Underground piping insulation

[heaterman]

I lost track of the thread but someone asked if I could document temp drops in various installations that we have done or been able to document.

I had a chance to visit a couple this past week and the numbers are posted below. I'm going to try to keep track of this post and add to it over the next few weeks. All temps were measured with a Fluke digital thermometer using a strap on thermocouple and taken on bare steel or copper piping.

Install #1 This installation consists of a 235' trench with supply and return being 1.5" Wirsbo pex. The tube was buried to a depth of about 25-30" and runs directly beneath about 55' of residential driveway. It was insulated with sprayed closed cell poly urethane foam to an average thickness of 3". Flow rate in the pex is calculated at 12.65GPM. The soil type is very light sand.

Temp at point of entry to supply 151*
Temp at point of entry to house piping 150*
Temp at point of return in house 144*
Temp at point of return to boiler 145*

I found this to be very interesting because the return pipe actually picked up a degree traveling back to the outbuilding in which the wood boiler is located. It would appear that there is no actual heat loss underground as that 1* of measured temp drop measured is being transferred to the return tube.

Install #2 This installation consists of 108' of trench and uses the generic 1" pex product wrapped in 1/4" foil/foam a few times and inserted in black corrugated drain tube. Approximate depth is 48" and it runs through normal sandy loam type soil and is in an area which can get damp seasonally. Calculated flow rate is 6.3 GPM

Temp at point of entry to supply 178*
Temp at point of entry to house piping 170*
Temp at point of return in house 153*
Temp at point of return to boiler 149*

The temp drop from the boiler to the house is 9* which would figure out to over 28,000 btu/hr at the calculated flow rate. Also note that the return trip drops the temp only 4* indicating that there is significant heat transfer between the supply and return pex in the tubing. If you assume that 4 degrees from the supply is actually going into the return piping on the trip back to the wood boiler you have an actual temp drop of 4* in the supply from boiler to house for an actual heat loss of about 14,000 btu's. Rough mental math would equate to a heat loss underground of approximately 2 pounds of wood per hour wasted or an extra 48 pounds per day that this owner has to process and handle.

 

[Duetech]

Interesting information. Are the supply and return lines touching each other or is there an insulation barrier between the lines?

 

[DaveBP]

What a luxury! An ice-free path out to the boiler shed! A mini golf fairway!

 

[heaterman]

Interesting information. Are the supply and return lines touching each other or is there an insulation barrier between the lines?

Yes the tubes are in contact in both instances.

 

[Floydian]

Thanks Heaterman-That was me with those questions.
I would really like to go with a Garn for heating two houses almost 400' apart. I would build a building for the Garn about halfway between both houses. I would have to cross our gravel driveway twice. Do you take extra precautions under driveways?
I would need to bring in the occasional concrete or gravel truck. Would that work?
My soil is sandy loam down about 1-2' then red clay below that. Our frost line is 2'. Would the sprayfoam work in the clay?
Thanks again for the info,
Noah

 

[heaterman]

Thanks Heaterman-That was me with those questions.
I would really like to go with a Garn for heating two houses almost 400' apart. I would build a building for the Garn about halfway between both houses. I would have to cross our gravel driveway twice. Do you take extra precautions under driveways?
I would need to bring in the occasional concrete or gravel truck. Would that work?
My soil is sandy loam down about 1-2' then red clay below that. Our frost line is 2'. Would the sprayfoam work in the clay?
Thanks again for the info,
Noah

In instances where heavy traffic is anticipated we have our foam company spray the tube, give it an hour to set then fill and compact with sand to about an inch or two above the foam. Then we place a couple inches of Dow blueboard (any EPS foam) over the sand and backfill the rest of the way. So far this has worked very well with no known failures of any kind. One such installation is on a farm only three miles from my home and it receives daily traffic in the 80,000 class along with monthly visits from me as it is kind of a test site for a number of reasons. Our frost level in that scenario would be in the 4-5 foot range and we can find no evidence of heat loss or compression under that drive. That job went straight into clay so hard I could barely dig it with my Kubota backhoe. I'd recommend backfilling with sand to cover the foam/tube and then cover with whatever you want.

