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Old 03-25-2012, 04:31 PM   #1
Ryan11
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Default Temperature Control

I'm trying to find the best way to control my temp in my chest freezer for fermentation. I have a temp controller with the probe in a bottle of water. I've noticed that by the time the freezer cools that bottle of water down to the desired temp, the freezer itself is WAY below the temp I want causing that bottle of water to continue cooling going well below the temp I want. Then it takes forever to come back up to my desired temp. This just causes too big of a temp swing. Any ideas on where to put the probe to keep it within a few degrees at all times?

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Old 03-25-2012, 04:38 PM   #2
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What temp controller? Try putting some gallons of water in the freezer so that it is not trying to chill an empty freezer.

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Old 03-25-2012, 04:42 PM   #3
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Different controllers have different thresholds for variances from the target temp. Most of the better ones have the ability to set that threshold. For example your target is 40 degrees, and the threshold is set to +/- 5, then it wouldn't begin to cool again until your temp hits 46, at which point it would have to cool heavily again to get to 40, and would probably undershoot the target temp.

I've set the threshold on mine to 1 degree and it doesn't kick on that often or for that long.

The only time I think I might have that problem is the very first time it cools from room temp to a lower temp. After that it seems to maintain fine. You may want to let it cool to target and maintain for a bit before putting in whatever you are chilling.

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Old 03-25-2012, 04:52 PM   #4
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Is the Johnson A419

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Old 03-25-2012, 05:03 PM   #5
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Badbrew is right. If you're doing this on an empty freezer you're more likely to have swings in temperate if your freezer is empty.

Water has about 4 times the specific heat capacity of air, so the freezer will maintain a regular temp much more easily with a few gallons in there.

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Old 03-25-2012, 05:28 PM   #6
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Quote:
Originally Posted by Ryan11 View Post
Is the Johnson A419
Good easy.

What is SP, DIF, OFF, ASD?

Mine iirc:
SP=38
DIF=5
ASD= 12 minutes
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Old 03-25-2012, 10:21 PM   #7
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Sp-62
dif-1
asd-12

The freezer isn't empty it has a full 5 gal carboy in it

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Old 03-25-2012, 10:34 PM   #8
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The best thing you can do is try to fill up the freezer with as many containers of water as you can fit because water holds heat (and is slower to absorb it) than air. So if the space is filled with water it will hold temperature better. But don't put the probe in a bucket of water to maintain the temp. Otherwise your freezer will run for half an hour to bring the temp down one degree. Measure the air and it may only run for five minutes.

You will probably see as much as a ten degree swing in the air temperature. That's okay. That's the freezer running and filling those coils with cold liquid. Even after the compressor shuts off you're going to see the temperature drop for a few minutes as that freon boils off. There's no way to avoid it. Just figure out what your swing is and try to set it so your target temp is in the middle.

For instance, if your freezer is showing a ten degree drop every time your freezer kicks on, set it five degrees higher than your target temp. So if you're shooting for 65 F, set it to come on at 70 F. Your range will be from 60-70 F for an average of 65.

I also like to put a couple slabs of wood in the bottom for the carboy to rest on just to keep it from direct contact with cold surface of the freezer.

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Old 03-25-2012, 10:36 PM   #9
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tape the probe to the carboy under a few folds of paper towel for insulation and set for desired ferm temp with a small differential and at least 5 min compressor protection. Your air temp might be a little colder but the fermenting vessel will be the right temp.

keep your probe out of water, they are not made to be submerged.

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Old 03-30-2012, 02:30 AM   #10
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Quote:
Originally Posted by cvstrat
Badbrew is right. If you're doing this on an empty freezer you're more likely to have swings in temperate if your freezer is empty.

Water has about 4 times the specific heat capacity of air, so the freezer will maintain a regular temp much more easily with a few gallons in there.
Keep in mind that specific heat capacity is energy per mass. The volumetric heat capacity is probably more relevant in this case. Water has about 3000 times the heat capacity of air in a given volume.
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