Yeah,
you can connect with HVACpro and manually change the mode from H to C
...if you have an NCM then write some JCBasic
...NAE ( pftt...who knows)
...Tridium create a point for H/C mode and copy/paste into each controller.
Hey guys,
I had to commission some PIUs today, johnson controls VMA controllers. Im kind of new to them (and control's in general I guess..2 yrs). when I override the fan or heat on they come on immediately and work fine, but if I override the space temp, to say, 1 degree Fahrenheit , it takes forever to go into heating mode, I didnt actually time it but id say at least 15 to 20 mins. Is this normal, or is there some logic somewhere that I can alter. Ive read the help manual and cant really find anything.
thanks for any input
Yeah,
you can connect with HVACpro and manually change the mode from H to C
...if you have an NCM then write some JCBasic
...NAE ( pftt...who knows)
...Tridium create a point for H/C mode and copy/paste into each controller.
1 + 1 = 3 ( *** for very large values of 1)
...everybody wants a box of chocolates and long stemmed rose
Be brave. You cannot get eaten by an imaginary tiger.
Don't know how you are doing your overrides but a VMA responds a bit faster if you change (override) the setpoint to 95 degrees than if you mess with the Zone Temp. The Zone Temp is "Gonkulated" internally with buffers and offsets before it hits the control loop. Give it a try
If sense were so common everyone would have it !You cannot protect the Stupid from themselves !"Experience is the ability to recognize a mistake Before you make it again!" (Stolen Quote)
FWIW,
I recently had to work on some VMA's that were serving an Art Museum's Galleries. They were having an exhibit that demanded tight temp control from the Parallel Fan-Powered VAV's with VMA's serving the area.
What I found was with the Occupied Bias (viewed thru HVACPro) set at 1 Degree prevents the VMA Heat or Cool Demand percentage from STARTING to build until the zone temp is 1 Degree from setpoint. I found the lowest the VMA101's will allow is a 0.150 Occupied Bias Setting.
So each now starts building when the Zone Temp is only 0.150 Degrees from Setpoint.
The Museum's 24 Hour Temperature Pen/Paper 24 Hour Chart Flatlined at setpoint...
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Overide the box mode to satisfied with zn-t less than actual heating setpt, this will bypass the saturation timer. As long as this is a recent hvacpro ver config (7.01^), this will work.
Like CCI Kelly stated - tweak the setpoint on the JCI stuff... don't override the AI points (Temp readings) - gets funky when you do
thanks alot guys, it seems that changing the set point as opposed to the AI actually does work faster......weird
the saturation timer is used to keep the box from switching into heat mode too quickly based on temp, giving time for the process variable to return to a satified value by simply reducing air flow first, rather then by bringing on box heat. When you change the setpoint, with the box satisfied so you dont have to go throught 2 modes, it is seen as a request for a new value and the saturation timer is disabled.
makes sense! thanks alot