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Old 06-10-13, 09:06 AM   #20
AC_Hacker
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Quote:
Originally Posted by Daox View Post
I mean what is your temperature setting and allowable range? A quick look at your code suggests 38 +/- 2 degrees F. But your latest posts seems to suggest you want the temperature held more steady.
OK, just to make sure that we're on the same page, I ordered a Chinese thermostat, and while I was waiting for it to arrive, I hacked together a Teensy (Arduino) thermostat that used an analog temperature sensor. Aside from the fact that it didn't have a temperature display, it worked pretty well.

Then when to Chinese version arrived I started using it (and as of this writing, still am). That's when I noticed the too-large swings and too-large steps in targeting the set-point temperature.

The reason this is important is that it looks possible to me that this setup may be capable of keeping food acceptably cool while avoiding most, if not all problems associated with frost buildup. This is because the chill area is larger than in a normal refrigerator, and the temps don't have to go as low in the evaporator coil to provide the cooling. It's the same thing as low temperature heating, only this is high temperature cooling. Low exergy, etc.

So, the behavior of the Freezerator seems to be such that if I can get right at the 'sweet spot' it should work better.

I have found that there is an optimum hysteresis swing amplitude, and that if the hysteresis is too tight, the compressor cycles too often, and that uses up more energy... if it's too loose, the system bounces between food-too-warm and frost formation on the coils.

Another issue connected to frost buildup is that making frost requires the refrigerator to supply additional energy that would not be required if I can avoid too-cold temperatures or too-low hysteresis swings.

A third issue with frost buildup is that it has a de-hydrating effect on produce, and shortens its storage life. Since I am becoming a vegetarian, this is a big deal. I have noticed that in general, the humidity inside the Freezerator is unusually high for a refrigerator, and my produce like it that way.

Another issue with the Freezerator Rev 1 is that my previous analog sensor was exhibiting irregularity that may have been due to humidity... I don't know for sure, but I do know that keeping the sensor dry is a good thing.

So in the next revision, I want to use a 1-wire sensor that is properly protected from humidity. And I want to make sure that I have precise control over temperature and hysteresis. And a display, and a proper interface that will give me the ability to change the set-point and hysteresis by using buttons rather than needing to hook up my PC to my refrigerator.

Hope this addressed your question.

-AC
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Last edited by AC_Hacker; 06-10-13 at 10:09 AM..
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