Trane VUV Installation, Operation And Maintenance Manual page 75

Occupied Bypass Mode
The controller can be placed in occupied bypass mode by
either communicating an occupancy request of Bypass to the
controller or by using the timed override On button on the
Trane zone sensor.
When the controller is in unoccupied mode, you can press the
On button on the zone sensor to place the controller into
occupied bypass mode for the duration of the bypass time
(typically 120 minutes).
Occupancy Sources:
controller's occupancy:
• Communicated request (usually provided by the building
automation system or peer device)
• By pressing the zone sensor's timed override On button
• Occupancy binary input
• Default operation of the controller (occupied mode)
A communicated request from a building automation system or
another peer controller can change the controller's occupancy.
However, if communication is lost, the controller reverts to the
default operating mode (occupied) after 15 minutes
(configurable, specified by the "receive heartbeat time"), if no
local hard-wired occupancy signal exists.
A communicated request can be provided to control the
occupancy of the controller. Typically, the occupancy of the
controller is determined by using time-of-day scheduling of the
building automation system. The result of the time-of-day
schedule can then be communicated to the unit controller.
Tracer Summit® with Supply Fan Control
If the unit is communicating with Tracer Summit® and the
supply fan control programming point is configured for Tracer®
(the factory configures as local), Tracer Summit® will control
the fan regardless of the fan mode switch position.
When the fan mode switch is set to Off or when power is
restored to the unit, all lockouts (latching diagnostics) are
manually reset. The last diagnostic to occur is retained until the
unit power is disconnected.
For specific instructions regarding Tracer® ZN520 Controller,
refer to:
CNT-SVX04*-EN Tracer® ZN520 Unit Controller Installation,
Operation and Programming Guide
Cooling Operation
The heating and cooling setpoint high and low limits are always
applied to the occupied and occupied standby setpoints.
During the cooling mode, the controller attempts to maintain
the space temperature at the active cooling setpoint. Based on
the controller's occupancy mode, the active cooling setpoint is
one of the following:
• Occupied cooling setpoint
• Occupied standby cooling setpoint
• Unoccupied cooling setpoint
UV-SVX005G-EN
There are four ways to control the
The controller uses the measured space temperature, the
active cooling setpoint, and discharge air temperature along
with the control algorithm to determine the requested cooling
capacity of the unit (0 percent–100 percent). The outputs are
controlled based on the unit configuration and the required
cooling capacity. To maintain space temperature control, the
cooling outputs (modulating hydronic valve, two-position
hydronic valve, or outdoor air economizer damper) are
controlled based on the cooling capacity output.
The cooling output is controlled based on the cooling capacity.
At 0 percent capacity, all cooling capacities are off and the
damper is at minimum position. Between 0 percent and
100 percent capacity, the cooling outputs are controlled
according to modulating valve logic (modulating valves) or
cycled on (2-position valves). As the load increases,
modulating outputs open further and binary outputs are
energized longer. At 100 percent capacity, the cooling valve or
damper is fully open (modulating valves) or on continuously
(and 2-position valves).
Unit diagnostics can affect fan operation, causing occupied
and occupied standby fan operation to be defined as
abnormal. Refer to "Diagnostics and Troubleshooting," p. 96
for more information about abnormal fan operation.
The controller operates the supply fan continuously when the
controller is in the occupied and occupied standby modes, for
either heating or cooling. The controller only cycles the fan off
with heating and cooling capacity in the unoccupied mode.
The economizer is used for cooling purposes whenever the
outdoor temperature is below the economizer enable setpoint
and there is a need for cooling. The economizer is used first to
meet the space demand, and other forms of cooling are used
if the economizer cannot meet the demand alone. See
modulating outdoor air damper operation for additional
information.
Cascade cooling control initiates a discharge air tempering
function if the discharge air temperature falls below the
discharge air temperature control low limit, all cooling capacity
is at minimum, and the discharge control loop determines a
need to raise the discharge air temperature. The controller
then provides heating capacity to raise the discharge air
temperature to its low limit.
Discharge Air Tempering
The discharge air tempering function enables when cold
outdoor air is brought in through the outdoor air damper,
causing the discharge air to fall below the discharge air
temperature control low limit. The controller exits the discharge
air tempering function when heat capacity has been at zero
percent for five minutes.
Start-Up
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