Zamil MAC-240, Installation, Operation & Maintenance Manual

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2.6 OPERATING FROM EXTERNAL POWER SOURCE
The equipment may also be operated from an external power source. The power source rating shall be having a nominal
voltage rating of 460V-3PH-60HZ and can adequately handle the equipment’s power consumption of 55KVA.
When the equipment is operated from an external power source, ensure that the generator’s circuit breaker is switched
“OFF” and the output feeder (power conductors from generator) connected to the main circuit breaker (CB6) in the main
control panel is removed. The power feeder (external power source) can then be fixed on the line terminals of the main
circuit breaker. The equipment can now be operated starting with the steps described in “Start-Up Sequence” 5.3(b) in
this manual.
3. REFRIGERATION SYSTEM
3.1 GENERAL DESCRIPTION
In the basic refrigeration cycle, there are four major components: compressor, condenser, expansion valve and the
evaporator. Let briefly review the function of each of these elements.
The standard unit is equipped with heavy-duty high pressure backward radial fan is capable of supplying required airflow
& static pressure. The fan discharge outlet can be connected to a flexible pre conditioned delivery hose. Flexible duct is
constructed by two-ply, abrasion resistant fabrics or PVC coated fabrics and is stowed inside the unit, when not in use.
Compressor
In the compressor, the low pressure refrigerant vapor is compressed to a high pressure refrigeration vapor. The com-
pressor pumps this refrigerant to the condenser and on through the system.
Condenser
The condenser, receives the high pressure vapor from the compressor, cools it with outdoor air, and then causes the
refrigerant vapor to condense into a high pressure liquid. It may also provide storage for liquid refrigerant in the
system.
Expansion valve
The expansion valve provides a control through which high pressure liquid refrigerant pass into the low pressure side of
the system i.e. evaporator.
Evaporator
The evaporator is a heat exchanger which absorbs heat and boils the low pressure liquid refrigerant, thus changing it into
o low pressure vapor. The low pressure vapor is then drawn back into the compressor and the cycle is repeated.
3.2 REFRIGERATION CYCLE
Whenever the compressor is in operation, there is continuous flow of refrigerant within the system. Liquid refrigerant from
the high pressure side of the system is metered by the expansion valve into the evaporator coil. A portion of the liquid
flashes into vapor resulting in a mixture at the valve outlet. The mixture as it passes through the nozzle orifice of the
distributor rushes with velocity, creating turbulence and thorough mixing. A pressure drop accompanies the mixture as it
passes into the low pressure side of the system. The liquid quickly expands extracting the heat from the air passing the
evaporator coil.
The suction action of the compressor draws the heat laden vapor from the evaporator coil. The pumping of the refrigerant
into the condenser raises its pressure and temperature. Air passing over the condenser surface carries the heat, being
expelled by the refrigerant, away from condenser, thereby lowering the temperature the pressure to allow the heat laden
vapor to be condensed into liquid.
The liquid refrigerant is stored in the condenser where additional heat is sub cooled prior to its passing through the
metering device (expansion valve) into the evaporator coil.