Insulating buried outdoor run

[ewdudley]

If I understand this right we have several objectives within the system.

1. Burn hot
2. Provide Storage - More is better?
3. Get the heat from the storage to the living area efficiently.

Questions:

What is the R value typically used on the Storage system?
Where is the storage typically placed? Close to the boiler or near the living area?

Thought

By constructing a water tight insulated cavity in the ground and then filling it with a medium I provide a means to get the heat from point A to point B as well as establish some heat storage.

The basic problem you're up against is that it takes proportionally more insulation to insulate a long skinny heat storage device than it would for a short fat heat storage device of the same volume.

Yes, with enough insulation it could be made to work, but you might well be happier spending less money to build a more compact heat storage device elsewhere, preferably somewhere where the heat loss from the storage device would escape into a space that needs the heat.

Another problem is that in the situation where the heat in the concrete pipe is depleted and perhaps the house is a little cooler than you'd like, you have to wait for the concrete pipe to heat up before you can get the house to heat up as fast as you'd like.

--ewd

 

[horrocksd]

I just couldn't see paying $15 per foot for insulated Pex either. I bought the cheaper triple-wrap insulation, O2 barrier pex in the black outer pipe for less than $6 per foot sold by a vendor that advertises on this website. Then I bought a bunch of 4" thick closed-cell foam board on craigslist for $3 per sheet.

From an addition on my house I had left-over construction grade vapor barrier plastic sheeting and laid it in the trench Cost $40 for the whole roll. On a table saw I cut the foam board sheets into 8" wide strips, 8' long and used them to make a "coffin" in the trench. Placed the bottom and sides of the 8" cut foam board in the trench, 8' at a time, and unrolled the black pipe with triple-wrapped pex into it, covered the pipe and filled any gap in the coffin with dry masonry sand and placed a 4 inch think foam board lid on it. Staggered the lid joints just for good measure. Wrapped the plastic completely around it as I went, and backfilled each 8' or so as I went. Not a lot of work (1/2 day to do 100') , not much money. Got dusty and a little sweaty in the trench but saved about $700 over the pricey stuff. Aggregate insulation value should be pretty good. May get some ground water seepage through the plastic but I'm hopeful it will be minimal as I made low spots in the trench every 15' and put crushed stone at these collection points for water.

It appeals to the cheapskate in me and I think it should work pretty well. : > )

 

[Scarecrow57]

That is the thing, I have access to a lot of that blue foam board at a really cheap price. The pipe looks awful pricey for what you get. and most of them have the feed and return side by side. I'm really concerned about the R value (which you can't seem to find) I know that 1 inch of foam is about 6r I'm thinking I want to get at least an R20 if not more with the buried pipe. Hence, a thickness of 4 inches gives me the necessary R value. I also don't want the feed and return lines touching or close to each other as that would mean the feed water would be heating the return water.

 

[horrocksd]

The cheaper stuff I bought does have one or two layers of the wrap insulation between the two pipes to minimize cooling. Frankly I was very pleasantly surprised at the quality of the wrapping, though I realize the insulation value isn't real high.

 

[rowerwet]

I went with thermopex at 12.50/ft it wasn't cheap but I didn't have to go below the frost line 12" is deep enough, and the loss rate is less than one degree per 100 ft, I have 85' and the ground over my run is fully frozen all winter, the septic tank melts through but not the thermopex run. For all the work and effort you are going to go through trying to come up with a different idea, just remember pipe is bought and buried once, btu's lost in transmission are $$$ lost into the ground as long as you heat.

 

[Scarecrow57]

I went with thermopex at 12.50/ft it wasn't cheap but I didn't have to go below the frost line 12" is deep enough, and the loss rate is less than one degree per 100 ft, I have 85' and the ground over my run is fully frozen all winter, the septic tank melts through but not the thermopex run. For all the work and effort you are going to go through trying to come up with a different idea, just remember pipe is bought and buried once, btu's lost in transmission are $$$ lost into the ground as long as you heat.

The BTUs lost is exactly the reason I am going for more insulation. I need to go down at least 18 inches as I am also running a power conduit as well as a fresh water supply to the out building. In fact, I plan to go down 30 to 36 inches. I am running 1 1/4 inch pipe, I don't believe the insulted 4 inch pipe stuff would do the trick. I am concerned that at tops there would only be 1 inch or so of insulation around the pipe.

The final solution is to run 2ea 1 1/4 inch lines. I will build and 8 inch box out of the insulation and frame it with furring strips. I am then getting some closed cell liquid expanding foam that I will use to seal the pipe and provide extra insulation. The 02 barrier 1 1/4 pipe cost $1.50 per foot (2 - 100 foot rolls) $300. The foam cost $260 plus $90 shipping $350. It is about an 80 foot run. I am currently at $8.75 per foot. I did find the tripe Wrap with one piece between the lines in 1 1/4 for about $600 which wold be less. I just don't feel that is enough insulation though. I also feel with the thin amount of insulation between the fed and return that there would be a heat transfer between the two lines. I don't want to heat my return water until it is in the boiler.

