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Sequence of Operation
deadband adjustment range from 0.2" w.c. to 1.0" w.c. The
setpoint is adjustable on the RTAM Static Pressure
Setpoint potentiometer or through ICS.
Example:
Supply Duct Static setpoint = 2.0" w.c. (RTAM)
Deadband = 0.2" w.c. (RTAM)
Duct Static Control Range = 1.9" w.c. to 2.1" w.c.
Mechanical Cooling with an Economizer
The economizer is utilized to control the zone temperature
when the outside air conditions are suitable. The method
used to determine economizer effectiveness, depending
on the available data, is described below in descending
order of complexity.
Table 20. Economizer effectiveness
Method used to determine
economizer effectiveness
Comparative Enthalpy
Reference Enthalpy
Reference Dry Bulb
Unable to determine effectiveness
The most sophisticated method available is always used.
Two of the three methods for determining the suitability of
the outside air can be selected utilizing the potentiometer
on the Economizer Actuator, as described below:
1. Ambient Temperature - controlling the economizing
cycle by sensing the outside air dry bulb temperature.
Table 21
lists the selectable dry bulb values by
potentiometer setting.
2. Reference Enthalpy - controlling the economizer cycle
by sensing the outdoor air humidity.
selectable enthalpy values by potentiometer setting. If
the outside air enthalpy value is less than the selected
value, the economizer is allowed to operate.
Table 21. Economizer configuration
Selection
Dry Bulb
A
73°F
B
70°F
C
67°F
D
63°F
E
55°F
3. Comparative Enthalpy - By utilizing a humidity sensor
and a temperature sensor in both the return air stream
and the outdoor air stream, the economizer will be able
to establish which conditions are best suited for
maintaining the zone temperature, i.e., indoor
conditions or outdoor conditions.
Off Mode
This mode is set at the zone sensor or by ICS. During this
status, no heating, ventilation, or mechanical cooling is
50
Required
OAT, OAH, RAT, RAH
OAT, OAH
OAT
OAT data is invalid or
unavailable
Table 21
lists the
Enthalpy Value
27 BTU/LB Air
25 BTU/LB Air
23 BTU/LB Air
22 BTU/LB Air
19 BTU/LB Air
being performed. When switching the "System" selector
to the "Off" mode from any other mode, any diagnostic
data and diagnostic indication signal will be retained as
long as the system remains in the "Off" status. Switching
the "System" selector from the "Off" mode back to any
other mode of operation will reset all diagnostics.
Heating Operation
Heating operation on units configured with Traditional
Multi-Zone VAV control will utilize two separate control
methodologies based on heating configurations. For all
"Staged" Heating types, the unit will utilize 100% full
airflow during all active heating periods like traditional
Constant Volume units. If the unit has modulating heat, the
unit can be made to do discharge heating with VAV control.
This is done by placing by placing a contact closure across
the "Changeover Input" on the RTAM. During this mode,
the unit will heat to the Supply Air Heating Setpoint ± 3.5°F.
During low load or low airflow conditions the actual
temperature swing of the discharge air will likely be
greater.
Zone Temperature - Unoccupied Heating
While a building is in an unoccupied period as designated
by a remote panel with night setback or ICS, the necessary
heating capacity will be controlled to maintain the zone
temperature to within the unoccupied setpoint deadband.
For traditional VAV systems, the VFD will operate at 100%
during this mode. It will be necessary to drive VAV boxes
to their maximum position through ICS programming or
the factory provided VHR relay. For Modulating Gas Heat
units, Full Airflow is not required but can be enabled by
connecting the changeover mode input J5-1 and J5-2 on
the RTAM module. For all Staged Heating types, the
Supply Fan will be controlled at maximum fan speed
during active heating operation as during Occupied
periods.
Gas Heat Control
The ignition sequence and timing are provided by a
separate heat control module. The RTRM only provides
the heating outputs to initiate 1
control the combustion blower relay. Both stages of the
furnace will start and operate for one minute and then
cycle back if only one stage is required. Units with
modulating heat capabilities will light on high fire for one
minute and then modulate to the appropriate heating rate
for the building load present.
Constant Volume or Variable Air
Volume Applications (SZVAV or
Traditional)
Clogged Filter Option
The unit mounted clogged filter switch monitors the
pressure differential across the return air filters. It is
st
nd
and 2
stages and
RT-SVX26R-EN
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