Temperature probe location

I have a temperature controller for an extra fridge that we have. I mainly make ales and I have a couple of questions.
1. Should I secure the temp probe to the side of my primary carboy?

2. Should I set the temp controller to the low end or even slightly below the low end of the recommended temps for my yeast to account for the heat being given off?

Thanks

Ideally you would use a thermowell which places the probe down the center of the liquid. With that you can set the temperature on the exact number you desire. Otherwise, tape the probe to the side of the carboy/bucket along the middle with some foam or bubble wrap over it. I would suggest setting the temperature on the bottom value of the recommended range in this scenario.

jeepinjeepin said:

Ideally you would use a thermowell which places the probe down the center of the liquid.

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This may not be a good idea, as you can get some severe oscillation /overshoot in temperature. The body of liquid that is your beer will have a huge thermal mass, and as such a probe in a thermowell will react very slowly to temperature changes.

Example: you put a temperature probe in wort at 70 and want to chill to 65. This could take a couple hours. Until that temperature is reached, your cooling device, perhaps a freezer, will be active. This would cause the compartment to become far colder than you intend.

If you do something like a thermowell, you need a "smarter" PID controller.

My suggestion is to just set the temperature probe near the fermenter (lately I've been placing mine on top of the buckets I've been fermenting in.) This will get you some pretty stable temperatures.

What stephelton says is true. I have five probes logging data. It has always been better to control the temp outside the fermentation vessel. You will get wild swings if you run the controller based on core temp or side of vessel.

It might just be my set up but I have never experienced these "wild swings" with my thermowell. The most my system has ever overshot the set point was 0.5 C and that was only when the initial temperature was far off from the set point. It then rises to the end of the deadban (0.5 C) and turns back on. After its fairly close to the set point, the range is about -0.2 to +0.5 C. I'm just using a simple on/off relay with my fridge.

stephelton said:

This may not be a good idea, as you can get some severe oscillation /overshoot in temperature. The body of liquid that is your beer will have a huge thermal mass, and as such a probe in a thermowell will react very slowly to temperature changes.

Example: you put a temperature probe in wort at 70 and want to chill to 65. This could take a couple hours. Until that temperature is reached, your cooling device, perhaps a freezer, will be active. This would cause the compartment to become far colder than you intend.

If you do something like a thermowell, you need a "smarter" PID controller.

My suggestion is to just set the temperature probe near the fermenter (lately I've been placing mine on top of the buckets I've been fermenting in.) This will get you some pretty stable temperatures.

Click to expand...

The "huge thermal mass" would be slow to change temperature, but the probe being in the center of it would change quickly according to its surroundings.

When making a large temperature change the compartment will be warmer or cooler than the bucket. This doesn't matter though. We are concerned with the temp of the wort not the chamber. It may swing past the desired temperature a few times due to the outside of the bucket being heated or cooled quicker than the wort can conduct the heat all the way through. My suggestion there would be to chill the wort to below yeast pitching temperature and let it warm without a heat source to pitch temp and then pitch the yeast. That should eliminate any temperature swings of any consequence.

He said he has a temperature controller.

pelipen said:

What stephelton says is true. I have five probes logging data. It has always been better to control the temp outside the fermentation vessel. You will get wild swings if you run the controller based on core temp or side of vessel.

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Now this interests me. What is your setup like. Are the five probes on separate vessels? Separate chambers? Airflow?

Sorry, I totally thread-crapped on you. I'll take a stab at your other question:

TnFarmer said:

2. Should I set the temp controller to the low end or even slightly below the low end of the recommended temps for my yeast to account for the heat being given off?

Click to expand...

I usually try to set the setpoint and range/tolerance around the average temperature I want. I've got a Marzen fermenting right now which I wanted to ferment about 51. So I set the setpoint (the point at which the controller deactivates) to 50 and the range (the amount the controller will tolerate before activating) to 2. This means the controller swings from 50 to (50 + 2) which should average close enough to 51.

stephelton said:

If you do something like a thermowell, you need a "smarter" PID controller.

Click to expand...

How would a PID work with a fridge? A PID controller looks at the magnitude of the error, the integral of the error, and/or how fast the error is changing. It then adjusts the output according to the tuning parameters. Fridges are simply on or off so you can't adjust the output.

Ryush806 said:

How would a PID work with a fridge? A PID controller looks at the magnitude of the error, the integral of the error, and/or how fast the error is changing. It then adjusts the output according to the tuning parameters. Fridges are simply on or off so you can't adjust the output.

