His latest argument is that an external temperature controller for the keezer is going to burn out the compressor faster because it will work at full bore, then shut off, then full bore, off, etc etc etc.
"Besides buying a controller with a short cycle delay setting, putting the sensor in/on a container of liquid to dampen its response will prevent short cycling without having the large temperature swings a large offset can cause."
Not true. You will have even larger temperature swings with a submerged probe. That's what the differential setting on the controller is for.
"Dampening the sensor response will also prevent cycling due to lid openings, which will happen if the sensor is a fast responding type, and is in air only."
So what? That's what the anti-short cycling feature is for. Mostly this doesn't happen much anyway as the cold air stays put in a chest freezer. IMO, fast probe response is advantageous and there is no need to dampen it.
"For fermenting in a keezer, putting the probe directly on/in the active vessel will give the tightest control over ferm temperature. Short cycling could occur for a vigorous fermentation, but as long the controller has a cycle delay, it isn't an issue."
Except that IMO, it doesn't. Your freezer will become an ice box by the time the controller responds when cooling and the reverse on temperature rise.
I've found that the positioning the controller probe in the air near the bottom of the freezer works best (when using a fan, where you place the probe makes little difference). Then, a separate digital thermometer is used to monitor the fermenter temperature with the probe attached to the side and covered with some bubble foil (or any other) insulation. I adjust the controller based on the thermometer reading. It holds within about 1*F. The thermometer probe could also be used with a thermowell in the fermenter, but not the controller probe.
At one time, I thought that putting the probe in a container of water would be a good idea. The problem is that it is difficult to use the controller as both a controller and a thermometer. We need to know the temperature in two different locations at the same time. Tough to do with a single probe.
catt speaks the truth.
My fridge controller is able to log data. here is some:
https://spreadsheets.google.com/ccc?key=0AriPJSz0jUx6dHBLS05ZUnIzVlplZmdKUXdUNk0wU0E&hl=en
note that i didn't set up the logs to record at the same time intervals. i can get better data when i get home. but there are two time columns so you'll have to match up accordingly.
my probe is sitting in air. just hangin' in the air. i have a big, 27cuft, 6x2.5x2 (ish) freezer.
as you can see in the data, my compressor runs for 2-4 minutes every hour.
catt is dead on about fermentor control. if you send a probe down the thermowell, the freezer will get very cold by the time the setpoint is satisfied. if you really wanted to go that route put the probe in air for the first 24 hours or so to let the beer temp get down, then you can send it down the thermowell
note, i just lagered at 35F with the probe in air temp, but i had another probe down the thermowell just to see. the probe down the well never changed temp.
I've been meaning to try to model this with an electric circuit analog, but so far haven't found the time. Anyway, here's my opinion.
The average temperature of your beer will stabilize at the average temperature of the air in the freezer. If your probe is in the air, the beer temperature will not vary much around its average level, but the freezer comes on and off more often, but is on for a shorter period. But the average beer temperature may be several degrees off from the controller setting - not a problem if you know what the difference is.
If you have your probe in a thermowell in the carboy, you will maintain tighter control between the controller set temperature and the average beer temperature, but the beer temperature will fluctuate more about the average level, and the freezer air temp. will get very cold. Having the probe in a container of liquid is a compromise between these two extremes.
The only problem I can see with having the probe in the air, assuming your freezer isn't short cycling, is that the difference between the temperature set on the controller and the actual beer temperature may vary depending on how active the fermentation is - a problem that is alleviated by having the probe in a thermowell, but at the expense of greater beer temp. fluctuation about the average.
I assume you are talking about active fermentations in your post.
The problem is different for keeping kegs cold, vs. maintaining active exothermic ferm temps, so keep that in mind in your analysis.
One advantage to dampening the probe response, is that a tighter differential can be set (for controllers that allow it) without worrying about short cycling. The thermal mass of the beer will hold its temp long after the freezer air/walls have risen above the set point. The same thermal mass will absorb the thermal inertia/carryover from the air/walls/freon loops, etc. without overshooting by a significant amount.
