Keezer temp control help needed
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kev211
Well-Known Member
Its not the freezer youre trying to keep constant temp, its the beer. Put the temp probe into a jug of water and set the set point (SP) to the desired temp. The freezer will run when needed to keep the beer at the constant (or near constant) temp
Hanging a controller probe inside an empty chest freezer will produce the worst result possible.
The lack of thermal mass and an air-coupled probe will result in a short compressor cycle period.
As well, chest freezers exhibit quite a bit of cooling overshoot after the compressor is stopped, as the evaporator is left full of dense vapor which will continue to suck BTUs out of the interior.
This is a plot from my keezer temperature logger showing the keezer air temperature (at the top and bottom of the cabinet interior) along with the beer temperature (as measured by a probe covered with a 4x4" square of inch thick closed cell foam strapped against a keg), the tap tower air temperature, room temperature, and finally the compressor on/off state. Yes, it's a keezer, not a ferm chamber, but the operating model is more similar than not.
As can be seen the air temperature swings rather dramatically with the compressor (~12°F scope) with the last part of the negative slope following compressor shut-down. Meanwhile the beer temperature is maintained precisely within +/- 1°F of target, with fairly smooth transitions through each cycle. That last point is due mostly to the good thermal coupling to the keg and good thermal isolation from the keezer air.
So...if your freezer is empty, expect the worst. Fill it with fementors, do a decent job of thermal coupling and isolation with your controller probe, and good things will happen...
Cheers!
The lack of thermal mass and an air-coupled probe will result in a short compressor cycle period.
As well, chest freezers exhibit quite a bit of cooling overshoot after the compressor is stopped, as the evaporator is left full of dense vapor which will continue to suck BTUs out of the interior.
This is a plot from my keezer temperature logger showing the keezer air temperature (at the top and bottom of the cabinet interior) along with the beer temperature (as measured by a probe covered with a 4x4" square of inch thick closed cell foam strapped against a keg), the tap tower air temperature, room temperature, and finally the compressor on/off state. Yes, it's a keezer, not a ferm chamber, but the operating model is more similar than not.
As can be seen the air temperature swings rather dramatically with the compressor (~12°F scope) with the last part of the negative slope following compressor shut-down. Meanwhile the beer temperature is maintained precisely within +/- 1°F of target, with fairly smooth transitions through each cycle. That last point is due mostly to the good thermal coupling to the keg and good thermal isolation from the keezer air.
So...if your freezer is empty, expect the worst. Fill it with fementors, do a decent job of thermal coupling and isolation with your controller probe, and good things will happen...
Cheers!
kev211
Well-Known Member
Dont lie, thats not a real graph. Thats just a poorly drawn map of texas with double vision
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