Trane Tracer ZN521, Инструкция по установке и эксплуатации

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38 CNT-SVX07D-EN
Sequence of operations
ASHRAE Cycle 1 conformance
Tracer ZN521 applications with an outside air damper support ASHRAE Cycle 1 conformance.
ASHRAE Cycle 1 operation admits 100% outdoor air at all times except during a warm-up cycle. A
tri-state modulating damper actuator is required for this operation. For Tracer ZN521 ASHRAE
Cycle 1 conformance, configure the minimum position of the economizer setpoint to 100% open
during occupied periods. If the zone temperature drops 3°F (1.7°C) below the active zone
temperature setpoint, the Tracer ZN521 closes the outdoor air damper regardless of the minimum
position setpoint.
ASHRAE Cycle 2 conformance
Tracer ZN521 controller applications with modulating outside air damper support ASHRAE Cycle
2 conformance. ASHRAE Cycle 2 operation allows the modulating outdoor air damper to
completely close when the zone temperature drops 3°F (1.7°C) or more below the active zone
temperature setpoint. If the zone temperature rises to within 2°F (1.2°C) of the active setpoint, the
damper opens to the occupied or occupied standby minimum damper positions. If the zone
temperature is between 2°F and 3°F (1.2°C and 1.7°C) below the active zone temperature setpoint,
the damper modulates between the minimum position and closed.
If the discharge air temperature is between the discharge air temperature low limit and the
discharge air temperature low setpoint, the damper modulates between the minimum position and
closed. If this situation is concurrent with ASHRAE Cycle 2 operation, the lesser of the two setpoints
will determine the actual damper position.
Economizing (free cooling)
Cooling with outdoor air, when the temperature is low enough to make this possible, is referred
to as
economizing or free cooling . Tracer ZN521 controller applications with modulating outside
air damper support economizing. The modulating outdoor air damper provides the first source of
cooling for the Tracer ZN521. The controller initiates economizing if the outdoor air temperature is
below the economizer enable point (configurable using the Rover service tool). If economizing is
initiated, the controller modulates the outdoor air damper (between the active minimum damper
position and 100%) to control the amount of outdoor air cooling capacity. When the outdoor air
temperature rises 5°F (2.8°C) above the economizer enable point, the controller disables
economizing and moves the outdoor air damper back to its predetermined minimum position
based on the current occupancy mode or communicated minimum outdoor air damper position.
If an outdoor air temperature value is not present, economizing is disabled.
Table 10. Relationship between outdoor temperature sensors and damper position
Outdoor air temperature
Modulating outdoor air damper position
Occupied or occupied
bypass Occupied standby Unoccupied
No or invalid outdoor air
temperature Open to occupied
minimum position
Open to occupied standby
minimum position
Closed
Failed outdoor air sensor
Open to occupied
minimum position
Open to occupied standby
minimum position
Closed
Outdoor air temperature present
and economizing possible
1
Economizing; damper controlled
between
occupied minimum
position and 100%
Economizing; damper controlled
between
occupied standby
minimum position and 100%
Open and economizing during
unit operation; otherwise closed
Outdoor air temperature present
and economizing not possible
1
Open to occupied minimum
position Open to occupied standby
minimum position
Closed
1
For an explanation of the economizing feature, see “Economizing (free cooling),” p. 38 .