Dual-zone fermentation chamber

Thanks to many ideas from this forum and around the web I've completed my fermentation chamber. The original idea came via a Son of Fermentation Chiller, but I wanted to plumb in some old fridge guts instead of having to swap out ice buckets. Well, a few weeks ago someone left a dorm fridge in the office breakroom with a note of "Free or Trash", so I was good to go. I didn't take any pics of the fridge guts removal process, but it was a pretty ugly process... hack saw, tin snips, chisels, hammer, etc, etc. It still cooled when I got it out, so I guess I was gentle enough at the right times.

It's a pretty standard foam box made of glued up Foamular 250. I couldn't find any 1 inch board locally, so I just glued together .5 inch boards. After some trials on the best way of cutting it I arrived at a razor and straight edge as the cleanest method. Cutting about 3/4 of the way through allows you to break off the rest with a pretty clean edge. I wrapped most exposed corners with aluminum tape for some extra durability.

Here's a shot from the outside, with a 5g BB for size reference:


To mount the fridge parts I built a frame of 2x4s screwed to a base piece of plywood, to which the foam box is also glued. I added a cross member to the frame to get the whole compressor assembly to the right height, and it also worked out to the right height and width to mount the condensor using the stock screw holes.



For the inside I built it with two chambers, with each big enough for a 6.5g carboy and blowoff bucket, or two corny kegs. The left chamber as you can see holds the cooling element from the fridge. The divider is removable since I have to slide any left chamber contents in under the cooling element.



The right chamber will be the warmer of the two. Based on ambient temperatures and the temp of the cooling chamber, I'll either be warming the right chamber via a heating pad, or I'll be cooling it with a muffin fan (yet to be installed) to exchange heat with the left chamber. Here it is fermenting with the heating pad. For these shots the cooling chamber was keeping the keg at 45F, and the heating pad keeping the carboy at 68F. I didn't time it closely, but I'd guess the heating pad was running every 30 minutes in this configuration, and about the same for the fridge.



I'm using a Johnson analog controller to control the fridge and left chamber, and a repurposed home thermostat rigged with a remote sensor to control the right chamber. The tstat is switching two 12v/120v relays in the electrical box, either heat or cool, based on whether I'm using the heating pad, or the yet to be installed muffin fan. If I were to do it again, I'd scrap the home tstat and use one of the ebay aquarium controllers, but it seems to be working fine.



I guess that's about it. It's big, pink, and ugly, but it's sitting in an unused storage room, so it's out of sight. It's doing a fine job though, and compared to adjusting space heaters and wet towels in a bathtub it's a dream. The only thing I miss is being able to sit and watch the fermentation churn in the carboy, but being able to "set it and forget it" is worth giving up that little bit of entertainment.

Cheers!

Dude, Nice work. I'm on the fence of doing something like this or looking for a freezer on craigslist. How cold can you get it?

How cold? I'd guess it could hold the left chamber in the mid 30's, but how often the fridge would have to run to maintain that temp, and how much that would affect the right chamber, I don't know. For example, trying to lager a few kegs in the left chamber at 35F, and at the same time ferment at 70F in the right chamber might have both the fridge and the heating pad running quite a bit. It should work, but I don't have any idea on how efficient it would be. I still don't have a good feel for the balance between the left chamber temp, right chamber temp, ambient temp, and heat exchange between the two chambers, but it should just be a question of efficiency.

Nice work. Any reason you made it open from the top instead of the front. Seems like it would be more difficult to lift 50#+ out of something than slide it out the front. Looks like an accident waiting to happen. Good luck, be careful!

I guess I was somewhat imitating a deep freeze, in that a top mounted lid keeps the cold air from spilling out whenever it's opened. That's not much of an argument though, since I don't open it that much, and the thermal mass of the contents would be hardly affected by any lost cold air while open. And you're right, it is a bit unnerving to get a full glass carboy in and out; the weight isn't too terrible, but I hate the idea of supporting all of that weight by the neck. I'll at least be getting some brew hauler straps to support the weight from the bottom. If I were to do it again, I'd seriously consider making it a side-loader.

looks good! nice work.

That thing is awesome. I was thinking of doing the exact same thing with my ferm chamber. Do you have any sort of airflow going from the right side to the left or vise versa? It seems like you would be able to adjust the temp in the right chamber by regulating airflow.

I don't currently have anything actively moving air from side to side. The removable divider is not sealed though, so I've been getting enough cool air leaking to the right side to ferment in the 60's. When summer comes along though, and ambient temperature in that room rises to near 80F, I may need the aformentioned muffin fan hooked up to the home tstat controller in cooling mode to recirculate cool air from the left.

jaydub said:

I don't currently have anything actively moving air from side to side. The removable divider is not sealed though, so I've been getting enough cool air leaking to the right side to ferment in the 60's. When summer comes along though, and ambient temperature in that room rises to near 80F, I may need the aformentioned muffin fan hooked up to the home tstat controller in cooling mode to recirculate cool air from the left.

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did you ever install that muffin fan? I am going to do this exact same thing, except I live in Florida, so i won't ever have to heat one side. I'd like to be able to cool one side to lager temps, and use the other side for 65-70F fermentation.
Just wondering if the cooling from one small dorm fridge is enough for that.