Fermentation chamber locked in cosmic heat vs. cold battle

I have a used chest freezer that I got for a fermentation chamber. For a while I had an inexpensive single-stage analog temp control/thermostat on it which would run it in cool mode only and that worked great.

Recently I upgraded to an STC-1000 and put a reptile heat lamp in there for a heating element. Everything is working but the heater and freezer both seem to consistently over-shoot the set temp - so i have it set at 16 deg C, and the freezer comes on to get it down there. At 16 the freezer kicks off but the temperature keeps dropping to about 14, of course making the heater come on which will warm it up to 16 but again the temperature keeps rising even after the heater is off up to about 17.5 or so. I understand the reason for this is that the heater is still warm for a little while even after it turns off (similarly the freezer coils are still cold after it switches off). I think I have the temp difference set at .5 deg. on the controller.

I think this is inefficient with the freezer and heater both running a lot. Any tips for getting it to not do this? Maybe I will try putting the temp sensor in a jar of water to see if the thermal mass of the water will help.

How is the temp probe positioned? If it is just in the air you will get the swings. Try taping the temp probe to the fermenter and cover it with some styrofoam insulation. The thermal mass of the beer will dampen the temperature swings seen by the controller.


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Agreed. You need to measure the temperature of the beer not the air. Air is a terrible conductor and will vary in temperature far quicker and widely then the beer itself. Tape that probe to the keg and insulate.

Once you establish an appropriate probe placement per the previous responses, monitor the over and under shoot and set the temperature difference to a hair more than the greater of the two.

Thanks for the hints, folks.

I have not started my fermentation yet (brew day will be this coming Saturday I hope) so I have time to experiment by taping the probe to the side of a carboy full of water. I also noticed that the air within the chamber stratifies significantly, with the hot air from the lamp rising to the top and not warming up anything at the bottom of the chamber. I ordered a small fan to put in there to get some convection going, hopefully it will help the temperature to be even throughout and increase efficiency.

This problem I have personal experience with. When I first hooked up the STC-1000, I had giant temperature swings also. Part of it was I didn't have the probe attached and insulated well enough. The second batch I made, I thought, which way is the temperature most likely to swing? At that point with the weather being cold outside, I knew all I was going to need was heat, so I set the temperature lower than I actually wanted to, to help prevent over swings of temperature. I knew the wort was cooler than 62* F, so I set the temperature at 58* F or 59* F. It called for cooling many times during the first day or so, but I left it alone. When it was a solid temperature reading, I bumped the temp a few degrees, I still left the cool mode off, and there were no more swings at that point in time. I pitched the yeast, set it at 62* F, turned the cool mode back on, and the temperature tracked in a straight line from that point on.
I hope this helps you to get your temperatures correct w/o the heat/cool, heat/cool, mode swings. I have a 200 watt Lasko heater with a built in fan.

rlmiller10 said:

How is the temp probe positioned? If it is just in the air you will get the swings. Try taping the temp probe to the fermenter and cover it with some styrofoam insulation. The thermal mass of the beer will dampen the temperature swings seen by the controller.


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DrunkleJon said:

Agreed. You need to measure the temperature of the beer not the air. Air is a terrible conductor and will vary in temperature far quicker and widely then the beer itself. Tape that probe to the keg and insulate.

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raouliii said:

Once you establish an appropriate probe placement per the previous responses, monitor the over and under shoot and set the temperature difference to a hair more than the greater of the two.

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+1 to these. Strap the probe directly on your fermentor, insulate.it with bubble wrap to keep it from the ambient air. Set your difference to 1 degree F, and the thermal mass of the beer will absorb the temperature swings, and you'll never be over or under by more than 1 degree. Skip recirculating fans, they are totally unnecessary.

I have my difference set to .7, and I've been unplugging the heat when I use the cold and vice versa. My logic is that I shouldn't ever need both to maintain stable temps on either side of ambient, and the probe is reacting a little faster than the liquid mass. This seems to work fine for me, but maybe not the ideal solution.

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ja09 said:

I have my difference set to .7, and I've been unplugging the heat when I use the cold and vice versa. My logic is that I shouldn't ever need both to maintain stable temps on either side of ambient, and the probe is reacting a little faster than the liquid mass. This seems to work fine for me, but maybe not the ideal solution.

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Your logic is flawed...

I ferment in a fridge so I just adjust the regular thermostat so it doesn't overshoot as much. I put a dimmer switch on my reptile heater so it doesn't get as hot. The STC-1000 is then able to keep things in a reasonable range.

