Stulz CeilAir CW - Flooded Head Pressure Control (Condenser Model SCS-AA with Fan Cycling, -30 °F); Intelligent Control (Condenser Model SCS-EC Only, -20 °F); Variable Condenser Fan Speed (Condenser Model SCS-SA, -20 °F)

58 OCH0006F08/13/2024
CEILAIR
®
CW & DX IOM
2.10.2.3 VARIABLE CONDENSER FAN SPEED CONDENSER MODEL SCSSA, 20 °F
2.10.2.3 Variable Condenser Fan Speed (Condenser Model SCSSA, -20 °F)
Used for outdoor installations where ambient temperatures may fall to -20 °F, a variable speed condenser fan
motor control is used to maintain head pressure. The variable speed motor is located closest to the header
end of the condenser. The fan speed control is a continual modulation of the motor’s speed. The controller is
factory installed in the outdoor condenser/condensing unit. The fan speed controller requires no adjustment.
The fan speed controller will automatically control the head pressure at a level to maintain design refrigerant
discharge pressures. The remaining motors cycle on and off based on pressure, on systems with more than
one condenser fan.
2.10.2.4 Intelligent Control (Condenser Model SCSEC Only, -20 °F)
Used for outdoor installations where ambient condenser air inlet temperatures may fall to -20 °F, intelligent
pressure control is designed to maintain discharge pressure by constantly modulating condenser fan speed.
SCS outdoor condensers are equipped with efficient, electronically commutated (EC), axial fans. The EC fan
speed is variable. The control system uses refrigerant pressure transducer(s) to monitor refrigerant discharge
pressure and control the EC fan(s) to the precise speed needed to maintain refrigerant discharge pressures.
2.10.2.5 Flooded Head Pressure Control (Condenser Model SCSAA With Fan Cycling, -30 °F)
Used for outdoor installations where ambient condenser air inlet temperatures may fall to -30 °F, flooded
head pressure control is designed to maintain head pressure during low ambient conditions. A head
pressure control valve and a receiver are used in the refrigeration circuit to back up liquid refrigerant into
the condenser coil. The head pressure control valve is a three-way modulating valve controlled by discharge
pressure.
When the A/C unit begins to operate, the discharge pressure rises—to approximately 320 psig (2.21 MPa)
for R407C; 440 psig (3.03 MPa) for R410A—and the condenser fan is cycled on, as described in sections
2.10.2.12.10.2.3. When the ambient temperature drops, the discharge pressure drops also. When the
discharge pressure drops, the head pressure control valve diverts discharge gas away from the condenser to
the receiver. Liquid flow from the condenser is restricted, causing liquid to back up in the condenser.
Flooding the condenser reduces the area available for heat transfer. The desired result is to increase the
pressure into the condenser, maintaining a minimum discharge pressure during low ambient operation, thus
ensuring proper condensing temperature. The head pressure control valve requires no adjustment.
While the fan is running, the flooded head pressure control valve modulates the amount of discharge gas
entering the receiver. As the pressure increases, the valve diverts more discharge gas to the condenser,
allowing more liquid to flow from the condenser to the receiver.