Trane HUV Installation, Operation And Maintenance Manual page 75

(either hard-wired or communicated) to determine
whether the entering water can be used for the desired
heating or cooling. If the water temperature is not usable
for the desired mode, the controller continues to compare
the entering water temperature against the effective space
temperature for a maximum of three minutes.
The controller automatically disables the entering water
temperature sampling and closes the main hydronic valve
when the measured entering water exceeds the high
entering water temperature limit (110°F). When the
entering water temperature is warmer than 110°F , the
controller assumes the entering water temperature is hot
because it is unlikely the coil would drift to a high
temperature unless the actual loop temperature was very
high.
If the entering water temperature is unusable—too cool to
heat or too warm to cool—the controller closes the
hydronic valve and waits 60 minutes before initializing
another sampling. If the controller determines the
entering water temperature is valid for heating or cooling,
it resumes normal heating/cooling control and effectively
disables entering water temperature sampling until it is
required.
Electric Heat Operation (Tracer ZN520)
The Tracer ZN520 controller supports one or two-stage
electric heat operation for heating. To control the space
temperature, electric heat is cycled to control the
discharge air temperature. The rate of cycling is
dependent upon the load in the space and the temperature
of the incoming fresh air from the economizer (if any).
Two-pipe changeover units with electric heat use the
electric heat only when hot water is not available.
Manual Fresh Air Damper (Tracer ZN520)
Units with the manual fresh air damper option ship with
the damper in the closed position, which is adjustable
from zero to 100 percent in 25 percent increments. To
adjust the position, first remove the air filter to expose the
damper stop screw on the control panel end. Relocate the
stop screw to the appropriate position. Then loosen the
stop screw wingnut and adjust the linkage.
Economizer Damper Option (Tracer ZN520)
With a valid outdoor air temperature (either hard-wired or
communicated), Tracer ZN520 uses the modulating
economizer damper as the highest priority source of
cooling. Economizer operation is only possible through
the use of a modulating damper.
Economizing is possible during the occupied, occupied
standby, unoccupied, and occupied bypass modes.
The controller initiates the economizer function if the
outdoor air temperature is cold enough to be used as free
cooling capacity. If the outdoor air temperature is less than
the economizer enable setpoint (absolute dry bulb), the
controller modulates the outdoor air damper (between the
active minimum damper position and 100 percent) to
control the amount of outdoor air cooling capacity. When
UV-SVN02C-EN
the outdoor air temperature rises 5°F above the
economizer enable point, the controller disables
economizing and moves the outdoor air damper back to its
predetermined minimum position based on the current
occupancy mode or communicated minimum damper
position.
Table 22. Relationship between outdoor temperature
sensors and damper position (Tracer ZN520)
Outdoor Air
Temp. Modulating Outdoor Air Damper
Occupied or
Occupied
Bypass Occupied Standby
None or invalid Open to Open to occupied
occupied standby minimum
minimum position
position
Failed Open to Open to occupied
occupied standby minimum
minimum position
position
Present and Economizing Economizing between
economizing minimum occupied standby
feasible postion to minimum position to
100% 100%
Present & Open to Open to occupied
economizing occupied standby minimum
not feasible minimum position
position
Dehumidification (Tracer ZN520)
Dehumidification is possible when mechanical cooling is
available, the heating capacity is located in the reheat
position, and the space relative humidity setpoint is
valid.The controller starts dehumidifying the space when
the space humidity exceeds the humidity setpoint.
The controller continues to dehumidify until the sensed
humidity falls below the setpoint minus the relative
humidity offset.The controller uses the cooling and reheat
capacities simultaneously to dehumidify the space. While
dehumidifying, the discharge air temperature is controlled
to maintain the space temperature at the current setpoint.
A typical scenario involves high humidity and high
temperature load of the space.The controller sets the
cooling capacity to 100 percent and uses the reheat
capacity to warm the discharge air to maintain space
temperature control. Dehumidification may be disabled
via Tracer or configuration.
Note: If the unit is in the unoccupied mode, the
dehumidification routine will not operate.
Data Sharing (Tracer ZN520)
Because this controller utilizes L
controller can send or receive data (setpoint, heat/cool
mode, fan request, space temperature, etc.) to and from
other controllers on the communication link, with or
without the existence of a building automation system.
This applies to applications where multiple unit
controllers share a single space temperature sensor (for
rooms with multiple units but only one zone sensor) for
both standalone (with communication wiring between
Startup
Unoccupied
Closed
Closed
Open &
economizing
when unit is
operating, closed
Closed
®
W technology, the
ON ORKS
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