Danfoss Pack Comtrollers

[Mattym_200]

Evening guys
I have a few questions relating to Danfoss pack controllers, I tried.askimg a colleague but he wasn't so sure, hopefully somebody can clear this up.

If a pack is set to 3.2 bar and the neutral zone is 0.4 is that 0.2 either way of the set point or 0.4?
Then there is + zone in bar and + zone in minutes and - zone in bar and minutes, then there's ++ zone in bar and minutes then - - zone in bar and minutes can somebody clear these up for me?

To my mind the pressure in the + zone is at this so long before staging in another compressor and the ++ zone is the same until reaches the - zone in bar for so long or would it stage it out at the -- zone.

Sorry for the ramble but I need a better understanding of this as the guys I work with can't amswer it looking at the danfoss paperwork its still not very clear.

Thanks

[Glenn Moore]

Basically the way it works is
The set point or reference is 3.2 Bar
The neutral zone is 0.4 Bar this sits on the set point ie 3Bar to 3.4 Bar
The + zone is just above the NZ and the — zone is just below the NZ
The ++ zone is above the + zone
Whereas the— — zone is below the — zone
The + and — zone say are set to 0.5 bar each with delay times set at 60 secs
The ++ and — — zones say are set to 30 seconds

So what happens as follows :-

At start up the pressures high say 7 Bar
So the systems in the ++ zone . So every 30 seconds another machine is switched on and so on.
After a while the suction pressure drops as the load drops and the suction pressure falls . So once the suction pressure drops to say 3.8 Bar it’s now in the + zone .As its now close to set point more load is introduce every 60 secs .the longer times allow the system pressure to stabilise. If the suction pressure continues to fall into the NZ no load or unload signals are sent to the controller. If the suction pressure now falls into the — zone ,every 60 seconds capacity is switched off to allow the suction to hopefully rise back up into the NZ . If the pressure continues to fall into the — — zone then the capacity steps are reduced every 30 seconds .so as the load drops off the suction pressure rises and the system goes from the shorter time capacity steps in the — — zone back into the faster unload steps in the — zone and then into the NZ and that’s where the desired control should be .
So by playing with the ++ and — — zone timer you can get either a quick response to bring on more load (++) or reduce capacity quickly (— —) .
The + and — zone are close to the set point /NZ area so the capacity steps load or unload are set for a longer time to allow the system to stabilise rather ramping up and down like a yo yo
Hope that helps if not pm me and I’ll talk you through. it
You need to see how quickly the capacity steps up and down change the suction pressure then set the NZ and the zone timers and setting to suit the equipment .
Big steps like compressors need longer delay times whereas unloaders normally need shorter time delays as the influence on the system is less

[al]

Excellent Glenn, I'm trying to get my head around one at the moment! On a side note, do danfoss have an app for the pack controllers?

[Mattym_200]

Thanks for that reply Glenn that's cleared it up quite well the paperwork that comes with controller doesn't explain it well at all, the reason I ask is I had a pack pumping down and tried going through the settings but didn't see anything that screamed it's this.

[Glenn Moore]

Matt
What settings have you got for the zones this would help in advising what settings may help you . What type of expansion valves can have a bearing on this as well

[Mattym_200]

No worries I know they are Danfoss AKV if I can get to site tomorrow and let you know that would be much appreciated.

[Glenn Moore]

Hi Matt
Just a little info for you .
When using AKV pulsed expansion valves it is often necessary to have small time periods in the — zone and the — — zones as if several AKV valves go off in quick succession then the suction pressure will fall rapidly and so short times are needed to quickly reduce the capacity to prevent LP trips