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O O p p e e r r a a t t i i n n g g P P r r i i n n c c i i p p l l e e s s
Reference
Figure 30, p. 57
the cycling MWU sequence. Cycling capacity MWU will
heat until MWU temperature setpoint is reached. Next,
a 60-minute timer begins. If the building load reaches
the MWU ventilation setpoint, or the 60 minutes expire,
whichever is first, the airside economizer will control to
the minimum position. MWU will end when the zone
temperature rises above the MWU terminate setpoint.
Timed Override Activation—ICS™
This function is operational whenever the unit's RTM
module is used as the zone temperature sensor source,
which can be set at the HI panel. When this function is
initiated by the push of the override button on the zone
sensor, the unit will switch to the occupied mode. Unit
operation (occupied mode) during timed override is
terminated by a signal from Tracer.
Timed Override Activation—Non-ICS
This function is active whenever the unit's RTM module
board is selected as the zone temperature source,
which can be set at the human interface panel. When
this function is initiated by the push of the override
button on the zone sensor, the unit will switch to the
occupied mode. Automatic cancellation of the timed
override mode occurs after three hours of operation.
VAV Drive Max Output
This is a single-pole, double-throw relay rated at a
maximum voltage of 24 vac, two amps max. The relay
contacts of this relay switch when the unit goes from
the occupied mode to the unoccupied mode by means
of the unoccupied binary input, night setback zone
sensor, or Tracer Summit. The contacts will stay
switched during the unoccupied and morning warm-up
mode. They will return to the position shown on the
unit wiring diagram when the unit returns to the
occupied mode. The intent of this binary output is to
signal the VAV boxes or other terminal devices to go to
a full open airflow position.
Occupied Sequence
All setpoints can be adjusted using the HI panel. Also,
cooling/heating setpoints can be adjusted in the zone, if
using an adjustable zone sensor. For a complete list of
unit setpoint default values and ranges, see the
IntelliPak™ Self-Contained Programming Guide, PKG-
SVP01*-EN.
Occupied Zone Temperature—Cooling
The unit transitions from unoccupied to occupied when
the occupied/unoccupied input on the RTM is open for
more than five seconds after having been closed. This
input can be received from Tracer Summit, the remote
NSB zone sensor, the timed override function, or a field
supplied contact. Dependent on unit options and the HI
programming, the following sequence will occur:
58
for a pictorial explanation of
•
The unit will begin MWU and then switch to the
occupied mode after the MWU setpoint is met.
•
Purge will be enabled by Tracer Summit. Then
Tracer Summit will enable the occupied mode.
•
The unit will switch from unoccupied to occupied
control immediately.
Upon entering occupied mode, the occupied/
unoccupied relay will de-energize.
Zone Temperature Control (Unit Model
Number Digit 9 = 4 or 5)
A zone sensor located directly in the space sends input
to the RTM while the CV unit is in occupied cooling
mode. When the unit is in occupied cooling, the RTM
controls the zone temperature within the cooling
setpoint deadband by modulating the economizer
option and/or staging mechanical cooling on and off as
required.
Supply Air Temperature Control (Unit
Model Number Digit 9 = 1, 2, 3, or 6)
When the VAV unit is in occupied cooling, the RTM
controls the supply air temperature to the specified
supply air cooling setpoint by modulating the
economizer option and/or staging mechanical cooling
on and off as required. The changeover relay contacts
(field supplied) must be open on units with hydronic
heat for cooling to operate.
Cooling
Upon entering occupied mode, the RTM receives an
input from either the HI, RHI, Tracer Summit, or the
GBAS to start the supply fan. The RTM supply fan
contacts close and energize the supply fan contactor.
When the supply fan starts, the fan proving switch
closes, signaling the RTM that airflow is established.
The VFD will ramp the fan, and/or the airside
economizer dampers will open to the user-defined
minimum position.
When a cooling request is sent to the RTM from the
zone sensor, the RTM evaluates the system operating
conditions using the supply air and outdoor
temperature input before sending the request to the
MCM for mechanical cooling. If outdoor conditions
(temperature and humidity) are suitable or the EWT is
within specified setpoints, the RTM will attempt to use
"free cooling" without using any compressors. The
RTM will use either the airside or waterside economizer
option. When outdoor air conditions are not suitable,
only mechanical cooling will function and outside air
dampers will remain at their minimum position. If the
unit does not have an economizer, mechanical cooling
will operate to satisfy cooling requirements.
SCXF-SVX01Q-EN
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