Heat loss on underground piping

[maple1]

Also, did you read this?:

https://www.hearth.com/talk/threads/underground-lines-not-the-place-to-skimp.50506/

 

[larryjbjr]

Also, did you read this?:

https://www.hearth.com/talk/threads/underground-lines-not-the-place-to-skimp.50506/

Yes, mostly. I can't say I read every word.

I mostly agree with it. But my wallet doesn't.

I check the place freeheat4u.com and found that they are not very far from me. So I am planning to buy from them and then pick it up, that will save me the shipping.

Now a question. Most people problem with the five wrap pex is that it will leak eventually. So I am assuming if I put that inside a sewer pipe, so that It can never leak, then it is good stuff?





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[hondaracer2oo4]

If you were able to get it into a "sewer" pipe(not sure what you are referring to) and it was water tight than yes the 5 wrap would probably be fine. The problem is trying to pull that pipe through the larger pipe. It will be close to impossible. Also 6 inch pvc is very expensive. At the end of the day it would cost likely close to the same as good pipe and you would never have any worries.

 

[Tennman]

OMG! Have you not read my horror story in the underground sticky regarding trying to do the underground on the cheap. I think I saw XPS mentioned above. Expanded polystyrene.... I seem to recall it not being closed cell and it being heavy and mushy when removed from being underground, meaning it sucked up water eventually like a sponge. If I didn't have the money to do the underground properly for this season, I think I'd temporarily use good split foam insulator and just keep it above ground like the large military bases and government facilities do. Energy loss due to hot lines being contact with wet dirt is a terrible thermal sink. I don't have time to do the math comparing good insulation but large temp difference above ground to less temp difference but terrible, wet insulation underground. My engineering instincts say well done temporary above ground is better than lousy underground.

This is a TRUE statement.... doing the underground once is miserable..... doing it twice.... well suddenly the price of propane becomes attractive.

Ok... I'll disappear again for a few months. Re-read the sticky.... years ago the topic of underground lines was my personal crusade to save the world. I've moved on to whirled peas.

 

[larryjbjr]

OMG! Have you not read my horror story in the underground sticky regarding trying to do the underground on the cheap. I think I saw XPS mentioned above. Expanded polystyrene.... I seem to recall it not being closed cell and it being heavy and mushy when removed from being underground, meaning it sucked up water eventually like a sponge. If I didn't have the money to do the underground properly for this season, I think I'd temporarily use good split foam insulator and just keep it above ground like the large military bases and government facilities do. Energy loss due to hot lines being contact with wet dirt is a terrible thermal sink. I don't have time to do the math comparing good insulation but large temp difference above ground to less temp difference but terrible, wet insulation underground. My engineering instincts say well done temporary above ground is better than lousy underground.

This is a TRUE statement.... doing the underground once is miserable..... doing it twice.... well suddenly the price of propane becomes attractive.

Ok... I'll disappear again for a few months. Re-read the sticky.... years ago the topic of underground lines was my personal crusade to save the world. I've moved on to whirled peas.

Yes I read the sticky. And I mostly agree with it. I see that was about 7 years ago that you did that. Is it still holding up for you?

Please correct me if I'm wrong, but it seems like the whole point is to keep whatever you put down there well insulated and dry, primarily dry. The pex at freeheat4you.com seems to be well wrapped therefore would be insulated. So if I took that stuff and pushed it through a 6 inch drain pipe, not drain tile, drain pipe, which would keep it dry, wouldn't that be just as good as the foam in place?

If not, please tell me. I am not trying to be argumentative. I am by no means saying that I am right and everyone else is wrong. I really want to understand.






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[Tennman]

Yes, Over 7 years and the energy loss over about 340', no change... I seem to remember ~1.5*F over about 140' boiler to HX. I posted it's performance in the sticky. It varies somewhat based on the demand cycle, less loss on very cold days when it's cycling more frequently. I went to the freeheat site and only saw Rehau foam filled. I couldn't find a Coefficient of Thermal Conductivity for bubble wrap to compare to polyurethane. No joy. Did see a table saying R value of air space vs polyurethane; air =1, polyurethane = 7. I understand, you basically want to create a dry chase to keep cheaper insulated pipe in. When you add everything up what's the difference in time and dollars vs just foaming in place. Me? I don't ever want to dig up my yard again. Best wishes.

 

[hondaracer2oo4]

How much is 6 inch pvc per foot? I think it is somewhere around $4 per foot. That means that you are looking at right around the same price for good foam pipe per foot.

