Is EPDM for tank liner a catch-22?

[tom in maine]

The issue with rigid polypropylene tanks is the potential stress loading. A number of people over the years have used them for solar storage.
Unfortunately, they can stress crack over time. A generalization is that plastic can tolerate temperature or pressure, not both together.
That is a broad generalization, that you might overcome with expensive plastics, which we cannot afford.

I have sold tank liners for rigid tanks that have stress cracked from heat stress. The bottom of any tank over two feet deep is taking a tremendous load.
An 820 gallon tank has about 7,000 pounds of water in it. All that weight loads the lowest area of the tank walls.

 

[jebatty]

On the concrete tank idea, if also (you probably thought of this) you put 3/8" or 1/2" rebar between most of the pex lines, you may get a stronger tank and more heat transfer. Just an idea.

The best IMO is the new or used propane tank. My 1000 gal used propane tank is problem free. But it is a beast.

 

[free75degrees]

I like the idea of the solid copper block heat storage. While I am at it i think i may swap out my refractory bricks for diamond bricks, cause I heard they last forever ;^)

 

[WoodNotOil]

On the concrete tank idea, if also (you probably thought of this) you put 3/8" or 1/2" rebar between most of the pex lines, you may get a stronger tank and more heat transfer. Just an idea.

The best IMO is the new or used propane tank. My 1000 gal used propane tank is problem free. But it is a beast.

Having read a lot in the boiler room, I agree that if you have the room and access to put in pressurized storage it is probably the way to go. If you don't have access, I still think EPDM lined tanks are a good alternative. The slightly lower temp can be overcome by sizing the tank slightly larger and by altering the zones to perform better with lower temp water. I have no complaints so far with my homemade tank and fully expect to have to replace the liner at some point in the future. I have a few tweaks to do to the way it connects to the heating system, but that comes with the DIY territory.

 

[free75degrees]

On the concrete tank idea, if also (you probably thought of this) you put 3/8" or 1/2" rebar between most of the pex lines, you may get a stronger tank and more heat transfer. Just an idea.

The best IMO is the new or used propane tank. My 1000 gal used propane tank is problem free. But it is a beast.

Yeah i'd live a propane tank but i can't get one into the basement. Plus I'd have to abandon my expensive copper coils.

Well I have at least several years to think about it. I just hit 181 at the top of the tank last night, which is typical, so i think I'll have to do something different eventually.

 

[free75degrees]

With careful design it can stratify as it stores heat and remain stratified as it gives up heat to the loads. With any solid ( assuming it can conduct the heat fast enough) you will have the temperature of storage rising evenly throughout with the amount of heat stored.

I think the aspect of a tank that allows stratification is the fact that heat always enter at one place and leave at another while charging and reverses while discharging. I see no reason why this would not work with a solid heat mass. I bet you could even make the heat separation happen horizontally. If one really wanted to take the concept far, one could make a series of separated heat masses - the 1st one would always be the hottest and the last one would be the coolest. There was some discussion about water stratification in a previous thread where it was argued that water does not stratisfy on it own like a column of air might. Instead water would lose its stratification over time. The density difference between hot and cold water isn't enough to cause stratification. Water may lose its stratification slower than a mass of concrete, but i am not so sure. Water has the density difference working in to its advantage - i.e. even though density is not enough to cuase stratification, it probably helps a bit to maintian it. However, any solid with lower heat conductivity than water would have the lower conductivity in its favor. Which of these two advantages is greater is unclear to me. It's a very interesting discussion anyway.

 

[DaveBP]

As long as we're kicking this around and because the coffee isn't done yet...

I have a problem mixing up my mental models of storage tank operation. Water storage can be done in at least 4 different configurations that I can think of so there must be more than that. Pressurized and closed, unpressurized and open are the two main categories kicked around in this forum. How each of those are plumbed effects the details of how it works but the principles are the same.

Water or air will stratify on their own (if you mean not being pushed by a pump) as long as heat is being added or extracted. You could have an open tank with the boiler supply coils wrapped around the outside, not in the liquid, and the warmer liquid will end up at the top. It's better to say the colder liquid will settle to the bottom. HEAT DOES NOT RISE!. Colder, denser liquids or gases settle down because gravity pulls it down. It's the denser material being pulled down that pushes the warmer less dense material up. Sorry, just one of my pet peeves... Which is why you're right; you could 'stratify' a solid mass horizontally; or upside down/hot on the bottom for that matter. But I will bet this cup of coffee that I just poured that if a tank of carefully stratified water (or air ) were insulated very well and just allowed to sit, it would lose its stratification and be the same temperature throughout. Might take a while. I don't know how long.

