Temp control for an AC based coldbox fermentation chamber

[jward]

I picked up a 5000 BTU AC unit which is tiny, meant only for 100-150 sq. ft. room. The initial plan is to cool a cold box and use an computer fan to help transfer cold to the fermenter (usually a 10g batch SS). The AC built in controller adjusts down to 60 degrees as it is. I have been considering different ways to control the temp.

The easiest approach would seem to be to set the AC to the desired temp, run the fan constantly and see how well it holds temp. I would expect the unit has some hysteresis that would allow the temp to fluctuate too much not to mention that air at the desired fermentation temp may have trouble pulling the fermentation temp down.

Another simple approach would be to run the AC set at 60F, run the fan, and use one of the thermostats (I already have one of the RediTemp? units like Derrin modified to put the thermistor in a thermo-well in the fermenter) set to the fermentation temp so that the AC runs at 60F but only when the fermenter need cooling. The AC unit should take care of itself and not require any modification. It would have some pull down, but would it be enough?

Another approach would be to open the AC unit and use the thermostat that measures the wort temp to control the AC unit. This should allow the AC to run air temp very low in the cold box providing better cooling. The thermostat may have hysteresis issues or short cycle the AC unit. I have never opened an AC unit, but have replaced thermostats before. Are there other issues?

When I do a 5g batch I use a foam cold box mounted on a dorm fridge that has only an analog circuit to control a computer fan which blows cold air from the fridge to the fermentation box. If its quiet enough one can hear the fan slow down and stop (still powered but not enough voltage to keep it running) and then later spinning pretty fast once the voltage rises enough to start the fan again. That controller holds the fermentation temp pretty well.

[backyard brewer]

What else is it going to do? Just cool a fermentation chamber or will it be larger with beer storage as well? 60* doens't seem cold enough for most applications.

Which ever way you are doing it, I'll be happy to help. Bring your thermostat over and I'll modify it for you.

[jward]

I was thinking about having room for some keg storage. I'd like to use only the 2 sheets of insulation I have, and I want to limit the amount of garage space I use too. I was thinking more cellaring beer then refrigeration.

I'll have to bring over the thermostat for sure, thanks.

How cool can an R22 AC cool?

[backyard brewer]

I was thinking about having room for some keg storage. I'd like to use only the 2 sheets of insulation I have, and I want to limit the amount of garage space I use too. I was thinking more cellaring beer then refrigeration.

I'll have to bring over the thermostat for sure, thanks.

How cool can an R22 AC cool?

Technically R22 boils at something like -41*F. But the compressor won't be designed to deal with the refrigerant at that low temperature and the efficiency falls off to where it hits as cold as it will go. Below freezing shouldn't be a problem in a well insulated small box.

[jward]

Another simple approach would be to run the AC set at 60F, run the fan, and use one of the thermostats set to the fermentation temp so that the AC runs at 60F but only when the fermenter need cooling. The AC unit should take care of itself and not require any modification.

The AC unit has a spiffy digital controller that sets itself to 79F on power up. That kinda messes up this approach.

Another approach would be to open the AC unit and use the thermostat that measures the wort temp to control the AC unit. This should allow the AC to run air temp very low in the cold box providing better cooling. The thermostat may have hysteresis issues or short cycle the AC unit. I have never opened an AC unit, but have replaced thermostats before. Are there other issues?

Didn't you take apart your AC and replace the thermostat? Do wall thermostats have safety features like delays in between compressor starts, running the fan after the compressor shuts off, etc?

I wonder how much energy fermentation puts out? Another approach would be to run the AC on lowest setting until the wort hit fermentation temp and then set the AC to the fermentation temp.

[backyard brewer]

Not all thermostats have short-cycle delays, but the 8029B you have does and would be fine.

Yes I did bypass the internal thermostat completely and could do so with yours as well. Bring them both over and we'll see what we can do.

[dhempy]

OH God! Derrin is such a Geek! Next year for The Fest I'm going to get a BrewCommune propeller hat for you'

I swear Derrin ... you're a real geek ... my kind of guy!!! I really wish we lived closer together ... we would have to have our own Tinkerers forum.

Brief hijack:

Check this system out. Serious geek for sure. WIth guys like you, this guy, and Yuri_Rage from the HBT board, we could do some real damage to manual processes

Dan

[kevinham]

Dan, you are on HBT too? Where you at on there?

[dhempy]

Dan, you are on HBT too? Where you at on there?

Same UID ... dhempy ... haven't posted much .. I mostly lurk and plagiarize stuff!

Dan

[kevinham]

Dan, you are on HBT too? Where you at on there?

Same UID ... dhempy ... haven't posted much .. I mostly lurk and plagiarize stuff!

Dan

I see, only 6 posts. You have probably seen my avatar on there. My name is findthefish.