user manual

44 UV-SVP01A-EN
Unit Operation
Automatic Outdoor Air
Damper Adjustment
The Tracer ZN.520 controller is ca-
pable of using different minimum
outdoor air damper positions for
high and low fan speeds, which are
configurable. This allows the venti-
lation rate to be maintained when
switching between fan speeds.
Note: The typical reduction in
airflow between high and low
fan speeds is 25%, however, if
precise control is desired, an
air balancer should be
consulted.
Economizer
Operation
Note: When there is a request
for 0% or 100% actuator
position, the actuator will
overdrive the actuator 135% to
help maintain calibration.
With a valid outdoor air tempera-
ture (hardwired or communicated),
Tracer ZN.520 uses the modulating
economizer damper as the highest
priority source of cooling.
The controller initiates the econo-
mizer function if the outdoor air
temperature is cold enough to be
used for free cooling capacity. If
the outdoor air temperature is less
than the economizer enable set-
point (absolute dry bulb), the con-
troller modulates the outdoor air
damper between the minimum po-
sition and 100% to control the
amount of cooling capacity. When
the outdoor air temperature rises
5°F above the economizer enable
setpoint, the outdoor air damper
returns to its minimum position
and mechanical cooling is initiated.
ASHRAE Cycle I
ASHRAE Cycle I admits 100% out-
door air except during the warm up
cycle or the unoccupied mode. To
set up the Tracer ZN.520 controller
for ASHRAE Cycle I conformance,
set the occupied outdoor air damp-
er minimum position to 100%.
ASHRAE Cycle II
The Tracer ZN.520 controller con-
forms to ASHRAE Cycle II by allow-
ing the modulating outdoor air
damper to maintain a minimum
position during the occupied mode
unless economizing is enabled or
the space temperature falls more
than 3°F below the effective set-
point.
If the space temperature falls more
than 2°F below the setpoint, the
outdoor air damper will begin to
close. When the space temperature
hits 3°F below the setpoint, the
outdoor air damper is completely
closed.
Figure 22: ASHRAE cycle 2
DX Operation
Tracer ZN.520 supports direct ex-
pansion (DX) compressor opera-
tion for cooling only.
The controller does not allow both
the DX compressor and economiz-
er to operate at the same time. This
prevents problems where the en-
tering air temperature is too low
for the evaporator coil to operate
as designed.
Tracer ZN.520 also includes a fixed
minimum on/off time of 3 minutes
for compressor operation to pre-
vent short cycling of the compres-
sor.
Electric Heat
Operation
The Tracer ZN.520 controller sup-
ports 1 or 2 stages of electric heat
control.
To control space temperature,
electric heat is cycled to control the
discharge air temperature. The rate
of cycling is dependent on the load
in the space and the temperature of
the incoming fresh air.
Baseboard Heat
Operation
The Tracer ZN.520 controller can
be configured to support one stage
of baseboard heat. A 2 position
valve or an electric heat contactor
will be energized at 2.5°F below
the effective heating setpoint. The
baseboard heat is de-energized at
1°F below the effective heating
setpoint.
The unit will provide heating ca-
pacity as required regardless of the
presence of baseboard heat. If the
unit can not maintain the space
temperature, the baseboard heat
will come on as a secondary stage.
If baseboard heat is to be used as
the primary source of heating, the
discharge air high limit should be
set to a moderate temperature.
This will allow the ventilation air to
be tempered and avoid a “drafty”
feeling. The baseboard heat will
then operate as the heating capaci-
ty for the space.
In the UNOCCUPIED mode, the
baseboard heat and unit heating
capacity are brought on simulta-
neously as needed to maintain the
unoccupied setpoint.
Exhaust Fan
Operation
The exhaust fan is coordinated
with the unit fan and outdoor air
damper operation. The exhaust fan
output is energized only when the
unit fan is operating and the out-
door air damper position is greater