DNT-T221-FCU Application Guide
Page 16 of 30
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If the Input temperature is between these two extents for Heating and Cooling, then the controller
is in a null zone
For all control applications the Controller Status (AV14) modulates from -100 to 100% and sequences any
necessary output stages. A value of 0 to 100% represents the heating output from the controller, while a
value of 0 to -100% represents the cooling output from the controller.
For heating lockout, the heating output from the controller is forced to 0%, and the heating icon is
disabled on the LCD. Similarly, for cooling lockout, the cooling output from the controller is forced to 0%,
and the cooling icon is disabled on the LCD. The Controller Status (AV14) is limited accordingly.
Controller Staging
Each controller can be split up into two stages. The number of stages is automatically determined by the
output configuration associated with the selected application control strategy. The controller stages are
sequenced.
Cooling
Controller
C1 / H1
C1 / H1
0%
100%
0%
100%
Reset Action (Reset Rate in repeats per hour)
If the Reset Rate is non-zero, reset action is enabled. As long as there is a difference (or error) between
the input value (i.e., space temperature) and setpoint value,the reset action increments or decrements the
Controller Status value (AV14) over time ( in proportion to the value of the reset rate and the magnitude of
the error) in an attempt to remove the error. In this way, the Controller Status value is continually
fluctuating in order to reach setpoint.
The amount of reset does not decrease internally as the input value approaches the setpoint, but the
reset value is frozen while in deadband. The only time the reset action has no effect on the controller
output, is when the input is equal to the setpoint (no error). For this reason, applying too much reset
action can cause unnecessary movement on the actuators. By setting Reset Rate to 0, the reset action is
disabled.
Setpoints
The BACstat III uses a series of setpoints, most of which interact with one another. For a complete list of
these setpoints, and other objects and their defaults, refer to the Object table on page 10. When you
change the units setting between ºC and ºF all of these setpoints revert back to their matching default
values (the BACstat does not do a conversion).
Day Setpoint (AV6) –
Used when in Day mode. With the Display Code (AV15) set to an appropriate value, the setpoint can be
adjusted up or down. Whether or not this setpoint is displayed or is adjustable on the LCD, it is used
internally for control. The units for the setpoint are ºC or ºF (as per AI1) unless the second digit of the
Display Code (AV15) is set to 3 (for Humidity), in which case the units become %RH. The value for Day
Setpoint can also be set in the Configuration Menu, or by commanding the variable (via GCL+ or
ORCAview OWS or 3
rd
Party devices).