As far as foam in trench method goes. I actually did this for 5 years myself. I too didn't have the money for good pipe and I wanted to run 4 one inch pex lines. So for $400 in pipe and $500 to foam the trench and my boiler I was in business. After 5 years I started to melt snow for about 20 feet from the boiler and then it would stop the melting. I believe the system was slowly absorbing water. When I built my garage and dug up some of the pipe to put the foundation, I found that the closed cell foam actually had absorbed water. When you broke off a piece and squeezed it water would come out. Now where this was done is very very wet. Likely water against the foam all year round. I stopped digging the trench at 3 feet when I hit ground water originally and set the pipes above that level but I bet the water rised to the pipes.

This time when I built my garage and replaced the pipe to a new boiler pad placement I bought 100 feet of leftover pipe from someone else's install for $11 per foot. Two years ago my boiler would cycle once per hour or so with no heat more from the house, last year with the logstor the boiler would go over 4 hours without a load.

 

[rowerwet]

OMG! Have you not read my horror story in the underground sticky regarding trying to do the underground on the cheap. I think I saw XPS mentioned above. Expanded polystyrene.... I seem to recall it not being closed cell and it being heavy and mushy when removed from being underground, meaning it sucked up water eventually like a sponge. If I didn't have the money to do the underground properly for this season, I think I'd temporarily use good split foam insulator and just keep it above ground like the large military bases and government facilities do. Energy loss due to hot lines being contact with wet dirt is a terrible thermal sink. I don't have time to do the math comparing good insulation but large temp difference above ground to less temp difference but terrible, wet insulation underground. My engineering instincts say well done temporary above ground is better than lousy underground.

This is a TRUE statement.... doing the underground once is miserable..... doing it twice.... well suddenly the price of propane becomes attractive.

Ok... I'll disappear again for a few months. Re-read the sticky.... years ago the topic of underground lines was my personal crusade to save the world. I've moved on to whirled peas.

The post about using XPS was about running it above ground, not burried, and using it to keep the cheap wrap pex in a pipe from ever contacting the ground, or having a larget delta between it and the air

 

[heaterman]

Larry I'm going to tell you something you probably don't want to hear...but you need to hear it.

Reading through the thread here, I gotta say it'd be best if you could wait to do this job until you had the funds to do it right.
If there is one "line item" on an outdoor boiler install that I see people regret more than any other, it's the underground lines.
Invariably, when people are trying to save money, the line goes in undersized and skimpy on insulation.
Both of those things will make you regret ever installing the boiler in the first place. I see it time after time after time.


The folks that put it in couldn't afford the good stuff any better when they redid their underground than when they put in the cheaper stuff to begin with.
I'm not trying to call you an idiot or anything like that. ... I've just seen so many people get turned off about burning wood because of poor system performance I couldn't even begin to count them up.

The laws of physics, heat transfer and fluid dynamics change for no man. Ever. They simply are what they are.

I'd like to see you happy with your results.

 

[larryjbjr]

OK, thank you for the advice. I really do appreciate it.

But in the end, I've just got to do what I feel like I've got to do. So I went ahead and bought 80 feet of five wrap 1 inch pex from a place local to me. I plan to put it this year in a wooden trough to protect it. Then, if it holds temperature decently, I will bury it next year. I am planning to add a second one next year anyhow and will just do both at the same time.

The place I bought it from assures me that it will only lose about 1.5° over 100 feet. If it does much worse than that I will return it. (I am a fighter and usually am able to hold people to their word).

I am so sick of paying so much for propane that I just cannot get myself to go another winter on propane. The pipe only cost me $300, so if I have to buy better stuff next year I should be in a better financial position to do so.

Please don't hold this against me in the future when I ask for advice.

And if it proves out that I was wrong, Lord willing I will return and confess my folly before you all and seek your forgiveness.

 

[maple1]

Did he say how long it would maintain the 1.5 loss? That's the kicker. It might do that brand new, but it's usually all downhill from there. Very interested to see how you make out , with periodic regular (and accurate) temp measuring all winter.

Good luck in any event.

 

[heaterman]

So here's the math. Assuming it's actually 1.5* temp loss.

I'm guessing you'll be circulating around 8GPM so...

8GPM x 8.33 (weight of 1 gl of water) x 60 (minutes per hour) x 1.5 = heat loss of 5,997.6 btu/hour

5997.6 x 24 means you'll be losing 143,942 btu per day.

Let's be charitable and assume you have a wood burner that will hit 40% efficiency giving you roughly 8.4MM btu per cord of wood burned.
8.4MM btu divided by that 143,942 = 58.36

So in a nutshell, every 58 days you will have lost an entire cord of wood into the ground.

I hear what you're saying about your budget and can truly sympathize with you.
I'm just saying, know your facts and make the best decision you can.

 

[larryjbjr]

OK, based upon your numbers...

