Reefer Insulation and Thermal Bridging

[jpendoley]

Hi Folks,
In the middle of a reefer rebuild and have an engineering question about heat loss. I can't afford to re-insulate with any of the exotics (Aerogels or VIPS) so I thought to use Tuff-R insulation a poyisocyanurate that is foil faced on both sides. I did this because its R value is 13.5 per 2" vs a R10 for 2" of the blueboard (now pink). I'm layering it to a depth of 4" for a theoretical R of 26 vs 20 for pink board. Because it is somewhat less water resistant than pink board, I taped the cut edges with foil tape to act as a vapor barrier.
Someone suggested that the tape will bridge the foil faces and create a thermal bridge resulting in a lot of heat loss. Does that sound likely? The foil facing on the foam is very thin....I am at a point where I could change materials with realtively little effort and cost. Its a big box 9 cubic feet or so.
Engineers chime in please!.

[a64pilot]

A thermal bridge that results in heat loss?
I thought the whole idea of the foil was to reflect heat, and the ideal would be an unbroken layer, that having it broken would result in heat loss?

Having it absorb moisture would be the way to lose heat, I think.

Course I could be completely misunderstanding

OK, reread it, the edges, that get placed against each other. I thought you were saying you taped the joints on one face after putting it together.
While I doubt the thermal bridge concept, it might I guess depending on the conductivity of the foil, which could be Mylar?
If the foam is at all capable of absorbing moisture, I'd do my best to seal it, maybe RTV on the edges?

[Stu Jackson]

Nope, not an issue. They butt insulation panels together all the time in buildings. As long as there's no big air gap, not an issue. You're getting a lotta smoke from your friend.

Taping the edges is not a vapor barrier, it seems like you're just trying to keep the edges intact. A vapor barrier is essentially/simply a sheet of plastic over the entire surface of the insulation to keep moisture migrating from one side of the insulation to the other.

[jpendoley]

This foam has foil on both faces. I think one side is meant as a radiant surface and vapor barrier, the other side (less shiny) is just there to protect the fragile foam and protect against vapor ingress. I taped the edges after they were cut to shape to both protect the edge and protect against moisture. My concern is that the foil faces would be bridged by the aluminum tape-come in contact with the next layer of similary edged foam and create a thermal bridge.

[a64pilot]

Stu, He has applied tape over the edges and is thinking he has now thermally connected the front and rear face of the foam and is wondering if he has now given heat a path around the foam if I understand

[Stu Jackson]

a64, I agree, but still NOT an issue. The insulation is the stuff in between and the area of "touching" is minuscule and not germaine, he's only connecting the two NON insulating property covers.

[a64pilot]

I don't think it's much of an issue myself, but if this foam can absorb moisture, it will and I think that is the bigger problem cause wet insualtion isn't much of an insulator anymore. I don't know how well you can really seal it out

[senormechanico]

That insulation is great until it absorbs water, which it eventually will.
I went through a fridge rebuild with it about 12 years ago, then again about 5 years ago with Aerogel after the water got to the polyisocyanurate Thermax.
The Thermax was mostly wet up to about 1/4 of the way from the bottom on the walls and the bottom was saturated.

Just do it with blue or pink board or Aerogel. If you use Thermax, you're treading on thin ice.

[jpendoley]

Senor,
Thanks for the first hand experience. Thermax is Tuff_R by a different name. 4" equals R27 vs R 20 for Blueboard. They say its moisture resistant and I had planned on encapsulating in 10 mil plastic. Does everyone believe no matter what, moisture will get through a vapor barrier? Figured I'd wrap it and tape the plastic down all around....

[sailorchic34]

Short answer: not a measurable issue.

Long answer: In theory the friend is correct. But the tape is probably 0.002" thick or less. Allow for 100 linear feet and its a total of 0.2 inch or roughly 0.0167 sf of surface area. Still not a measurable issue.

[chris mac]

If that is the same insulation I'm using for residential siding(iko enerfoil is the brand I'm using) then the rated r value is on the actual insulation. The foil facing does reflect heat or cold but can't be rated as an r value (at least here). Taping the seams works more to limit air transmission.
I'm not an engineer by any means, but in my experience a thermal bridge needs a non insulating product spanning through the insulation. Like studs in an insulated wall. The tape will not be doing anything like that.
And yes It can absorb water so I would make sure it has the ability to drain as well.

[jpendoley]

Thanks SailorChic and Chris. I'm now more concerned about water intrusion than thermal bridging.

[a64pilot]

I believe that boats are most often in high humidity environments, and things that are cold condense water on them.
So my belief is that yes, if it can absorb moisture, it will. How much I do not know, but enough to seriously degrade it's insulating value, yes. All it takes is very slight damage to that foil skin?

[a64pilot]

Originally Posted by jpendoley

Thanks SailorChic and Chris. I'm now more concerned about water intrusion than thermal bridging.

That is the way it always is here, you ask a question and you will get completely opposing views, and sometime they are both right.

[jpendoley]

a64-better to find out now than after I have it all buttoned up. I don't think the foil would be damaged once the panels are in place and secured. The moisture travels from the outside of the box in from my understanding-from a warm environment to cool like fog on a mirror-which is why I was going to use 10 mil wrap-the foil was just an extra barrier. How well sealed I could make it would be a question, that and the panels are vertical on the walls only so they could theoretically drain too. The floor is blueboard (pink board 0 and much more moisture resistant from what I hear.