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Old 07-20-2009, 07:33 PM   #1
stoutaholic
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Default Two-stage temp control with a single-stage controller

Tell me if this is a dumb idea. It is really simple, but I haven't read of this technique before, and it seems like it would work.

I only have a single-stage temperature controller - a RANCO ETC-111000. But when I want to ferment ales, sometimes the ambient temperature of my house varies around the setpoint that I want to maintain. If I had a two-stage controller, I could put a heating pad around the fermenter and put the fermenter in the fridge, and then hook both up to the two-stage controller. However, I was thinking, why not just hook the heating pad up to my single-stage RANCO and then set the refrigerator temperature to about 10 degrees below my desired fermentation temperature? The refrigerator, using its OWN thermostat, will then ensure that the fermentation temperature never exceeds the setpoint, and the RANCO, together with the heating pad, will ensure that the fermentation temperature never drops below the setpoint (or, at least, not for very long). An added advantage of this approach is that the refrigerator will not have to cycle on and off as frequently - it can operate on a pretty lenient differential, thereby saving wear and tear on the compressor.

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Old 07-20-2009, 08:49 PM   #2
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Might work. But I think your fridge will just try to work harder to get the temp down, without regard for the heating pad. Even though you set it higher, it is just going to keep working hard to get where it wants to go.

It might work, but I think it will actually be less efficient because you have two devices working against each other. It's like driving a car with the hand brake on.

It's worth an experiment though.

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Old 07-21-2009, 04:09 AM   #3
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I think it might work. I do not think it will be more efficient for the reason discussed by noeldundas. The way I read it is that the controller will be controlling the fridge and not the heating pad. Although it may not be extremely effecient it may be better than having to buy more equipment. Give it a shot.

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Old 07-21-2009, 07:18 AM   #4
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My first question would be--'how much amperage is the heating pad drawing?', since I'm guessing it will be on all the time? You might give it a test run with the fermenter filled with water. As long as the fridge is not cycling too often, it may be okay.

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Old 07-21-2009, 07:07 PM   #5
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Thanks, these are good points. As you all pointed out, the main concern is that the heating pad and the refrigerator could be constantly "fighting" against each other. This would occur if the refrigerator's setpoint is significantly lower than that of the heating pad, thus requiring the heating pad to run almost constantly, and for the refrigerator in turn to run much more frequently. This makes me think that this approach would not work so well for ales, because I wouldn't be able to set the refrigerator's thermostat close enough to the fermentation temperature. For instance, if my fermentation target was 65 F, and the refrigerator's differential was 5 degrees, then I would want to set the refrigerator's thermostat to 60. But I don't think any refrigerator allows you to set the thermostat that high.

I think this method would work, though, for maintaining lager fermentation temperatures. If the refrigerator's thermostat could be set within, say, 5 degrees below the target fermentation temperature, and the refrigerator has a differential of 5 degrees (i.e. it only turns on when the temp rises 5 degrees above its setpoint), then it will kick on only when the air temperature in the refrigerator is equal to the fermentation temperature. If the air temperature is only ever 5 degrees lower than the desired fermentation temperature, then there will be a significant time delay for the fermentation temperature to drop 1 degree. In other words, if the fermentation temp is 50 and the air temp in the refrigerator is 45, then it will take a while for the fermentation temp to drop to 49. At that point the heating pad will kick on for a while and heat the fermentation temp back up to 50. But this will not immediately bring the air temp in the refrigerator back up to 50, so there will also be a delay until the refrigerator kicks on again. Thus, neither the refrigerator nor the heating pad should be running constantly if the two setpoints are close enough. So, for lagers, I think this technique would work.

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