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Old 03-17-2011, 08:36 PM   #1041
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-1 insulating probe.

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Old 03-17-2011, 08:52 PM   #1042
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Originally Posted by ChshreCat View Post
You might want to tape something over the probe as well to insulate it from the air and make sure it's reading the temp of your fermenter. Something as simple as a wash cloth folded over a couple times would suffice.

Good tip. Will do.
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Old 03-17-2011, 09:25 PM   #1043
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I believe that placing your probe in water/ beer is a bad idea unless you are actually heating the liquid via a water heater element or something of this nature. It will take a great deal of heat to bring the fluid up to temp if your using a radiator or fan heater, then it will continue to heat after it is shut off because now your air temp is much greater than the fluid, and vice versa for the cooler.

If you maintain the proper air temperature the fluid temp will follow. I have my probe against the side of my carboy and i dont have any cool mode kicking in because its colder outside than it is inside, but i'm not lagering.

I have the F2 function ie temp differential set to 1 degree. My target is 23C and it heats till it hits 23 shuts off the heater and in turn the temp starts to drop until it hits 22C then heats again to 23... If it was hotter ouside and i was using an airconditioner it would be the opposite.
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-1 insulating probe.
Most of your comments are contrary the laws of thermodynamics and control theory. The only one that is correct is that the secondary body (beer) will "follow" the primary body (air), if the probe is placed in the primary body (air again), but that is not a good thing in our case (more later). It can get complicated when the body being controlled has a lower thermal mass than the heat/cool input, but that is not the system (usually) we deal with when using a fridge/freezer for what we do.

The most stable and accurate temp (of the beer/wort, which is what we are concerned with, not the air temp) will be maintained by placing the probe on the keg/fermenter and insulating it (the probe) from surrounding air, or placing the probe in the keg/fermenter (thermo well) and using a conductant (oil, water, etc.) inside the well.

For a kegerator/keezer where active fermentation is not happening, putting the probe in a container of liquid sufficient.

Not following this strategy for a fermentation chamber, the beer/wort temp will always "follow" the air temp, but may never get there and could vary considerably during exothermic phases. It will also cause more frequent cycling of your heat/cold source which in the case of your compressor which will shorten its life, and the various starter circuit fiddly bits.
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Old 03-18-2011, 12:06 AM   #1044
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Yes it is complicated! I still stand by what i said and without getting into credentials lets looks at the scenero. I'm slightly sleep deprived and i've been wrong before (more right than wrong usually! ) so i'm not trying to suggest i'm more knowlegable about this but i would like to seek some clarification because i'm curious as to what the best method is going to be, obviously.

SO your heating your air and it will continue to heat until your beer has reached temp 'cause thats where your probe is, right? Now your air temp is going to be several (if not more) degrees higher than your beer because your beer has a greater thermal mass than that of the air. Now your probe turns off the heater and the air is still hotter than the beer so it will continue to heat your beer until your beer gets to a temp where your set point is to cool, now you will start to cool and that will take your air lower than your set point is because your probe is in the beer which will take some time to actually cool since again it's a larger thermal mass than the air....

If your heating the air its easier to just keep the air at say 20C and your beer will follow, i have a 1 degree differential and my beer stays pretty much on mark this way.

Now i understand that your beer is going to give off heat durring fermentation 'cause its 'exothermic' but isn't this kind of trivial when your dealing with a small volume like a carboy? I could see it being an issue with a 1000 gallons of beer, but not a carboy.

I mean to be technical its kind of an improvised method what we are doing in the first place. Breweries use fluid filled jacketed fermenters and they heat and cool the fluid, so if you want to get real technical, thats what we should do too.

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Old 03-18-2011, 02:18 AM   #1045
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Now i understand that your beer is going to give off heat durring fermentation 'cause its 'exothermic' but isn't this kind of trivial when your dealing with a small volume like a carboy? I could see it being an issue with a 1000 gallons of beer, but not a carboy.
In the early stages of fermentation, you can get close to a 10 degree difference between ambient temp and what's going on in your fermenter.

I'd much rather have the thermostat keeping my beer at the proper temp than the air around it. If I have to keep the air temp at 55 to keep the beer at 60, that's what I want it doing. As the ferment slows down and less heat is generated, the freezer will adjust automatically because you're measuring the temp of the beer.

True, the ambient temp in the chamber is going to overshoot the temp of the beer, but 5 gallons of beer does have quite a bit of thermal mass and isn't going to change that quick. Say you're heating the chamber because it's in your garage in the winter. You want your beer at 60 and the temp has dropped. The heater will run until the beer gets back to 60. By then the air in the chamber might be closer to 70. Once the heater shuts off, it's going to start cooling down again. The beer might only gain another degree or two before the air temp inside has dropped to meet it.
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Old 03-18-2011, 02:37 AM   #1046
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[QUOTE=Salmonhouse;2747513]

Now i understand that your beer is going to give off heat durring fermentation 'cause its 'exothermic' but isn't this kind of trivial when your dealing with a small volume like a carboy? I could see it being an issue with a 1000 gallons of beer, but not a carboy.



This also depends on the area you have for a fermenting chamber. I have a 5 ft chest freezer and my carboy definitely heats that sucker up. In the early stages of fermentation, I drop mine to about 58 ambient. After a few days I bring it up to about 62 for most ales.

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Old 03-18-2011, 04:06 AM   #1047
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Now your air temp is going to be several (if not more) degrees higher than your beer because your beer has a greater thermal mass than that of the air. Now your probe turns off the heater and the air is still hotter than the beer so it will continue to heat your beer until your beer gets to a temp where your set point is to cool, .
this last bit is not true. say the air temp is ten degrees warmer than the beer - the amount of energy contained in the air for this temp difference is too small to heat something with the heat capacity of water up much at all. the heat will be lost through the insulation etc as well. I would explain better, and possibly even bring out a heat transfer textbook from my shelf, but I'm typing on an iPhone which isn't easy...
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Old 03-18-2011, 04:11 AM   #1048
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I finally wired mine up today. works great with only one issue... the tightening screws for the cold wires will not tighten at all. so the wires wiggle a bit. since they are solid core, 14 gauge, they are quite stiff, so I keep it in contact with the terminals by jamming a piece of corrugated cardboard underneath the wires. works for now, and it will keep working as long as I don't jostle it too much, hopefully.

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Old 03-18-2011, 05:38 AM   #1049
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Originally Posted by ChshreCat View Post
In the early stages of fermentation, you can get close to a 10 degree difference between ambient temp and what's going on in your fermenter.

I'd much rather have the thermostat keeping my beer at the proper temp than the air around it. If I have to keep the air temp at 55 to keep the beer at 60, that's what I want it doing. As the ferment slows down and less heat is generated, the freezer will adjust automatically because you're measuring the temp of the beer.
.
OK i think i'm starting to see how that works now, thanks for the clarifying. Although i feel more questions brewing as a result of this information. Do you set your temp and forget it or adjust it at all during the ferment?

Does using a space heater with a larger thermal mass change anything?
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Old 03-18-2011, 05:45 AM   #1050
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[quote=EricT;2747860]

Quote:
Originally Posted by Salmonhouse View Post

This also depends on the area you have for a fermenting chamber. I have a 5 ft chest freezer and my carboy definitely heats that sucker up. In the early stages of fermentation, I drop mine to about 58 ambient. After a few days I bring it up to about 62 for most ales.
Eric, are you measuring the air temp or are you trying to probe the fermenter? Seems kind of low for ale so i assume that's your air temperature?
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