CeilAir CW series Instrukcja Operatora Pobierz pdf (Strona 33)

(©July, 2008)

CeilAiR OHS Series Installation, Operation & Maintenance Manual

ir Technology Systems, Inc.

2-22

2.9.2 Head Pressure Controls-

Air Cooled Systems

2.9.2.1 Condenser Fan Cycling

(Condenser Model SCS-AA, 0°F)

Used for outdoor installations where ambient con-

denser air inlet temperatures are 0°F or higher, this

method utilizes a high-pressure differential control

switch with SPST (Single Pole, Single Throw) con-

tacts and an automatic reset. The switch activates the

condenser blower contactor when the discharge

pressure reaches 275 psig to maintain the condensing

temperature.

Factory setting: Switch contacts are set to close on a

pressure rise to 275 psig and open at 205 psig.

Setpoint range is 170 to 375 psig. The differential is

non-adjustable and set at 70 psi.

2.9.2.2 Condenser Multi-Speed Fan Switch

(Model HES-CAA , 0°F)

Used for indoor installations where ambient condenser

air inlet temperatures are 0°F or higher, the condenser

fan speed switch senses refrigerant discharge pres-

sure and changes the condenser blower speed to

maintain proper condenser pressures. The condenser

fan speed switch changes the fan (blower) from low to

high speed at approximately 325 psig and returns the

fan (blower) from high speed to low speed at approxi-

mately 255 psig.

Factory setting: On pressure rise, the high fan speed

contacts are set to close at 325 psig. This will

increase the condenser fan speed. A pressure drop to

255 psig will close the low fan speed contacts and

reduce the fan speed. Set point range is 170 to 400

psig. The differential is nonadjustable and set at 70

psi.

NOTE

This switch and settings does not apply to units

designed for a power supply greater than 277V.

2.9.2.3 Variable Condenser Fan Speed

(Condenser Model SCS-SA, -20°F)

Used for outdoor installations where ambient tempera-

tures may fall to -20°F, a variable speed condenser

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 con-

denser/condensing unit. The fan speed controller

requires no adjustment.

The fan speed controller will automatically control the

head pressure. On systems with more than one fan

on the condenser, the remaining motors cycle on and

off based on pressure.

2.9.2.4 Intelligent Control

(Condenser Model SCS-EC only, -20°F)

Used for outdoor installations where ambient con-

denser air inlet temperatures may fall to -20°F,

intelligent pressure control is designed to maintain

discharge pressure by constantly modulating con-

denser fan speed. SCS outdoor condensers are

equipped with highly efficient, electronically commu-

tated (EC), axial fan(s). The EC fan speed is infinitely

variable up to full speed. The control system utilizes

refrigerant pressure transducer(s) to monitor refriger-

ant discharge pressure and control the EC fan(s) to

the precise speed needed to maintain design refriger-

ant discharge pressures.

2.9.2.5 Flooded Head Pressure Control

(Condenser Model SCS-AA with Fan

Cycling, -30°F)

Used for outdoor installations where ambient con-

denser 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 3-way modulating valve controlled by discharge

pressure.

When the A/C unit begins to operate, the discharge

pressure rises to 275 psig and the condenser fan is

cycled on, as described in Section 2.8.4.1. When

ambient temperature drops, the discharge pressure

drops also. When the discharge pressure drops to

approximately 180 psig, 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.

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