Introduction (continued)
Freecooling units
Freecooling models consist of an evaporator coil, a
compliant scroll compressor, high and low pressure
switches, an externally equalised, adjustable, thermostatic
expansion valve, service ports, refrigerant line sight glass,
filter drier, stainless-steel plate heat exchanger, a
head-pressure control valve (water regulating valve), a
2-way modulating valve and a freecooling coil.Pressure
relief valves are fitted downstream of the plate heat
exchanger.The refrigerant circuits are precharged with
refrigerant in the factory.
Models CP20F, CP24F, CP28F, CP34F, CP40F are single
circuit. Models CP26F, CP32F, CP42F and CP46F are dual
circuit.
The units operate with water in a closed circuit from an
external drycooler.
When operating in a closed circuit, it may be necessary
(depending on outside temperatures) to add monoethylene
glycoltoprevent thewaterfreezinginwinter, refertothe unit
Installation Manual for applicable percentages.
A pump is used to circulate water (water/glycol) through the
unit (not supplied as standard).
Operation
Freecooling units have two modes of operation, depending
on the outside temperature.
In normal operation, the unit cools the air in the conditioned
space using the compressor and refrigerant coil (direct
expansion).
When outside temperatures are low enough, water from the
external drycooler is used to cool the air in the conditioned
spacedirectly usingthe Freecooling coil.This temperatureis
the ZET or Zero Energy Temperature.
Dual source air cooled
Dual Source Air Cooled models consist of an evaporator
coil, a compliant scroll compressor, high and low pressure
switches, an externally equalised, adjustable, thermostatic
expansion valve, service ports, refrigerant line sight glass,
liquid receiver with pressure-relief valve, filter drier, 3-way
motorised modulating valve and a chilled water coil. The
units are shipped with a holding charge of dry Nitrogen.
Models CP20D, CP24D, CP28D, CP34D and CP40D are
single circuit. Models CP26D, CP32D, CP42D and CP46D
are dual circuit.
Air cooled units require matched air cooled condensers. Fan
speed controlled condensers are available from Liebert for a
full range of outside ambient temperatures. Refer to the
Condensers Technical Data Manual (P/N SLE CD TDM) for
full details.
Operation
In normal operation, when the temperature of the second
sourceislowenough,thechilledwatercoilis usedtocoolthe
air in the conditioned space. If the temperature of the chilled
water rises above the temperature required to maintain the
load, chilled water cooling is stopped and the compressor is
started. The load is then maintained using dx cooling.
4SLE CP TDM E.1 (06/99)
Challenger Plus - Technical Data Manual
Figure 3 - Freecooling Upflow UnitFigure 4 - Dual Source Air Cooled Downflow Unit
