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UV-SVP01A-EN 43
Figure 19: Vertical unit with face-and-
bypass damper operations
Upon power-up, the controller cal-
ibrates the face-and-bypass damp-
er to the full bypass position by
overdriving the damper actuator.
During normal operation, whenev-
er the Tracer ZN.520 controller
generates a face-and-bypass
damper position request of zero or
100%, the unit calibrates the actu-
ator by overdriving the damper ac-
tuator 135%.
Entering Water
Temperature
Sampling
Units with 4-pipe changeover and
2-pipe changeover require an en-
tering water temperature to deter-
mine if the appropriate water
temperature is present for the re-
quested mode (heating or cool-
ing). This temperature may be
communicated in an ICS system or
hardwired to the Tracer ZN.520
controller for standalone applica-
tions.
When a unit uses 2-way modulat-
ing valves, it is possible for the wa-
ter near the entering water
temperature sensor to migrate to-
wards ambient temperature. The
Tracer ZN.520 controller has a wa-
ter sampling feature for these ap-
plications. When the sensed water
temperature is not sufficient for
the requested heat/cool mode
(5°F above the zone temperature
for heating or 5°F below the zone
temperature for cooling), the con-
troller drives the valve fully open.
The controller then monitors the
water temperature until the appro-
priate temperature is sensed or
until the three minute time limit
expires. If the water temperature is
acceptable for the requested ca-
pacity, the unit continues normal
operation. If the three minute tim-
er expires and the water tempera-
ture is still unsuitable, the unit
closes the valve and waits one
hour before invoking the sampling
feature again.
1. Assumption based on absence of a valid
entering water temperature
Modulating Outdoor
Air Operation
The Tracer ZN.520 controller oper-
ates a modulating (3-wire floating)
outdoor air damper actuator ac-
cording to the effective occupan-
cy, outdoor air temperature, space
temperature, effective setpoint,
discharge air temperature, and
discharge air temperature set-
point. Default minimum damper
positions are provided and can be
changed for occupied and occu-
pied standby modes, or for low
speed operation. The controller
can also receive a communicated
outdoor air damper minimum po-
sition from Tracer Summit. A com-
municated minimum position
from Tracer Summit has priority
over all configured setpoints.
During the OCCUPIED mode the
outdoor air damper will always be
controlled to the effective mini-
mum position unless ASHRAE Cy-
cle I, ASHRAE Cycle II, or
economizing modes are active.
Figure 20: OA/RA actuator mounting for
the vertical unit ventilator
Figure 21: Figure 2: OA/RA actuator
mounting for the horizontal unit ventilator
Figure 11: Ultra low-leak damper seal for
Table 22: Water assumption chart
Unit Configuration
Temperature
Assumed
1
2-pipe Heating valve Hot
2-pipe cooling valve Cold
2-pipe H/C valve with
auto changeover enabled
Hot
2-pipe H/C valve with
auto changeover
disabled
Cold
Unit Operation