It is time for another story in the unending saga of my life. I have been working on my chiller settings today since it is getting warm in Texas. I have been trying to understand "hysteresis" and "cooling difference." The manual is less than clear on the issue and after some research I would say that it is not completely correct.
I was searching and searching for this information on-line. The specific issue that I was having is calculating the cut-off point. I wanted to know the point that the chiller turned on and the point where the chiller would turn off.
The manual has a formula for calculating the turn on point, but does not explain the point that the switch turns off.
The formula for when the chiller turns on is X = Nominal Temperature + 5/6 times hysteresis + cooling difference.
So if the nominal temperature that I want is 78, hysteresis of .6 and a cooling difference of 0, then the chiller will come on at 78.5. The equation is X = 78 + 5/6 * .6 + 0. X equals 78.5. What is the shut off point?
There is nothing in the manual that tells you what the shut off point will be. The manual makes it appear that the shut off point would be 78. But this is not correct. I believe it can be calculated using the following formula X= Nominal Temperature + 1/2 times hysteresis + cooling difference. So if the numbers are the same as the example above then the equation would be x = 78 + 1/2 * .6 + 0. Therefore, X would equal 78.3.
So what is the funny story about this? Well in searching the internet I found a forum post that sets out this exact same problem from 10 years ago and it explained a possible solution. The post was made by ME. You can see it
HERE.
Now taking the information that I posted from 10 years ago and the other knowledge I learned in my new set up. Here is my solution for heating and cooling to a temperature of 78 (and reviews are welcome).
1. I used the existing temperature sensor and set the nominal value at 78.1 and set it to Pulse Variable mode with a 10 minute pulse and a 1 minute pause. This works really well at keeping the temperature between 77.9 and 78.
2. I set up a virtual temperature probe that I set up to regulate the chiller. The reason I did this was because there were comments that you should not use the pulse variable mode to regulate a chiller. On this probe I sent the nominal value at 77.5. I set the cooling difference at 0 and hysteresis at 1.49. Using these numbers the chiller should come on at 78.75 and turn off at 78.25.
Finally, I would just mention that to a non-math person the manual on this issue might as well be written in Chinese. Let me give you just one example and that is what does the "cooling difference" even do.
Does it just add to the temperature before the chiller turns on and then cools the aquarium to the original temperature set point? The instructions make it sound like this is what it is intended to do because it says that it allows more time between cycling the chiller.
But it appears that this is not what it means. What is really means is the it adjusts the on and off points for the chiller by the amount of the "cooling difference."
Now if you are a math person this may seem very clear to you in reviewing the "formula." But to us non-math people it might as well be Greek. Ha!
So thanks in part to memory lane regarding a post I made on this same issue 10 years ago, I solved my chiller settings issue today.
