Old unpressurized tank post mortem

[tom in maine]

Hi,
I don't usually get to tank old tanks apart, but thought this would be interesting to some of you.
The photos here are the inside of a liner from an unpressurized tank that we installed 23 years ago (yikes!) at the University of Maine at Orono.
It was part of a heating system that Dick Hill and I installed at a house as part of a project that allowed us to test different heating
systems.
This was all unpressurized, with tank water going to a solar drainback system, an unpressurized wood boiler and a ground coupled heat pump.
The tank water also was fed directly into a radiant floor. The only heat exchanger was for DHW. I will have photos of that soon. That is also 23 years old and looks fine.

We used cast iron pumps but had treated the water with a corrosion inhibitor. After 23 years, there is no rust. I think what you can see is some sludge that might've formed in the radiant
floor, after being off all summer. There is very little sludge and the water was clear.

The PVC liner here is from our Blue Phase and is not as rugged as what we are using today. But is it still flexible and was holding water fine.

We are rebuilding the solar system and wanted to install a newer tank, so it was great fun to cut this one up to have a look.

Tom

 

[sdrobertson]

That is really good to see...How high of temps did they run the tank at usually? Its good to see actual data and pictures of a product after many years of service.

 

[tom in maine]

To be honest, I do not think this ran as hot as its limit. It did for some time when the wood system was in place.
It also did most summers, since the solar system was over sized (a lot of collector into a small tank--150 square feet of collector into a 60 gallon tank!)

As of late, it was operating with solar and a gas backup system. The gas was set at about 150F, with the solar running up to 180F in the summer on a daily basis.

What I am pleased about is the flexibility of the liner. In this case, straight PVC is susceptible to embrittlement over time, in the worst case. In a tank where the water is not changed and using a high temperature material, my experience is that the material is pretty much as it was when first installed.
I have been into tanks before, but this is the oldest that I have taken out.

There is really no sign of aging.

Wait till you see the heat exchanger. That looks really good, too. I left it at the site for now, but Dick Hill took some photos which he will forward to me.

Tom

 

[pybyr]

The only heat exchanger was for DHW. I will have photos of that soon. That is also 23 years old and looks fine.

We used cast iron pumps but had treated the water with a corrosion inhibitor. After 23 years, there is no rust.
Tom

Tom- thanks for sharing this info-- can I ask what compound(s) you used as a corrosion inhibitor that was OK with both the iron in the pumps and the DHW HX (which I assume was copper)?

 

[tom in maine]

I still have some corrosion inhibitor left.

It was originally used for nuclear power plants and is still working after 23 years!
It did have a slight smell to it, even now. It was not nasty, but after drenching myself while removing all the syphon lines,
I came home and changed clothes after a hot bath.

I think it is somewhere in our new shop. Probably should get some more. 5 gallons would do a big tank. The 007's and 009 cast iron pumps
were still rust free.
Will post tomorrow.
Tom

 

[CANUCK GLAZIER]

Hi Tom,

Great post!! I do have a couple questions. I noticed you said the whole system was unpressurised. I just installed my EKO 25 midway through the heating season and didn't get my storage tank hooked up yet(500 gl lined wood tank). I too would like to hook it up the same way you did this one with the only HX being for DHW and eventually a solar drainback system.

If you could email me a sketch of the layout I would be forever in your debt.

My other question was the treatment process for the water. How does the testing work to determine what you need for the water?

I am trying to get my storage going before this heating season so any help is a plus.

Thanks again

Rob