Using Temperature Ramping on a Freezer

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RiverCityBrewer
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Using Temperature Ramping on a Freezer

Post by RiverCityBrewer »

I've been using the BCS quite a bit for brewing, and recently acquired an upright freezer for fermentation control. I've already wired it for cooling and heating and I have 13 gallons on pils in it right now fermenting at 52 degrees. I am interested in using the ramp feature to slowly lower the temperature about 15 degrees, but I am concerned with how often it will cycle the compressor on the freezer since it uses a differential or PID. In my normal state I have the freezer run a constant ON until a temp setpoint is reached and then it turn off for a certain time before it can run the compressor again. My main concern is short cycling the compressor, so does anyone have any experience with using ramping with a cooling unit that can explain how it works a bit better?

Thanks,

Joe
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Re: Using Temperature Ramping on a Freezer

Post by BCS Portland »

Did you read this thread? http://www.embeddedcontrolconcepts.com/ ... 04797#p921

Think it will have some good info for you.
RiverCityBrewer
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Re: Using Temperature Ramping on a Freezer

Post by RiverCityBrewer »

I actually used that thread to help me develop the initial cooling state, but unless I missed it somewhere I didn't see anything about using ramping during a cooling process? Any ideas?

Thanks,

Joe
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ECC
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Re: Using Temperature Ramping on a Freezer

Post by ECC »

Hi Joe. There are two ways to keep your freezer from cycling too often.
  1. Create a temperature deadband. Use the differential control of the output, and make sure that your "Differential Swing" is set to a reasonable value. For example, if the setpoint is 40deg and you have the Diff Swing set to (the default) of 4deg, the Freezer will hold the temp between 38-42deg. Since it takes significant time for the freezer to cool (or warm), you will have a built in delay that will slow the cycles.
  2. Slow down the "PID Sample Period". This setting is not only for PID control, it affects how often the BCS samples the temperature to determine when to assert outputs. It defaults to 3sec, but if you slow it down to say 60sec, it will only read update once a minute. So, keeping our Differentially controlled freezer output example, if the BCS read a temp reading of 41deg, it wouldnt' read teh temperature again for a full minute. But this means that if it read 43deg and asserted the output to cool, at a minimum it wouldn't stop cooling until after it read a temperature below 38deg (in 60sec increments).
#1 is most commonly used, but if you want to keep a smaller deadband you might experiment with #2. We don't recommend using PID control for freezer, since the Differential Swing setting has no effect in PID control mode.
RiverCityBrewer
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Re: Using Temperature Ramping on a Freezer

Post by RiverCityBrewer »

Ok, so you are saying that if I wanted to use ramping to crash a beer that I should use a differential control with a swing of 3-4 degrees? I'm assuming that I set that when I set the ramping up for the state and assert the output with diff control?

Thanks,

Joe
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ECC
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Re: Using Temperature Ramping on a Freezer

Post by ECC »

Exactly. Set Differential Control in the output table. Normally the temperature setpoint is entered in this table as well, but in this case it will be overridden by the ramp mode calculated temperature setpoint. The ramp will vary the setpoint based on start/stop/duration of the ramp, all the while using the Differential Swing setting that you program in the System Settings page.
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Re: Using Temperature Ramping on a Freezer

Post by RiverCityBrewer »

Its working perfectly, thanks for the help and explanations.

Joe
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