Trane Tracer ZN521, Инструкция по установке и эксплуатации

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CNT-SVX07D-EN 33
Sequence of operations
will be placed in occupied bypass mode and remain in that mode until either the
CANCEL
button is
pressed on the Trane zone sensor or the occupied bypass time expires.
Zone temperature control
The Tracer ZN521 zone controller uses two methods of zone temperature control:
• Cascade zone control—used in the occupied, occupied bypass, and occupied standby modes
• Simplified zone control—used in the unoccupied mode
Cascade zone control
Cascade zone control maintains zone temperature by controlling the discharge air temperature to
control the zone temperature. The controller uses the difference between the measured zone
temperature and the active zone temperature setpoint to produce a discharge air temperature
setpoint. The controller compares the discharge air temperature setpoint with the discharge air
temperature and calculates a unit heating/cooling capacity accordingly (see
Figure 1 ). The end
devices (outdoor air damper, valves, etc.) operate in sequence based on the unit heating/cooling
capacity (0–100%).
Figure 18. Cascade zone control
If the discharge air temperature falls below the Discharge Air Control Point Low Limit (configurable
using the Rover service tool) and cooling capacity is at a minimum, available heating capacity will
be used to raise the discharge air temperature to the low limit (see
“Discharge air tempering,”
p. 33 ).
Simplified zone control
In the unoccupied mode, the controller maintains the zone temperature by calculating the required
heating or cooling capacity (0–100%) according to the measured zone temperature and the active
zone temperature setpoint. The active zone temperature setpoint is determined by the current
operating modes, which include occupancy and heat/cool modes.
Discharge air tempering
If the controller is in cooling mode, cascade zone control initiates a discharge air tempering function
when the discharge air temperature falls below the Discharge Air Control Point Low Limit
(configurable using the Rover service tool) and all cooling capacity is at a minimum. The discharge
air tempering function allows the controller to provide heating capacity (if available) to raise the
discharge air temperature to the Discharge Air Control Point Low Limit.
The discharge air tempering function is often initiated under the following circumstances: Cold
outdoor air is brought in through the outdoor air damper when the damper is at (a high) minimum
Active zone
temperature
setpoint
Difference
Calculated
discharge air
temperature
setpoint
Calculated unit
heating/cooling
capacity
Measured
zone
temperature
Measured
discharge air
temperature
Difference