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6 - MAJOR SYSTEM COMPONENTS
6.2 - Evaporator function
The units use a flooded shell-and-tube evaporator: The water
(heat-transfer medium) circulates in the tubes and the refrigerant
is inside the shell. A single shell is used to serve both refrigerant
circuits. There is a centre tubular plate which separates the two
refrigerant circuits. The tubes are copper, and 3/4" in diameter,
with a finned surface inside and out. There is just one water circuit
with two water passes.
The evaporator has been tested and stamped in accordance with
the applicable pressure code. The maximum standard operating
pressures are 2100 kPa relative for the refrigerant side and
1000 kPa relative for the water-side. These pressures may differ
according to the regulation and the code applied.
The evaporator has thermal insulation formed of 19 mm thick
polyurethane foam and aluminium cladding (optional), and is
equipped with a water drain plug and a vent.
The heat exchanger water connections are Victaulic type
connections. As an option, the evaporator is equipped with frost
protection ("evaporator frost protection" option).
Products used for the thermal insulation of components during
hydraulic connection must have a chemically neutral effect on the
surfaces to which they are applied. All original materials supplied
by Carrier comply with this requirement.
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6.3 - Economizer function
The economiser function includes a liquid valve, a filter drier,
two electronic expansion valves (EXVs), a plate heat exchanger,
and protection devices (fusible plug or valve).
At the condenser outlet, a small fraction of the liquid is expanded
via the secondary EXV in one of the plate heat exchanger circuits
and then is returned as a gas to the compressor via the economiser
port. This expansion enables to increase the liquid subcooling of
the other fraction of refrigerant entering the evaporator via the
main EXV. This enables the system's cooling capacity and
efficiency to be improved.
6.3.1 - Electronic expansion valve (EXV)
The EXV is equipped with a stepper motor (2785 to 3690 steps,
depending on the model) that is controlled via an electronic circuit
board.
The EXV is also equipped with a sight glass used to check the
mechanism movement and the presence of the liquid gasket.
6.3.2 - Moisture indicator
Located on the EXV, this enables the unit charge to be controlled
and indicates moisture in the circuit.
The presence of bubbles in the sight-glass indicates an insufficient
charge or non condensable gases in the system.
The presence of moisture changes the colour of the indicator paper
in the sight-glass.
6.3.3 - Filter drier
The role of the filter drier is to keep the circuit clean and moisture-
free. The moisture indicator shows when it is necessary to change
the element. A difference in temperature between the filter inlet
and outlet shows that the element is dirty.
6.4 - Sensors
The unit uses thermistors to measure temperature, and pressure
transducers to monitor and control the operation of the system.
Refer to the SmartVu™ control manual for a more detailed
explanation.
6.5 - Condenser function
The condensers in the units are micro-channel coils made entirely
of aluminium.
Depending on applications, silicon cover caps are required to be
put on condenser coils block fittings. Please contact Carrier Service
for more information.
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