Trane IntelliPak SAHL Series Installation, Operation And Maintenance Manual page 95

Unit Start Up
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 fresh air enters the unit through the Traq 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 fresh 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) fresh air and return air temperatures. As this mixed air
temperature falls below the Preheat Actuate Temperature 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.
When the optional CO sensor is installed and the CO Reset is enabled, as the CO concentration
2 2 2
increases above the CO Reset Start Value, the VCM will modify the minimum outside air CFM
2
setpoint to increase the amount of fresh air entering the unit. The setpoint will be adjusted upward
until the CO Maximum Reset Value is reached. The maximum effective (reset) setpoint value for
2
fresh air entering the unit is limited to the systems operating CFM. As the CO concentration
2
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