Economizer Control
If you have configured the GPCPlus as a very simple Air Handling Unit, it has the ability to control the outside air dampers in a true first stage economizer cooling mode. This mode requires a Minimum Ventilation position that it maintains whenever the economizer is not enabled for cooling. It also needs to know which relay has been configured as the first compressor stage. Use the Outdoor Air Enable limits to set when the free cooling mode can be used in conjunction with scheduling and temperature demands.
Alternate Override
There are situations where we want normal control to be suspended temporarily whenever an unusual situation occurs. For example: we are using the economizer control method and we have installed a CO² sensor on this controller to use for Indoor Air Quality. If the CO² reading exceeds a specified level, this Alternate Override can take charge and move the output signal to a
Proportional Reset Signal
As the Reset Source goes from its Maximum Reset Source to its Minimum Reset Source the Controlling Setpoint goes from its Minimum Reset Setpoint limit to its Maximum Reset Setpoint limit.
Since the reset limits can be set to any desired value, the user can initiate a reverse acting proportional reset or a direct acting proportional reset of the setpoint simply by crossing the min and max values if direct acting is required.
Direct Acting = As Temperature Rises the Setpoint Drops
Reverse Acting = As Temperature Rises the Setpoint Rises
An example of using Proportional Reset would be for Boiler Control. As the outside air temperature rises, we would like the boiler output temperature to drop. We would use the outside air temperature as the control source and set the Max Setpoint and Min Setpoint to the range we want to vary the voltage from 0 to 10.0 vdc. If we set the Max Setpoint to 50° and the Min Setpoint to 60° then as the outside air rose from 50° to 60°, the output signal would drop from 10.0 vdc @ 50° to 0.0 vdc @ 60°. This is because we made the output Reverse Acting by setting the Max Setpoint lower than the Min Setpoint.
18