Honeywell EXCEL 5000 User Manual page 267

EXCEL CARE CONTROL ICONS
Air Heater Controller
The ZEB heating setpoint (Y3 output) connects to the controller for the air heater
valve as the reference variable. If the ZEB statement initiates heating (YD1=1), the
positioning signal from the controller reaches the valve drive. If YD1 equals zero, the
controller is overridden and the valve is closed.
Cooler Controller
The ZEB cooling setpoint (Y4 output) connects to the controller for the cooling valve
as the controlled variable. The connection is made as the controlled variable to
reverse the direction in which the controller works. If the ZEB statement initiates
cooling (YD2=1), the positioning signal from the controller reaches the valve drive.
In addition, the mixed air setpoint connects to the damper controller for
dehumidification when cooling is active.
If YD2 equals zero, the controller is overridden and the valve is closed.
Mixed Air Damper Controller
ZEB releases the mixed air dampers if neither heating nor cooling is active (YD1
and YD2 are zero) or if cooling is active (YD2 is 1).
If neither heating nor cooling is active, all temperatures are within the zero energy
range. ZEB releases the dampers for air regulation.
If cooling is active, ZEB must also release the dampers because dehumidification
can activate cooling and then damper intervention is required. A switching table
releases the dampers.
The mixed air setpoint (Y5) connects to the damper controllers as the controlled
variable (for reversal). The positioning signal from the controller reaches the damper
drive when the dampers are released.
If the dampers are blocked, the controller is overridden and the dampers are closed
to a minimum outdoor air proportion of 20 percent.
The SWI control icon can provide the zero and 20 percent constants that override
the controller when necessary.
To guarantee a minimum outdoor air proportion when the dampers are released,
minimum controller output has to be 20 percent.
CAUTION
If the system is off, the control loop must guarantee that the outdoor air
dampers are closed, as in other standard control applications to prevent
unacceptable outdoor air within the system. Use separate switching tables to
guarantee this action.
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EXAMPLES
74-5577–33 (US)
EN2B-0184 GE51 R0518 (Europe)