BCXC-SVX01A-EN
35
single or two-speed fan to work coopera-
tively to meet precise capacity require-
ments, while minimizing fan speed
(motor/energy/acoustics) and valve
position (pump energy/chilled water
reset). As the capacity requirement
increases at low fan speed, the water
valve opens. When the low fan speed
capacity switch point is reached, the fan
switches to high speed and the water
valve repositions to maintain an equiva-
lent capacity. The reverse sequence
takes place with a decrease in required
capacity.
Units with 2-speed fans on low or high:
The fan will run continously at the
selected speed and the valve option will
cycle to meet setpoint.
Continuous Fan Operation
During occupied and occupied standby
modes, the fan normally is on. For
multiple speed fan applications, the fan
normally operates at the selected or
default speed (off, high, or low). When fan
mode is auto, the fan operates at the
default fan speed.
During unoccupied mode, the fan is off.
While unoccupied, the controller will heat
or cool to maintain the unoccupied
heating and cooling setpoints. In unoccu-
pied mode, the fan runs on high speed
only, with heating or cooling. See Table O-
SO-7 on page 36
The unit fan is always off during occupied,
occupied standby, and unoccupied modes
Table O-SO-3. Fan Sequence of Operation
Fan Speed
Tracer ZN Controller
Sequence of Operation
Off
all
• fan is off
• control valves and damper option are closed
• low air temperature detection option is still active
Low or High
ZN010
• fan operates continuously at selected speed
(Continuous Fan)
ZN510
• 2-position control valve option cycle as needed
• 2-position damper option opens to an adjustable
mechanical stop-position
Low or High
ZN520
• fan operates continuously at selected speed
(Continuous Fan)
• modulating control valve option cycles as needed
Auto
ZN010
• fan, 2-position damper cycle, & control valve cycle as (Fan
Cycling)
ZN510
needed
• in cooling, fan cycles from off to high
• in heating mode fan cycles from off to low
• when heating/cooling is not required, the fan is off & the 2-
position damper option closes
Auto
ZN520
• fan cycles between high and medium, and never turns off
unless the controller is in unoccupied mode
• modulating or 2-position control open to maintain setpoint
when the unit is off due to a diagnostic or
when the unit is in the off mode due to the
local zone sensor module, a communi-
cated request, or the default fan speed
(off).
If both a zone sensor module and
communicated request exist, the commu-
nicated request has priority. See Table O-
SO-6 on page 36.
Fan Cycling Operation
Tracer
ZN520 does not support fan
cycling in occupied mode. The fan cycles
between high speed and off in the
unoccupied mode only. The controller’s
cascade control algorithm requires
continuous fan operation in the occupied
mode.
Fan Off Delay
When a heating output is controlled off,
the Tracer
ZN controller automatically
holds the fan on for an additional 30
seconds. This 30-second delay allows the
fan to blow off any residual heat from the
heating source, such as a steam coil.
When the unit is heating, the fan off delay
is normally applied to control the fan;
otherwise, the fan off delay does not
apply.
Fan Start on High Speed
On a transition from off to any other fan
speed, the Tracer ZN controller
automatically starts the fan on high speed
and runs the fan at high speed for 0.5
seconds. This provides ample torque
required to start all fan motors from the
off position.
Table O-SO-2. Tracer ZN520 Fan Configura-
tion
Auto
Fan
Fan
Speed
Operation
Default
Heating
Continuous
Off
Low
High
Cooling Continuous
Off
Low
High
Operation
Sequence of
Operation