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PID:

P - proportional - represents the absolute difference between setpoint and actual temp at a given time
I - integral - accumulates as error is not corrected
D - derivative - represents the change in "direction" (are we getting better or worse)

Your output is either on and off, as you say. At any instantaneous point in time, you could be either on or off, but over a period of time, you could potentially be on and off in any combination (on for 5 minutes, off for 5 minutes). A PID controller that I wrote for a fermentation chamber I built a few years ago does just this. The trouble with a compressor (e.g. a freezer / fridge) is that it's duty cycle has a large impact on its lifespan.

However, in my original example, a PID controller could certainly be used to avoid excessive overshoot. The contribution of D (the derivative) is what would allow a PID controller to work in this case.

[oops, sorry for the double post]

I take a lazier approach. My ferm chamber is set to maintain 40F because I have all my kegs in there too. For fermentation I use a simple STC-1000 with the probe in the wort via a thermowell and drive a FermWrap to bring the fermentor up to whatever temp I want it to maintain. I have 4 STC-1000's so I can do lagers and ales side-by-side this way.

stephelton said:

PID:

P - proportional - represents the absolute difference between setpoint and actual temp at a given time
I - integral - accumulates as error is not corrected
D - derivative - represents the change in "direction" (are we getting better or worse)

Your output is either on and off, as you say. At any instantaneous point in time, you could be either on or off, but over a period of time, you could potentially be on and off in any combination (on for 5 minutes, off for 5 minutes). A PID controller that I wrote for a fermentation chamber I built a few years ago does just this. The trouble with a compressor (e.g. a freezer / fridge) is that it's duty cycle has a large impact on its lifespan.

However, in my original example, a PID controller could certainly be used to avoid excessive overshoot. The contribution of D (the derivative) is what would allow a PID controller to work in this case.

Click to expand...

Yeah I guess you could use the "D" to get the fridge to shut off at a certain point so it didn't overshoot if you got the tuning just right. Sounds like a bunch of extra coding and tuning work to me though when a few degrees won't make much of a difference IMHO.

Ryush806 said:

Yeah I guess you could use the "D" to get the fridge to shut off at a certain point so it didn't overshoot if you got the tuning just right. Sounds like a bunch of extra coding and tuning work to me though when a few degrees won't make much of a difference IMHO.

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Earlier I almost added a word of caution against over engineering to make exactly this point

+/- 1 degree has been working perfectly well for me, and my retired fermentation chamber can go down in history as a fun engineering project.

FWIW......Jamil always recommended fastening the probe to the side of the fermentation vessel. That's what he always did when he was homebrewing

teddy4xp said:

FWIW......Jamil always recommended fastening the probe to the side of the fermentation vessel. That's what he always did when he was homebrewing

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I bet if you ask him what he's doing as a professional that he would tell you he uses a thermowell. Maybe several.

Enough with the bickering. I want to see numbers. I'll change how I do it if someone can prove their way is better. Heck, I'll run my chamber on my STC-1000 and get a good PID to cycle a fermwrap to keep temps up if it would make a big enough difference.

jeepinjeepin said:

Enough with the bickering. I want to see numbers. I'll change how I do it if someone can prove their way is better. Heck, I'll run my chamber on my STC-1000 and get a good PID to cycle a fermwrap to keep temps up if it would make a big enough difference.

Click to expand...

Test it yourself

I'll tell you right now it doesn't make a big difference. Keep the ambient temp where you want it and pitch yeast near desired ferm temp and you'll have an awesome fermentation.

Agreed. Much better than no control at all. I recently started temp control in a minifridge and am using a thermowell for the first time on the current batch. Before I was taping it to the side and before that it was a swamp cooler. I've just made the progression that makes sense in my conceptual physics brain.

Do you watch the temperature of the fridge itself as it goes throughout its cycle? You'd almost necessarily get more temp swing with a thermowell than without.

I bungee to the side with styrofoam over it. The reason is that as stephelton says, I'm mainly concerned with the overall ambient temp, but I want the fridge to help counter the temp increase during fermentation, at least a little. I can't keep all ambient temps out of the equation this way, so overshoots are rare. Mostly it's just trying to avoid huge spikes in temp without some counter-cooling.

Thus far I've not had any underattenuating beer or any off flavors to speak of. My sample size is somewhat small, having only controlled about 4 batches this way thus-far.

I'm sure the fridge swings a fair bit. I feel like the wort/beer would swing very little with the probe insulated against the side and less with a thermowell. I wish I had the engineering knowledge or the $$$ to get a 3 probe logger to monitor a fermentation while only one of them affects refrigeration/heating decisions.

