Air vs insulation for Ale cold conditioner

[JOHNSMITH59]

I am planning to build a no-electric "passive" cold conditioner for beer brewing with the concept being maintaining a keg at 40-50F by periodic replacement (every few days?) of a portion of the water surrounding the keg with ice. I have attached a sketch of two options...one using insulation board (two layers, each at 4" thick and R26) and the other using just air. I would endeavour to seal the air cavity option to prevent outside air intrusion.

Which option do you think provides better insulation? Would the air cavity geometry (the height of the cavity would be 26") be such that significant convection woukd occur making it less effective than the insulation board? Perhaps a comprimise between the two...2" air cavity plus 2" insulation board?

 

[LittleInch]

http://new-learn.info/packages/clea..._fabric/elements/cavities_and_air_spaces.html

Basically any air gap> 50mm is suspect.

Why not use rock wool?

Also think about using freezer blocks instead of ice. Much easier to swap out.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JOHNSMITH59]

The insulation I plan to use (from Home Depot) is 2 inch thick 4'x8' "Super Tuff-R" which has an R-value of 13 (it is closed-cell foam). So two of those gets me R-26, plus the foam board rigidity is a plus for what I am doing. The rock wool looks to be about R-15 for 3-1/2.

I might have to stick with ice cubes as the space around the "side" of the keg is small and there won't be much room on top for a block...still designing though. I am hoping one water/ice swap (approx 2 qts) will last me a few days...the beer (5 gallons) temp is to stay between 40-50F and the room ambient could swing up to 80-85F in summer.

This rube-goldberg is the price I pay for not having room for a fridge and being cheap and being an enginerd

 

[LittleInch]

Just remember the brewing process emits heat so too little water might not work. Others seem to use bath tubs.

https://byo.com/bock/item/1869-controlling-fermentation-temperature-techniques

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[chicopee]

If you could evacuate the air space, the radiation heat transfer would be the required evaluation within a vacuum space.

 

[JOHNSMITH59]

No worries on fermentation heat - this is strictly for cold conditioning and fermentation will be done (i.e. Secondary).

A vacuum...whew, nice thought but too complicated for my build