Installation and Maintenance Manual

Startup
74 UV-SVN02C-EN
Tab l e 19, Table 20, and Table 21.
Continuous Fan Operation (Tracer ZN520)
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, medium, or low). When fan mode is auto, the fan
operates at the default fan speed.
During unoccupied mode, the controller controls the fan
off. While unoccupied, the controller heats and cools to
maintain the unoccupied heating and cooling setpoints. In
unoccupied mode, the fan is controlled on high speed only
with heating or cooling.
The unit fan is always off during occupied, occupied
standby, and unoccupied modes 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 communicated request, or
the default fan speed (off).
If both a zone sensor module and communicated request
exist, the communicated request has priority.
Fan Cycling Operation (Tracer ZN520)
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 (Tracer ZN520)
When a heating output is controlled off, the Tracer ZN520
controller automatically holds the fan on for an additional
30 seconds. This 30-second delay gives the fan time 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 (Tracer ZN520)
On a transition from off to any other fan speed, the Tracer
ZN520 controller automatically starts the fan on high
speed and runs the fan at high speed for 0.5 seconds. This
provides the ample torque required to start all fan motors
from the off position.
Entering Water Temperature Sampling
Function (Tracer ZN520)
Only units using the main hydronic coil for both heating
and cooling (2-pipe changeover and 4-pipe changeover
units) use the entering water temperature sampling
function. Two-pipe changeover and 4-pipe changeover
applications allow the main coil to be used for heating and
for cooling; therefore, these applications require an
entering water temperature sensor.
When three-way valves are ordered with a Tracer ZN520
control, the controller is factory-configured to disable the
entering water temperature sampling function, and the
entering water sensor is mounted in the proper location.
Disabling entering water temperature sampling
eliminates unnecessary water flow through the main coil
when three-way valves are used.
The controller invokes entering water temperature
sampling only when the measured entering water
temperature is too cool to heat or too warm to cool.
Entering water is cold enough to cool when it is five
degrees below the measured space temperature. Entering
water is warm enough to heat when it is five degrees
above the measured space temperature.
When the controller invokes the entering water
temperature sampling function, the unit opens the main
hydronic valve for no more than three minutes before
considering the measured entering water temperature. An
initial stabilization period is allowed to flush the coil. This
period is equal to 30 seconds plus half of the valve stroke
time. Once this temperature stabilization period has
expired, the controller compares the entering water
temperature against the effective space temperature
Table 19. Local fan switch enabled (Tracer ZN520)
Communicated Fan Speed
Input
Fan Switch
(Local)
Fan
Operation
Off Ignored Off
Low Ignored Low
Medium Ignored Medium
High Ignored High
Auto Off
Low
Medium
High
Auto Off
Low
Medium
High
Auto (configured default, determined by heat/cool mode)
Table 20. Fan operation in heating and cooling modes
(Tracer ZN520)
Fan Mode
Heating Cooling
Occ. Unocc. Occ. Unocc.
Off Off Off Off Off
Low Low Off/high Low Off/high
Medium Med Off/high Med Off/high
High High Off/high High Off/high
Auto Default fan sp. Off/high Default fan sp. Off/high
Table 21. Local fan switch disabled or not present (Tracer
ZN520)
Communicated Fan Speed Input Fan Operation
Off Off
Low Low
Medium Medium
High High
Auto (or not present) Auto (fan runs at the default speed)
UV-SVN02_-EN.book Page 74 Thursday, January 24, 2013 4:48 PM