Geothermal Depth Length

Blas

Just wondering if any of you guys have had experience with geothermal. We have installed it before with a different builder 2 trenches 6 feet wide 100 feet long by 7' deep. Last Friday we started excavation for another builder who had a different engineer who said we had to have 2 trenches 80 feet long 8 feet wide by 22' deep. Why would anybody have to be 22' deep. That just seems overkill to me. Ground freeze never gets deeper than 4 feet around here unless there is heavy traffic. Hell water main is at 7'. What are the advantages of being so deep. I know for a fact that the engineer has been ripping the builder off with his underground piercing guy and since we saved the builder about $15,000 by open trenching he is maybe trying to make us suffer with unnecessary depth. Maybe the engineer is from the northern tip of Greenland where you have to have to be 22 feet deep to hit constant temperature. What do you guys think. Looks like I need to fire up the old GOOGLE engineer and get some education on the this matter.

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billie-t

i live in ontario canada..i have three trenches...5 feet wide 500 feet long with a loop in each trench.....3000 feet of pipe dug 5 feet deep....10 years old...never a problem...why 22 feet deep?....ask for explanation..and it better be good!

Blas

I already questioned him and all I got was the eye roll (your to dumb to talk to me about my design look) and something about system performance being increased by 4 degrees with depth crap!!!!!

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billie-t

a littel searching on the net comes up with ..every meter (about 3 feet) gains you .045 degree F...so a littel math ..if i am right ....
22 feet in meters is about 7..so 7 x .045 is .315 or about 1/3 of a degree for his 22 feet...tell him he is dreaming...unless he wants you to go to a depth of 3.5 kilometers (about 2 miles) and you will be at 100 C (212 F)

billie-t

of course this is all after you get below the frost line

rino1494

I've done a few units. Last one I did had 20 wells connected in series and parallel. I dug 2 trenches each about 200' long with 3 cross trenches. The heating guy wanted them about 5-6 feet deep.

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tgeb

22' sounds ridiculous to me.

I did some looking around and found this site,

http://www.igshpa.okstate.edu/publication/manuals.htm#2


It looks like you can get a copy of the design standards and learn more about the systems and have some ammunition for your argument that 22' is nothing but a costly way of installation, or you may find that it is justified.

The fact that he would not explain his position leaves me to think he has no basis for the increased depth.

I may order this for my self, just to have the knowledge in the event one of these systems comes my way.

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Tom

www.gebcon.com

ch0mpie

Sounds like he's borderline on needing to go over to wells, and is trying to make up the difference with a deep trench. I don't know where billie got his info, but you can gain a few degrees within 20ft, depending on the site.

Blas

Thanks for all the replies guys. I have done some research and what I have found is that there are as many ways to do this as there are stars in the sky. After consulting a friend who is a engineer, I found that for this region 22 feet is definitely overkill, however if you can get the loops into the water table it performs a little better, probably not enough to offset the cost of going deeper. Fortunately for me on this project I hit water at 12 feet and there is no need to go deeper. I got lucky because I gave the builder a price at 7 feet deep and now I don't have to pester him for more money but next time I will get all details prior to shooting numbers.

Thanks for the help

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"It is what it is"

Blas

Thank you for this information. I doubt I will be installing these very often but it is nice to back up your argument with facts.

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billie-t

chompie..i couldnt find the original site i was on...it was some universtiy in the states but here is a quote form another paper i found on line--as i read it you need to go about 45 to 90 feet to gain one degree so i would say (not wanting to be smart or argumentive) where did you get your information...maybe every study differs?

"At the depth of 50 feet from the sea-level, the temperature of the earth is the same winter and summer. . . . At the Killingworth coal mine, the mean annual temperature at 400 yards below the surface is 77 degrees Fahrenheit, and at 300. yards, 70 degrees; while at the surface it is but 48 degrees, being about one degree of increase for every 15 yards. Hence, at 3300 yards, the heat would be equal to boiling water, taking 20 yards to a degree. This explains the origin of hot springs. The heat of the Bath waters is 116 degrees; hence they would appear to rise from a depth of 1320 yards. By experiments made at the Observatory at Paris, for ascertaining the increase of temperature from the surface of the earth towards the interior, 51 feet, or 17 yards, correspond to the increase of one degree Fahrenheit's thermometer. Hence the temperature of boiling

water would be at 8212 feet, or about one and a half English miles, under Paris."

ch0mpie

billie,
my info comes from site specific studies. Your sourse seems correct about calculating the tempurature within the earth, but its not taking into account that the surface groundwater is going to remove heat from the system in a geothermal application.

billie-t

i see your point..so i will not disagree with you ..... i still contest that the 22 feet the guy was asking was outragous

i did search the net and out of 8 water furnace sites 5 suggested 4 to 6 feet depth and 2 said 4 to 7 and one said 10

in my area of ontario canada where it gets wet and cold most are 5 to 6

billie-t

on another note...deep burying of your loop could be right (i been thinking) if your horizontal loop is in a high traffic area on an area where you will be removing snow .... i read every year of how some water mains explode 7 feet or so below ground in the city due to snow removal and and driving over the area push the frost deeper than normal

i live in the country and never remove the snow from where my pipes are burried

i guess i owe an appology..to someone..heck maybe everyone

going back to my cave now