[hvacr]

Hey,
Im working on a Mcquay WMC just looking for some clarification. I have the EXV gain set at 175 and slope at 100. Can anyone tell me in english what the gain and slope refer to.
I want to speed up the unloading the chilled water leaving is at 45 and it doesn't start to unload untill 44.7 any sugestions.
I know that the EXV gain and slope have nothing to do with the unloading time Im just curious any info would be awesome.

 

[allchlrstech]

increasing the gain makes the evap run wetter(opens the valve % more as the condenser
delta t increases.)Increasing the slope changes the angle of the % open from 0-10deg
other words you use the gain to set discharge superheat loaded and you increase the slope to open the valve up more at lower loads to keep dicharge superheat down.
If you adjust one then the other needs to be checked at its low delta/higher delta t
condenser temp(10 deg cond temp should be fully loaded)

 

[450R]

Do you have access to the Turbocor software. If the compressor is in a chocke or surge the compressor will ramp up and not unload until the compressor is out of the chocke or surge condition. The settings can be adjusted to unload faster if these conditions don't exist.

 

[allchlrstech]

There is a upgrade software but you have to be a retrofit dealer to have it.You can adjust exv settings and try to run lower condenser water temps ,but if you look at the run envelope it will stay within the envelope to keep it from surging. a tubocore cannot handle a surge very well.Smarte and multistack are retrofits,McQuay does not do retrofits.Adjusting the exv will lower the lift,be carefull not to floodback the chiller,It will also cause a failure

 

[Randy S.]

Wouldn't you want to play with staging up and down rather than the TXV?

 

[hvacr]

Hello,
Thanks for the replys. I have the turbcor software. I was stacking refrigerant in the condenser. I had a full sightglass in the cond and evap was empty. I adjusted the lift to maintain about 40 degree lift. My low pressure alarm went away. I have a 3/4 full evap sight glass my cond is now empty i have adjusted my slope to maintain about 1.5 -2 degree approach through all my load ranges. My main concern was the low pressure alarm it was going off on.
Any input would be great.
TTYL.
Thanks again

 

[allchlrstech]

Slow the loading and stageing down and triy to get one compressor to load up before bringing the other on.Also check you mcquay presure limit settings.Hopfully you have a bypass and a fan vfd for your tower.

 

[hvacr]

Single compressor unit. I was going to ask on th wmc where can you fine tune the proportinal or the rate of unload. I would like to get it to start to unload quicker. spt at 45 starts to unload at 44.8. No tower bypass but the chiller is controlling the tower fan vfd.
Thanks
again