What kind of unpressurized storage tank liner

I have a smaller but similar concrete tank in my basement. I use an EPDM liner. They are marketed as pond liners, just search Google. Buy it much bigger than you think you need, by the time you get it to lay right in the tank it takes a lot.

I too used EPDM in my tank with a similar design. 180* is the temp limit for these liners and they say they last longer if you max out at 175*. I also used a flat plate hx. The pond liner you are looking for made by Firestone and you simply buy a piece big enough to set in there and fold the excess on itself in the corners. You also need a piece for a lid. The lid design can be tricky. You should take a look at my articles on my tank at my site to see how I slowed flow down in order to preserve stratification. Also, make sure you use a large port size and lots of plates on your plate hx. Mine is a little undersized for my application and I get boiler idling as a result. I plan to upgrade eventually to one with larger ports and more plates. Good luck and let me know if you have any specific questions.

I bought the Firestone and at the time they had 45 mil and 60 mil. I went with the 60 thinking it might last longer and the price wasn't very much more.

http://americansolartechnics.com/epdm.html

EPDM is a great liner material but it does tend to breakdown over time. The higher the temps, the worse it breaks down.

We have used it (EPDM) intermittently over the years and have seen the same kind of deterioration over time.
The copper heat exchangers always seem to appear like those in our photo.

That being said, we have never had a liner break down from aging. Our oldest tanks are approaching 30 years old.
I have been into several that are 25+ years old and they are pretty much the same as the day they went it. (Being clear, they sometimes
get an off white appearance in some areas--with no change in flexibility or strength).

We have started making flat liner sheets of our material for DIY'ers. It is more expensive than EPDM.
It installs the same way.

All that being said, EPDM is everywhere, it is initially strong, just be mentally prepared that you might have to deal with it in the future.

emesine said:

Thanks for the info on liners. I will look into it.

As to HX, etc...... I bought a large HX and am planning on heating storage UNstratified. Basically, my system pulls water from the top of the tank, through the HX, then back to the bottom of the tank. I have a variable speed pump running water through the tank. During heating of the tank, the pump will blast water through the HX, limited by the temperature return to the boiler. When heating the house from the tank, the same pump will give just enough circulation through the HX to deliver a 20 degree delta T to the house. There are relays on the temperature sensors to make sure the pump is listening to the right sensors. I will publish something here on the setup once I have proved that it works

Andrew

Click to expand...

If you look at my tank side piping you will see that adding an aditional pump in your line would be simple and allow you to pump in both directions. This would allow you to keep the tank stratified. Stratification is extremely important with heat storage. I am not sure how you deliver the heat (ie radiant, radiators, baseborads) but the difference in output of running 180* water (what most zones are designed for(except for radiant)) and running 140* water is significant. With the limit of the liner already around 175*, by mixing the water your usable temp will drop quickly when drawing from the tank as you are mixing the return water with the drawing water. For instance a stratified tank that is at 175* at the top and 145 at the bottom will put the 175* out to transfer to the plate. The same tank mixed would all be at 155*. Not only that, as you return 135* water it would mix and bring the usable temp down quickly. I would highly recommend finding a way to stratify your tank!

EPDM is the normal liner of choice due mainly to its vast availability and cost.

However, there are better liners out there and I recently installed (5 months ago) a PVC liner in a customers 1,200 gallon wooder storage tank.

These liners have a max temp. rating of 600 F (I put a small piece on the top of my EKO40 chimney exit 5 months ago and its not changed form/shape at all).

His liner cost approx. $250-$300

Thanks,

NWM

just wanted to echo WNO: you want to ENCOURAGE stratification, not eliminate it.

Andrew,

I like to encourage experimentation as much as the next guy. Maybe more. But it isn't an experiment unless you can compare it to something.

When you hook up the UNstratified plumbing think about doing it so you could maybe flip a few valves and do it Stratified to compare.

I suspect that pumping water through a plate hx will destroy stratification a lot more than a coil heat exchanger, which is passive within the tank, just relying
on buoyancy driven convection.

I find that in my system, which does not use a hx for space heating, since we pump tank water through the boiler and also through the heat distribution system, the tank
is well stratified until we start up the boiler. The boiler is using a 007B, but is a short loop with a lot less pressure drop than the heat distribution loop, so the flow is a lot higher.

It takes about a half hour for the tank to mix evenly to a slightly lower temperature (while the boiler is inputting about 50-60k btu's/hr).

A well designed coil hx will maintain the stratification better, whether you are putting heat in or taking it out.
I think placement of the inlet and outlet and pump sizing is critical to accomplishing this with plate hx.

This all becomes a lot less of an issue with low temp heat distribution systems. This should be part of your system if you want to get the most out of the wood you burn, whether
it is pressurized or not.

I manage to maintain good stratification even pumping the water through a plate hx. The key is to slow the water and distribute it evenly in the tank. I did this by having a pipe run the length of the tank with small holes drilled in it. There is one on the top and bottom. I am able to pump in both directions so that drawing comes from top and charging from bottom.