Yes, fascinating topic. Glad I found some propane tanks so I know which direction I'm headed. And I'm glad I put that 44" wide door into the basement.

 

[Der Fuirmeister]

This whole epdm issue is my only concern/regret with how I set up my system. In the end I am not sure if I had any other options though. Are there any other options for the do it yourself tank builder with the constraint that the parts have to be small enough to fit through a standard doorway? The only other thing I can think of, and I wish I has pursued, was a solid concrete storage mass. Concrete has half the heat capacity as water per volume, but I'd be willing to make it twice as large if it meant that I'd never have to worry about it again. My thought is a large mass of concrete with 1/2" embedded pex and with no more than 2 or so inches between each run of pex. I'd also add lots of strips of aluminum flashing embedded in the concrete to help spread the heat.

Anybody ever do anything like this? Any thoughts on whether it would work? I definitely push my tank to 180* so if it starts to weep in 7 years I may do this.

Thermal storage is a big advantage of in-slab radiant heat with PEX. Wish I had installed it in my home when we built. We installed it in our shop. You still need to insulate under the slab. Water has so many advantages over concrete that I would not consider concrete over it. How much does a EPDM liner cost vs. all the required PEX tube? How hard to replace (once every 10-20 years)?

If available a silicone material liner might be considered, but I'll bet the cost / benefit ratio would lead you back to EPDM.

What about fiberglass over EPDM? Has anyone tried this?

 

[Der Fuirmeister]

As long as we're kicking this around and because the coffee isn't done yet...

... HEAT DOES NOT RISE!. ....

Don't tell that to a hot air balloon pilot.

 

[jebatty]

What about fiberglass over EPDM?

Several threads on this - a search would reveal lots of discussion.

Reference:
http://www.proco-fwi.com/pdf_files/selecting.pdf

 

[DaveBP]

Don’t tell that to a hot air balloon pilot.

The hot air balloon pilot knows that hot air that is much less dense than the surrounding air will rise through that surrounding air until it gets to the altitude where the air density is the same as the hotter air inside the balloon. The air up there is way colder than the air down at lower altitude. That doesn't mean that heat sinks.
Heat and hot air, two different things.

 

[pybyr]

With careful design it can stratify as it stores heat and remain stratified as it gives up heat to the loads. With any solid ( assuming it can conduct the heat fast enough) you will have the temperature of storage rising evenly throughout with the amount of heat stored.

The density difference between hot and cold water isn't enough to cause stratification.

hmm- not sure I know the definitive answer, but if what you assert is true, then how is it that many stationary and Ag engines up until roughly the 1940s or 1950s made do with no water pump, relying solely on thermosyphon for coolant circulation,

and how is it that ponds and lakes go through certain seasonal turn-overs at certain times of year based on the difference between the prevailing temperatures at the surface, where they contact the air, and the underlying earth/ rock?

 

[Der Fuirmeister]

Don’t tell that to a hot air balloon pilot.

The hot air balloon pilot knows that hot air that is much less dense than the surrounding air will rise through that surrounding air until it gets to the altitude where the air density is the same as the hotter air inside the balloon. The air up there is way colder than the air down at lower altitude. That doesn't mean that heat sinks.
Heat and hot air, two different things.

Guess I should have put one of those smiley faces on my attempt at a joke so that everyone would get it.......

I've been a pilot for 22 years, and well aware of the principles of flight.

 

[DaveBP]

Guess I should have put one of those smiley faces on my attempt at a joke so that everyone would get it.......

I had an inkling that there was an invisible smiley there. I'm a little touchy about certain basic physics concepts. The result of too much righteous indignation about the education system in this country. Sometimes I drop into lecturer mode and make a nuisance of myself.

This forum has taught me no end of new applications for old physics. Downright fascinating. I hope to understand more than 1/3 of it someday.

Makes me want to defend it from misinformation, sometimes. I've noticed it has the same effect on others, too.

