Unpressurized Storage Evaporation

[Rory]

Although I built my storage tank, I contracted out the plumbing and wasn't home the day the coils went in and the lid sections went on. Consequently, the plan to spray a layer of foam for the lid to set on wasn't executed, and I haven't sealed the seams between the lid sections. In the 8 or 9 weeks since I went live, I lost about 3 or 4 inches from the 4x8 tank I built. Thankfully, my plumber installed a threaded faucet right where the DHW exits the tank, so refilling is easy. I wonder, though, if there's a risk of building up scale or something from replacement water, and if I shouldn't make a summertime project of reseating and sealing the lid sections.

 

[tom in maine]

No likelihood of scale, but you need to seal it well. We use neutral cure silicone caulk. That amount of water loss is extreme.
Remember that water is leaking into your house and will probably wind up in the attic, where it can condense if the attic is not sealed well and properly ventilated.

It's a lot easier to seal the tank well.

 

[Duetech]

Rory,
In another thread here and in some of the European sites I have visited I found they use a pound or two of paraffin on the top of the water to prevent evaporation even in outside tank installations and they rarely see much evaporation.

 

[Rory]

Thanks for the responses. We regularly humidify the air during the winter, so putting a little moisture in the air wouldn't seem to be a problem. However, after stabilizing the pH, it seems like you'd want to seal the tank and be done with it for a good slice of time.

 

[NHFarmer]

I added 2lbs. of paraffin as suggested by Nofossil. It forms a layer on the top and I have had very little evaporation

 

[tom in maine]

I would be concerned about damage to the liner. Sealing the cover is not rocket science. People have done it for years with silicone with very good results.
This would void our warranty and I assume it would with anyone using EPDM that does not have a DIY tank.

Tom
www.americansolartechnics.com

 

[Rory]

This is exactly what I need to hear, stuff like possible damage to the liner. I wasn't aware of that. While it's not rocket science, lifting my lid sections to seat them on a foam layer like I intended would be very difficult with all the plumbing in place, as two sections, including the largest, have pipes passing through them, and I have heat traps that would prevent them from being lifted very far unless I took the piping apart. I could seal the seams with silicone and hope for the best.

I actually rigged a cool hoist on the final section of lid that doesn't have any plumbing going through it, and I sort of hate to lose the ability to lose it and check on things. The paraffin sounds like a great solution.

 

[tom in maine]

I am not sure I made myself clear, paraffin or a layer of oil would void the warranty. I do not think this is a viable solution over proper sealing.

You can try canned foam as a sealant. It is better than nothing.

If you used EPDM and it is out at the edge of the tank, I would simply seal the cover to the liner at the edge. This would be simple to seal.

You can use acetoxy silicone caulk (the vinegar smelling type--not the low odor one), this will not bond as well and can be removed and replaced if the cover is
open.

There should be no reason to get into a tank once it is sealed. There should be an access port for checking the level without opening the tank.

 

[mole]

When I built my tank last fall, I was worried about sealing it, as I had read about peoples' problems water loss and moisture. As I thought about it, I had trouble understanding how you can seal a tank perfectly. I calculated that the water level of my tank rises by roughly 1" when the water is heated from 60F to 170F due to thermal expansion. That means the air in the space above the water level will have to either be displaced(find a way out) or the tank will become pressurized. Then when the water cools, the water will contract and suck some air back in.... So it seems that some "breathing" as the water warms and cools is unavoidable. Rather than trying to fight this process, I sealed the tank very well with silicon, then added a condenser/vent to allow the tank to breathe. It's simply a 10ft coil of 1/2" copper refrigeration tubing attached to my CPVC water level sample port. The coil spirals up sowly from the top of the tank. The idea is that as the moist air rises from the tank, it meets the the cool copper tubing which is kept cool by my 60F basement. Any moisture that wants to get out will be condensed in the long coil and drip back down into the tank. The copper tubing always feels cold to touch, and I have NEVER seen ANY signs of moisture coming from it. Since the tubing is attached to a CPVC pipe which protrudes into the top of the tank, the copper does not draw any noticable heat out of the tank either.

Has anyone else done something like this?

JR

 

[flyingcow]

Rory,
I haven't sealed my cover down yet, haven't seen any noticeable drop in water level yet. But i plan on getting some foam gasket, maybe 2 inches wide and about 1/4 to 1/2 inch thick. No glue on either side of foam, and then screwing the cover down. The screws came with the tank. This was ok'd by the manufacturer of the tank. The tank was supplied with the correct kind of caulk, may still do that if i can't find the gasket material.

I easily put things off, as this should have been done a long time ago.

 

[tom in maine]

Mole, you did it fine.
I am not worried about pressurizing a tank that is sealed too well, it has never happened, it would pop the vent of some part of a seal, if it was too tight. There will always be some leaks, we just need to minimize them.
Your way is a right way!

 

[mole]

Thanks Tom,
It seems to be working great. Just wanted to share it since I haven't heard of anyone else who intentionally vented their tank.
JR