TnFarmer- the correct answer is that optimal placement of the temp probe depends on which thermostat you have. You can tape it to the side of the fermenter -- a set-it-and-forget-it situation. But if you have a thermostat with large differential (such as the Johnson analog), you'll get some undesirable big swings in beer temp during fermentation. So this works best if the differential is 0.5F or 1.0F.

So if you have a t'stat with large differential, you'll want to leave it either hanging in the air (or stuck in a glass of water if you're seeing too much compressor cycling). The "Pro" is that you'll get fewer swings in beer temp, but the "Con" is that you have to closely watch and adjust the set point during the first few days of fermentation when you're trying to get the wort cooled and trying to maintain your goal temp.

jeepinjeepin said:

Now this interests me. What is your setup like. Are the five probes on separate vessels? Separate chambers? Airflow?

Click to expand...

Different things at different times. They are constantly logging once per minute. So, sometimes I have ambient, chiller, water bath, keg, etc. just depends what I'm interested in.

jeepinjeepin said:

Enough with the bickering. I want to see numbers. I'll change how I do it if someone can prove their way is better. Heck, I'll run my chamber on my STC-1000 and get a good PID to cycle a fermwrap to keep temps up if it would make a big enough difference.

Click to expand...

Can Do. I wouldn't say prove, but everyone has their own preference. This is mine.
It depends on how you are chilling. Air as a medium is very different than water. Much more thermal mass in water. As a result, water can have much greater carry over. This also depends on where and how you control the temp. I'll post a few examples. Some of these I've posted in other threads.

First up This is what happens when the temperature controller is attached to the side of the carboy (glass in this case) measuring the beer temp. The water circulating through the water bath was in the 50's.
Here is the problem: the water bath cools to the 50's very quickly. The beer takes awhile to drop to the set point on the temp controller. Once it clicks off, the delta between water bath temp and beer temp is quite large. The beer continues to cool, the water bath warms up, until either equilibrium is reached, or the controller trips again. This is an example of what not to do, and it looks like this:
Beer temp measured at core


Air is interesting because you can get away with huge swings in ambient temp with much smaller deltas in beer temp. This is handy for those times when you open a refrigerator or freezer. Air has low heat capacity. So, a keezer can have a wide setting on the temp controller, and still maintain relatively constant beer temps. Same is true for fermenting, but I found the water bath transfers heat much quicker. Those wild cycles look like this, and are quite interesting. Over a long period, you can see the effect of ambient room temp on freezer efficiency.
Beer temp measured on side


The low points in the blue freezer temp are directly related to ambient room temp.


The final step was to control the temperature of the water bath by putting the temperature controller probe into the cooling medium, and ignoring the beer core, or side temp completely. This works very well. The cycles are short. If you tried to keep it this tight in air, I think the compressor would cycle like a hummingbird and burn out in a day.
Beer temp measured at core


Moral of the story, controlling the temp of the cooling medium has always worked better for me, but you have to tune it to your setup. Air can give you a wider margin to work with. I prefer water.
I'm currently doing this with re-frozen bowls of water using a couple small pumps to keep the bath constantly circulating, injecting cold water only when needed per the temp controller. Next I will use a refrigerator coil which should be much more reliable and consistent.

I have an analog Johnson controller that I thought was a 3 degree differential but I will have to check. With that controller if I put the probe near the carboy but not attached and I set it at the low end of the yeast recommended temperature do you think I will have too large of a temp swing. I could then increase the temp setting after a couple of days as the wort becomes less active? Sound good?

Wow!! Love all the data! Sounds like I run a similar set up...a temperature controlled water bath using the STC-1000. One side controls an aquarium heater and the other controls a pump. The pump sends water from the water bath through an immersion cooler sitting in cooler of ice water and returns it to the water bath. I just tape the submersible probe to the side of the fermentor. I have a question though....I ferment in a stainless Sanke keg. I would think that the SS keg would have much better conductivity than glass or plastic fermentors. In other words I wouldn't be getting the swings in temperature, or at least not as much, using stainless. Your thoughts?

TnFarmer said:

I have an analog Johnson controller that I thought was a 3 degree differential but I will have to check. With that controller if I put the probe near the carboy but not attached and I set it at the low end of the yeast recommended temperature do you think I will have too large of a temp swing. I could then increase the temp setting after a couple of days as the wort becomes less active? Sound good?

Click to expand...

Hmm, thanks for making me check... turns out the differential is 3.5F (link); I guess I saw some bad info. Many folks may still consider that too much swing for the fermenting beer. So it's a judgment call, but it seems like too much swing to me, so placing in air seems better.

