General Information
14
RT-SVX24J-EN
Leaving Recovery Exhaust Temp Sensor
Analog input device used on CV andVAV applications with
Energy Recovery option installed. It is used to monitor the
temperature of the leaving air on the Exhaust Fan side of
the energy recovery wheel. This temperature is used to
determine if the temperature of the wheel is too cold as
compared to the Recovery Frost Avoidance Setpoint. The
result is used to determine when to enable energy wheel
frost avoidance functions.
Supply, Exhaust and Return Fan Airflow
Proving Switches
Supply Airflow Proving Switch is a binary input device
used on CV and VAV applications to signal the RTM when
the supply fan is operating. It is located in the supply fan
section of the unit and is connected to the RTM. During a
request for fan operation, if the differential switch is
detected to be open for 40 consecutive seconds;
compressor operation is turned “Off”, heat operation is
turned “Off”,the request for supply fan operation is turned
“Off” and locked out, exhaust dampers (if equipped) are
“closed”, economizer dampers (if equipped) are “closed”,
and a manual reset diagnostic is initiated.
Exhaust/return Airflow Proving Switch is a binary input
device used on all rooftop units equipped with an exhaust
fan. It is located in the exhaust/return fan section of the unit
and is connected to the RTM. During a request for fan
operation, if the differential switch is detected to be open
for 40 consecutive seconds, the economizer is closed to
the minimum position setpoint, the request for exhaust
fan operation is turned “Off” and locked out, and a manual
reset diagnostic is initiated.The fan failure lockout can be
reset at the Human Interface located in the unit control
panel, by Tracer, or by cycling the control power to the
RTM Off/On.
Lead-Lag
A selectable mode of operation through the Human
Interface. It alternates the starting between the first
compressor of each refrigeration circuit. Only the
compressor banks will switch, not the order of the
compressors within a bank, providing the first compressor
in each circuit had been activated during the same request
for cooling.
Charge Isolation
During the OFF cycle, most of the charge is isolated
between the compressor (internal) discharge check valves
and liquid line solenoid valve.This reduces the OFF cycle
charge migration, and liquid feedback during subsequent
startup.The liquid line solenoid is energized (opened) with
the start of the circuit compressor.
Supply, Exhaust and Return Fan Circuit
Breakers
The supply fan and exhaust fan motors are protected by
circuit breakers or fuses. They will trip and interrupt the
power supply to the motors if the current exceeds the
breaker's “must trip” value. The rooftop module (RTM)
will shut all system functions “Off” when an open fan
proving switch is detected.
Low Pressure Control
Low Pressure Control is accomplished using a binary input
device on CV and VAV applications. LP cutouts are located
on the suction lines near the scroll compressors.The LPC
contacts are designed to close when the suction pressure
exceeds 41 ± 4 psig. If the LP control is open when a
compressor is requested to start, none of the compressors
on that circuit will be allowed to operate.They are locked
out and a manual reset diagnostic is initiated.
The LP cutouts are designed to open if the suction
pressure approaches 22 ± 4 psig. If the LP cutout opens
after a compressor has started, all compressors operating
on that circuit will be turned off immediately and will
remain off for a minimum of three minutes. If the LP cutout
trips four consecutive times during the first three minutes
of operation, the compressors on that circuit will be locked
out and a manual reset diagnostic is initiated.
Saturated Condenser Temperature Sensors
Analog input devices used on CV and VAV applications
mounted inside a temperature well located on a
condenser tube bend. They monitor the saturated
refrigerant temperature inside the condenser coil and are
connected to the MCM. As the saturated refrigerant
temperature varies due to operating conditions, the
condenser fans are cycled “On” or “Off” as required to
maintain acceptable operating pressures.
Head Pressure Control
Accomplished using two saturated refrigerant
temperature sensors on CV and VAV applications. During
a request for compressor operation, when the condensing
temperature rises above the “lower limit” of the
controlband, the Compressor Module (MCM) starts
sequencing condenser fans “On”.If the operating fans can
not 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.
Содержание SEHJ090-162
Страница 40: ...Dimensional Data 40 RT SVX24J EN Figure 13 Evaporative condenser water connection locations RIGHT SIDE VIEW ...
Страница 48: ...Installation 48 RT SVX24J EN Figure 18 Ductwork conversion ...
Страница 58: ...Installation 58 RT SVX24J EN Figure 36 5 Connected tubes 6 install panels Connected tubes 5 6 ...
Страница 75: ...Installation RT SVX24J EN 75 Figure 51 Hot water coil piping Figure 52 Steam coil piping ...
Страница 87: ...Installation RT SVX24J EN 87 Figure 57 Typical field wiring diagram for 90 to 162 ton CV control options ...
Страница 89: ...Installation RT SVX24J EN 89 Figure 59 Typical field wiring diagram for 90 to 162 ton VAV control options ...