What's a reasonable expectation for temperature drop in well-insulated buried lines? In this case, we're looking at 150 feet or so, with 3-4gpm average flow.
Buried line temperature drop?
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Good question, there are some free online pipe loss calculators, all I can find is for piping in air space, not underground.
Maybe Rovanco or one of the manufacturers of underground tube have some data.
http://www.rovanco.com
http://www.engineersedge.com/heat_t...ulated_pipe_equation_and_calculator_13169.htm
Maybe Rovanco or one of the manufacturers of underground tube have some data.
http://www.rovanco.com
http://www.engineersedge.com/heat_t...ulated_pipe_equation_and_calculator_13169.htm
In my experience, using Thermopex with my OWB, I would think anything over 3-4 degrees would be unacceptable.
So a 16 degree drop might indicate a problem? I have a client who's seeing that. What's interesting is that it appears to be just the supply line. The return line shows almost no drop.
I'll have real data in a day or two. Don't know the brand of the buried line, but it's two 2" PEX lines, each individually wrapped, and then packaged together in an outer plastic conduit. Seems like this started a few weeks ago (the lines have been in use for years).
They have two buildings with separate lines to each. The second building seems fine, but I'll get some data from that as well.
Any idea what could cause such a loss? The only thing I can imagine is if the outer conduit failed and ground water got in.
I'll have real data in a day or two. Don't know the brand of the buried line, but it's two 2" PEX lines, each individually wrapped, and then packaged together in an outer plastic conduit. Seems like this started a few weeks ago (the lines have been in use for years).
They have two buildings with separate lines to each. The second building seems fine, but I'll get some data from that as well.
Any idea what could cause such a loss? The only thing I can imagine is if the outer conduit failed and ground water got in.
With that size pipe and at that flow rate, what is the speed of the water through there. Curious what the transit time end-to-end is.
The return might be heated by the supply line losses warming it as it flows back.
The return might be heated by the supply line losses warming it as it flows back.
Ground water would be my first guess. Although I have seen homemade insulated pipe types above ground in a cooler space (garage) actually have water inside the outer shell. My guess would be condensation built up over time from inadequate insulation. The water can never evaporate, thus continually being heated and cooled by the appliance, thereby robbing usable heat before the destination.
Not saying this is true, just saying what I have seen.
Not saying this is true, just saying what I have seen.
The return might be heated by the supply line losses warming it as it flows back.[/QUOTE]
Or this. The insulation between the two pipes has failed. Time to dig it up.
Or this. The insulation between the two pipes has failed. Time to dig it up.
maple1
Minister of Fire
Or this. The insulation between the two pipes has failed. Time to dig it up.[/QUOTE]
Sounds like the whole thing has failed.
From what I have read in numerous applications, properly insulated underground lines will only have a degree or so at most of temp drop over 100 feet or so...16 degrees is definitely indicative of something being wrong...
i was just going to post this same question. I noticed my system not performing as usual. checked output temp of 170 and 150' to the house the temp coming in was 160. so I am losing 10 degrees one way. system is about 8 years and in years past I have seen about 2 to 3 degrees drop. I am 6 feet down with 2 inch pink homemade box insulation with divider in between.
a dig up is not on my horizon. time to rethink this thing.
a dig up is not on my horizon. time to rethink this thing.
maple1
Minister of Fire
In the Underground sticky in posts, 49, 62, and 64 I posted a 1.5-2 degF temp drop in about a 400' round trip. When I observed those numbers our Taco 0013 ran continuously pushing ~8-10 gpm whether the fan was on or not. This was observed when the fan was off measuring just the round trip temp loss. It was measured by an AZEL in/out sensor where the water left and returned to the boiler barn. For our system this indicates about a .5degF/100' or .005degF/foot loss. If I had to guess, I'd bet 30-50% of our temp loss was after the pex exited the underground foam and passed thru the root cellar, HX, and black iron autofill manifold. I'll try to check this again this weekend by turning on the 0013. The 0013 is now linked to the furnace blower ON command unlike in the simple, inefficient, old days. The gpm estimate is based on the computed head of our system and 0013 pump spec. No measured gpm data.
i hope that water did not get in there. There is no water around where it is buried but I guess you don't know until there is a problem.
