So I bought a giant keg box
with a Ranco controller. I am going to start kegging, but in the meantime (and afterward) I want to use this to cold condition ales, and ferment lagers and lager starters. So I figure if I can get everything I put inside this to 48°F, then I'm good. It's on the low end of what most lager yeasts can still ferment at, keep my on tap beers cold (but not too cold), and it should still help cold crash ales in secondary.
I have my ranco set at 48°, with a 5° differential (centered), so it will kick on the compressor until it reaches 43°, then shut off until it reaches 53°. In my mind it seems like the average temperature is 48°, so eventually anything I put in there will reach the same temp. I have calibrated this with several thermometers inside the unit, and the ranco probe is within a degree or two of agreeing with all of them.
But what I'm finding out is that it either takes a very long time for these masses of liquids to come down to temp, or the air temperature needs to be lower in order to get the beers down to the temp I want:
I put 7 gallons of doppelbock (in primary, but done fermenting) in, with a thermometer lead inside the liquid. It was 51° when I put it in, now it is at 52° after 24 hours.
I put 5 gallons of cream ale (in secondary, cold conditioning) in, again with a thermometer inside, and after 48 hours it has gone from 64° to 54°.
So I am not a physics major by any means, but are there any general rules for setting a thermostat on a fridge (when using the inside air temperature for reference) to control the temperature of large volumes of liquid? Should I set the temp 5° lower, just be more patient, or is it a trial and error thing?