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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