I am on a job trying to fix up some programming issues on a universal controller. This controller is controlling 3 VFDs. Two of the VFDs are feeding outdoor air into the outdoor air section of some AHUs. The other VFD is controlling a Relief Fan. I am controlling the Relief Fan VFD off of Space pressure. The AHUs are on the first floor of this department store. The outdoor fans are on the roof which is about 25 ft above the AHUs. The outdoor fans pull outside air in and push it into the AHUs. I haven't seen a set up like this before. I need a way to control the fan speed. I am thinking about doing it by tracking the outdoor damper position. I am not sure if that is the best way to do it or not, but it doesn't seem to be too critical. I am having a hard time finding the right algorithm to perform this function. I am looking for some assistance on setting something like this up. Right now they have a Analog Single Loop PID trying to control this function. I tried assigning my damper position to the algorithms setpoint but it will not recognize it as a setpoint. It keeps defaulting to SETPT01. Is there some easy way that I can set something like this up? I have reviewed the manual and cannot locate a similiar situation.
Thanks for any help on this.