Sequence Of Operations; Power-Up Sequence; Random Start; Occupancy Modes - Trane Tracer ZN521 Installation And Operation Manual

Sequence of operations

The Tracer ZN521 zone controller will operate to maintain the zone temperature setpoint. This
chapter discusses many of the operational sequences used by the controller to accomplish this
goal.

Power-up sequence

When 24 Vac power is initially applied to the Tracer ZN521 zone controller, the following sequence
occurs:
1. The green status indicator LED turns on (see
2. All outputs are controlled off. All modulating valves and dampers close, and the face-and-
3. The controller reads all input local values to determine initial values.
4. The random-start timer begins (see
5. If a hard-wired zone-temperature value is not detected, the controller begins to wait for a
6. The random-start timer expires.
7. The power-up control wait function begins automatically if the configured power-up control
8. Normal operation begins assuming no diagnostics have been generated.

Random start

Random start is intended to prevent all units in a building from energizing at the same time. The
random-start timer delays the fan and any heating or cooling start-up from 5 to 30 seconds. If
neither heating nor cooling is initiated, or if fan operation is not required during the delay, the
random-start timer will time-out.

Occupancy modes

Occupancy modes can be controlled by any of the following:
•
•
•
•
A communicated request, either from a BAS or a peer controller, takes precedence over local
requests. If a communicated occupancy request has been established and is no longer present, the
controller reverts to the default (occupied) occupancy mode after 15 minutes (if no hard-wired
occupancy request exists). The Tracer ZN521 has the following occupancy mode options:
•
•
•
•
CNT-SVX07D-EN
bypass damper calibrates to bypass (when present).
communicated value. (This can take several minutes [15-minute default] and occurs
concurrently with the remainder of the power-up sequence.)
wait time is greater than 0 seconds. When this function is enabled, the controller waits for the
configured amount of time (from 0 to 120 seconds) to allow a communicated occupancy
request to arrive. If a communicated occupancy request arrives, normal operation can begin.
If a communicated occupancy request does not arrive, the controller assumes stand-alone
operation.
The state of the local (hard-wired) occupancy binary input BI3 (see
binary input, " p. 14)
A timed override request from a Trane zone sensor (see
A communicated signal from a peer device (see
A communicated signal from a BAS
Occupied
Unoccupied
Occupied standby
Occupied bypass
"Interpreting LEDs, " p.
"Random start, " p. 31).
"Timed override control, " p.
"Peer-to-peer communication, " p.
47).
"BI3: Occupancy or generic
32)
40)
31