 

[benjamin]

The more conducter )(concrete) the more surface are you need to insulate away from the ground temperature.

hr

this is the most important factor in my mind, why do you want to create a larger surface area to lose heat through?

Everyone here has said that concrete is a bad idea in this application. By all means use the cheap foam, blue board is actually a very good foam. Just don't put any concrete or sand or anything that's not a very good insulator between the tubing and the foam.

now I see you've posted again, glad you decided to go with the foam inside.

 

[Tennman]

All blue foam board I know of is styrofoam not polyurethane. Not sure if it is closed cell or not. Check it out. I think the foam board will be of little benefit except to create form for the pour foam. Using pour foam will be difficult vs using spray. You will be mixing continuously and poured foam expands dramatically differently from spray. After digging up my first method, everything was wet. I personally would never use the wrapped stuff since over time, unless the black exterior is absolutely watertight, it will get full of water. I was shocked to see all the microscopic perforations in the black corregated pipe I bought. Lots of pin holes. Not a big deal if filled with closed cell foam, but in my case got filled with water and fine mud! Please don't take this the wrong way, but roughly how much do you think you're saving vs buying a product like logstor. If you're savings are less than $300-400, I'd really think twice. If you've never messed with mixing and pouring foam, I highly recommend you play with it before training on the system component that has the potential of your greatest energy loss. All the mentioned complexities compound when you're working deep in a narrow ditch. Back to football....

 

[Scarecrow57]

All blue foam board I know of is styrofoam not polyurethane. Not sure if it is closed cell or not. Check it out. I think the foam board will be of little benefit except to create form for the pour foam. Using pour foam will be difficult vs using spray. You will be mixing continuously and poured foam expands dramatically differently from spray. After digging up my first method, everything was wet. I personally would never use the wrapped stuff since over time, unless the black exterior is absolutely watertight, it will get full of water. I was shocked to see all the microscopic perforations in the black corregated pipe I bought. Lots of pin holes. Not a big deal if filled with closed cell foam, but in my case got filled with water and fine mud! Please don't take this the wrong way, but roughly how much do you think you're saving vs buying a product like logstor. If you're savings are less than $300-400, I'd really think twice. If you've never messed with mixing and pouring foam, I highly recommend you play with it before training on the system component that has the potential of your greatest energy loss. All the mentioned complexities compound when you're working deep in a narrow ditch. Back to football....

Absolutely will experiment first. It expands about 20 times the original size. There aren't any spray folks around here that I could find. And as you say, I have serious reservations about the manufactured pipe unless you get the stuff that cost $15 a foot. it is a niche market and I don't think you get what you pay for.

 

[Frozen Canuck]

Have to agree with the advice given..... to go with spray foam.

I have seen board foam fail in applications such as this far too often. (30+ years in construction) The product was never engineered to be used as a sandwich, that may work fine in an attic access hatch.... but not underground....Far too many factors that are beyond your control for that type of underground application to be successful long term.

If it were me I would be on the phone to out of area foam contractors asking them to call when they are in my area next...get the trench open.....all the prep work done.... plastic in trench to keep dirt from getting into the foam while it is being sprayed....pipe in place....& be ready for the spray foam contractor when they are ready for you.

2-3 pound foam should do nicely in this application & there are some pro's here that can help with proper density of foam for this application. Doing it once the right way will always save money in the long run.

Learn from the posts here by people who tried to save some $$$$ & wound up losing more $$$$ in the long run.

BTW bravo for their honest posts on said attempts.... helps us all learn faster & hopefully with less pain, aggravation etc, while keeping more of those $$$$ in our pockets long term.

 

[Como]

Some SIPS use PU.

 

[woodsmaster]

Have to agree with the advice given..... to go with spray foam.

I have seen board foam fail in applications such as this far too often. (30+ years in construction) The product was never engineered to be used as a sandwich, that may work fine in an attic access hatch.... but not underground....Far too many factors that are beyond your control for that type of underground application to be successful long term.

If it were me I would be on the phone to out of area foam contractors asking them to call when they are in my area next...get the trench open.....all the prep work done.... plastic in trench to keep dirt from getting into the foam while it is being sprayed....pipe in place....& be ready for the spray foam contractor when they are ready for you.

2-3 pound foam should do nicely in this application & there are some pro's here that can help with proper density of foam for this application. Doing it once the right way will always save money in the long run.

Learn from the posts here by people who tried to save some $$$$ & wound up losing more $$$$ in the long run.

