Will my chest freezer balance out?

Hey all,

I'm geared up for brew day this Sunday and wanted to plug my new Johnson Control (the blue digital A419 model) into my new chest freezer (fermentation chamber). I set the temperature I wanted with a differential of 3 degrees. The freezer kicked on and I came back later to find the Johnson Control shut off, but my freezer was about 15 degrees below my target!

I have the temperature probe hanging from the freezer basket so the probe isn't touching the wall or anything. It's literally in the middle of the air of the freezer. Has anybody else seen this? Is this just a symptom of the first "boot up" of the cooling lines and it will balance out, or is there something else I'm missing?

Thanks everybody,
A.J.

 

I suspect because the freezer is totally empty that the expansion coil had enough "inertia" to keep dropping the air temperature even after the controller shut off the compressor. I would expect that behavior to continue until you start putting some thermal mass inside...

Cheers!

 

Thanks for the response. Anybody else seen the same thing he's mentioning when their freezer is empty?

 

You did plug the freezer into the controller, right?

 

Yep, the freezer is plugged into the controller. The controller did shut the freezer off, but it's like the coldness of the lines continued to cool the air past my setting.

 

It's going to do that unless you add a heat source to compensate (unless you can program the controller to shut off the freezer a few degrees before your target). You've got a large cold mass (the freezer walls) cooling the interior and when the compressor shuts off, that mass still has sufficient thermal energy to continue reducing temperature (and it will until an equilibrium point is found). Even with a carboy or two in there you will get an overshoot if the thermostat cuts the power at the exact temperature set and there is no heat source to compensate.

 

So do a lot of people around here with fermentation chambers and keezers tend to use a heat source?

 

i'm assuming he means a heat source as a room temperature keg that will still need to get cold.. once it has gone through a couple cycles it won't need to turn on as long to keep it cool and there won't be as much of an effect with the sidewalls

 

Definitely get more thermal mass in there! Once you have a fermenter in there (if it's a larger freezer, a 5-gallon bucket of water in addition wouldn't be a bad idea) then you'll see significantly less overrun.

In my fermentation chamber (built on a dorm fridge, admittedly not a freezer!) I seem maybe a half degree overshoot. There really shouldn't be a need to get a heat source in there, unless the ambient temperature outside your fermenter drops much below your desired temp...

Also - once you get a fermenter in there, make sure to affix the temperature probe to the side of your fermenter. You're more concerned with the wort temperature than you are with ambient temps, and unless you've got a thermowell, sticking the probe to the side of your fermenter is the best way to get those temps.

 

Thanks for all the info everybody. I guess I'll have to see how it goes after putting a fermenter in it this weekend. I'm just a little nervous about putting it in a fermentation chamber that was overshooting my temp by 10+ degrees. But this may be one of those RDWHAHB situations!

 

How did this work out for you?

I have the same controller and the same problem, though the swings aren't as drastic. For example, the other day I set it to 65F with a 1 deg differential. It cut off at 64F as expected but then overshot down to 59F. That was with a full 6.5 gallon carboy in there and the probe hanging in the air.

The problem (like the other guys said) is that the momentum from the cold walls keeps bringing down the temperature. This is also the reason I don't tape the probe to the fermenter. It takes a lot of work for the chest freezer to bring 6 gallons of actively fermenting beer down to 65F that by the time the beer gets there, the freezer is so damn cold that the beer temp keeps dropping. I've had stuck fermentations because of this.

To monitor the beer temp, I use a 6 foot k-type thermocouple taped to the fermenter & digital reader, then adjust the controller accordingly. It's a more manual process than I would like but it works.

 

This worked out great. Once I got the fermenter in there, I actually ended up taping the temperature probe to the side with styrofoam around it to act as insulation. You're right, it did take awhile to bring the beer down to temp. But after that, it stayed within my temperature range and didn't continue to cool beyond that. I only have a 5 cu. ft. freezer, so maybe it's not powerful enough to continue cooling 5 gallons of beer after shutting off.

 

Good to hear. I think you're right about the size. Mine is ~ 10 cu. ft. which is a lot more cooling capacity. Might switch to a smaller one if I can find it cheap.

 

I have a 7.2 cu.ft. freezer and an anolog controler from Thompson. I have it set for 60* and w/4 two gallon buckets inside the temp on those stick on tape thermometers read about 67*