Burying water tanks

[whistler]

I have an off-grid cabin in way northern Minnesota. Recently I picked up 4 200 gallon water tanks I plan to hook in series and bury. They are approximately 24" in diameter by 80" long. (Utilizing a small electrical pump I plan to run a supply line supply line to the inside of the cabin from these underground tanks.)

Given that frost sometimes goes 4+ feet into the ground during a brutal winter here, I want to dig a very deep trench to lay these in. However, I might be prevented from doing so by bedrock. We don't have a whole heck of lot of soil. My question is thus: Is there something I can use for backfill in the trench that would be a better insulator than dirt?

Thanks for the help.

Whistler

[Bearfootfarm]

How about insulation? Not sure how it would work but maybe you could surround the tanks with sheets of styrofoam before backfilling. You may have to support the tanks somehow to keep from compressing it on the bottom. And where will the water be coming from to fill the tanks?

[freeinalaska]

It is common to use blue foam board with buried water tanks and septic systems up here. Some folks will use that spray on foam insulation instead.

[whistler]

Originally Posted by freeinalaska

It is common to use blue foam board with buried water tanks and septic systems up here. Some folks will use that spray on foam insulation instead.

Originally Posted by bearfootfarm

How about insulation? Not sure how it would work but maybe you could surround the tanks with sheets of styrofoam before backfilling.

I was thinking of doing something with sheets of styrofoam like this but wasn't sure it was a better insulator than dirt. I guess when you think about it, styrofoam has a higher r value than concrete which is probably higher than dirt.

Originally Posted by bearfootfarm

You may have to support the tanks somehow to keep from compressing it on the bottom.

I'm thinking that I won't have to insulate underneath. The cold seeps down through the ground from the surface and if it gets cold enough that the ground freezes around the bottom the tank I will probably be hosed no matter what.

Originally Posted by bearfootfarm

And where will the water be coming from to fill the tanks?

A room cachement system that will be disconnected for the winter. Putting 33 degree snowmelt down into the tanks would only accelerate the freezing process.

I am still at a snag as to how I should insulate the inflow and outflow pipes so as not to send cold air down into the ground. Or maybe this isn't really a big deal?

Thanks for the advice and help, keep it coming.

Whistler

[The Paw]

Originally Posted by whistler

I am still at a snag as to how I should insulate the inflow and outflow pipes so as not to send cold air down into the ground. Or maybe this isn't really a big deal?

Thanks for the advice and help, keep it coming.

Whistler

My septic field has 4 inch pvc cleanouts that come to the surface in each drain line. I built planter boxes with a hollow bottom, lined it with styrofoam board and plop them on top. It seems to keep the cold from transferring down the piping into the field. If you had a surface disconnect, you could probably do something similar.

[whistler]

Originally Posted by The Paw

My septic field has 4 inch pvc cleanouts that come to the surface in each drain line. I built planter boxes with a hollow bottom, lined it with styrofoam board and plop them on top. It seems to keep the cold from transferring down the piping into the field. If you had a surface disconnect, you could probably do something similar.

Cool idea. That should work well.



whistler

[wy_white_wolf]

Originally Posted by whistler

....Is there something I can use for backfill in the trench that would be a better insulator than dirt? ....

Insulation will only help if there is a heat source. Since the are not heated you much rely on ground heat to keep then thawed. If you can't dig down below frost level them you need to overfill to achieve the depth.

[YoungOne]

If you have a large enough diameter well on the property (asuming you have a well) you could do a jerry-rigged geothermal heater for the water.

Using a very low power pump (it has static water to move/ no head) it would circulate the tank water down into the well via sealed piping and back to the surface (bringing with it warmer ground temperatures). Here in the SW it is common to have dedicated geothermal wells (hundreds of feet deep) on a heat pump unit to get cheap cooled air.

[SolarGary]

Hi,
I think that if you bury them as deep as you can, and then put 2 inch extruded polystyrene rigid insulation board above the tank and extending out horizontally from it for (say) 3 ft, that you will be OK. You could also insulate the vertical sides of the tanks with the same type of insulation board.
The heat loss path from the tanks during the winter is up to the cold surface, so extending the insulation out makes for a longer path and less heat flow.

The R value of dirt is about R1 per foot (or R 0.1 per inch) -- Rvalue of the rigid foam board is about 4 to 5 per inch -- so the foam board is about 50 times better per inch than dirt.

The water in the tank has a lot of thermal mass, so if you make a high resistance path from the "warm" tank to the cold surface, it will likely never be cold long enough to freeze the tank.

Use the extruded polystyrene (the pink or blue stuff), because it holds up well to outdoor conditions, and does not absrob water. Try to pick an area where the soil drains, because wet soil has a much lower R value than dry soil. I'd put a layer of the 6 mil poly over the extruded insulation board.

I would group the tanks in as close a grouping as you can, so that the group has as little exposed surface area to lose heat as possilbe. That is, 4 tanks arranged in a line has an area exposed to heat transfer of about 200 sqft, whereas if you group them 2 by 2 you about cut that heat loss area in half.