With active fermentation releasing heat into the beer (which in turn is released into the air) and the probe in the air, due to the thermal resistance between the beer and the air, the beer temperature will not be at the average air temperature, as was assumed in 1. above, but will be at a higher temperature, maybe several degrees higher. With no fermentation, the assumption that the average beer temp. is the same as the average air temp. holds.
.......
Your analysis is mostly right. The only part that may be off a bit is the amount of effect the thermal inertia/hysteresis of the freezer air/walls/freon loops will have on the temp of the beer. Their thermal mass is much smaller than the beer, especially if there are multiple vessels in the freezer.
"At this point, the air is super cold and the beer will continue to cool, so the beer temperature varies more about its average than in situation 1."
This would only be true for very small quantities of beer in a large freezer. A situtation easily remedied by adding some containers of liquid.
Putting the probe in a jug of water instead of on a keg, is more about convenience. The gains for reduced cycling and tighter temp control aren't worth the hassle of moving the probe each time the keg floated/moved/etc. At least not for me. Putting the probe on/in a ferm vessel during active fermentation is worth the added temp control, for me at least.
If someone (not you DeafSmith) doesn't like the idea of putting the probe in a jug or on/in a ferm vessel, that is their choice. It doesn't change the laws of physics, though.
Cat22 has posted his opinion about not dampening response of the temp probe and not placing it on/in the ferm vessel in several threads, and continually gets questioned about his questionable logic/science. It hasn't stopped him yet, and I guess it won't now either.
Cat22 has posted his opinion about not dampening response of the temp probe and not placing it on/in the ferm vessel in several threads, and continually gets questioned about his questionable logic/science. It hasn't stopped him yet, and I guess it won't now either.
What I've been doing with my fermentation freezer is to put the probe inside of an empty White Labs yeast vial, surrounded only by air. This dampens the response of the probe some without the risk of shorting something out by putting it in liquid. This setup, in combination with a fermometer stuck to the side of the carboy for manual controller setpoint adjustment, has been working well enough for me, but I admit it is not ideal. I'm debating whether or not get a thermowell. The yeast vial may, however, work fine for my keezer when I start kegging (soon - I'm accumulating all the pieces).
Why not try taping the controller probe to the side of the ferm vessel, topped with some insulation. That will give you a close idea of how a thermowell will perform, and might be good enough for your tastes.
You speak with authority, unfortunately IMO it's all B.S. At least you got the very last part right. I think that should be worth something.
I tried that on my last batch and it seemed to me that the temperature varied more than the way I had been doing it.
catt speaks the truth.
My fridge controller is able to log data. here is some:
https://spreadsheets.google.com/ccc?key=0AriPJSz0jUx6dHBLS05ZUnIzVlplZmdKUXdUNk0wU0E&hl=en
note that i didn't set up the logs to record at the same time intervals. i can get better data when i get home. but there are two time columns so you'll have to match up accordingly.
my probe is sitting in air. just hangin' in the air. i have a big, 27cuft, 6x2.5x2 (ish) freezer.
as you can see in the data, my compressor runs for 2-4 minutes every hour.
catt is dead on about fermentor control. if you send a probe down the thermowell, the freezer will get very cold by the time the setpoint is satisfied. if you really wanted to go that route put the probe in air for the first 24 hours or so to let the beer temp get down, then you can send it down the thermowell
note, i just lagered at 35F with the probe in air temp, but i had another probe down the thermowell just to see. the probe down the well never changed temp.
cwi, that data was just fridge air temp and basement temp. this is for my keezer which I occasionally lager in. I was just trying to answer the OP's question about how hard the controller runs the keezer.
i certainly agree with you that controlling to the thermowell is more accurate.
it's probably the way to go IF your starting wort temperature is at or close to your setpoint, otherwise the keezer will get very cold before your wort does.
