Cooling (Cv Or Sz Vav Only); Heating; Economizer; Gas Heat Control - Trane Voyager Commercial Installation, Operation And Maintenance Manual

Zone Temperature - Unoccupied Cooling
(CV or SZ VAV Only)
While a building is in an unoccupied period as
designated by a remote panel with night setback, ICS
or RTRM J6-11 and J6-12, the necessary cooling
capacity will be controlled to maintain the zone
temperature to within the unoccupied setpoint
deadband. If an economizer is enabled, it will modulate
in an attempt to maintain the zone temperature to
within the setpoint deadband.
N N o o t t e e : : On SZ VAV units, the Supply Air Fan Speed will
be controlled as during normal occupied
conditions in order to meet the requirements of
the zone. Unoccupied mode does not require full
airflow on a SZ VAV unit during Cooling
operation.
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 SZ VAV systems, the
Supply Air Fan VFD will remain in control as during
normal occupied periods and will be controlled in order
to meet the space requirements. The minimum fan
speed will be based on the configured unit heating
type. For Modulating Heat units, Full Airflow is not
required for SZ VAV applications during Unoccupied
periods. For all Staged Heating types, the Supply Fan
will be controlled at maximum fan speed during active
heating operation as during Occupied periods.
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.
The most sophisticated method available is always
used.
Table 33. Economizer effectiveness
Method used to
determine economizer
effectiveness
Comparative Enthalpy
Reference Enthalpy
Reference Dry Bulb
Unable to determine
effectiveness
RT-SVX34R-EN
Required
OAT, OAH, RAT, RAH
OAT, OAH
OAT
OAT data is invalid or
unavailable
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:
• Ambient Temperature - controlling the economizing
cycle by sensing the outside air dry bulb
temperature. Table 34, p. 59
bulb values by potentiometer setting.
• Reference Enthalpy - controlling the economizer
cycle by sensing the outdoor air humidity.
34, p. 59 lists the selectable enthalpy values by
potentiometer setting. If the outside air enthalpy
value is less than the selected value, the
economizer is allowed to operate.
• 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.
Table 34. Economizer configuration
Dry bulb
Potentiometer
changeover
Setting Point
Point
A 73°F
B 70°F
C (a)
67°F
D 63°F
E 55ºF
(a) Factory setting

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 1st and 2nd stages and
control the combustion blower relays. Both stages of
the furnace, when initiated after each cycle, will start
and operate for one minute 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.
When the fan selection switch is in the " " A A U U T T O O " " mode
and the unit is configured as a Constant Volume with
staged or modulating gas heat, or SZVAV with staged
gas heat, the fan will be delayed from coming on for
approximately 30 seconds after a call for heat has been
initiated. The fan will remain on for approximately 90
seconds after the heating setpoint has been satisfied. If
the unit is configured for SZ VAV with modulating heat,
the fan will be energized with the call for heating in
order to begin circulating airflow through the unit for
discharge air temperature control. Once the call for
S S t t a a r r t t u u p p
lists the selectable dry
Table
Reference
Enthalpy
27 BTU/lb.
25 BTU/lb.
23 BTU/lb.
22 BTU/lb.
19 BTU/lb.
59