General Information
RT-SVX24J-EN
17
Supply Air Tempering
On CV units equipped with staged gas heat, if the supply
air temperature falls 10°F below the occupied heating
setpoint temperature while the heater is “Off”, the first
stage of heat will be turned “On”.The heater is turned “Off”
when the supply air temperature reaches 10°F above the
occupied heating setpoint temperature.
Variable Air Volume (VAV) Units
Occupied Heating—Supply Air Temperature
When a VAV unit is equipped with “Modulating Heat”, and
the system is in an occupied mode, and the field supplied
changeover relay contacts have closed or per a BAS
command, the supply air temperature will be controlled to
the customer specified supply air heating setpoint. It will
remain in the heating status until the changeover relay
contacts are opened or BAS has released the heat
command.
Occupied Cooling—Supply Air Temperature
When a VAV unit is in the occupied mode, the supply air
temperature will be controlled to the customer specified
supply air cooling setpoint by modulating the economizer
and/or staging the mechanical cooling “On and Off” as
required.The changeover relay contacts must be open, or
BAS command set to auto or cool, for the cooling to
operate.
Daytime Warm-up
On VAV units equipped with heat, if the zone temperature
falls below the daytime warm-up initiate temperature
during the occupied mode, the system will switch to full
airflow. During this mode, the VAV box/unocc relay will be
energized (this is to signal the VAV boxes to go to 100%).
After theVAV box max stroke time has elapsed (factory set
at 6 minutes), the VFD output will be set to 100%. The
airflow will be at 100% and the heat will be turned on to
control to the occupied heating setpoint.
When the zone temperature reaches the daytime warm-up
termination setpoint, the heat will be turned off, the relay
will be de-energized, releasing the VAV boxes, the VFD
output will go back to duct static pressure control and the
unit will return to discharge air control. If the occ zone
heating setpoint is less than the DWU terminate setpoint,
the heat will turn off when the occ zone heat setpoint is
reached, but it will stay in DWU mode and cycle the heat
to maintain setpoint.
Unoccupied Heating—Zone Temperature
When aVAV unit is equipped with gas, electric, or hydronic
heat and is in the unoccupied mode, the zone temperature
will be controlled to within the customer specified setpoint
deadband. During an unoccupied mode for a VAV unit, the
VAV box/unocc relay will be in the unoccupied position
and theVFD output will be at 100%.This means that if there
is a call for heat (or cool) and the supply fan comes on, it
will be at full airflow and the VAV boxes in the space will
need to be 100% open as signaled by the VAV box/unocc
relay.
Supply Air Tempering
On VAV units equipped with “Modulating Heat”, if the
supply air temperature falls 10°F below the supply air
temperature setpoint, the heat will modulate to maintain
the supply air temperature to within the low end of the
setpoint deadband.
Supply Duct Static Pressure Control
(Occupied)
The RTM relies on input from the duct pressure transducer
when a unit is equipped with aVariable Frequency Drive to
set the supply fan speed to maintain the supply duct static
pressure to within the static pressure setpoint deadband.
The transducer compares supply duct pressure to ambient
pressure. Refer to
Figure 43, p. 65
.
Space Temperature Averaging
Space temperature averaging for Constant Volume
applications is accomplished by wiring a number of
remote sensors in a series/parallel circuit.
The fewest number of sensors required to accomplish
space temperature averaging is four. The Space
Temperature Averaging with Multiple Sensors figure
illustrates a single sensor circuit (Single Zone), four
sensors wired in a series/parallel circuit (Four Zone), nine
sensors wired in a series/parallel circuit (Nine Zone). Any
number squared, is the number of remote sensors
required.
Wiring termination will depend on the type of remote
panel or control configuration for the system. Refer to the
wiring diagrams that shipped with the unit.
Figure 6.
Transducer voltage output vs. pressure input
with VCM and TRAQ™ sensing
Transducer Voltage Output vs. Pressure Input
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
-0.5 0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Pressure (inches w.c.)
Volt
s
