RT-SVX46C-EN
33
Unit Start-Up
Verifying Proper Air Flow
Sequence of Operation
General Standby Mode
During normal occupied periods, when there is no space
cooling or heating demands, the user will be able to
choose Constant or Cycling supply fan operation. During
this period, if the supply fan is operating due to a Constant
Fan Mode selection or due to a ventilation request, the
supply fan will operate at 50% of the user selected,
application specific, maximum airflow. The unit controls
will be compatible with BACnet™ and LonTalk™ Building
Automation System communication interfaces.
Cooling Operation
Default Operation:
During Cooling operation, the
control will monitor the Space Temperature and Space
Cooling setpoint and with a PI control algorithm determine
if active cooling capacity is required. As the Space
Temperature deviates from the Space Cooling Setpoint,
the unit controller will calculate an active Discharge Air
Cooling setpoint that the economizer (if installed) and
compressor and outdoor fan outputs will be modulated to
meet. This active Discharge Air Cooling setpoint will be
calculated between the Space Cooling setpoint and a user
adjustable minimum (65°F default for Single ZoneVariable
Air Volume SZVAV). Once the control determines that a
discharge air temperature equal to the user selected
minimum (65°F default) is required to meet the space
cooling demand, if the space demand continues to
increase, the supply fan speed will be allowed to increase
above its minimum speed proportionally to meet the
additional demand.
Alternate Economizer Operation:
Under the Default
Operation, as described above, the supply fan speed will
remain at minimum speed, as determined by the active
cooling stages, until the space demand requires an
increase in supply airflow. The customer will have the
ability to choose to allow the supply fan speed to increase
when the economizer is enthalpy enabled in order to
realize the maximum cooling capacity of the economizer,
prior to energizing compressor outputs, when the space
requires active cooling capacity. All cooling capacity
demand decisions will function as described in the
“Default Operation” section above with the exception of
the supply fan speed when the unit has an active cooling
demand and the economizer is enthalpy enabled.
Heating Operation
During Heating operation, the control will monitor the
Space Temperature and Space Heating setpoint and with
a PI control algorithm determine if active heating capacity
is required. As the Space Temperature deviates from the
Space Heating Setpoint, the unit controller will increase
the supply airflow up to the user selected, application
specific, maximum airflow and begin to stage heating
outputs (gas or electric) to meet the space demand. The
customer will also have the ability to enable Supply Air
Tempering control which will allow the unit to bring on one
stage of heating when the discharge air temperature falls
below the Space Heating Setpoint - 10°F and the unit is
operating in a minimum ventilation state with the supply
fan running (not actively heating or cooling). The supply
fan output will increase to the user selected, application
specific, maximum airflow during Supply Air Tempering
operation.
Enhanced Dehumidification
Enhanced Dehumidification will be available on all units
equipped with a Space Humidity sensor. Once the Space
Humidity value exceeds the Dehumidification Setpoint
and dehumidification is enabled the unit will maintain the
compressor operation and reduce the indoor fan airflow to
increase latent capacity. If the Space Humidity value
exceeds the Dehumidification Setpoint during no active
call for cooling, the unit will energize the compressor and
fans to an optimum capacity for dehumidification. If
during active enhanced dehumidification the Space
Humidity falls below the Dehumidification Setpoint – 2%,
Dehumidification will be terminated and the unit will
transition back to normal Cooling or Heating control.
Supply Air Temperature Control with an
Economizer
The economizer is utilized to control the supply air cooling
at +1.5°F around the supply air temperature setpoint range
of 40°F and 90°F providing the outside air conditions are
suitable. To reduce the risk of evaporator coil freeze-up
supply air temperature should not be set below 50° F.
While economizing, the mechanical cooling is disabled
until the economizer dampers have been fully open for
three minutes. If the economizer is disabled due to
unsuitable conditions, the mechanical cooling will cycle as
though the unit had no economizer.
Note:
The RTRM is designed to maintain a selectable
supply air temperature of 40°F to 90°F with a +/-
3.5°F deadband. However, to reduce the risk of
evaporator coil freeze-up in Precedent andVoyager
WARNING
Live Electrical Components!
During installation, testing, servicing and
troubleshooting of this product, it may be necessary to
work with live electrical components. Have a qualified
licensed electrician or other individual who has been
properly trained in handling live electrical components
perform these tasks. Failure to follow all electrical safety
precautions when exposed to live electrical
components could result in death or serious injury.
