Insulated Underground Pex Tubing

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Lightning
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Post by Lightning » Sun. Mar. 01, 2020 9:40 am

I am currently trying to determine the heat loss of my underground pex run for the out building salon/studio. The out building is on a primary/secondary circuit where the primary loop is kept hot 24/7. This primary loop includes 100 ft of Badger 5 wrap 1 inch insulated pex (2 lines) inside a 6 inch corrugated pipe 12-18 inches under the soil. I'm wondering if I should be keeping that primary loop hot all the time or if I should consider a different way.

My confusion is about their specs on the heat loss. Should I be doubling the BTU loss since there are 2 lines? Doubling it would be 3100 BTUs of line loss, and I would imagine that would be per hour. Given 10,000 BTU per pound of coal burned net, this would be 7.5 pounds per day. 200 heating days would equal 1500 pounds and I'm sure there are other losses I'm not accounting for so its probably closer to a ton per heating season keeping that primary loop hot. This is assuming I'm right about doubling their given loss in the spec report.

Any insight to this would be certainly appreciated :)

I thought we could start a good discussion on underground pex lines..

Edit - to sentence above..

I thought we could start "an intelligent" discussion on underground pex lines but instead we're insulating them with manure now.

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Last edited by Lightning on Sun. Mar. 01, 2020 11:35 am, edited 2 times in total.


 
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Post by McGiever » Sun. Mar. 01, 2020 9:54 am

12"_18" buried depth is smack dap in the ever-changing temps of local frost zone, below local frost line is a constant temp...maths will be either difficult or inaccurate because of being in frost zone...

 
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Post by Lightning » Sun. Mar. 01, 2020 10:01 am

For now, let's assume that isn't a contributing factor to keep things simple.. :)

I'm mostly interested in knowing if I should be doubling the spec's line losses..

 
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Post by coaledsweat » Sun. Mar. 01, 2020 10:10 am

It's a major factor, no way around it.

 
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Lightning
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Post by Lightning » Sun. Mar. 01, 2020 10:14 am

coaledsweat wrote:
Sun. Mar. 01, 2020 10:10 am
It's a major factor, no way around it.
Right.. But what about keeping that primary loop hot all the time.. I think there could be savings by doing something different. And what about that line loss? Is it really 3100 BTU per hour?

 
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Post by freetown fred » Sun. Mar. 01, 2020 10:14 am

Lee, simple would be--no matter what, numbers, theory's, calculations don't mean squat--ya know an underground line is going to have losses--soooo, do over-kill on the insulation! That's SIMPLE!!

 
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Post by Lightning » Sun. Mar. 01, 2020 10:16 am

Thanks for your input Fred but I really want to get to the nuts and bolts of it :)


 
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Post by freetown fred » Sun. Mar. 01, 2020 10:19 am

Hard for me to believe Lee!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! LOL BUT, after all is said & done you WILL come to the same conclusion. :)

 
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Post by Lightning » Sun. Mar. 01, 2020 10:37 am

The underground line can't be further insulated..

 
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Post by Lightning » Sun. Mar. 01, 2020 10:45 am

So at first thought, if the primary loop only were to run when the out building needed heat you'd have a situation where the water in the primary loop would be allowed to cool down. Then the boiler would have to reheat the whole loop. During most of winter, the loop would be circulating somewhat frequently anyways to keep the building at 50 degrees so the loop wouldn't really have much chance to cool down anyways. This tells me that a majority of any savings would be in the shoulder months when the loop would cool down to ambient temperature and remain in that state for periods of time.

Does that make sense?

 
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Post by freetown fred » Sun. Mar. 01, 2020 11:25 am

Lee, I had a gravity feed water line run approx. 100 yds(from spring to house) that was only about 6-10" deep due to all ledge, slag, etc. in Vt. It kept freezing up on me till an old farmer neighbor brought his honey wagon over & we put cow *censored* under & over the 3/4" black plastic pipe & even in sub-zero temps--the line never froze again--PLUS--I could dig down to the water line months later & the cow-*censored* was still warm!! I doubt if there was any heat loss--or possibly minimal--- Don't tell me your pex can't be further insulated!!!! Just sayin my young friend. Moral might be--cow *censored* worked better then ANY calculations!!! :lol:
Lightning wrote:
Sun. Mar. 01, 2020 10:37 am
The underground line can't be further insulated..

 
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Post by Lightning » Sun. Mar. 01, 2020 11:27 am

The wife isn't gonna stand for a trail of cow dung down to her salon Fred.. thanks for the input though..

 
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Post by freetown fred » Sun. Mar. 01, 2020 11:30 am

Ya put dirt/sod over the cow *censored* Lee-- am I losin ya on this common sense theory/suggestion--damn city dwellers!!!! LOL

 
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Post by Lightning » Sun. Mar. 01, 2020 11:34 am

freetown fred wrote:
Sun. Mar. 01, 2020 11:30 am
Ya put dirt/sod over the cow *censored* Lee-- am I losin ya on this common sense theory/suggestion--damn city dwellers!!!! LOL
Over time the cow dung will dissolve and decompose.. it would only be a temporary solution.

 
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Post by CapeCoaler » Sun. Mar. 01, 2020 11:52 am

you will loose heat no matter what...
Circulating or not...
More @ 180*...
Less @ 100*...
Convenience factor say constant circulation...
What if it freezes once...
How much will that cost ya...
What if someone wants an early appt...
How much do you loose if you say no room is too cold...
How much if the line gets slushy and you loose a day of business...
1500# cost you how much...
Maybe $240...
Just sayin'...


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