Unit Start Up
RT-SVX36K-EN 87
temperature is above 50°F, the outside air damper will
remain closed and DX mechanical cooling will occur for
the duration of Rapid Restart.
Supply Fan Operation – Speed Control:
• VAV:The supply fan speed will ramp to 50%, then
release to normal discharge static pressure control,
limited only by the high duct static limit functionality.
• CV: The supply fan speed will turn on full airflow.
• SZVAV:The supply fan speed will ramp to full airflow.
Units without an Economizer
Upon entering an “occupied” mode of operation, the RTM
receives input from the remote panel to start the supply
fan. For constant volume applications, the RTM supply fan
contacts K2 close which energizes the supply fan contactor
1K16. When the supply fan starts, the fan proving switch
(3S68) closes, signaling the RTM that airflow has been
established.The VFD will begin to ramp the fan, (if
equipped).
When a cooling request is sent to the RTM from a zone
temperature sensor, the RTM evaluates the operating
condition of the system using the supply air temperature
input and the outdoor temperature input before sending
the request to the SCM/MCM. Once the request is sent to
the SCM/MCM, the compressor module checks the
compressor protection circuit before closing “Stage 1”
(K10 on SCM or K11 on MCM). After the first functional
stage has started, the compressor module monitors the
saturated refrigerant temperature and closes the
condenser fan output contact “1A”, when the saturated
refrigerant temperature rises above the “lower limit”
setpoint.
Units with an Economizer
Upon entering an “occupied” mode of operation, the RTM
receives input from the remote panel to start the supply
fan. For constant volume applications, the RTM supply fan
contacts K2 close which energizes the supply fan contactor
1K16. When the supply fan starts, the fan proving switch
(3S68) closes, signaling the RTM that airflow has been
established.The RTM opens the economizer dampers to
the specified “minimum position”.
When a cooling request is sent to the RTM from the zone
temperature sensor, the RTM evaluates the operating
condition of the system using the supply air temperature
input and the outdoor temperature input before sending
the request to the SCM/MCM for mechanical cooling. If the
outdoor conditions are suitable for cooling (temperature
and humidity are within specified setpoints), the RTM will
attempt to maintain the zone temperature without using
any compressors. If the zone temperature can not be
maintained within the setpoint deadband, the RTM sends
a cooling request to the SCM/MCM.The compressor
module checks the compressor protection circuit before
closing “Stage 1” (K10 on SCM or K11 on MCM). After the
first functional stage has started, the compressor module
monitors the saturated refrigerant temperature and closes
the condenser fan output contact “1A”, when the saturated
refrigerant temperature rises above the “lower limit”
setpoint.
Units with Return Fan
The return fan is started once the supply fan is verified ON
by the supply fan proving function. If equipped, the
variable speed return fan is modulated to control return
plenum pressure to the Return Plenum Pressure Setpoint
and Return Plenum Pressure Deadband.
For the first two minutes of return fan operation, the
outside air damper control and if equipped, building space
pressure control are disabled so that the exhaust damper
remains closed. After the two minute delay, the outside air
damper is released to normal ventilation requests, and
exhaust damper control will either track the outside air
damper or if equipped, the exhaust damper control is
released to normal space pressure control.
Units with Traq Sensor
The outside air enters the unit through theTRAQ Sensor
assembly and is measured by velocity pressure flow rings.
The velocity pressure flow rings are connected to a
pressure transducer/solenoid assembly.The solenoid is
used for calibration purposes to compensate for
temperature swings that could affect the transducer.The
Ventilation Control Module (VCM) utilizes the velocity
pressure input, the RTM outdoor air temperature input,
and the minimum outside air CFM setpoint to modify the
volume (CFM) of outside air entering the unit as the
measured airflow deviates from setpoint.
When the optional temperature sensor is installed and the
Preheat function is enabled, the sensor will monitor the
combined (averaged) outside air and return air
temperatures. As this mixed air temperature falls below
the Preheat ActuateTemperature Setpoint, the VCM will
activate the preheat binary output used to control a field
installed heater.The output will be deactivated when the
temperature rises 5 above the Preheat Actuate
Temperature Setpoint.
Figure 53. Typical rapid restart timeline
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