Unusual Temp experience

Ok, so last monday I brewed an 11 gallon batch of a Classic American Pilsner and split it into 2 carboys, one was a Big 6.5 gallon "Fat" smooth sided carboy and the other is a "Tall" 6.5 gallon raised textured (strengthening ridges), both have exactly the same amount of beer in them, and both have temperature strips on the outside of the carboys.
they have been fermenting at 50 degrees (as measured by 2 different temp probes). the funny thing is the the "Tall" carboys temp strip is showing 45 -46 degrees F and the Fat one is holding steady at 50 degrees F.
have any of you ever noticed differences in yours located in the same environment?
I am not really concerned at all, I was just wondering how accurate they are from others experiences. the thermal mass is exactly the same, but with the tall one being narrower (smaller cross section), do you think its really possible for it to be colder than the fatter one?

 

What happens when you swap the strips? Maybe they are just calibrated differently.

But the closer a bottle is to a sphere, the more heat that will be retained.

 

I think of temp strips as being an educated guess and they get less accurate with age.

 

I dont really use them for anything but general idea anyway, the question was focused more on the actual discrepancy between them and the carboy size.....

 

Surface area to volume ratio is the answer...the taller carboy has more beer touching the surface of the carboy...the fatter one has more beer insulating itself from the environment. More surface area will disipate heat formed from the exothermic reaction of fermentation better than the fatter carboy. Its the same principle in humans...babies have a larger surface area/volume ratio, meaning they are more prone to losing heat.
-Jefe-

 

Remember the control temp is set at 50F. One reads correctly at the control temp, 50F. The carboy whose temperature is off is 45F. More efficient heat transfer doesn't explain being 5F colder than the control temp.

 

You're right. I didnt see it that way. I guess if the fermentation chamber is set at 50 its pretty hard to get an exothermic reaction to be get lower than ambient temp.

David42 is probably right...its probably a bad temp strip.

of course, the set temp of 50 degrees means that's the "average" temp...meaning that temp swings will occur above and below that measurement. So its possible that the strip is only a few percent off whilst appearing much more.
-Jefe-