RT-SVX24Q-EN
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starts sequencing condenser fans “On”. If the
operating fans cannot bring the condensing
temperature to within the controlband, more fans are
turned on. As the saturated condensing temperature
approaches the lower limit of the controlband, fans are
sequenced “Off”.
The minimum “On/Off” time for condenser fan staging
is 5.2 seconds. If the system is operating at a given fan
stage below 100% for 30 minutes and the saturated
condensing temperature is above the “efficiency check
point” setting, a fan stage will be added. If the
saturated condensing temperature falls below the
“efficiency check point” setting, the fan control will
remain at the present operating stage. If a fan stage
cycles four times within a 10 minute period, the control
switches from controlling to the “lower limit” to a
temperature equal to the “lower limit” minus the
“temporary low limit suppression” setting. It will utilize
this new “low limit” temperature for one hour to
reduce condenser fan short cycling.
For evaporative condensing units, head pressure is
monitored with pressure transducers attached to the
saturated condensing line and converted to a
temperature by the MPM. This temperature is used to
control the variable speed fan and sump pump. When
the temperature rises above the upper limit (120°F) the
sump pump is energized. If the condensing
temperature drops below the lower limit (70°F) the
sump pump is de-energized.
High Pressure Limit Controls
High Pressure controls are located on the discharge
lines near the scroll compressors. They are designed to
open when the discharge pressure approaches 650 ± 10
psig. The controls reset automatically when the
discharge pressure decreases to approximately 550 ±
10 psig. However, the compressors on that circuit are
locked out and a manual reset diagnostic is initiated
after the fourth occurrence of a high pressure
condition.
High Compressor Pressure Differential
Protection
(eFlex™ variable speed compressor units)
The eFlex variable speed compressor units provide
High Compressor Pressure Differential protection for
the equipment, also referred to as Low VI compressor
protection. This protection is active on a per circuit
basis and prevents scroll involute stresses from
exceeding levels that could cause compressor damage.
Two levels of control are implemented to support the
High Compressor Pressure Differential protection: Limit
and Diagnostic trips.
During a Limit trip, the controller will determine when
the pressure differential has exceeded predetermined
limits and will then take action by either limiting the
compressor capacity or by unloading/reducing the
compressor capacity on that circuit. Once the pressure
differential returns to an acceptable level, the circuit
will become unlimited if still needed for temperature
control.
During a Diagnostic trip, the controller will determine
when the pressure differential has exceeded acceptable
levels for the equipment and will then de-energize the
circuit completely. Once the pressure differential
returns to an acceptable level, the circuit will be
allowed to re-energize if still needed for temperature
control. If four Diagnostic trips occur within the same
request for compressor operation, the circuit will be
locked out on a manual reset diagnostic.
If actively limiting or controlling compressor outputs
OFF due to a High Compressor Pressure Differential
event, the Limit/Diagnostic event will be found under
Status/ Compressor Status Submenu at the human
interface . During a diagnostic trip a diagnostic will be
indicated at the human interface .
Outdoor Air Humidity Sensor
An analog input device used on CV and VAV
applications with 100% economizer. It monitors the
outdoor humidity levels for economizer operation. It is
mounted in the outside air intake section and is
connected to the RTM.
Return Air Humidity Sensor
An analog input device used on CV and VAV
applications with the comparative enthalpy option. It
monitors the return air humidity level and compares it
to the outdoor humidity level to establish which
conditions are best suited to maintain the cooling
requirements. It is mounted in the return air section
and is connected to the ECEM.
Space Humidity Sensor
Analog input device used on CV and VAV applications
with modulating dehumidification option and/or
humidification field installed option. It is used to
monitor the humidity level in the space and for
comparison with the dehumidification and
humidification setpoints to maintain space humidity
requirements. It is field mounted in the space and
connected to the RTM.
Status/Annunciator Output
An internal function within the RTM module on CV and
VAV applications that provides:
•
diagnostic and mode status signals to the remote
panel (LEDs) and to the Human Interface
•
control of the binary Alarm output on the RTM
•
control of the binary outputs on the GBAS module
to inform the customer of the operational status
and/or diagnostic conditions
Low Ambient Compressor Lockout
Utilizes an analog input device on CV and VAV
applications. When the system is configured for low
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