Thermowell Question

[jmadway]

I just upgraded to a thermowell to use in my chest freezer fermentation chamber. For the last 2 years I've been controlling fermentation temps with a temp controller that I set 5 degrees or so below the fermentation temp I am shooting for. The temp probe would hang in the freezer itself and measure the ambient temp in the freezer. Generally, this method has worked well for me, but I have wanted more precise control.

My first experiment with my new thermowell was with a pale ale that I wanted to ferment at 65 degrees. I cooled my wort to 63 degrees, pitched the yeast, put the probe in the thermowell, put the thermowell in the wort, and set my temp controller to 65. My temp controller is set to start cooling when the temp goes 1 degree above the set temp and will cool until it goes 1 degree below the set temp.

So here's my question/issue:

When my fermenting wort hit 66, the freezer began to cool. When the wort fell to 64 the freezer turned off, but because the freezer was so cold after running for quite a while to get the wort down 2 degrees, that when all was said and done, the wort actually cooled to 62. So, throughout the early parts of fermentation, my temp was slowly fluctuating between 62-66, up and down.

My ambient temp control method seemingly controlled my temps better than this. What can I do to fix this issue?

 

[RM-MN]

Set your lower limit to 65. That way the freezer will chill it to 65 and shut off. You still might have it chill the beer to 64 but it won't stay there long. You have a controller working the way it should when you use a thermowell.

 

[jmadway]

Set your lower limit to 65. That way the freezer will chill it to 65 and shut off. You still might have it chill the beer to 64 but it won't stay there long. You have a controller working the way it should when you use a thermowell.

I'm not as concerned about nailing the 65 temp as I am about the 4 degree temp fluctuation. I can't imagine that this is acceptable for most people. What do others do?

 

[hannibalmdq]

I'm not as concerned about nailing the 65 temp as I am about the 4 degree temp fluctuation. I can't imagine that this is acceptable for most people. What do others do?

If your chamber is packing that much power, I'd just scrap the thermometer and tap the probe the side with some insulation on top. It'll cut off a little earlier and your thermal inertia won't take it down quite as far.

Lots of folks do it that way.

 

[doug293cz]

I just upgraded to a thermowell to use in my chest freezer fermentation chamber. For the last 2 years I've been controlling fermentation temps with a temp controller that I set 5 degrees or so below the fermentation temp I am shooting for. The temp probe would hang in the freezer itself and measure the ambient temp in the freezer. Generally, this method has worked well for me, but I have wanted more precise control.

My first experiment with my new thermowell was with a pale ale that I wanted to ferment at 65 degrees. I cooled my wort to 63 degrees, pitched the yeast, put the probe in the thermowell, put the thermowell in the wort, and set my temp controller to 65. My temp controller is set to start cooling when the temp goes 1 degree above the set temp and will cool until it goes 1 degree below the set temp.

So here's my question/issue:

When my fermenting wort hit 66, the freezer began to cool. When the wort fell to 64 the freezer turned off, but because the freezer was so cold after running for quite a while to get the wort down 2 degrees, that when all was said and done, the wort actually cooled to 62. So, throughout the early parts of fermentation, my temp was slowly fluctuating between 62-66, up and down.

My ambient temp control method seemingly controlled my temps better than this. What can I do to fix this issue?

A thermowell deep in the wort/beer is not optimal for avoiding over/undershoots. It's due to the lag time for the beer to cool/heat to where the controller shuts off the cooling/heating. The chamber has way over/under shot by then, so the beer continues to cool/heat. With a single temp probe, you are better off attaching the probe to the outside of the ferm vessel with a little bit of insulation from ambient. Don't use too much insulation, or you will have the same problem you have with the thermowell. There are solutions that work better for beer temp stability that use two temp probes. Two of these are an STC-1000+ with software version 1.06 or higher, and BrewPi. There are very popular threads for both of these on HBT.

Brew on

 

[Majd]

Right on guys, thank you this thread was very helpful to me.


Sent from my iPhone using Home Brew

 

[Queequeg]

Use a water bath and an aquarium heater for your heating phase. I do this and because of the thermal mass of the water(~40L) I get only a 0.4°C variation between max and min temperatures.

 

[LLBeanJ]

I use a thermowell and have no problem maintaining ±1°F. It will overshoot when trying to swing the temp a large distance, say from 75 to 65, but in that case I would set it to stop short, say around 68, and it will usually overshoot right to about where I intend it to be.

 

[hannibalmdq]

I use a thermowell and have no problem maintaining ±1°F. It will overshoot when trying to swing the temp a large distance, say from 75 to 65, but in that case I would set it to stop short, say around 68, and it will usually overshoot right to about where I intend it to be.

I think a lot of it has to do with the cooling power and insulation of your refrigeration system and the size of your batches. People using a chest freezer or doing large batches have a lot of thermal mass/inertia in play.

If they only need to cool a degree, and their freezer kicks on blowing 0 degree air into the heavily insulated chamber and their thermowell is deep inside a large volume of wort it's totally possible that they've overshoot by a large amount.

By contrast, I'm using a Son of Fermenter chamber with a thermowell in a 2.75 gallon batch. My temps are pretty much pegged within a degree during the whole ferment. When my fan kicks on, it's only going to drop the air temp about 10 degree to 15 degrees (max). Most of the time is only about 3 to 5 degrees. There's not a lot of temp different to overshoot and while it's insulated, it's nothing close a sealed and well built fridge.

Different effects on different systems.

 

[LLBeanJ]

I use a chest freezer and ferment 5.5 gal batches. My freezer doesn't have a fan, though. It's just radiant cooling in the freezer, as well as radiant heating using a paint can heater w/ 40w bulb.

I do agree with you that different configurations would likely result in different behavior as far as temp swings go. I guess I got lucky that my config is such that I don't have any issues.

 

[jbb3]

I use a thermowell with an STC-1000. When it was set with a 1 degree differential, it would over or undershoot the temp by a few degrees. I changed the differential to .5 degrees and now it over/under shoots the temp by only a few tenths.