Gary
www.BuildItSolar.com

[whistler]

Originally Posted by wy_white_wolf

Insulation will only help if there is a heat source. Since the are not heated you much rely on ground heat to keep then thawed. If you can't dig down below frost level them you need to overfill to achieve the depth.

Since the cold comes from the surface while the heat comes from beneath, my goal is to block the cold from coming down through the soil while retaining the heat already present in the surrounding soil. What is the best way of doing that?

Originally Posted by youngone

...well...

Unfortunately, I do not have a well on the property and likely never will. It's a good idea just not workable for me. Thanks though.

Whistler

[whistler]

Originally Posted by SolarGary

Hi,
I think that if you bury them as deep as you can, and then put 2 inch extruded polystyrene rigid insulation board above the tank and extending out horizontally from it for (say) 3 ft, that you will be OK. You could also insulate the vertical sides of the tanks with the same type of insulation board.
The heat loss path from the tanks during the winter is up to the cold surface, so extending the insulation out makes for a longer path and less heat flow.

The R value of dirt is about R1 per foot (or R 0.1 per inch) -- Rvalue of the rigid foam board is about 4 to 5 per inch -- so the foam board is about 50 times better per inch than dirt.

The water in the tank has a lot of thermal mass, so if you make a high resistance path from the "warm" tank to the cold surface, it will likely never be cold long enough to freeze the tank.

Use the extruded polystyrene (the pink or blue stuff), because it holds up well to outdoor conditions, and does not absrob water. Try to pick an area where the soil drains, because wet soil has a much lower R value than dry soil. I'd put a layer of the 6 mil poly over the extruded insulation board.

I would group the tanks in as close a grouping as you can, so that the group has as little exposed surface area to lose heat as possilbe. That is, 4 tanks arranged in a line has an area exposed to heat transfer of about 200 sqft, whereas if you group them 2 by 2 you about cut that heat loss area in half.

Thanks Gary. Would I be better off putting the polystyrene directly above the tanks and then backfilling or first backfilling and putting the insulation a few inches below grade?

[patarini]

Do a google search on this and alaska -- the state has directions online for burying tanks, if memory works 1 inch blueboard is equal to 1 foot of dirt, dont have my puter so cant send u the article.

[SolarGary]

Originally Posted by whistler

Thanks Gary. Would I be better off putting the polystyrene directly above the tanks and then backfilling or first backfilling and putting the insulation a few inches below grade?

Hi,
I think I would put the insulation not far above the tanks. It would be less exposed to freeze/thaw cycles, and it makes for a bit longer a heat flow path to the surface?

One thing that I'm sure you have thought about already is that if something goes wrong down there, or the tanks need a cleaning you have a lot of digging to do Maybe some kind of filter in an accessible part of the line before the tank might be a thought?

Gary

[whistler]

Originally Posted by SolarGary

Hi,
I think I would put the insulation not far above the tanks. It would be less exposed to freeze/thaw cycles, and it makes for a bit longer a heat flow path to the surface?

That's what I was leaning towards.

One thing that I'm sure you have thought about already is that if something goes wrong down there, or the tanks need a cleaning you have a lot of digging to do Maybe some kind of filter in an accessible part of the line before the tank might be a thought?

Yes, I have thought a whole lot about this issue because I certainly don't want to be digging all this up again in a year or two. One idea that I was kicking around is backfilling until the tanks are just covered, brace the sides of the trench so it doesn't cave, and then backfilling with insulation. That could get spendy though.

[oldcj5guy]

When i had family living up north, they sat cold frames above their inground tanks for a couple of years until they could afford to repair prev owner laziness. When you do it you might consider mounting some RV tank heaters on the tanks and some kind of heaters along the pipes. That way if it gets too bad, you can fire up the gen to help things out.

[fantasymaker]

run a loop back into the tank so that when the water temp coming out approaches 32 you can run heated water back into it I ran a 1/2 inch line inside my 2 inch line from the well so I could keep the well thawed out when I lived in Alaska

[Chas in Me]

I think that if you bury them as deep as you can, and then put 2 inch extruded polystyrene rigid insulation board above the tank and extending out horizontally from it for (say) 3 ft, that you will be OK. You could also insulate the vertical sides of the tanks with the same type of insulation board.

This is from Gary's post.

I'm told frost will freeze downward at a 45 degree angle from an insulated area. This means that if you only cover the tanks, frost will find its way to the sides of them. By capping them at some distance from their vertical edge, you will protect them better. Also, bury the insulation board because it doesn't hold up well to sunlight.
Chas

[Bearfootfarm]

A big compost pile on top of the tanks would generate heat also

[Vera]

Where in northern Minnesota is your cabin, and how did you determine that the ground freezes 4 feet deep?

[whistler]

Originally Posted by Vera

Where in northern Minnesota is your cabin...

My cabin is between Cook and Buyck.

...and how did you determine that the ground freezes 4 feet deep?

This one doesn't explicitly state what the frost depth will be in my neck of the woods but it is pretty easy to infer that my cabin will see at least 48" in most winters.
http://climate.umn.edu/doc/journal/frost2003.htm

This one comes from the 'official' department of labor requirements for footing depths.
http://www.doli.state.mn.us/pdf/bc_g..._depth_map.pdf


Whistler