CeilAir DX Series Manual del operador descargar pdf (Pagina 33)

(Mar, 2012)

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

condenser air inlet temperatures are 0°F or higher,

this method utilizes a high-pressure differential

control switch with SPST (Single Pole, Single

Throw) contacts 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 con-

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

condenser fan speed switch senses refrigerant dis-

charge pressure 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 approximately 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

temperatures 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 condenser/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

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 highly efﬁ cient, electronically

commutated (EC), axial fan(s). The EC fan speed is

inﬁ nitely variable up to full speed. The control system

utilizes refrigerant pressure transducer(s) to monitor

refrigerant discharge pressure and control the EC

fan(s) to the precise speed needed to maintain

design refrigerant 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

condenser air inlet temperatures may fall to -30°F,

ﬂ ooded 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 ﬂ ow 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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