I need around 35,000 BTUs per hour to heat my house on average. Using your number, I will need 3 cords of wood a month to heat my house?

I really hope you're wrong. But I have a feeling that you're not.

That just means I'm going to have to work harder to get most of my wood for free or very cheap.

But still, if I lose 1.5° over 80 feet, and tennman loses 1.5° over 340 feet, then, while I may be less efficient, we both will use the same amount of extra wood for a month. So I'm no worse off than the person who puts their boiler further away from the house.

I know, that is assuming that I will only lose 1.5° heat loss. And if I lose more I will return it. Or maybe next year if I am in better financial condition I can simply bury it and surround it with foam.




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[maple1]

Have you done any flow calcs - do you know what your gpm flow will be? That means matching to a circulator that will deliver what you need. All kinds of cans of worms to consider up front when you start digging into it.

(Did the pipe seller fellow say anything about what GPM that 1.5 drop was 'good for'? If you flow less, you will see more temp drop, generally speaking - and less BTU being transferred overall).

 

[larryjbjr]

Have you done any flow calcs - do you know what your gpm flow will be? That means matching to a circulator that will deliver what you need.

I have 83 feet one way, which figures out, using the normal rule of thumb, to be around 10 feet of head. Looking at my pump curve that will give me about 7 gallons per minute.

All kinds of cans of worms to consider up front when you start digging into it.

You telling me! I have been surprised over the last couple years that I have been working on this how much there is involved in it! Looking back now I wish I had done just about everything different.

(Did the pipe seller fellow say anything about what GPM that 1.5 drop was 'good for'? If you flow less, you will see more temp drop, generally speaking - and less BTU being transferred overall).

I'm really not sure. I guess I could call them and ask.




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[Ashful]

OK, based upon your numbers...

I need around 35,000 BTUs per hour to heat my house on average. Using your number, I will need 3 cords of wood a month to heat my house?

Using Stevens Point climate data, and assuming your 35k BTU number is for your coldest month (Jan = 1614 HDD), your 3 cords per month would extrapolate to 15.6 cords per average (8385 annual HDD) year. That's a metric buttload of wood, but not nearly as bad as assuming you'll be at 3 cords per month x 9 months.

I process a lot of wood, for my two woodstoves. Possibly more than any two or three average stove-burning members of this forum, but thanks to augmenting my wood heat with oil heat, I've never exceeded ten cords burned in a year. It can be real tough to fell, buck, haul, split, stack, move, and load that amount of wood, if you have any other demands on your time (eg. family), especially in those first few years when you're trying to collect maybe double your usage rate, to build a stockpile of seasoned wood.

Every situation is different, and as I said, I found a way to deal with my demand issue. Others might have splurged for even bigger wood-processing equipment than I own, or found other ways to get their processing efficiency up, but it's real tough to beat what I have without spending some big money.

I'd go into this with the mentality that any reduction of your heating costs beyond one-third of your equipment investment is a success. That way, you can be satisfied with a 3-year amortization your your investment, and not want to kill yourself with wood processing, trying to feed the beast. It may be necessary to continue using some form of traditional heat, to keep the wood demand within your personal limits.

 

[maple1]

How much wood do you have ready to go for this winter?

 

[larryjbjr]

None that is seasoned.

I've ordered 4 cords to be delivered next week. Plan to get more as I need it


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[larryjbjr]

I have access to a lot of dead elm. Last year I cut some and it measured in the mid to low 20s for moisture content. So, while not ideal, I'm hoping it will get me through the winter along with the wood I am buying.

Just waiting till I have enough time to go out there and cut it bring it home and split it.


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[larryjbjr]

I am also getting a lot of free wood from a local tree trimming business that I expect to take care of me next year.


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[Highbeam]

Let's be charitable and assume you have a wood burner that will hit 40% efficiency

That seems really low. Is that 40% number correct? I thought the wood boiler guys were getting very high numbers.

The OP wouldn't disclose which boiler he is using....

 

[TCaldwell]

Unfortunately most outdoor wood boilers have a efficiency rating between 28 and 40 pct!

 

[maple1]

That seems really low. Is that 40% number correct? I thought the wood boiler guys were getting very high numbers.

The OP wouldn't disclose which boiler he is using....

Pretty sure it's ballpark for an ordinary OWB. That's without losing heat to the ground....

 

[TCaldwell]

In my neck of the woods ironically the owb's have taken to lg green rounds because they last longer, further reducing any chance of efficiency. The log piles are right next to the boiler with no splitter in sight

 

[Ashful]

I assume this is why I hear so many boiler guys talk about 20+ cords per year, whereas most woodstove operators run 3-4 cords per year. My stove is rated 80% - 86%, depending on burn rate.