench potentially higher performance.

You asked if something would enhance loop performance besides more loop; no but- mind pumping cost and design.

Dewayne Dean's loopfield is admittedly oversized and is not indicitive of the performance of all systems (nor an indictment of systems with lower EWT's).

Are most people running calculations based on some average data for soil conductivity? Are test holes excavated to inspect the geology? I have no problem calculating everything but without the soil data, it is more or less a guessing game. Or should I make my own test probes and try to log the data? Is that overkill for this?

what type of soil do you have and what is the moisture content?

the driest clay has a TC of around .5, saturated sand can give a TC of 2+ I would pick a value that you know is safe and go with that. Trying to log the data yourself would be a night mare!!

Are there any geological services or agencies that have data on this?

At the depths we are talking we should have some reasonably moist clay with some sand. Should not have any rock and certainly won't be all sand or gravel. The topsoil is sandy loam. I may have no choice but to just drop the excavator bucket down to depth and look at the soil types. I was hoping I could find a chart or reference material on different soils and TCs. I had the thought to pull a sample and seal it up for moisture testing so I could determine the % of moisture in it.

Wouldn't the moisture content be different at different times of the year....pros?

maybe  this will help.

Robin,
Soil moisture content does vary some which is why most of us pick a value that we are comfortable with (As Dewayne suggested). Mostly dry or damp. Pretty much have to install in a swamp for me to call it saturated soil.
Further if you are traversing hundreds of feet, what is true of the soil on one end of the loops may not be on the other.

Dean, what unit of measure are those values?

The Cond value is Formation Thermal Conductivity = Btu/hr-ft-°F ..... The Diff value is Formation Thermal Diffusivity » ft2/day