if you have a dedicated keezer for fermentation control, you're right, you really don't give a crap what happens aside from beer temp. but i have kegs/bottles in mine that i don't want to freeze
i still can't get on board with your idea that controlling to the thermowell will cause less overall temperature swing. right now, controlling to air, the compressor runs 2-3 minutes and swings (sp is 41F) between 39.4326F and 42.1447. there's 3 5g kegs, a 5g carboy, and a bunch of bottled beer in there. not packed full but decent mass.
what do you think the time constant is for the fermenting beer? you think it will cool down to setpoint within 3 minutes? any longer and I would have larger temp swings.
note, my control strategy is just "on at >41F, off at <41F". i have a 2 minute "min/on min off" restriction on that output.
You speak with authority, unfortunately IMO it's all B.S. At least you got the very last part right. I think that should be worth something.
5. The fermenter temps are very stable with this method usually varying less than one degree F. I have found it necessary to dial the controllers down well below target temps during the first few days of fermentation when the high activity is generating a lot of heat. I then raise the temperature over several days once the activity slows. I have found that it is best to cool the wort well prior to pitching as once the high activity begins it is much more difficult to bring the temperature down.
Wow, sorry guys, maybe I should have been more specific. This freezer will not be for lagering, so all the argumentation about such is frivolous. Thanks for the concise answers that are gonna help with my consideration of controlling a keezer with kegs of finished beer.
Again, thanks.
If it were me, I would just remove the small vessels (bottles), and put them in a cooler/refrig for the day/days.
When ramping with the probe placed on/in the vessel, there will be some temp overshoot (for each initial ramp cycle), and possible collateral freezing damage if other vessels' thermal mass isn't great enough to endure the initial heat loss without freezing.
I don't know what you mean by "overall temp swing". The important temp swing/avg is the temp swing/avg of the beer, and most importantly the fermenting beer, if there is any. How could it not be more accurate with the sensor in the beer or ferm'ing wort?
Are you are talking about overshoot caused by the keezer's thermal inertia? That is an issue caused by an improperly sized chiller, but can be mitigated. In general, the keezer's inner air/walls/foam/freon thermal mass is small enough relative to the probed ferm vessel and other vessels that the thermal inertia has a negligible impact. I think you said your freezer is >25cf.
If you are trying to both maintain an active ferm temp as accurately/tightly as possible, and keep the temp of some other vessel at the same ferm temp, that is impossible. You might as well ask the controller to chew gum and pat its head at the same time. You would have to personally choose some balance point between keeping the active ferm temp stable and keeping the other vessel within temp bounds.
I am not sure exactly what the on/off parameters you refer to do, but it sounds like you may be placing too much of yourself in the control loop.
From your data,your compressor appears to be cycling much more than I would like mine too
For ramping temps with other vessels in the same chamber, that is a balancing act. You just need to know the options, and set priorities.
cwi,
IMO, your pseudo science is junk science. The only thing you have accomplished is thoroughly muddying the waters for anyone trying to sort this stuff out. The only way to know for sure is to do some actual unbiased testing. The key word there being unbiased. So, have a nice day and while your at it, insert this.
...or PID it if you want more control...
lol! you can't control non-proportional devices (ie, a fridge compressor) with a PID loop....
I believe you can, if just for overshoot. It may be the fuzzy logic or auto-tune capability available on many PID controllers. There is a guy on here that does industrial temp controls systems, and has used them.
I just wouldn't want to rely on a PC or micro-controller board to stay up 100% of the time.
autotune? fuzzy logic?? wtf? what does autotune have anything to do with it? If he's using a PID in a industrial temp controller he's probably controlling a cooling valve or a fan, ie, a proportional output
But I sit a few feet away from the guy that literally wrote the book (and multiple patents) about control theory.
circling back, i've already agreed with you. Controlling fermenting beer inside a keezer is probably best accomplished with the probe in the thermowell, since it's exothermic.
catt speaks the truth.
catt is dead on about fermentor control
I still think controlling finished beer is more accurately controlled by air temp, because, as i've stated before, the swing in air temp is so small it's dampened by the thermal mass of the beer, so the beer temp never changes. Obviously, it does require human intervention. If you were to control finished beer with the probe in the thermowell, it would oscillate +- a few degrees (whatever you set your deadband to). Which is usually good enough, and you don't have to keep screwing with it.
huh???
