Fermenter Temp Probe Positioning?

[mjphoto]

Hello All,

I know this question has been asked time and time again but I am programming code using an arduino (not using BrewPi) to set up a fermentation chamber (fridge).

I am wondering if anyone knows; does brewpi use both temp probes (one in the thermowell/taped to the side and the ambient temp of the fridge) to control the temp or is it controlled off one of the probes and just monitors the other?

I keep flip flopping between wanting to control the temp from the thermowell to the ambient with pros and cons both ways. What is the best way people have found?

 

[Pkrd]

The thermowell is the best reading of the temperature of the beer, you should definitely use that.


Welcome to HBT!

 

[FunkedOut]

Timely thread. I've been asking myself the same question.

I'm using a 7.1cf chest freezer that fits a couple buckets. It will have more cooling power than a fridge, so things might be different in a fridge.

I hooked up an inkbird in a thermowell, and it would consistently undershoot by 2*F then overshoot by 1*F. Not bad, really.
Peeking inside at max/min wort temps, I'd see a range of ~50*F to ~70*F air temp.

I figured controlling by air temp would produce less wort fluctuations but may take longer to reach desired temp.

Then there's the 'insulated tape it to the side' method for the controller probe...

Anyway, racked the beer and have 5gallons of starsan in there now, running some tests every which way. I bought a second inkbird to monitor 2 temps at a time without disturbing the peace.
If you have a week or so to wait, I'll have some data soon.

Trade you data for code?

 

[mjphoto]

So I would get a more stable temp from the chamber as opposed to the ambient temp of the fridge. I would have thought you would get big over and under shoots on the chamber as theres a lot of thermal mass to be heated/cooled and the fridge would be working pretty hard getting quite hot and quite cold to keep up??

 

[day_trippr]

An empty chamber will exhibit the worst behavior wrt big overshoots. Thermal mass will fix that. Then the question is, what do you want to actually control - air temperature, or wort/beer temperature.

fwiw, here's a simplified plot of one of my ferm chambers just showing the beer and fridge (and room) temperatures. You can see the chamber temperature is all over the place while the beer temperature - taken from a well-insulated probe strapped to one of the two carboys - plods along in a predictable low-hysteresis mode.



Similarly, a plot of my keezer temperature log, showing a +/-1°F deviation from set point for the keg being tracked (again, with a strapped well-insulated probe) while the keezer interior temperature swings a solid 12°F.



I assume a thermowell would provide similar results - many anecdotal testimonials claim they're perhaps a half-degree F more accurate as they're not directly affected by air temperature. But they're a bit of a pita to deal with (one more thing to sanitize) and pretty much a non-starter for kegs. And I'm not sweating over a half-degree F...

Cheers!

 

[mjphoto]

For anyone interested it appears BrewPi use 3 different PID controllers. They control the temp of the fridge by using a PID algorithm comparing the fermentation chamber to the ambient fridge temp working out what the set point of the fridge needs to be, then have two other pid controls to control the heat and the cooling. They seem to use some sort of PWM or time proportional control.