heat exchanger in abandon oil tank

[megachase]

Here in the NW most homes are or were heated by oil. The biggest cost of switching to gas (as geothermal is very expensive) is decommissioning the old buried oil tank, in many cases up to 675 gal. cap. I was pondering weather the old tank could be filled with a solution and somehow figure out how to get piping into the tank without digging it up and using it as a fluid to fluid heat exchanger for HVAC. Anyone wanna run with that ball?

[FredGarvin]

I wouldn't want to try to clean that tank. I also wouldn't want to be within a country mile if someone started welding fittings on it without a ton of inert gas.

You may have to check with your state environmental laws, but you may run into an issue with an underground storage tank not being used for it's expected intent. You may find out you can't legally do what you want to do without the hassle you are trying to avoid.

All of my tanks were either next to the house or in my basement. Neither were buried.

Even if you do get by all of that, what would you want to do with it? You would have a rather constant temp relatively cool fluid. If you wanted to heat it you would have to impart that energy to it. You would lose a ton of it in heat transfer to the surrounding ground since you are using an uninsulated steel tank. If you use it, you could possibly use it to cool in the warm weather.

[russ_watters]

The OP wants to use it as a source/sink for a water source heat pump.

Since the tank has a small aspect ratio (not much surface area, lots of volume) and is closed, you won't be able to use it as a heat pump source/sink. All you'll do is heat it up quickly in the summer and render it useless after a couple of hours and freeze it solid after a couple of hours in heating mode in the winter.

Ground source heat pump loops are dug deep for two reasons.
1. There is a lot of surface area to exchange heat with the ground without warming or cooling the ground to much.
2. Whether the system is open or closed, digging it deep will get it below the water table where water can flow past it and help keep it at a constant temperature.

[Naty1]

Post #3 reflects my understanding.....