Sample #2

The user would like to use the GPC Plus as a Lead/Lag Air Handling Unit Controller. The installation is located in a critical area that does not tolerate the space temperature going out of control. The method chosen was to install a backup AHU that would take over in case of failure on the Lead AHU. Also, since the units are identical, the owner wanted to equalize the run-times to lengthen the time between routine maintenance service calls. The easiest method for handling this was to use two, standard, off the shelf AHU controllers and a GPC Plus controller that would enable the appropriate AHU based on changeover and failure mode conditions. The GPC Plus would use contact closures to the Forced Occupied inputs of the AHU controllers to activate and de-activate the units. A failure mode would be indicated by the failure of the Supply Air Temperature to drop below or stay below a 60°F setpoint. Any temperature excursions above 60°F for more than one minute would indicate a failure had occurred and that the Lag AHU should be activated and an Alarm generated to let building maintenance know there was a problem.

Analog Input #1 Configured as Thermister Type III Sensor to measure Supply Air

As you can see, this input does not use a schedule for Night Setbacks since the unit will run 24 hours a day. It does however, monitor the Supply Air Temperature for values that are out of limits for more than a half hour and generates an alarm condition. This is a fall