Temperature control for fermentation

[Brownman]

I just got my ranco temp. controller hooked up to my chest freezer and want to use it to control fermentation temp. mainly. I'm having problems with over shooting my target temp. (65 degrees). I have my set point at 65 with the variance at 1 degree. When the freezer cuts on it lowers the temp. and then cuts off but because the freezer is colder than the set point my wort continues to cool and usually ends up at about 62 or 63. Then after several hours when the temp rises to 66 the cycle repeats. Is there any way to get it to stay closer to my set point? I'm using a probe sleeve so my probe is inside my fermentation bucket.

Thanks for any help,
Brownman

 

[tesilential]

I have the Ranco and I just use the stock temp probe and let it hang in air next to the fermentation bucket. To ferment at 64*, I set the Ranco to 61 with a 3 degree differential. This keeps the freezer from running nonstop and ensures the fermentation doesn't exceed 64*. The freezer temp swings faster than the bucket so the temp stays right around 64.

You having the temp probe in the wort may actually he hurting you, since the Ranco is waiting for your wort temp to go up before it kicks in.

 

[fredtheseal]

I have the Ranco and I just use the stock temp probe and let it hang in air next to the fermentation bucket. To ferment at 64*, I set the Ranco to 61 with a 3 degree differential. This keeps the freezer from running nonstop and ensures the fermentation doesn't exceed 64*. The freezer temp swings faster than the bucket so the temp stays right around 64.

You having the temp probe in the wort may actually he hurting you, since the Ranco is waiting for your wort temp to go up before it kicks in.

I'm confused. Your yeast are swimming in the wort, this is their environment, so shouldn't the goal be to regulate the temperature of the wort/their environment? I always thought the best approach was to use a "sleeve" like the OP that allows you to take the internal temp of the fermenter since yeast activity is exothermic and increases the internal fermenter temp.

 

[bruin_ale]

You're correct, the goal is to regulate the temp of the fermentation, but if you're using a standard temp controller like a Ranco - it'll leave the freezer on until the wort gets to the temp you want. Unfortunately, the temperature of the freezer will be much colder than that due to the lag time it takes to move 5 gallons of wort to the setpoint. That's why the wort continues to chill past the setpoint. A PID would be a better choice for that, as you could dial in the settings to account for how slowly the temperature will respond.

 

[Brownman]

Thanks for the responses, I think I worked it out. By setting my set point 1 degree higher ( 66 instead of 65) and the differential at 2 degrees my temperature stays at 65-66 degrees consistantly.

 

[o4_srt]

You're correct, the goal is to regulate the temp of the fermentation, but if you're using a standard temp controller like a Ranco - it'll leave the freezer on until the wort gets to the temp you want. Unfortunately, the temperature of the freezer will be much colder than that due to the lag time it takes to move 5 gallons of wort to the setpoint. That's why the wort continues to chill past the setpoint. A PID would be a better choice for that, as you could dial in the settings to account for how slowly the temperature will respond.

A 2 stage controller works as well, sort of. You still have overshoot, but when the wort hits the set point and starts to go past, heater warms the chamber up.

I reduce ringing by stepping down to fermentation temps gradually, in 10 degree increments, sometimes less depending on how far I have to cool.

 

[tesilential]

Thanks for the responses, I think I worked it out. By setting my set point 1 degree higher ( 66 instead of 65) and the differential at 2 degrees my temperature stays at 65-66 degrees consistantly.

The other dude beat me too it. My way my fermenter stays at 65 while the ambient varies between 62-65 (in reality it's also sometimes a little higher or lower).

Your way the wort will go from 65-67. Again in reality it will a little higher or lower.

 

[cwi]

A cause of the original issue could be the probe reacting too slowly. If the thermowell can't be filled with a thermal conductant (better than air) due to a non-waterproof probe, there will be a delay in the probe reaching the actual temp. There is also a temp difference between the center of the wort, and the wort close to the vessel walls during the "chiller on" phase. This evens out after the chiller cuts off, causing overshoot. Placing the probe on the vessel wall, then insulating it, causes an overshoot compensation effect by the probe being influence slightly by freezer ambient air.