This question is probably more academic than practical, but here goes:
I'm using a Johnson A419 temp controller on my newly finished keezer. I have the set point at 42*F with a differential of 4*, which means the lowest temp the kegs will see is 38*F. I'm assuming an average temp of 40*, although maybe that oversimplifies the thermodynamics of the situation, I dunno.
So my question is, when using the volumes of CO2 tables (or Beersmith, in my case) to calculate the pressure to set my regulator at if I want, say, 2.5 volumes of CO2, should I be using the lowest temperature the kegs see to determine the correct pressure, or the average temperature they sit at? My gut tells me to go with the average, but if a little bit more CO2 gets into solution every time the keezer cycles down to 38*, I'm not sure how quickly it will equilibrate back out of solution as it warms back up to 42 after the compressor is done cycling.
Bottom line, I doubt this really matters enough to tell the difference in volumes of CO2 when actually drinking the beer, but my academic curiosity and futile pursuit of perfection in my homebrewing has gotten the better of me.