Installation and Maintenance Manual

RTWD/RTUD Operating Principles
RLC-SVX09H-EN 127
Evaporation of refrigerant occurs in the evaporator. A
metered amount of refrigerant liquid enters a distribution
system in the evaporator shell and is then distributed to
the tubes in the evaporator tube bundle.The refrigerant
absorbs heat and vaporizes as it cools the water flowing
through the evaporator tubes. Refrigerant vapor leaves
the evaporator as saturated vapor (State Pt. 1).
The refrigerant vapor generated in the evaporator flows to
the suction end of the compressor where it enters the
motor compartment of the suction-gas-cooled motor.The
refrigerant flows across the motor, providing the
necessary cooling, then enters the compression chamber.
Refrigerant is compressed in the compressor to discharge
pressure conditions. Simultaneously, lubricant is injected
into the compressor for two purposes: (1) to lubricate the
rolling element bearings, and (2) to seal the very small
clearances between the compressor’s twin rotors.
Immediately following the compression process the
lubricant and refrigerant are effectively divided using an
oil separator.The oil-free refrigerant vapor enters the
condenser at State Pt. 2.The lubrication and oil
management issues are discussed in more detail in the
compressor description and oil management sections that
follow.
For RTWD units, a discharge baffle within the condenser
shell distributes the compressed refrigerant vapor evenly
across the condenser tube bundle. Cooling tower water,
circulating through the condenser tubes, absorbs heat
from this refrigerant and condenses it.
For RTUD units, air flows across the condenser coils,
absorbing heat from the refrigerant and condenses it.
As the refrigerant enters the bottom of the condenser
(State Pt. 3), it enters an integral subcooler where it is
subcooled before traveling to the electronic expansion
valve (State Pt. 4).The pressure drop created by the
expansion process vaporizes a portion of the liquid
refrigerant.The resulting mixture of liquid and gaseous
refrigerant then enters the Evaporator Distribution system
(State Pt. 5).The flash gas from the expansion process is
internally routed to compressor suction, and while the
liquid refrigerant is distributed over the tube bundle in the
evaporator.
The RTWD/RTUD chiller maximizes the evaporator heat
transfer performance while minimizing refrigerant charge
requirements.This is accomplished by metering the liquid
refrigerant flow to the evaporator’s distribution system
using the electronic expansion valve. A relatively low
liquid level is maintained in the evaporator shell, which
contains a bit of surplus refrigerant liquid and
accumulated lubricant. A liquid level measurement device
monitors this level and provides feedback information to
the CH530 unit controller, which commands the electronic
expansion valve to reposition when necessary. If the level
rises, the expansion valve is closed slightly, and if the level
is dropping, the valve is opened slightly such that a steady
level is maintained.
Figure 48. Pressure enthalpy curve
Pressure
Enthalpy
Liquid
Gas
1
2
3
4
5