Trane Zone Controller Zone temperature control, Cascade zone control, Simplified zone control

Chapter 5 Sequence of operations

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 dis- charge 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 18). The end devices (outdoor air damper, valves, etc.) operate in sequence based on the unit heating/cooling capac- ity (0–100%).

Figure 18. Cascade zone control

Active zone
temperature
setpoint	Difference

Calculated discharge air temperature setpoint

Difference

Calculated unit heating/cooling capacity

Measured

zone

temperature

Measured

discharge air temperature

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 temper- ing” on page 39).

Simplified zone control

In the unoccupied mode, the controller maintains the zone temperature by calculating the required heating or cooling capacity (0–100%) accord- ing to the measured zone temperature and the active zone temperature setpoint. The active zone temperature setpoint is determined by the cur- rent operating modes, which include occupancy and heat/cool modes.

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