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Home Brew Forums > Home Brewing Beer > Equipment/Sanitation > Temp Controller Can't Read Air Temperature
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Old 07-12-2013, 02:06 PM   #11
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Your controller is likely reading just fine. It is not surprising that it indicates an air temperature far different than the beer. The air and liquid temperatures will only read the same during two points in the cooling cycle. Once while the compressor is on and the air temperature is falling and once while the compressor is off and the air temperature is rising.

The air in the keezer has very little thermal mass, which is basically its heat retaining capacity. The kegs have a very large thermal mass. When the compressor cycles on, the air loses heat quickly and the temperature drops quickly to the setpoint. However, during this same time, the kegs lose heat very slowly and the liquid temperature only drops a small amount.

Air temperature in a keezer has widely varying temperatures during cycling as well as temperature stratification if inadequate air movement exists. IMO, if you want to control the temperature of the beer, then monitor the temperature of the beer.

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Old 07-12-2013, 04:11 PM   #12
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Another interesting thing I found this morning: I had taped the probe to the keg last night and lowered the temperature to 40 degrees. THis morning I poured a small beer and it was 57 degrees. The second one was 40 degrees. Apparently even when the kegs are at 40 degrees, the air temp in the keezer is close to 60 and is warming the beer in me lines. Strange. I figured if the keezer was cold enough to keep my kegs at 40 that it would keep my beer lines cold too.

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Old 07-12-2013, 04:15 PM   #13
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Quote:
Originally Posted by raouliii View Post
Air temperature in a keezer has widely varying temperatures during cycling as well as temperature stratification if inadequate air movement exists. IMO, if you want to control the temperature of the beer, then monitor the temperature of the beer.
That makes sense if the probe is reading beer temp. The air would fluctuate widely to get the beer to cool just a little bit. It doesn't explain a wide air temp range when the probe was just hanging in the keezer. If the temp range of the air fluctuated, wouldn't the probe read this? By reading the air temp with the controller, I was trying to keep the air at the constant temp. It would take longer to get the kegs cold, but it would maintain the entire system at my desired temp.
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Old 07-12-2013, 07:21 PM   #14
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Attached is a data log I made in my fermentation chamber of the temp beer in a fermenting bucket vs. the air temp in the chamber..

The temp in the beer was an immersion probe directly into the center of the beer and the air temp was taken by an exposed junction probe. Both the immersion probe and the air probe are/were Type K thermocouples.

You can see the (approximately) sawtooth pattern of one trace which is the air temp in the chamber. The air temp rises and falls closely approximating the H and L setpoints of the controller. The controller was actually connected to a third exposed junction thermocouple co-located with the one reporting the temp to the data logger. All three thermocouples were checked against each other for consistency and equivalency of temperature readings.

The gently sloping trace is the immersion probe showing the beer temp gradually dropping into the swing range of the H and L setpoints. When this all stabilized the beer temp was essentially dead center of the swing range. Also note that as the beer temp got lower the time between cycles (the sawtooth pattern of the air temp) got longer/wider. Based on the downward slope of the sawtooths, the time the compressor ran stayed fairly consistent (slightly shorter towards end) as one might expect because the air cools fairly quickly but the time between cycles was longer due to the mass of cooling beer keeping the air cooler for a longer period of time.

What H and L setpoints are you using in the controller?

Do you have the temp control on the keezer set as cold as it will go?

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Old 07-12-2013, 07:37 PM   #15
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Quote:
Originally Posted by raouliii View Post
Air temperature in a keezer has widely varying temperatures during cycling as well as temperature stratification if inadequate air movement exists.
I agree to some degree, but wouldn't you expect the temp (at least at the point where the sensor is) to remain essentially within the H and L setpoints of the controller? I would.

IOW, with the probe in the air and the controller set to say 45F, with +/-5F, the probe should pretty much always be returning something within the range of 40-50F. May get some swings slightly lower or higher, but I'd think not too much.
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Old 07-12-2013, 07:59 PM   #16
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Quote:
Originally Posted by whoaru99 View Post
I agree to some degree, but wouldn't you expect the temp (at least at the point where the sensor is) to remain essentially within the H and L setpoints of the controller? I would.

IOW, with the probe in the air and the controller set to say 45F, with +/-5F, the probe should pretty much always be returning something within the range of 40-50F. May get some swings slightly lower or higher, but I'd think not too much.
That's what I would think. The kegs have been in the keezer for over 3 weeks, so they should be within the range of the H and L of my controller. Your chart is exactly what I would expect. I wouldn't expect the beer temperature line to stay above the zig-zag pattern of my controller for 3 weeks.
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Old 07-13-2013, 12:18 AM   #17
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Quote:
Originally Posted by whoaru99 View Post
I agree to some degree, but wouldn't you expect the temp (at least at the point where the sensor is) to remain essentially within the H and L setpoints of the controller? I would.

IOW, with the probe in the air and the controller set to say 45F, with +/-5F, the probe should pretty much always be returning something within the range of 40-50F. May get some swings slightly lower or higher, but I'd think not too much.
I would agree as well, unless a compressor delay is allowing the temperature to rise above H. Air warms and cools very fast and H may be reached before a long compressor delay has timed out.

OP: does your controller have settings other than H and L? Like a compressor delay? Do you use a fan to stir the air up in the keezer? Is it an actual converted freezer or some other kind of unit?
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