1000 Gal Oil Tank into a Ground Source?

[David Lang]

I'm switching off of oil heat and will end up with a 1000 gallon tank to retire. I was wondering if it was possible to do something useful with it. Like fill it up with Prestone and use it a ground sink for a heat pump.

Would this work, does it even make sense?

[lemagr67]

1000 gallons of prestone might be a little pricey to begin with. You could make it work, but it seems like a ton of effort when you are just using the ground as the heat sink anyway once that heat conducts through the tank. On top of that, you could end up in some serious trouble with the EPA if you somehow leak 1000 gallons of methanol or ethylene glycol into some ground water sources. Unless you are REALLY strapped to save space, it doesn't seem like a great idea to reinvent the wheel for a little better performance.

[David Lang]

Antifreeze aside. Will the tank work as a ground source/sink?

[lemagr67]

If you're talking about keeping it above ground, I wouldn't think so. You could do a heat transfer calculation on it, but I would think it would stay cooler than ambient in the summer or hotter than ambient in the winter

[lemagr67]

Got that backwards

[David Lang]

It's an in-ground tank.

[lemagr67]

Did a little napkin math and assuming the tank is a rectangle, which its probably not, and using the same fluid as a geothermal loop would, it is the equivalent of about 200ft of geothermal pipe. If it's a spherical tank, which its probably not, you are looking at even less. So, best case scenario, the tank alone could conduct as much heat as 1/3 a roll of standard geothermal pipe... enough to handle a 1/3ton unit. This is obviously just a quick ballpark number, but even tweaking those figures to the best you could get, I wouldn't expect to get anything over a 1/2 ton heat pump to work with just the tank alone. And that 1/2 ton is assuming you are using something like mercury to conduct the heat in the tank. And I'm even assuming this tank is below the frost line where the ground temp is consistent. All in all, you will still need a loop, so there's no sense in fiddling with an underground tank and making sure it's not leaking anything... not to mention figuring out how to get the fluid to flow in it without just channeling the same water in and out without getting any of the cooled/heated stuff that you want.

Once again, it's just napkin math, but with it being so far away from feasible, I don't think really digging into the exact thermal conductivities and what not will yield a green light.

[sweat hog]

Most places I have been, those tanks need to be removed or decomissioned if no longer in use . They can become a problem for property value.

[teeball57]

Did a little napkin math and assuming the tank is a rectangle, which its probably not, and using the same fluid as a geothermal loop would, it is the equivalent of about 200ft of geothermal pipe. If it's a spherical tank, which its probably not, you are looking at even less. So, best case scenario, the tank alone could conduct as much heat as 1/3 a roll of standard geothermal pipe... enough to handle a 1/3ton unit. This is obviously just a quick ballpark number, but even tweaking those figures to the best you could get, I wouldn't expect to get anything over a 1/2 ton heat pump to work with just the tank alone. And that 1/2 ton is assuming you are using something like mercury to conduct the heat in the tank. And I'm even assuming this tank is below the frost line where the ground temp is consistent. All in all, you will still need a loop, so there's no sense in fiddling with an underground tank and making sure it's not leaking anything... not to mention figuring out how to get the fluid to flow in it without just channeling the same water in and out without getting any of the cooled/heated stuff that you want.

Once again, it's just napkin math, but with it being so far away from feasible, I don't think really digging into the exact thermal conductivities and what not will yield a green light.

Your not the first one to ask the question but that is a pretty good answer.
The idea of a loop is to spread the pipe to cover a large area of ground to extract or reject the needed BTUs. Typically 1 ton of loop is 600 feet long in a horizontal loop configuration depending on soil conditions.