Insulation R-value question

[Belgian Samurai]

Hi,

I would like to build a DIY fermentation chamber like the one documented here on Home Brew Talk, but I have a question or several about some modifications. From what I've gleaned across the internet, the larger the volume of space the mini fridge (4.6 cu. ft. in my case) has to cool for three carboys, the lowest achievable temperatures will not be as low compared to a single carboy inside of a mini fridge. To resolve this issue, or to improve the ambient temperature, better insulation is the key, which brings me to my question: If 1" foam board insulation often has an R-value of R3 to R6, why not use R13 fiberglass wall insulation in the 2x4" framework and as for the liner, use FRP sheets (or silver-faced foam board insulation) for easy beer cleanup? In the scenario of the latter, would that put the R-value at R16-20??

Side note: When I build my version, I will not enclose the fridge, so there will be better heat dissipation.

Thoughts?
Belgian Samurai

 

[NeoBrew]

Both insulations can work. One thing to note about stud walls is that the stud has less insulating value than the fiberglass. To get to equivalent thermal transmission you need to do a composite calculation that figure the whole wall assembly.

A stud wall box is going to be a lot heavier if you ever have to move it.

One other important parameter about efficiency is to ensure that the box is water tight. This is critically important if you are going to do lagers or plan to cold crash. Condensation from warm room air getting into the cool chamber can create condensation of epic proportions.

[edit to correct autocorrect mistake]

 

[day_trippr]

I would go with rigid foam insulation inside a minimalist supporting structure so the R-rating of the structure materials is moot.
A sturdy platform for the vessels surrounded by uber lightweight framing with the foam applied within.
There are 2" foil faced foam panels that are R10 rated or higher, I'd look at those...

Cheers!