I'm having a similar issue, although not as bad. I have the temp set to 18.3C with a differental of 0.3C (STC-1000) My probe is located in wort at the very center of the fermentor.

When the temp rises to 18.6C the freezer kicks on and the temp drops. At 18.3C the freezer kicks off but since it's now cold in the freezer the temp keeps dropping.

It gets to 18.0C and then the heater kicks on. It heats it back up to and at 18.3C the heater kicks off. I use a fermwrap so it directly heats the fermentor and doesn't really heat the inside of the freezer too much, so the inside is still cold. This all happens in about 45 minutes.

Because it's still cold in the freezer, the temp begins to drop again but only goes down to around 18.1C so the heater doesn't come back on. Then the temp slowly rises over a few hours to 18.6C where the freezer kicks on and the cycle repeats. This is during active fermentation.

I've been thinking about moving the probe to the side of the fermentor but not sure if it will make it worse. There is a lot of variables in play, power of freezer, power of heater, location of heater, how much heat the fermentation is giving off, ambient temp, insulation of freezer, insulation around fermentor, etc.

It will take a lot of experimenting to figure out what works best in your situation. I'm happy with mine, but feel that it could be improved.

petrolSpice said:

....There is a lot of variables in play, power of freezer, power of heater, location of heater, how much heat the fermentation is giving off, ambient temp, insulation of freezer, insulation around fermentor, etc.

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The questions below are rhetorical, as only testing can answer them. I'd posted on the same topic before and got pretty beatup over it. I started to do tests but need to clearly define the test criteria, and be able to measure and record chamber and liquid temps over time, but only have 1 recorder, so that means 2 passes for each test. I'll get to this soon, but in the meanwhile some food for though. I'm only considering heating in this example, and not exothermic heat from fermentation.

It takes 0.2931 watts for 1 hour to raise 1 lb of water 1 degree. 5 gallons is 42.15 lbs.

That is 12.35 watts for 1 hour (12.35 w/hr) for 5 gallons to gain 1 degree.

My 250 watt heater running for 3 minutes will produce almost exactly 12.35 w/hr. My 24 watt fan will take 30 minutes.

So, how long does it take for the 5 gallons to rise that 1 degree to stop the heater from running (based on 1 degree differential)? I don't know, but I'll bet it's WAY longer than 3 minutes. So how hot does the chamber get while the 5 gallons is taking way more than 3 minutes to heat up? And how much overshoot will the 5 gallons go?

I was using fans & heater last winter, monitoring only air temperature. They would run about 15 seconds, then be off for around 20 min. The STC1000 was set for 1C differential. The fermometer on the carboy was the same every time I looked at it, regardless of the heat cycle. With a closed system the carboy will be the same temp as the air once it reaches steady state. You maintain the same air temp, the carboy will be the same, period.

This winter I wanted to have better control over the chamber temperature stratification, so I re-wired to have the fans run 100% of the time, and only the heater cycling. All was well while I watched it. Came back 2 hours later and the temp was 5C too high. After analysing the situation I found that the 24 watt fans were creating more than enough heat to maintain the set point temperature. I've not run a heater since, and am cycling only the fans, a .5C differential now, and they are off more than they are on.

Once the carboy reaches the set point (assuming it's below to start) the only heat needed is to overcome losses in the chamber, and for a well insulated and sealed chamber, it's very little. And measuring the air is far more accurate than measuring the liquid temperature at steady state. (Let the battle begin....)

If you are doing temperature steps, a lager for example, then the rise/fall of liquid temp is a factor, but still will be a very controlled rise/fall with the air temp. It's then more an issue of how quickly you want it to change. If your drest is 12F higher, and your probe is in the middle of the carboy, the outside will be MUCH higher due to slow heat transfer from outside to inside. What impact will that have on the beer?

I'll post my test results in a new thread where everyone can point out the flaws in my system again.

John

jleiii, do you have a link to the thread where you took so much heat yourself?

Your thermal calculations make sense. As long as the fridge itself stays off and closed, there's not much added heat needed, since the fermentation adds some by itself. But it should come on when the beer temp starts to rise past the set temp to avoid it going out of hand (too high).

Then the ambient outside-fridge temperature starts to play a larger role once it becomes significantly different from the set target temp on the inside.

I'm still puzzling myself over how to best control these kind of systems. I use a fridge with the STC-1000, probe taped against carboy with 1/4" of foam over it to insulate it from the ambient air. I don't have much insight what the actual temp of the fermenting beer in the carboy is. A few months ago I started to measure with a submerged probe, but without a recorder it is haphazard with only very few quantitative data points, so I gave up on that branch of "scientific brew research."

