RT-SVX46G-EN
43
Unit Startup
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 Zone Variable 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 staged 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.
During modulating gas heating operation, the control will
monitor the space temperature and space heating setpoint
and with a PI control algorithm determine if active heating
is required. On a single-zone VAV unit, as the active
discharge air temperature setpoint deviates from the
active supply air heating setpoint, the unit controller will
modulate airflow between the user selected maximum
and minimum fan speed to maintain the active discharge
air temperature setpoint. On a multi-zone VAV unit, the
control will modulate the airflow between the user
selected maximum and minimum fan speed to maintain
the duct static pressure.
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.
WARNING
Live Electrical Components!
Failure to follow all electrical safety precautions when
exposed to live electrical components could result in
death or serious injury. When 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.
