Fermenter thermowell need and depth

[bruce_the_loon]

Got a STC1000C controlling my fermentation chamber, sensor is pinned to the side of the stainless steel fermenter by a 1/2" thick block of thermal insulation foam, located on the opposite side of the chamber to the chiller panels and fans. I'm seeing a reasonable duty-cycle on the compressor at fermentation temps, but at cold crash the temperature sensed by the STC1000C varies more than that of the body of beer as sensed by a Tilt and the compressor runs at 66% time on.

Given thermal transfer via conduction and convection in the beer volume, would I get a better sensing of temperature by putting in a thermowell and locating the STC sensor in the liquid volume directly? Am I cycling too rapidly because of the surface cooling on the fermenter tank or will I get the same issue no matter where the sensor is placed.

Another thing to consider in my mind is the depth to place the sensor in the liquid body. The fermenter is 12" across and 18" tall and I was thinking between 1 and 2 inches deep about halfway up the tank. I don't want to go in too deep as I'm concerned about introducing lag because of the thermal capacity of the beer.

Am I overthinking this or not? Calling on the centuries of wisdom in this forum.

 

[McMullan]

would I get a better sensing of temperature by putting in a thermowell and locating the STC sensor in the liquid volume directly?

Yes. I've been sticking thermowells in fermenting wort for several years now. Just this week I have confirmed why. I've been fermenting a lager in a corny keg in my small keezer. After monitoring keezer/compressor behaviour, specifically relating to probe position, it's clear in the liquid volume itself is the easiest way to get relative stability. So much so, when the keezer is serving, I'm going to use a keg thermowell to monitor/control temperature. Compressor fires up occasionally and undershooting target/set temperature is within 1°C.

 

[Control Freak]

Yes. I've been sticking thermowells in fermenting wort for several years now. Just this week I have confirmed why. I've been fermenting a lager in a corny keg in my small keezer. After monitoring keezer/compressor behaviour, specifically relating to probe position, it's clear in the liquid volume itself is the easiest way to get relative stability. So much so, when the keezer is serving, I'm going to use a keg thermowell to monitor/control temperature. Compressor fires up occasionally and undershooting target/set temperature is within 1°C.

Fully agree. I locate the Thrermowell 1/3 in from the exterior and approximately at the mid point height wise and get very consistent results.

 

[McMullan]

If we want to measure [it] stick a probe in [it]. That's the best option. Anything else is a compromise we have to be willing to accept.

 

[bruce_the_loon]

Cool, thanks for the info. So a 4" long thermowell at the mid-point will be best from your experience?

Time to order and find the step-bit.

 

[McMullan]

Mine range from 4" to 18". Depends what I'm sticking them in. Sticking it in somewhere about mid point is probably best generally.

 

[tracer bullet]

FWIW agreed that a thermowell is better and I always aim for the middle-ish of the height. Basically trying to get it in the middle from all directions. I have a few and just eyeball it.