Liebert Air Cooled - Manual (Page 6)

Introduction
2
1.2.3 Liebert Lee-Temp
™
Refrigerant Control
The Liebert Lee-Temp head pressure control system is designed to maintain proper operating head
pressures in outdoor temperatures down to -30°F (-34.4°C). The condensers utilize head pressure con-
trol valves, extra refrigerant and insulated refrigerant receivers with heater pads. It works by flood-
ing the condenser coil with liquid refrigerant to a level that balances the system condensing
requirements with the condenser coil surface available to reject the system heat. During the summer,
the system requires the entire condenser coil surface for heat rejection and most of the refrigerant is
stored in a receiver. In the winter, the same amount of heat can be rejected by only a fraction of the
coil surface. As head pressure begins to fall, the control valve restricts the flow of liquid refrigerant
exiting from the condenser. This extra liquid refrigerant reduces the effective condenser surface area
available for heat transfer. The head pressure control valve also bypasses hot gas into the receiver to
warm the liquid and maintain liquid pressure for proper operation of the expansion valve. Condenser
fan controls are either fan cycling on ambient temperature or constant on. Lee-Temp control is
required for Quiet-Line Condensers.
1.3 Sound Level Options
1.3.1 Standard Condenser
All Fan Speed and VFD Condensers are standard condensers with moderate operating sound levels.
Lee-Temp Condensers with standard-size coils matching Fan Speed and VFD coil sizes are standard
sound level condensers.
1.3.2 Quiet-Line Condenser
Quiet-Line condensers can help your facility meet the strictest noise codes and do so at less cost than
traditional condensers with acoustical shielding. The Quiet-Line condensers utilize the same reliable
construction features of the standard condensers and have oversized coils and slower speed fan
motors which yield the required heat rejection needed at significantly lower sound levels. Lee-Temp
control is required for Quiet-Line Condensers.
1.4 Transient Voltage Surge Suppression Option
Transient Voltage Surge Suppression (TVSS) panel is standard in the VFD Condenser models only.
Surge protection is necessary because rooftop voltage supply often is not conditioned the same as the
voltage supply inside the data center. The TVSS is designed to protect sensitive electronic condenser
components from high voltage transients, up to 25kVA/phase.
An illuminated green LED indicates power supply is On and panel status is OK. An illuminated red
LED indicates conditions require service and the TVSS may require replacement to restore surge pro-
tection to the condenser.
1.5 Typical System Configurations
Figure 2 shows a single refrigeration circuit diagram, displaying the indoor air conditioning unit, the
outdoor condenser (VFD, Fan Speed Control or Lee-Temp) and field supplied interconnection piping.