Hot water storage - steel tank

[veggie]

Anyone out there using a standard steel tank for coolant/heat storage.?

I have a 60 gallon vertical air receiver tank and I'm wondering if it can be used as a heat store for the greenhouse project.
The engine could heat the tank (along with a heating element) inside the garage.
A glycol line to the greenhouse could fetch the heat from the tank via a plate heat exchanger that I have.

The concern I have is internal corrosion.
Any comments or experience using air compressor tanks ?

veggie

[veggie]

Thanks Jens,
Good idea about the metal testing.
My fear about using old hot water tanks is that the previous user took it out of service for a reason.
I have a phobia about coming home from work and seeing 60 gallons of water (or water/glycol) on the floor.
I suppose the ideal tank would be a lightly used electric hot water tank. Then I could use the element as a load dump.

veggie

[mobile_bob]

u can buy corrosion inhibitors from any truck dealer, ask for DCA additive/fluid
the directions are on the bottle as to how much coolant it will treat

its relatively cheap and is good stuff

bob g

[oiler]

Veggie

Your air tank should be pressure tested to say ten bars before you even consider using it.

You can use plain tap water in your tank. Corrosion will not be an issue since there will be no oxygen in the water....three weeks after filling the water will be "dead" as we say here

My storage tank is an old heating oil tank. It is in it's 12th year as heat storage.

If you need to empty the tank for any reason, try to reuse the "dead" water.

[veggie]

u can buy corrosion inhibitors from any truck dealer, ask for DCA additive/fluid
the directions are on the bottle as to how much coolant it will treat

its relatively cheap and is good stuff

bob g

Thanks Bob,

For anyone interested, here's the product...

veggie

[BioHazard]

I've seen a lot of really good looking water heaters on craigslist in the $50-100 range. Free they are not, but, generally they have only been used for a short period of time before a remodel or changing from electric to gas or whatever. Way better than the $600 or so for a new one. 

FWIW, I have a gas water heater at my house and 2 electrics at my shop, all have been in service since about 1995 and they all still appear to be in good shape. I don't worry about them...

[mobile_bob]

i once bought a house with a glass lined water heater tank, it was just shy of 30 years old and was
still in the house 10 years later doing it thing.

lot longer than i would have thought possible

bob g

[veggie]

Hi Jens,

In my case, I intend to use a pressure vessel (ASME air reciever) in a non-pressurized application.
An expansion tank will be mounted high in the system and I will attempt to limit any oxygen intrusion.
My main concern is corrosion and the potential for corrupting the rest of my system.
If I can control the corrosion with inhibitors or anodes, I will be happy.
These tanks do have a corrosion allowance for pressure service.
Unpressurized, I expect reasonable life from the tank. I'd be happy with 5 years.
The tank is brand new and best of all it's free.

veggie

[cognos]

In an unpressurised, water only system, I can't see any problem with a steel tank, if clean, fresh water is used for the first fill, and the system is flushed free of contaminants. The water will soon de-ionize, and the system will will come to equilibrium - reaction-wise.

If one were to add corrosion inhibitors in the form of additives or antifreeze, all the better. Suspend an anode in the tank for good measure, if you want.

Your biggest corrosion issue will be at the air/water interface, or with dissimilar metals, the water acting as an electrolyte. I would think red iron oxide precipitation will eventually coat all the interior surfaces not exposed to high flows. But I wouldn't expect severe pitting, hydrogen bubbling, etc. to be an issue.

Industrial vessels are often just plain ole' carbon steel, in both pressurized and atmospheric applications, in some pretty severe service, and the service life is good.

[BioHazard]

The cost of replacing a tank at the end of the warranty is inconsequential compared to the cost of a catastrophic leak if the tank is located in a finished area of the house. Count yourself lucky if all you have is a pinhole leak.

If your water heater is installed in such a way as to leak water into a finished space, then you didn't install it right. Period. My 1995 water heater is in my garage, with a drain pan underneath it, and the pressure releif valve properly plumbed to a drain. It can leak all it wants and nothing will happen except a large water bill. There is actually wording on the front of the tank similar to what I just wrote.

The ones at my shop are installed improperly. One is located on top of a bathroom, with no pan or plumbing on the pressure relief. If it blows the bathroom is a gonner. It's also installed in such a tight space that I cannot attach a hose to the drain valve, nor can I access the anode, so neither have ever been touched, in 15 years. Still not worried............

Hell, the pipes in your wall get old too, and can burst at any time. Lifes too short to worry about crap like that...

[BioHazard]

First, there are literally millions of homes out there that have a water tank in a finished space.

Yeah, that's why they sell the drain pans. If it's properly installed it can be in the middle of your living room and a leak shouldn't be an issue. That's what the codes say. That's why it's printed right on the front of the heater. Ironically the only signs of damage on my 15 year old water heater is on the top of the OUTER steel case, where the incoming water line dripped for a few years.

A proper drain pan should be more than adequate to contain the 3/4" water line that feeds most heaters. If your pipes are throwing out more water than that, you need a pressure regulator...

The high pressure air tanks I keep around my shop worry me much, much, much more than any water tank ever could. 99% of the time they only fail with a small pinhole too...

[Fat Charlie]

As far as the rest, you know how the saying goes .... ignorance is bliss !

And that's why finished spaces exist in the first place.