 

[mwk1000]

When I was planning a pond outside I looked into spray on polyUrea a material similar to truck bed liner. I was pretty neat in that you just needed a smooth surface and it made a very durable and elastic covering. It is being used in many comercial tank resurfacing projects. You can have someone from the pond industry do the spray. For a 1000-2000 gal tank the cost might be reasonable, It was a bit high for my 40x60 pond so I did EDPM.

I was not as concerned since I am doing well at 170-100 range with my tank. I will reline it at the first sign of moisture, it is not that hard to do.

You might check on the temperature tolerance for PolyUrea as a possible DIY liner sprayed right on wood, insulation, concrete, whatever. I know it is health enough for KOI fish ( and they are pretty picky critters )

Google polyurea and you will get a bunch of data. Might be worth looking at as the application systems are becoming much more DIY frendly.

Update, I looked and while some are only rated for 175 * F there are others rated to 250* F "Polyshield HT" was one I found with a high temp rating.

 

[Fred61]

I talked to the people at Herculiner, the do-it-yourself bedliner and they gave me a maximum high temp rating of 230*. They did specify "water only" no chemicals. Im considering coating a 500 gallon steel tank with it.

 

[mwk1000]

Interesting since one of the things particularly good about polyurea is its resistance to chemicals, However many of the bed liner products are not polyurea. Not sure about Herculiner. You can probably get the material saftey sheet for it and get more detail.

 

[Fred61]

Perhaps it's the rubber chips suspended in the material or perhaps chemicals-OK --- heat-OK but chemicals and heat-NO.

 

[free75degrees]

I used herculiner in my truck and it sucks. It dries out and gets all powdery and if you brush against it you get black crap on you. And it is wearing down to nothing in some spots now. Maybe this is due to the sun, but i would never buy it for a truck again.

 

[Rory]

The top of my tank's 170 right now, so I decided not to stoke.

 

[peakbagger]

I used to have flat industrial roofs done on occasion and over the years, I switched over to white PVC as the EPDM didnt seem to last in a pulp mill environment. Plus the white PVC kept the temp in the buildings a little lower as it reflected heat in the summer. The roofer that did the work brought it over in rolls and heat bonded the seams, with a pretty simple resistance heating device (basically an electrically heated roller). He used an IR thermometer to check the temp on occasion and would do test strips every few rolls. When a load was applied to the strips, the material would fail rather the joint. A similiar product was used on an "inside out" roofing system for specialized applications over heated damp processes (like papermachines) where the roof temps could exceed 140F. The PVC was laid down directly on the roof decking and then heat welded to roof drains, then insulation blocks topped with concrete were set on top of the roof. The roof systems had a 20 year guarantee.

This leads me to believe that a PVC liner would work and if you find the right roofer, he might be able to make you up a liner fairly quickly. Its been several years but Gracie Roofing out of St Johnsbury VT was the one that did the roof work.

 

[tom in maine]

We use high temperature PVC for our liners that is custom made for us. Many vendors tell me that their material, PVC, PVC alloys and the like with stand up to 180+F.
I would be very careful trying to use roofing material in a tank environment. A roof that is occasionally wet and occasionally hot is a lot different than a tank that is up to temp every day during the heating season. Welds also have to withstand a lot more pressure than some simple ponding that occurs on a flat roof or a parapet.
Liner welding is more of an art for liners than it is for roofing!

That being said, we have researched materials for over 30 years trying to find the most appropriate material for this application and for solar tank applications.

One bit of advice, being the first one to use something new for a tank liner carries the potential for leaks. That is from experience. Expensive experience.
The reward might be great, but the failure sucks.

If you want to use a readily available liner, EPDM is a reasonable DIY material. Use 60 mil. And treat the water regularly since EPDM does do funny things to water over time.

 

[mwk1000]

Treat the water with what ? That is something that has been on my mind since I will have to do something soon.

 

[tom in maine]

To be honest with you, I am not sure.(I want to say baking soda, but that is from the foggy recesses of my memory!) I believe the pH needs to be a little basic. I am sure others here know better than I.
We do not use EPDM for our products.

 

[flyingcow]

Treat the water with what ? That is something that has been on my mind since I will have to do something soon.

while researching what i wanted for a heat system, I talked to STSS that supplies the epdm lined tanks for tarm, and it was mentioned to check water for ph. At least I think that was it. Contact STSS.