Liebert Air Cooled - Manual (Page 5)

Introduction
1
1.0 I
NTRODUCTION
1.1 Product Description and Features
The Liebert condenser is low-profile direct-drive propeller fan-type air cooled unit suitable for mount-
ing outdoors. It provides for the heat rejection of either one or two separate refrigeration circuits,
matching heat rejection capacity varying with the outdoor ambient temperatures with each corre-
sponding compressors heat rejection requirements. Constructed with an aluminum cabinet and a cop-
per-tube aluminum fin coil, the unit is quiet and corrosion resistant. The condenser is quickly and
easily installed, because all internal wiring is completed at the factory with only electrical connec-
tions to be made at the job site. All electrical connections and controls are enclosed in an integral
weatherproof section of the condenser.
Figure 1 Liebert two-fan condenser
1.2 Head Pressure Control Types
1.2.1 Fan Speed
Fan speed control utilizes a wave-chopper control to vary the air volume over the condenser coil,
based on refrigerant head pressure. The fan motor next to the electrical panel (two fans on 6-fan and
8-fan models) is a single-phase, permanent split capacitor motor with motor speed adjusted in
response to refrigerant pressure. The balance of fans on multi-fan units cycle on ambient thermostats.
The control system provides refrigerant head pressure control for outdoor ambients as low as
-20°F (-28.9 °C).
1.2.2 Variable Frequency Drive
VFD Condenser control system utilizes a variable frequency drive, inverter duty fan motor operating
from 0% to 100% motor RPM based on head pressure, sensed by refrigerant pressure transducers.
VFD, ambient-temperature thermostat(s), motor overload protection and electrical control circuit are
factory-wired in the integral control panel. VFD controls the fan adjacent to the connection end of the
condenser and remains energized with active compressor operation. The balance of fans on multi-fan
units cycle on ambient thermostats. This system provides refrigerant head pressure control for out-
door ambients as low as -20°F (-28.9°C).