Thursday, November 4, 2010

The Fermentation Chamber Finale, the fruits of labor

After countless hours of test-fitting, cutting, sanding, bending and tweaking the Fermentation Chiller Phase IV is complete.  When I last wrote about this, I showed the internal construction and what it looked like with no front on it.

IMG_0149[1]I calculated what I wanted needed for door sizes and built the internal bracing to hold the doors first.  This was purposely left as hollow channels for running power and signal cables.  After running power to two outlet boxes that face the inside of the chamber, I also wired a light switch that controls the internal lighting.  The bracing is constructed of 3/4” plywood that is 3 1/2” wide so that it is the same dimensions as the 2x4 construction of the outer walls with half of the thickness to allow more internal space in the channels.  Everything was still a tight fit.IMG_0161[1]

The next step was to add door frames to improve the sealing edge around the doors.  I can’t afford to cool my entire garage in the summer.  I used pine 1x2 to frame around all the door openings.  The first piece can be seen in the photo below, lower left corner.  This was then coated in spar varnish just in case something sprayed liquid all over the inside.  I hope this never happens, but best to be prepared. 

IMG_0151[2]The doors were each constructed to fit each opening (inside the 1x2 frames) as there were slight variances in each opening.  Even though the two top doors were intended to be the same size, when you are trying to keep tolerances as low as possible to keep the cold air in the box, a 32nd of an inch (1 mm) matters.  The doors were framed from the same 3/4” x 3 1/2” plywood strips intended to keep all framing to the same dimensions (a 2x4 isn’t really 2” x 4”, it’s 1 1/2” x 3 1/2”).  Then I used the same pine 1x2 to provide a mating edge to the door frames built previously.  The frames were then skinned using the 5mm plywood thatIMG_0235[1] covers the rest of the box, but not before filling them with insulation.  In hind sight I should have built better door handles into the doors and I may have to come up with an alternative solution.  Once each of the doors was fitted, I added foam rubber insulation to the mating surfaces of the door frames.

With the doors fitted and functional I was ready to fire the box up and see if I could chill it down to the magical 65 degrees F that I needed for fermenting ales.  After it ran for several hours it had dropped from an internal temperature of 88 degrees to 86 degrees.  Hmm, not what I was hoping for.  I realized that the compressor for the mini-fridge I had cannibalized to cool this thing was going into thermal overload and shutting down.  The compressor was heating up because it couldn’t exchange enough heat from inside the box to outside.  It was the little engine that couldn’t.  I even spent several hours building an elaborate heat exchanger with a box fan for the external coils.  They were no IMG_0237[1]longer hot to the touch and the low pressure line was building up frost on it.  The chiller coils were even building up ice on them, but it just wasn’t enough.  Either the box had to shrink or the cooling engine had to get bigger.  I certainly was not going to start over on the box.  I knew I would quickly run out of space inside it and I had built it as big as I could for the space I had available.  There was only one option.  I drove to Home Depot and bought a $99 window air conditioning unit, ripped out the mini-fridge compressor and elaborate exchanger coil with $100 of copper soldered to it and resized the opening in the back to fit the window unit.  Less than 4 hours of work, start to finish.  The cheezy framing around it will have to do for now.  I had to compromise between and exact fit and trying to work through framed door openings now.  This picture (at left) doesn’t show the capabilities tooIMG_0199[1] well as the difference in temperature from inside to outside is minimal.  This one at right is more dramatic in that the temperature in the garage is 94.7 and the temperature in the box is 62.  With the season changing in November, I had to do some rewiring and add a space heater to ensure that the temperature doesn’t drop below 65 F.  I have another Johnson Controls A419 on the way to manage the heating more precisely.  For now the “temp” knob on the heater is a failsafe.  The recently written about Strapping Numpty is currently fermenting away at a nice even 68 degrees and the not so written about Amber Waves American Wheat was just fermented and conditioned in there so the box has been in service for at least 6 weeks as of today.  I have an old IMG_0234[1]laptop with a webcam in the box as well connected to my home network and publishing images every 15 seconds to a web page.  Unfortunately, the wireless doesn’t work very reliably to the inside of the box so I’m not publishing that for anyone else to see yet.  I have a spool of cat-5 cable in the garage so  may wire it to the network to improve the reliability.  Just in case you want to watch stuff ferment.  I had put it in there so I could remotely monitor the temperature, but the resolution isn’t high enough to see the numbers on the thermometer.  This was a long, 6 month project that if I was independently wealthy, I would have just bought a commercial, glass front, display cooler.  But, I’m relegated to the do it yourself cheap way.  I’m just happy with the results.


  1. I love your design but was wondering what is the lowest temp you were able to drive to? I just acquired an old Continental 3 door refrigerator and wanted to fit a A/C unit to it since the original ceiling mount compressor stopped working. I already have a re-purposed fridge I use as a fermentation chamber but am running out of keg space. Anyway I would be interested in knowing what is the lowest temp achieved?


    1. Depends on your ambient temperature. This was in my garage where ambient temps could get as low as 34 deg F and as high as 110. Another interesting "variable" is the relative humidity. The more humidity in the air the harder it is to cool it.

      As a practical example, the temp in my garage was often 85 deg F with 85% relative humidity in the summer (gotta love Houston). In this scenario, it was difficult to get below 58 degrees without the coil freezing. That was with one of the squirrel cage fans blowing directly on the coil to keep it from freezing. Without the extra airflow 62 degrees was a challenge. This worked okay for most ale fermentation.

      Now, if I lived in a dryer climate, I suspect achieving temps below 40 would be attainable and have read of others able to do that without issue.

      Another concern for me, is that given the outside temps of 85 degrees for extended periods the water used for chilling wort was around 85 as well and the fermentation chamber had to pull double duty of cooling the wort further before stabilizing at 64-65 degrees for pitching yeast. This could take a great deal of time to accomplish this cooling chore.

      Finally, the straw that spelled the demise of this project was the blasted humidity. It eventually caused mold to grow everywhere, even in what I thought were sealed panels. It got so bad that I could see mold staining the opposite side of the plywood. Hence the Failed Experiments post.