Installation and Maintenance Manual

Startup
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speed (motor/energy/acoustics ) and valve position (pump
energy, chilled water reset ). As the capacity requirement
increases at low fan speed, the water valve opens. When
the low fan speed capacity switch point is reached, the fan
switches to medium speed and the water valve repositions
to maintain an equivalent capacity. The reverse sequence
takes place with a decrease in required capacity.
Low/Med/High
The fan runs continuously at the selected speed and the
valve option will cycle to meet setpoint.
UC400 Controller Operation
Off
Fan is off; control valve options and fresh air damper
options close. The low air temperature detection option is
still active.
Auto
Fan speed control in the auto setting allows the
modulating (3-wire floating point) or 2-position control
valve option and 1-, 2-, 3- or variable-speed fan to work
cooperatively to meet precise capacity requirement, while
minimizing fan speed (motor/energy/acoustics) and valve
position (pump energy, chilled water reset). As the
capacity requirement increases, the water valve opens.
When the fan speed capacity switch points are reached,
the fan speed ramps up and the water valve repositions to
maintain an equivalent capacity. The reverse sequence
takes place with a decrease in required capacity.
Low/Med/High
The fan runs continuously at the selected speed and the
valve option will cycle to meet setpoint.
Tracer ZN520 Sequence of
Operation
The Tracer ZN520 operates the fan in the following modes:
1. occupied
2. unoccupied
3. occupied standby
4. occupied bypass
5. Tracer Summit with supply fan control
Occupied (Tracer ZN520)
When the controller is in the occupied mode, the unit
attempts to maintain the space temperature at the active
occupied heating or cooling setpoint, based on the
measured space temperature, the discharge air
temperature, the active setpoint, and the proportional/
integral control algorithm. The modulating control
algorithm used when occupied or in occupied standby is
described in the following sections. Additional
information related to the handling of the controller
setpoints can be found in the previous Setpoint operation
section.
Unoccupied Mode (Tracer ZN520)
When the controller is in the unoccupied mode, the
controller attempts to maintain the space temperature at
the stored unoccupied heating or cooling setpoint, based
on the measured space temperature, the active setpoint
and the control algorithm, regardless of the presence of a
hard-wired or communicated setpoint. Similar to other
configuration properties of the controller, the locally
stored unoccupied setpoints can be modified using Rover
service tool.
In unoccupied mode, a simplified zone control algorithm is
run. During the cooling mode, when the space
temperature is above the cool setpoint, the primary
cooling capacity operates at 100 percent. If more capacity
is needed, the supplementary cooling capacity turns on (or
opens to 100 percent). During the heating mode, when the
space temperature is below the heat setpoint, the primary
heating capacity turns on. All capacity is turned off when
the space temperature is between the unoccupied cooling
and heating setpoints. Note that primary heating or
cooling capacity is defined by unit type and whether
heating or cooling is enabled or disabled. For example, if
the economizer is enabled and possible, it will be the
primary cooling capacity. If hydronic heating is possible, it
will be the primary heating capacity.
Occupied Standby Mode (Tracer ZN520)
The controller can be placed into the occupied standby
mode when a communicated occupancy request is
combined with the local (hard-wired) occupancy binary
input signal. When the communicated occupancy request
is unoccupied, the occupancy binary input (if present)
does not affect the controller’s occupancy. When the
UV-SVN02_-EN.book Page 71 Thursday, January 24, 2013 4:48 PM