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Operating Principles
This section contains an overview of the operation
of CGAF / CXAF air-cooled liquid chiller / Heat Pump
equipped with microcomputer-based control systems.
It describes the overall operating principles of the CGAF
chiller / CXAF Heat Pump.
Note: To ensure proper diagnosis and repair, contact a
qualified service organization if a problem could occur.
General
The Model CGAF / CXAF units are scroll compressor(s),
single or dual circuit, air-cooled liquid chillers. These
units are equipped with unit-mounted starter/control
panels and operate with R410A refrigerant.
The basic components of a CGAF / CXAF unit are:
• Unit-mounted panel containing starter and
Tracer UC800 controller and Input/Output
LLIDS
• Scroll compressors
• Brazed plate / Shell & Tube evaporator
• Air-cooled MCHE / Fin & tube condenser with
sub cooler
• Electronic Expansion Valve (EEXV)
• Related interconnecting piping
Refrigerant Cycle
The refrigeration cycle of the Model CGAF chiller / CXAF
Heat Pump is conceptually similar to other Trane air-
cooled chiller products. The CGAF chiller / CXAF Heat
Pump uses a brazed plate / Shell & Tube evaporator
and an air-cooled MCHE / Fin & tube condenser. The
compressors use suction gas cooled motors and an
oil management system to provide almost oil-free
refrigerant to the condenser and evaporator for
maximum heat transfer while lubricating and sealing
compressor rotors and bearings. The lubrication system
helps to assure long compressor life and contributes to
quiet operation.
Refrigerant condenses in the MCHE / Fin & tube
air-cooled heat exchanger. Liquid refrigerant is metered
into the brazed plate or Shell and Tube evaporator
using an electronic expansion valve to maximize chiller
efficiency at full and part load operation.
The CGAF chiller / CXAF Heat Pump is equipped with a
unit-mounted starter and control panel. Microprocessor
based unit control modules (Trane Tracer™UC800)
provide accurate chilled water control and providing
monitoring, protection and adaptive limit functions.
The adaptive nature of the controls intelligently prevent
the chiller from operating outside of its limits, or
compensates for unusual operating conditions while
keeping the chiller running rather than simply shutting
off the chiller. If problems do occur, the UC800 controls
provide diagnostic messages to help the operator in
troubleshooting.
Oil System
The oil is efficiently separated inside the scroll
compressor and will remain in the scroll compressor
during all run cycles. Between 1-2% of the oil circulates
around with the refrigerant.
See compressor section for oil level information.
Condenser and Fans
The air-cooled micro-channel condenser coils use all
aluminium brazed fin construction and Fin & tube
condenser coils use Copper tube and aluminium fin
construction.
The MCHE coil is composed of three components: the
flat micro channel tube, the fins located between the
micro-channel tubes, and two refrigerant manifolds.
Coils can be cleaned with high pressure water (see
Condenser Coils maintenance for instructions).
Whereas Fin & Tube coil is composed of four
components: the holding frame, Circular tube, U-bends
joining the tube ends, the aluminium fins located above
the tubes, and two refrigerant Headers. Coils can be
cleaned with high pressure water (see Condenser Coils
maintenance for instructions).
The condenser coils has an integral sub-cooling circuit.
Condensers are factory proof and leak tested at 45 bars.
Direct-drive vertical-discharge airfoil condenser AC/EC
fans are dynamically balanced.
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