Insulation breakdown?

[Rory]

I have a Tarm Solo 30 that I've used 5 seasons now with a 4' by 4' by 8' unpressurized tank I built. It's a big plywood box lined with EPDM and insulated with two layers of 2" foil faced foam (polyiso, I believe) all around. The lid is in three sections, with 2 layers (4") of the foam glued to plywood and covered with EPDM, plywood side up. Last winter we noticed much more heat than usual in the basement, and yesterday after a DHW burn I confirmed that a lot of heat was bleeding through the plywood in the vicinity of the heat exchanger, though most of the lid and definitely the sides were only room temperature. My conclusion is that the insulation in the lid has simply broken down and needs to be replaced, but I wondered if anyone else has had a similar experience or has any recommendations on a construction technique that will help avoid this problem next time around.

 

[BoilerMan]

Polyiso can take on water, or moisture over time. As we all know water is a great conductor of heat....... Not sure if there is a good way to dry it out, could remove the EPDM and leave it outside in the sun for a few days??? I would use an XPS like blue board on the lid as it will not take on water from the steam above the water.

I am ion no way a pro in this are though, TomInMaine comes to mind!

TS

 

[Fred61]

Right on Boilerman. He now has a wet sponge as insulation.

 

[tom in maine]

Did you use the polyiso as a cover directly over the water?
There should be a layer of plastic or EPDM between the water and the foam. The foam, if exposed to the hot water vapor will saturate.
Don't use styrofoam or EPS for the cover, it will melt. Only use Polyiso.

 

[BoilerMan]

Don't use styrofoam or EPS for the cover, it will melt. Only use Polyiso.

Thats why I said I'm in no way an expert in this area! I stand corrected

TS

 

[Rory]

The only thing contacting steam or water should be the EPDM. The lid is in 3 sections though, and 2 of them, including the problem one, have big sags, probably causing the EPDM to contact the water and possibly even some plumbing. I made the 3rd piece as a removable section and used channel steel on top to secure the rubber and hook my hoist to, and that section has remained nice and level. I think I'll do something similar when I rebuild the other ones.

 

[tom in maine]

I am not sure if I misread the original post or you changed it, but if the EPDM barrier is intact, I would suspect a hole om the EPDM, such as a penetration.
Sounds like you need to rebuild it with new foam, then glue the EPDM to the plywood or foam and caulk any penetrations generously.
If screw holes that hold the cover in place are not sealed from water vapor, they will be a pathway for water to migrate into the covers over time.

Not sure if you need the plywood, but I would avoid using it if there are no structural needs for it.

 

[Rory]

Well, there's penetration where the pipes pass through. We filled the gaps with pipe insulation, but much of that has broken down now. I'm thinking my best bet might be to trim the pipe insulation, seal those openings and the edges, and just apply another layer of insulation on top. It would save cutting and rejoining the pipesl

 

[tom in maine]

That's the problem. If you use these connections, you need to seal them with silicone caulk. Insulation and foam tape will saturate and leak.
Tough to seal from the topside. Good Luck.