BTW bravo for their honest posts on said attempts.... helps us all learn faster & hopefully with less pain, aggravation etc, while keeping more of those $$$$ in our pockets long term.

I wouldnt dig a trench untill you know when the contractor is coming. If you get a bunch of rain the trench will collapse and you will have to re dig it.

 

[Tennman]

Since I've got a second here at work I'll clarify my previous comments last nite on poured vs sprayed foam. Yes, you are correct the ratio of expansion is the same and 20:1 seems reasonable. But exactly like spraying paint on a surface you keep hitting gun until you're satisfied with the coverage, we were able to spray MANY thin layers per 2' section, delay about 5 seconds, watch it expand and enclose around the voids and pex, then hit it again until happy. By applying many layers per section you can precisely control voids and final thickness. A pouring process will be very difficult to pour in the necessary areas at the right amount to create a uniform, void-free insulator. AND then dash off, mix the next batch and have it in the right place before it mushrooms out of your bucket. Have used poured foam in our shop where we just needed to fill a void or something to shape for a mold, but didn't really care about carefully controlling thickness. We always had some type of secondary process to shape the resulting blob. I really wish I could shed my obsession with trying to help folks with the underground stuff...... Oh well..... gotta go split some wood. Finally less than 100F with the heat index around here.

 

[in hot water]

I'm still concerned about foam in the ground around tubes.

InsulSeal is a company that specializes in underground piping. They use a PVC pipe with a choice of R-value, then a plastic "blast hole" liner around the outside. Pipe is glued, tape the seams on the outer liner.

I've used the smaller 3" for two 1" lines and a wire conduit or water line.

hr

 

[Scarecrow57]

What I am doing is putting in a trench with 3 inches of Styrofoam board, close cell type, in a box shape. I am then building standoffs made out of the foam to hold the pipe up off the bottom and center it. The foam board is in an R value of five per inch giving and r value of 15. The foam will be poured in to seal out the water and keep the pipe separated and put in place. Should some of the foam rise above the top of the form that is not a problem is I can cut it off. I will then put a top piece on sealing it using caulk. This will provide a highly insulated pipe that will have a low loss of heat.

As I looked at the manufactured pipes, it looked as though the most I would have for insulation would be around 1 1/2 to 2 inches. This give an R value of around 8 to 10.

 

[rkusek]

I agree with others. Your talking a few hundred dollars with your approach. Pink foam board and concrete are not cheap. Find an insulation contractor that sprays urethane in your area. Sealrite was a local company I found that sprayed a 350 ft. trench for me for $675. I would think you can find someone to do 100 ft. for about $350. I know it's not cheap but it only took them about 2-3 hrs. If water infiltrates anywhere the whole thing would become useless.

If water infiltrates anywhere the whole thing would become useless

I would be worried about "cold joints" as you're pouring the foam since mixing the material is going to take some time since I don't believe you can make the entire batch at once. Your could put blue board dams every so often (like pouring concrete) but this would leave a likely place for water to infiltrate. I really think you are setting yourself up for failure.

 

[Scarecrow57]

I agree with others. Your talking a few hundred dollars with your approach. Pink foam board and concrete are not cheap. Find an insulation contractor that sprays urethane in your area. Sealrite was a local company I found that sprayed a 350 ft. trench for me for $675. I would think you can find someone to do 100 ft. for about $350. I know it's not cheap but it only took them about 2-3 hrs. If water infiltrates anywhere the whole thing would become useless.

If water infiltrates anywhere the whole thing would become useless

I would be worried about "cold joints" as you're pouring the foam since mixing the material is going to take some time since I don't believe you can make the entire batch at once. Your could put blue board dams every so often (like pouring concrete) but this would leave a likely place for water to infiltrate. I really think you are setting yourself up for failure.

After further consideration I plan to line the inside of the foam boards with 4 mil plastic sheet. As for the cold joints I'm not to concerned. The foam board is a 40lb board and comes in 2'x8' sheets, 3 inches thick. I will make sure the joints fall at or around the 4' mark. Also, as the foam expands it can be pushed around a little; that is if it is like the stuff in the can.

As an update. Boiler to be delivered on Friday, Poured Foam arrives Monday. In my possession I have a circulator pump, 200' 1 1/4" pex tubing, brass adapters for the pex to 1 1/4 thread. The pex arrived in a nice little roll. Having worked with the black plastic pipe I decided to roll the pex out to let it lose some of the "curl" Darn stuff is stiff!

I haven't been able to find a tool to crimp on the fittings to the pex. Since all four ends will be exposed I am going to use hose clamps. As far as I can tell the crimps are faster and provide an accurate pressure. If they don't work I will go to plan B, which at this time there is no plan B.