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-   -   keezer temp probe? (http://www.homebrewtalk.com/f35/keezer-temp-probe-341764/)

brewQC 07-16-2012 11:43 AM

keezer temp probe?
 
Over the weekend I finally 'finished' my keezer. It only seems to keep the temperature between the setpoint and differential of the temp controller for about 10 minutes, then it cycles back on. Is the temp probe supposed to be submersed in water or dangling in air? It seems like you'd want it to not read just the air temp since that would change faster.

I have a johnson digital temp controller with the probe taped to a water bottle on the compressor 'hump' with the setpoint at 40, 3 degree differential and a 8 minute anti-short cycle delay.

Taking suggestions from threads about this I already insulated the collar with 3/4 blue foam insulation, and have a computer fan mounted to some L-brackets drilled into the collar. The wood collar is a little cooler than the freezer body, the lid is by far the coldest outside part.

carlisle_bob 07-16-2012 12:20 PM

Hi

Try taping it to the wall of the freezer about half way between the top and bottom of the wall. Bump the differential up to about 8 degrees. You indeed do not want it hanging in air. A "large" differential on the wall still means a small differential in the keg since the keg averages out the temperature swings.

If it's a small freezer, the freezer is empty, and the room is warm, it will cycle a bit. Even more so if one of more sides has poor airflow.

Bob

brewQC 07-16-2012 12:37 PM

Hi, Thanks for the reply! I'll try that out tonight when I can sit around and monitor the temp/times. What would be a good amount of running time vs not-running time?

bucfanmike 07-16-2012 01:58 PM

i have found the best results for me was taping it to the side of one of my kegs. The large volume of the kegs doesnt fluctuate like the air temp, and besides its measuring the temp of the beer which is what i want to control anyway.

raouliii 07-16-2012 02:18 PM

I would recommend attaching the probe to one of the kegs under some insulation. Monitoring the temperature using an item with a large thermal mass is the best way to control the temperatures. It helps even out fluctuations caused by door opening and temperature stratification. And isn't it the beer temperature that we're trying to control in the first place?

I would think attaching the probe to the freezer wall would result in very short cooling cycles if directly adjacent to a cooling coil. Using the temperature differential to then average out the beer temperature, while it may work, seems like a round-about way of temperature control when a more direct method can be used.

carlisle_bob 07-17-2012 11:34 AM

Hi

The idea is to control the temperature *before* it hts your beer. The keg will indeed average the temperature out, but that's not what you want in a controller. You want the control loop to respond quickly to changes and to "control" them out. Put another way, you don't want the beer to change temperature at all.

If you put the probe about half way down the wall, you are well away from any cooling coils on normal freezers. The cycle rate is actualy a bit slower than the originaly designed cycle rate on the freezer.

Bob

raouliii 07-17-2012 03:08 PM

Quote:

Originally Posted by carlisle_bob (Post 4257469)
....The idea is to control the temperature *before* it h(i)ts your beer.....

This might be YOUR idea but it certainly is not THE idea, based on the majority of posts I have read on this forum.

To control the temperature of the beer, which IS our ultimate goal, one can use an indirect or direct method. While boths methods can work, the majority of posts here seem to recommend a direct method. A direct method is generally simpler, consistent, and safer.

That being said, many commercial coolers use an indirect method of temperature control of their contents. My stock TRUE GDM-12 corny cooler uses an indirect method but with a well engineered process. Probe placement is fixed and thermostat cut-in and cut-out is fixed to a specific range. It is designed as a refrigerator with alternating cooling/defrost cycles and works very well.

carlisle_bob 07-18-2012 11:43 AM

Quote:

Originally Posted by raouliii (Post 4257884)
This might be YOUR idea but it certainly is not THE idea, based on the majority of posts I have read on this forum.

To control the temperature of the beer, which IS our ultimate goal, one can use an indirect or direct method. While boths methods can work, the majority of posts here seem to recommend a direct method. A direct method is generally simpler, consistent, and safer.

That being said, many commercial coolers use an indirect method of temperature control of their contents. My stock TRUE GDM-12 corny cooler uses an indirect method but with a well engineered process. Probe placement is fixed and thermostat cut-in and cut-out is fixed to a specific range. It is designed as a refrigerator with alternating cooling/defrost cycles and works very well.

Hi

If you tape the probe to a keg, and then swap around kegs, your controll point is going to change every time you do anything. Regardless of where the controll point is, you *will* need to calibrate things. That calibration will only be valid for a single control location. Why do it the hard way? There is 100+ years of engineering experiance out there on how to do this...

Bob

cwi 07-18-2012 04:06 PM

Quote:

Originally Posted by carlisle_bob (Post 4254879)
Hi

Try taping it to the wall of the freezer about half way between the top and bottom of the wall. Bump the differential up to about 8 degrees. You indeed do not want it hanging in air. A "large" differential on the wall still means a small differential in the keg since the keg averages out the temperature swings.

If it's a small freezer, the freezer is empty, and the room is warm, it will cycle a bit. Even more so if one of more sides has poor airflow.

Bob

Are you really recommending this approach, again?
Putting the probe on a chest freezer wall, or recommending it, is idiotic.
All freezers are different, and which wall chills first is different- and it complicates things because you aren't monitoring what you are trying to keep cold: the beer.

Put the probe underneath some insulation on whatever is the smallest thermal mass you are going to have in the keezer- a bottle or a keg. This will prevent freezing of small things. For kegs, a gallon jug is a good enough if you don't want to deal with swapping the probe between kegs.

cwi 07-18-2012 04:18 PM

Quote:

Originally Posted by carlisle_bob (Post 4257469)
Hi

The idea is to control the temperature *before* it hts your beer. The keg will indeed average the temperature out, but that's not what you want in a controller. You want the control loop to respond quickly to changes and to "control" them out. Put another way, you don't want the beer to change temperature at all.

If you put the probe about half way down the wall, you are well away from any cooling coils on normal freezers. The cycle rate is actualy a bit slower than the originaly designed cycle rate on the freezer.

Bob

The idea is to not have to monkey around finding out where the cooling coils are so you don't tape near one or where the ones that get cold first are. Also, not to have to spend days figuring out what magical temp and differential setting will keep you beer at the actual temp you want.
Just put the probe on the actual beer, or some facsimile, then insulate over the probe.

The differential on most controllers is adjustable down to .5F. That is more than sufficient.

Your 'control loop' doesn't even include the beer temp, unless you count yourself constantly monitoring the beer to determine how much to adjust the controller temp or differential of the cooling coils to get the beer temp you want.

Most people buy a controller to do the controlling, and don't want to put out a bunch of effort to maintain temps, which is why they bought a controller.


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