PS, A Garn would be ideal for your installation. Depending on the heating load in each of the structures you would probably want to use at least 1.25" pex for a 400' round trip to each building.

 

[flyingcow]

on the #2 install, as time goes by, obviously it's going to be worse. Can't imagine what that'll do when it's a wet summer into fall. Seems to me as a homeowner, it would be worth digging this up and doing it right. I'm curious what mine will do, but I used thermopex, 3ft down with sand/screened gravel, 2 inches of blue board and where it gets closer to the ground 4 inches. It's only 50 ft so I assuming it'll be fine.
Thank You Heaterman.

 

[Duetech]

Interesting information. Are the supply and return lines touching each other or is there an insulation barrier between the lines?

Yes the tubes are in contact in both instances.

The reason I asked was because of the the temp change in the return I did not think there was a desire to get heat transfer between the lines (?). When I installed mine I used a flexible 1/2" thick closed cell foam tube like that used in basements etc. to insulate pipes for moisture/condensation prevention and or heat loss and netted about 1" barrier between the lines as both pex lines were insulated. I do have analog type gauges but do not see any more than a 1* drop, in winter, from boiler to the house on the supply line. The run is 45' one way. How would I calculate my btu loss for that one degree I use a taco 007 with 1" pex. I am hoping to move my boiler to a "boiler house"/storage/wood shed (85 feet one way) and need to know any mod's that need to be done for the move and re-plumb. Thanks...

 

[deerhuntrer]

How much is to purchase an infared temprature gun?

 

[MyOutdoors]

I just checked mine as well. I used Sequoya's BHS pipe, basically it's 2-1"pex pipes enclosed in one large peice of pipe foam all in 6" corrugated pipe. The pipe is down 18" in a sand bed and gravel top.

Temp at point of entry to supply 181*
Temp at point of entry to house piping 175*
Temp at point of return in house 165*
Temp at point of return to boiler 165*

This is more loss than I'd like, so I may dig it up this summer and enclose it in spray foam or rigid insulation board.

 

[flyingcow]

I just checked mine as well. I used Sequoya's BHS pipe, basically it's 2-1"pex pipes enclosed in one large peice of pipe foam all in 6" corrugated pipe. The pipe is down 18" in a sand bed and gravel top.

Temp at point of entry to supply 181*
Temp at point of entry to house piping 175*
Temp at point of return in house 165*
Temp at point of return to boiler 165*

This is more loss than I'd like, so I may dig it up this summer and enclose it in spray foam or rigid insulation board.

Did you maintain the integrety of the insulated pipe thru the concrete wall, or did you strip the insulation off and drill seperate holes for the supply and return? I think the concrete will wick alot of heat off of the bare pipe.

 

[heaterman]

I just checked mine as well. I used Sequoya's BHS pipe, basically it's 2-1"pex pipes enclosed in one large peice of pipe foam all in 6" corrugated pipe. The pipe is down 18" in a sand bed and gravel top.

Temp at point of entry to supply 181*
Temp at point of entry to house piping 175*
Temp at point of return in house 165*
Temp at point of return to boiler 165*

This is more loss than I'd like, so I may dig it up this summer and enclose it in spray foam or rigid insulation board.

How long is the run from boiler to the house?

 

[MyOutdoors]

I wish I could blame the concrete, but I brought the entire corrugated /insulated pipe through the wall. Total run is 170 feet. I'm running a taco 013 to the house and a 007 to circulate from the oil boiler and the 50 plate HX.

 

[rowerwet]

How much is to purchase an infared temprature gun?

mine cost $40 at home depot, it has a laser, ones without laser cost less, check Ebay.