Qualitatively the beer temp was quite stable, and near the set temp on the STC, within 1-2 degrees, and tasted great.

acidrain said:

Your logic is flawed...

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Nice. Your wisdom has almost convinced me to do otherwise. As long as the desired temp is maintained, it doesn't really matter how you go about it. I actually use a donkey walking in circles which spins a friction plate inside my chamber to create heat. It's not very efficient.

IslandLizard said:

I use a fridge with the STC-1000, probe taped against carboy with 1/4" of foam over it to insulate it from the ambient air. I don't have much insight what the actual temp of the fermenting beer in the carboy is.

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The good news is that you actually do have a very good idea of what the real temp of the fermenting beer is. More than one HBTer has checked simultaneous readings from the side of the bucket (and insulated) and with a probe inside a thermowell in the middle of the fermenter.

The difference during active exothermic ferment was a mere 1*F. Since the beer around the outside is going to be a tiny bit cooler than in the middle, the average temp throughout the volume of beer is likely in between those two values, so you're off by maybe half a degree. I can live with that.

ja09 said:

Nice. Your wisdom has almost convinced me to do otherwise. As long as the desired temp is maintained, it doesn't really matter how you go about it. I actually use a donkey walking in circles which spins a friction plate inside my chamber to create heat. It's not very efficient.

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This horse has been beat to death... I (and others) could go into great detail why your logic is flawed, but why? You guys will do what you do, and believe what you want. I seriously wonder why the questions are asked... they don't want to know the answer, and will do whatever they want anyway.
There are hundreds, if not thousands of homebrewers using the STC1000 successfully including myself. There are four things that are required.
1) Both heating and cooling need to be used even if the ambient temperature makes you think you don't need it.
2) the probe must read the beer, not the air.
3) the difference set value should be low.
4) the compressor delay time should be set high.

I'd say 90% of the people that have problems is because they don't measure the temperature of the beer.
5% are people that just don't have the settings correct.
5% are people that believe they don't need both cooling and heating during the winter or summer.

You don't need to calculate heat loss and thermal mass and insulation values and ambient temperature swings and the rotation of the earth and the phase of the moon.

Follow those guidelines and it will work.

IslandLizard said:

jleiii, do you have a link to the thread where you took so much heat yourself?

Your thermal calculations make sense. As long as the fridge itself stays off and closed, there's not much added heat needed, since the fermentation adds some by itself. But it should come on when the beer temp starts to rise past the set temp to avoid it going out of hand (too high).

Then the ambient outside-fridge temperature starts to play a larger role once it becomes significantly different from the set target temp on the inside.

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The other thread.
More of a been there, done that, response.

acidrain said:

There are four things that are required.
1) Both heating and cooling need to be used even if the ambient temperature makes you think you don't need it.

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You're wrong. It seems that YOUR logic is flawed.

^^How's that for a useful response

If I left my response at that then I would call it "*****ey" but I'll elaborate a little bit. My fridge sits in my garage at 85-95-100°F. My controller cools the inside of the fridge to 64°F at which point the condenser shuts off. Do I need to say any more? I can if you need me to, otherwise your #1 requirement above is moot - thus, your flawed logic.

stpug said:

You're wrong. It seems that YOUR logic is flawed.

^^How's that for a useful response

If I left my response at that then I would call it "*****ey" but I'll elaborate a little bit. My fridge sits in my garage at 85-95-100°F. My controller cools the inside of the fridge to 64°F at which point the condenser shuts off. Do I need to say any more? I can if you need me to, otherwise your #1 requirement above is moot - thus, your flawed logic.

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Haha. You beat me to it. I guess he assumes we're all idiots and we need his help?

I have monitored both the outside of the fermentor (stc + 2 layers insulation) and the actual wort temp (long digital thermometer) during fermentation, and the temps have always been within 1* of each other, and have confirmed I don't need both heat & cool with MY PARTICULAR SETUP.

acidrain said:

I seriously wonder why the questions are asked... they don't want to know the answer, and will do whatever they want anyway.

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Yes, we'll all bow down and listen to you next time.

acidrain said:

I'd say 90% of the people that have problems is because they don't measure the temperature of the beer.
5% are people that just don't have the settings correct.
5% are people that believe they don't need both cooling and heating during the winter or summer.

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You forgot the 1% of *****ebags that think they know everything.

I can't remember if I am following the flawed logic or the other logic, but I taped the probe to the side of a carboy full of water with some styrofoam packing sheet taped over it, and I set up the fan I got so it also turns on when my reptile light does. I turned the compressor delay up to ten. No more temp swings, everything looks good. Thanks folks.