I had enough exposure to control theory to know I didn't want to do it professionally, especially designing hardware for it. Your cubemate would be a good guy to ask what the best approach/controller would be good for several standard scenarios. I don't think cat22 would be happy about his answer, either.
moto said:the best control for a staged output is to define a deadband, and a safety min on/ min off time.
What part of running "code" (software) on a PC or micro-controller board, and worrying about the PC/board staying up for extended periods, do you not understand?
Motobrewer, it's funny that you "lol" about me suggesting that a PID controller could be used to control overshoot/temps in a keezer.
You feel that your 1 cycle per hour freq is "pretty good". If you are happy with that, and feel/know that a lower cycle freq will cause too much temp swing (beer temps, bottle temps, etc.), then that is what is best for you. It is strange to me that your control settings function almost equally as sensor and fixed run time based (chosen by you). This is from the high number of "min on time" duration cycles in your data. Your sensor control appears to want to shut off earlier.
so much text...
let me start off by saying this:
yes, my original post was misleading. What I really meant by it was, "my system probably cycles the most, and its only 2-4 minutes an hour. therefore you should be good". Also, what I said in that about ferm temps was wrong. In my head I was thinking about was ramping down a non-fermenting beer, not controlling actively fermenting beer.
i did, here:
Quote:
Originally Posted by moto
the best control for a staged output is to define a deadband, and a safety min on/ min off time.
the part where all our controllers are "micro-controller" boards (our supervisory controllers are actually small windows CE machines) and they run for years on end, in highly critical applications (air quality / smoke control for hospitals, for example).
A "PID controller" isn't something you buy, it's a feedback control loop mechanism.
Remember all your "fancy book learnin?" LaPlace transforms, transfer functions, etc?
I'm not saying i'm good at it, control theory was a b*tch of a class. But anyway, the output of a PID calculation is an analog value, 0-100%. Period. That can get processed in a few different output signals on the electrical side, 0-10 volts, 0-1 volts, 4-20mA, etc. Send that to a valve with an actuator on it, and you have a variable flow system. Or feed that into a VFD and you have a variable fan. How are you gonna take a 0-10 volt signal and put it to a fridge compressor? How are you gonna take a 0-100% command and put it to a piece of equipment that's either on or off? The only way is to set limits - on at 75%, off at 50%, or whatever. Just like I stated before.
A PID is not the best control loop for a staged output (staged output is something that's either in one stage or the other. On/off, high/med/low, etc. Not like a valve where you can be 0% open, 100% open, 33% open, 33.42451% open, etc.).
The fact that you thought "autotune" or "fuzzy logic" could make a "PID" (seems like you think a "PID" is a chip you buy) control a staged output is what makes me thing you really don't know all the "fancy book learnin" you mentioned before. maybe you do.
Originally Posted by cwi
You feel that your 1 cycle per hour freq is "pretty good". If you are happy with that, and feel/know that a lower cycle freq will cause too much temp swing (beer temps, bottle temps, etc.), then that is what is best for you. It is strange to me that your control settings function almost equally as sensor and fixed run time based (chosen by you). This is from the high number of "min on time" duration cycles in your data. Your sensor control appears to want to shut off earlier.
I think it's pretty good, do you? Is yours better?
I really have no point of reference. You're right, the freezer seems to be held on at some instances by the min timer I selected. Most times it runs longer than 2 minutes tho. I felt the deadband created was adequate, and didn't want to turn down the timer because that would create more cycling. I didn't want to increase the timer because that would create a larger deadband.
oh, please lay off the '/'.
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