34
BCXC-SVX01A-EN
Operation
Sequence of
Operation
Between 0 and 100% capacity, the
heating output is controlled according to
modulating valve logic (ZN520 only) or
cycled with 2-position valves. As the load
increases, modulating outputs open
further and binary outputs are energized
longer. At 100% capacity, the modulating
valve is fully open (Tracer ZN520 only) or
on continuously with 2-position valves.
Economizer Damper (Tracer ZN520 Only)
The economizer damper option is never
used for as a source for heating, but only
for ventilation. Therefore, the damper is
at the occupied minimum position in the
occupied mode. The damper control is
primarily associated with occupied fan
operation.
Dehumidification (Tracer ZN520 only)
During dehumidification, the Tracer
ZN520 controller adjusts the heating
setpoint up to the cooling setpoint. This
reduces the relative humidity in the
space with a minimum of energy usage.
The controller uses the measured space
temperature, the active heating setpoint,
and discharge air temperature (Tracer
ZN520 only) along with the control
algorithm, to determine the requested
heating capacity of the unit (0-100%). The
outputs are controlled based on the unit
configuration and the required heating
capacity.
Fan Mode Operation
For multiple fan speed applications, the
Tracer ZN controller offers additional fan
configuration flexibility. See Table O-SO-2
on page 35 for fan operation sequences.
Separate default fan speeds for heating
and cooling modes can be configured
using Rover service software.
The fan runs continuously at selected
speeds, high or low. When the fan mode
switch is in the auto position or a
hardwired fan mode input does not exist,
the fan operates at the default configured
speed. See Table O-SO-3 on page 35 for
Tracer ZN520 default fan configuration
for heating and cooling modes. During
unoccupied mode, the fan cycles be-
tween high speed and off with heating
and cooling fan modes. If the requested
speed is off, the fan always remains off.
During dehumidification, when the fan is
in auto, the fan speed can switch depend-
ing on the error. The fan speed increases
as the space temperature rises above the
active cooling setpoint.
Additional flexibility built into the control-
ler allows you to enable or disable the
local fan switch input. The fan mode
request can be hardwired to any of the
Tracer ZN controllers or communicated to
the Tracer ZN510 or ZN520 controller.
When both inputs are present, the
communicated request has priority over
the hardwired input. See Table O-SO-2 on
page 35.
Fan Speed Switch
Off: Fan is turned off, two-position
damper option spring-returns closed.
High or Low: Fan runs continuously at the
selected speed. The two-position damper
option opens to an adjustable mechanical
stop-position.
Tracer ZN010 and ZN510
Off: Fan is off; control valves and fresh air
damper option close. Low air
temperature detection option is still
active.
Auto (Fan Cycling):
Fan and fresh air
damper cycle with control valve option to
maintain setpoint temperature. If the unit
has a 2-speed fan, in cooling mode the
fan cycles from off to high and in heating
mode it cycles from off to low (factory
default that can be field-adjusted using
Rover service software). When no
heating or cooling is required, the fan is
off and the fresh air damper option
closes. Units with 2-speed fans can also
be field-configured using Rover to run at
a defined speed when the fan speed
switch is in the auto position.
Low or High (Continuous Fan): Fan
operates continuously while control valve
option cycles to maintain setpoint
temperature. Fresh air damper option is
open.
Tracer ZN520
Off: Fan is off; control valve options and
fresh air damper options close. The low
air temperature detection option is still
active.
Auto
: Fan speed control in the auto
setting allows the modulating (three-wire
floating point) control valve option and
