best way to control ferm temps with thermowell

So here's my quandary: i've read that placing the controller probe in a thermowell will cause drastic overshoot. but if i'm using a dual stage with a heater attached, would that not counteract the overshoot and give me more stable temps? if not, would it be best to use the ranco to control ambient temp, monitor the fermenter temps with a separate thermometer, and adjust the ambient temp accordingly?

i would suspect that the second option would be the best, but i'm not able to check my temps that often. does anyone have experience with the first method? at this point, i don't really care how often my freezer or heater cycle on, so long as i can accurately control my temps.

I'm only using a single stage controller (for cooling), but the only time I get any noticeable overshoot is if I want to cool the wort by more than about 4 or 5 degrees F. The only time that happens is in the summer when the tap water is too warm to cool the wort to the desired temperature. When this happens, I insert the probe so that it is in the neck of the thermowell. There is enough conductivity for the wort to warm the body of the thermowell, which switches the freezer on, but because the probe is so close to the opening and the body of the thermowell (where the probe is) is surrounded by air, it cools sufficiently quickly to shut the compressor off before things get to cold. After 3 - 4 hours, the wort temperature is within a degree or two of where I want it, and I can push the probe all the way in, and forget about it.
If you need to adjust the temperature by a large amount, and you are monitoring the temperature of the wort which has to be warmed/cooled then you will get an overshoot because the wort will take a lot longer to respond to the heating/cooling than the air surrounding the fermenter.

-a.

thanks for the input, ajf. i use a post-chiller to make sure i get to pitching temps, so that's not a problem. i just want to be able to set my controller to the ideal temp and be able to walk away, without worrying about drastic temp swings and variances. and from what you're telling me, it sounds like there should be no issues when placing the probe directly into the thermowell. but i know i've read of others who had such problems. hopefully some others will chime in.

I have a single stage controller in my chest freezer and get good results with securing the probe to the outside of the carboy with a little added insulation (i.e. towels or styrofoam). The reason I dont use my thermowell is because I found that it resulted in larger "ambient" (inside the freezer) swings that would affect whatever other project I had inside the freezer at the time. My current method seems to work great. Right now I am lagering at 35 and the freezer kicks on about 3-4 times a day. You might have more compressor cycling this way but I think its worth it for the more stable ambient temperatures.

MedicinalMarisOtter said:

I have a single stage controller in my chest freezer and get good results with securing the probe to the outside of the carboy with a little added insulation (i.e. towels or styrofoam). The reason I dont use my thermowell is because I found that it resulted in larger "ambient" (inside the freezer) swings that would affect whatever other project I had inside the freezer at the time. My current method seems to work great. Right now I am lagering at 35 and the freezer kicks on about 3-4 times a day. You might have more compressor cycling this way but I think its worth it for the more stable ambient temperatures.

Click to expand...

I use this method as well, without the insulation. I use better bottles. I have found that duct tape will hold well to a clean, dry area on the side of the BB. It took awhile to dial in my process with a standard fridge and an analog single stage controller. By setting my controller 4-6 F colder than my target, I usually keep the temp on the stuck on thermometers within 2F of my target, if not dead on.

I have been toying with the idea of either a thermo-well or finding some other way to submerge the controllers probe so that it will be less susceptible to ambient temperature swings. Not wanting to put any additional ports in my BBs or bungs, I am considering using a small plastic pitcher of water in the fridge/ferment chamber. I figure I can place the probe in a large plastic bag to keep it from coming in contact with the water.

The water, having greater mass than the air in the fridge, should change temps more slowly. I would have to re-calibrate my process, but I would think this would allow me to keep a smaller differential between my set temp and my target temp.

The thinking is that this would make it less likely that the beer is subjected to large temperature swings.

MedicinalMarisOtter, did those large ambient temp swings also occur in the fermenter, or did that actually help keep the fermenter temp steady. what i want to know is if this will happen: set point is 67. probe in thermowell reads 68 and freezer kicks on to cool. by the time the probe reads 66, ambient is 45 (or less) and ferment temp continues to cool. the heater kicks on to warm, but in the time it takes the space heater to affect a change in the fermenter, the ferment temp is 63. then this process goes in reverse to the high side.

For me the biggest problem was the big drop in ambient temperature required to drop the fermentation vessel temp one degree. As you have described, the temp of the fermenting wort will continue to fall since the freezer temp has dropped so low. I dont remember it dropping more than another degree or two, but the problem for me was that the other things in the freezer (i.e. one gallon fermentors, bottles, etc) would experience large temp swings.

I found that by taping the probe to the outside of the carboy there are much smaller ambient temp swings and the vessel stays at a relatively constant temperature usually about 1 or 2 degrees above the ambient freezer temp during active fermentation. I would suggest giving this a try and possibly monitoring the beer temp with another thermometer in the thermowell for proof of a stable temp. Also, if your freezer and space heater are working against each other that sounds very ineffective. I dont have much experience with heating my chest freezer since I live in Arizona I only ever need to make things cooler, but the single stage controller works great for me