underground storage tank

[powerspec]

Does anyone have some experience to share in using propane tanks installed underground for thermal storage? I have a thousand gallon one that would leave a lot of room in the house if I buried it in the clay outside the basement wall. Sure would like to hear from someone who has tried it. We have -40 degree winters so I will spray urethane foam under and around the buried tank. Water connections will be at the top with a dip tube for cold water flow at the tank inside bottom.

 

[stee6043]

I'm sure there are people on this site that have done it, or at least who know people who have done it. The biggest downside to having any storage outside is that 100% of your heat loss is true loss. When your storage is inside the heat lost from the tank is lost to the house. I don't know how "efficiency crazy" you want to get but it could be significant, especially with the temps you're talking about...

 

[DaveBP]

Is your tank rated for burial? The tanks that are designed to be buried have a sacrificial anode to limit corrosion and perhaps other differences that I am unaware of.
I guess that if you did a perfect, waterproof foam job the tank would be fine regardless of it's design intent.
If your soil is clay does it move around at different seasons? You would need to make sure that your piping was done in a way that could flex with the seasons.

 

[RobC]

I've considered this approach but my big concerns were serviceability with pipe fittings and temp probes. Also, when they install underground propane tanks they have install kits that include ground rods, sacrificial anodes etc for electrolysis, more problems. You also mentioned clay. U/G tanks need to be buried in sand to keep the water away from them because of rust and electrolysis but in a heat storage application because of the thermal loss also. I figured that I was eliminating potential problems by finding a way to keep the tank in my house. I have just enough room to stack 2 X 500G between cars in garage and walk by comfortably. For me plan "B" would be build a small shed for tank(s).
If I were to do an underground tank I would put concrete riser(s) with a cover on top so I could get to the fittings for service 24/7. Consider putting the insulated pex pipe in a 6" or 8" (pull) pipe so you wouldn't have to dig from house to tank in the future. At -40 below if you need to get at anything you won't be digging through the frost.

 

[Nofossil]

I'll echo the comments about corrosion. I'd also worry about being able to insulate it well enough. You want a LOT of insulation around the tank, especially above it. Insulation has to be dry to be effective, and some foams will eventually get waterlogged.

I ended up putting mine under the deck (above ground) and building a superinsulated doghouse around it. I think if I were to do it again, I'd build a slightly larger enclosure as an extension of the garage.

If I were to design the house again, I'd build in space in the basement for the storage.

 

[powerspec]

Thanks all for your comments. I do not plan to use cathodic protection since the tank will be insulated electrically by at least 6 inches of urethane foam. I calculate the heat loss to be minor comparing indoor vs outdoor and worth the gain in usable space inside the home. All said I would be a lot happier to speak with someone who has done this before! I can't believe I'm the first to do it.

 

[Gooserider]

Must say that I don't like the idea of burying things that don't have to be buried, and that I might want to dig back up again... I'm almost certainly going to do non-pressured storage, for several reasons, but what I had been thinking about if I was to do pressurized would have been to use the 2x 500g stacked approach, and put them up against the wall of the house, with an insulated extension over and around them... However this seems like an overly complicated thing for several reasons, so the idea was rejected.

Gooserider

 

[fowlerrudi]

What about digging a 4ft insulated hole in your basement (thinking new home construction) and dropping in a tank and insulating it. Have a wooden cover over it so basement space could still be used. Does pressurized storage need to be at the save level as the boiler?

 

[Gooserider]

What about digging a 4ft insulated hole in your basement (thinking new home construction) and dropping in a tank and insulating it. Have a wooden cover over it so basement space could still be used. Does pressurized storage need to be at the save level as the boiler?

Storage (especially pressurized) does not need to be at the same level as the boiler, though it's somewhat preferable. (at least most people do it that way) However there are a couple of issues with your idea...

1. As others have mentioned, burying a tank tends to have other complications, such as corrosion prevention, tank material and design choices, etc. that make it more complicated.

2. Unless you are where there is really no concern about water tables, it isn't going to be very good - figure if the basement is down 8' from grade, and the tank is another 5-6, you are going to be digging down 15 feet or so, which is likely to find water in many places - insulating a tank that is below the water table gets to be VERY problematic...

3. Someday that tank will need to be replaced - getting it up in order to get it out might be a problem...

Gooserider

 

[fowlerrudi]

I was thinking of having a square compartment - not just burying underground. Good point about the water table though....never thought of that.

 

[Hydronics]

Another consideration with the water table is the hydrostatic pressure it induces. It can cause a tank to pop out of the ground. Consider the force it takes to hold a small ball under water in the pool, let go & what happens. The forces holding a tank down are the weight of the tank, weight of the liquid (NOT IF IT'S EMPTY), weight of any soil above & the friction against the soil on sides.

 

[Eric Johnson]

Same thing happens from frost with culverts if you don't anchor them down with big rocks or other heavy/fixed objects.

 

[Gooserider]

Same thing happens from frost with culverts if you don't anchor them down with big rocks or other heavy/fixed objects.

Never mind culverts, the same thing happens with SOLID ROCKS - Ask anyone that tries to grow stuff in New England - the veggies might or might not do much, but the annual crop of rocks never fails... >:-(

Gooserider

 

[tom in maine]

As convenient as it seems to bury a tank to get it out of the way, when you consider the heat loss, lack of convenience for service and costs, I can't think of any situation where this is a logical solution.
I think it would be much more practical to build a separate building to house a tank.

As much fun as I think it is to have a backhoe and dig holes in the yard, fussing with a 1000 gallon tank that can screw something up in the winter is never a good time.

 

[pybyr]

Same thing happens from frost with culverts if you don't anchor them down with big rocks or other heavy/fixed objects.

culverts have an open air space within which lowers the frosline some

True- about open things like culverts allowing the cold to get deeper in the soil- but Goose is right about new rocks surfacing every year in New England farm fields that have been cultivated for decades or centuries.

 

[jebatty]

As to rocks, I always thought the process of a new crop had more to do with the freeze/thaw cycle than hydrostatic pressure. A rock will sink to the bottom of the ocean regardless of its weight and the water pressure. But frost heave will lift almost anything. The heave leaves small cavities under the rock which, as the thaw cycle starts, allows water carrying fine material to settle into, and the fines fill the small cavities. Then as the thaw progresses, the rock settles back down, but this time higher than when it started because the space below is now "filled." Thus, the rock rises. Similar action with minute earth movement below the frost line. Is there more to it than this?