I think this would be the end of the wood boiler experiment as I am have built some other things and concrete patio over the buried lines.
what is a solid way to check the water temps? I have in-line thermos but they are two different brands on each end. Temp gun with black tape?
I think this would be the end of the wood boiler experiment as I am have built some other things and concrete patio over the buried lines.
what is a solid way to check the water temps? I have in-line thermos but they are two different brands on each end. Temp gun with black tape?
Google AZEL Digit-Stat DS-60. Boiling water is a good way to verify calibration. Lots of other ways, but this device has two sensors and one readout.
well I have in floor heat in the kennel that I quit trying to get working so maybe this will focus my attention on what is wrong there and shut the lines to the house off and look for something else for that part. I see $$$$ in the future no matter what I do....
Well at least it's not warmer than when it left the house which would indicate X talk.
Flow rate is hard to quantify. There are 14 zones in the building with lots of cycling on and off. There's a Grundfos Alpha that's creating the flow, but the rate fluctuates depending on the number of open zone valves. Mostly it's about 3 gpm, but often less (or zero).
We have some data from last year, but it only shows supply and return temps at the boiler / storage building. It does look like we're seeing lower return temps this year vs. last, which would make sense if the house is heating with water that's arriving cooler to begin with.
They noticed that the pellet boiler was running more than it should - that's what started this whole investigation. Looks like very high quality buried lines, supposedly buried at least 6' deep and surrounded with sand.
It will be interesting to see temps at the second building.
We have some data from last year, but it only shows supply and return temps at the boiler / storage building. It does look like we're seeing lower return temps this year vs. last, which would make sense if the house is heating with water that's arriving cooler to begin with.
They noticed that the pellet boiler was running more than it should - that's what started this whole investigation. Looks like very high quality buried lines, supposedly buried at least 6' deep and surrounded with sand.
It will be interesting to see temps at the second building.
maple1
Minister of Fire
Perhaps it's time to go around the system with the camping stove and a sauce pan full of boiling water to calibrate each sensor.
See how accurate the measurements of deltaT really are.
See how accurate the measurements of deltaT really are.
cpeltier
Member
Sounds like the whole thing has failed.[/QUOTE]
If the jacket failed and water got to the foam it will eventually absorb it. Once this happens the insulation value goes to zero and the heat conducts out.
Closed cell foam will absorb water if submersed.
Does SPF absorb water?
Closed-cell foams, by nature, are resistant to water absorption, and are approved by FEMA as a flood-resistant material. Open-cell foams can absorb and retain liquid water at varying rates. It is important to consider the different properties for each foam type for each application.
Closed-cell foams, by nature, are resistant to water absorption, and are approved by FEMA as a flood-resistant material. Open-cell foams can absorb and retain liquid water at varying rates. It is important to consider the different properties for each foam type for each application.
cpeltier
Member
It is water resistant but not water proof. There are plenty of online references. If subjected to submersion or 100% humidity it will eventually fail by absorbing water. Every hot tub owner knows this lesson as we typically have to replace our waterlogged closed cell foam based covers every 5 years or so. Open cell foam is obviously a poor choice in this application.
BoilerMan
Minister of Fire
Remember that any material which is not a metal is actually only a vapor retardant, and not truly water proof. To the best of my knowledge anything buried directly in the earth which is not in a continuous welded/soldered metal pipe will eventually take on water. Every and I do mean EVERY underground electrical service I have pulled out of the ground has had good insulation still on it, but the conductors have failed due to water, conduit is of no help either as all fill with water.
The only way I would bury underground heating lines is if they were in a 6"+ PVC pipe and the thermopex (or whatever brand you choose) can be freely pulled out, and air can be blown in one end of the PVC in one building and exhausted out the other end in the heated building. Assuring that the insulated pex assembly was indeed in a dry conduit.
TS
The only way I would bury underground heating lines is if they were in a 6"+ PVC pipe and the thermopex (or whatever brand you choose) can be freely pulled out, and air can be blown in one end of the PVC in one building and exhausted out the other end in the heated building. Assuring that the insulated pex assembly was indeed in a dry conduit.
TS
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