But placing it "near" the carboy is little different than 2 feet away since you're just measuring ambient air temp. Measuring air temp will result in very little swing of the beer temp. But for the first couple days, you'll have to closely watch the beer temp, so make sure you have the stick-on thermometer strip.

I'm toying with a modified process for the Johnson analog unit: for the first 12 hrs, insulate the probe next to the carboy, just to get down to temp. Then once fermentation gets going, move it to the air to keep temp swings down. Might be worth experimenting with different configurations.

I did a heat study on one of my fermentations. Taped the temp controller sensor to the outside of the bucket in a foam block and dropped an oven thermometer in through the airlock hole. The wort was consistently 2 degrees higher than the controller reading. That was using the controller's standard 3 degree temp swing. Now I just set the controller a few degrees above the lower end of the yeast temp range and call it good.

william_shakes_beer said:

I did a heat study on one of my fermentations. Taped the temp controller sensor to the outside of the bucket in a foam block and dropped an oven thermometer in through the airlock hole. The wort was consistently 2 degrees higher than the controller reading. That was using the controller's standard 3 degree temp swing. Now I just set the controller a few degrees above the lower end of the yeast temp range and call it good.

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2 degrees makes me happy. If I can keep within 2 degrees of ideal, I'll take it. I set my STC to 0.5* C variance and set it down to the low end of where I want it.

william_shakes_beer said:

I did a heat study on one of my fermentations. Taped the temp controller sensor to the outside of the bucket in a foam block and dropped an oven thermometer in through the airlock hole. The wort was consistently 2 degrees higher than the controller reading. That was using the controller's standard 3 degree temp swing. Now I just set the controller a few degrees above the lower end of the yeast temp range and call it good.

Click to expand...

Yes, but did you calibrate one against the other, or both against a reference? I had to set my Control Products controller -2F offset to get it to be closer to my probes. Unfortunately these controllers are only integers, and it's very annoying trying to use them for 1 degree tolerances. Nearly impossible. They flutter like butterflies because of what appears to be integer resolution internally.

All my probes were calibrated in the same water bath between 40 to 80 degrees. I calculated slope and intercept against my brewing probe thermometer which I chose as reference (you have to pick something...). When I log data, I apply the correction factors to each reading before storing. This is how I know i'm not off by 2 degrees between probes.

Phunhog said:

Wow!! Love all the data! Sounds like I run a similar set up...a temperature controlled water bath using the STC-1000. One side controls an aquarium heater and the other controls a pump. The pump sends water from the water bath through an immersion cooler sitting in cooler of ice water and returns it to the water bath. I just tape the submersible probe to the side of the fermentor. I have a question though....I ferment in a stainless Sanke keg. I would think that the SS keg would have much better conductivity than glass or plastic fermentors. In other words I wouldn't be getting the swings in temperature, or at least not as much, using stainless. Your thoughts?

Click to expand...

we have a pretty similar setup. You're using a heat exchange method, I'm pumping cold water from one container to the other. The cold water is in a cooler, I pump to the bottom of the container holding the carboy. A pump in the carboy container circulates the water at a slight upward thrust to get good mixing. The drain is at the top, and constantly recirculates the water back into the cooler as long as the cooler pump runs. I periodically recharge the cooler water with blocks of ice.

Stainless conducts much quicker. I can see that in my kegs, the temp drops immediately. I haven't figured out a good way of measuring core temp in kegs under pressure, so I also use a block of insulation cut to fit the prob exactly, exposing one side slightly, then I strapped it down to the side hard, so it's well sealed.
I think with stainless, during active fermentation, your temp differential should be less than with glass or plastic.

TnFarmer said:

I have an analog Johnson controller that I thought was a 3 degree differential but I will have to check. With that controller if I put the probe near the carboy but not attached and I set it at the low end of the yeast recommended temperature do you think I will have too large of a temp swing. I could then increase the temp setting after a couple of days as the wort becomes less active? Sound good?

Click to expand...

I have found that during active fermentation, the core temp of the beer floats along the top of the water bath peaks, then eventually falls to the middle. So I do exactly that, I set the controller one degree cooler than I want, then as fermentation is less active, I set it back up one degree.
I wish I could set these to half a degree, because it's possible to sustain temps within less than half a degree with the right setup.
As long as you have a fan in there blowing the air around, you'll be fine. Without a fan I think you would find the carboy warms up the air in a zone around it. I haven't measured this, but that's what I would expect.