Fan Program...what am I doing wrong?!

[Bill_Moorman]

Hello all!

I have been having the darnedest time with this fan program.

Fallback Off
If tmp > 80.9 then on
If tmp < 79.6 then off
Min time 015:00 then on

I want it to come on at 81, stay on at least 15 minutes, and then turn off at 79.5

However it’s currently 79.1 and the fan is still running.

Help?

 

[ihavecrabs]

Hello all!

I have been having the darnedest time with this fan program.

Fallback Off
If tmp > 80.9 then on
If tmp < 79.6 then off
Min time 015:00 then on

I want it to come on at 81, stay on at least 15 minutes, and then turn off at 79.5

However it’s currently 79.1 and the fan is still running.

Help?

Try adding "Set OFF" after the fallback command.

#Apexusers

 

[ihavecrabs]

Oh and I'm not sure about your min time statement.. I think what it is doing is turning your fan on again after 15 minutes of it turning off. This might be your problem.

If you are looking for it to stay on for a minimum of 15 minutes, I'd use the following command.

Defer 015:00 Then OFF

Add it after the ON command

 

[Bill_Moorman]

So something like:

Fallback OFF
Set OFF
If Tmp > 80.9 Then ON
Defer 015:00 Then OFF
If Tmp < 79.6 Then OFF

Does that look right?

 

[ihavecrabs]

So something like:

Fallback OFF
Set OFF
If Tmp > 80.9 Then ON
Defer 015:00 Then OFF
If Tmp < 79.6 Then OFF

Does that look right?

Yes..

However, now that I think about it, based on the order it is in, it may turn off after 15 minutes without getting down to 79.6, but will turn back on again when it gets above 80.9.

Is that what you were looking for.

 

[Bill_Moorman]

I just am trying to prevent it from cycling on and off giving around a half degree. Not sure the best way to go about it!

 

[ihavecrabs]

I'd try both and see which one works best.

 

[Pezking182]

You can prevent cycling by setting a dead band. So...

if tmp > 80 + . 5 then on
If tmp < 80 - . 5 then off

In this case your target would be 80 and the temp would be allowed to drift +-0.5deg. If it was above 80.6 it would turn on until it dropped below 79.6

You could also add an or statement like...

If tmp < 79.6 or min time >015:00 then off

This would shut off the fan if either condition is true.

I dont know what controller this is as I dont have one. But I am a control engineer and write code for commercial building automation systems. Generally anticycling is done with a minimum off duration, not a minimum run time, but I understand why you want want minimum run time. Also, programs will execute the last command given. So in your case,
Min time 015:00 then on will execute and turn the fan back on.

Again, just my .2 cents

 

[Drauka99]

So something like:

Fallback OFF
Set OFF
If Tmp > 80.9 Then ON
Defer 015:00 Then OFF
If Tmp < 79.6 Then OFF

Does that look right?

I would replace the Defer line with the Min time like you had the first time, So:

Fallback OFF
Set OFF
If Tmp > 80.9 Then ON
Min time 015:00 then ON
If Tmp < 79.6 Then OFF

that should do as you want. The fan will run of a minimum of 15 minutes when it is triggered.

IMO, The defer command likely works but Defer is more to "defer" a command for a time to ensure a state BEFORE something is triggered, like a float switch bouncing between open and closed.

 

[Sleepydoc]

You're trying to use min time and defer to avoid rapid cycling of the fan, but you already have a hysteresis built into your program by having the on temp 1.3º higher than the off temp. There's no way your tank will cool down by 1.3º in less than 15 minutes, but if it did, you wouldn't necessarily want the fans to keep going and drive the temp down further.

Also, adding the 'set OFF' statement defeats the hysteresis.

You should be able to use:

Fallback OFF
If Tmp > 80.9 then ON
If Tmp < 79.6 then OFF

 

[SuncrestReef]

This is what I use for my fan. The Defer commands turn it on once the temp reads 78.2 for at least 15 seconds, and stays on until the temperature reads 78.0 for at least 15 seconds. I've found it runs for about 7 - 10 minutes roughly once or twice per hour and maintains the temperature between 78.2 - 77.9, which isn't much of a noise nuisance.

Fallback OFF
Set OFF
If Tmp > 78.1 Then ON
If Tmp < 78.1 Then OFF
Defer 000:15 Then ON
Defer 000:15 Then OFF