REFRIGERATION
SYSTEM:
COMPONENTS
INTRODUCTION:
• The job of refrigeration plant is to cool articles or substances down to , and maintain
them at a temperature lower than the ambient temperature.
• Refrigeration can be defined as a process that removes heat.
• The oldest and the most well-known among refrigerants are ice, water, and air.
• In the beginning, the sole purpose was to conserve food.
• The Chinese were the first to find out that ice increased the life and improve the taste of
drinks and for centuries Eskimos have conserved food by freezing it.
• At the beginning of the last century, terms like bacteria, yeast, mould, enzymes etc. were
known.
• If had been discovered that the growth of microorganism is temperature-dependent, that
growth declines as temperature falls, and the growth becomes very slow at temperature
below +10 C.
COMPRESSOR: CONCEPTS
• A refrigerants compressor is a component of refrigerator which is designed to compress
the refrigerant used to cool the refrigerator.
• Compressors can also be found on other devices which are designed to be used for
cooling. The refrigerant compressor is part of a closed system which keeps the
refrigerant moving in a loop; in some system is on continuously to maintain a very
stable temperature, while in others it may cycle on and off.
• The compressor has two functions in the refrigeration cycle.
It removes refrigerant vapor from the evaporator and reduces the pressure in the
evaporator to a point where the required temperature can be maintained.
The compressor raises the pressure of the refrigerant vapor to a high enough level
that it can be changed into liquid as it follow through the condenser.
SCROLL COMPRESSOR PROTECTION
Scroll compressors have a internal thermo-disc discharge gas
temperature protection. This thermo-disc opens a gas passage from
the discharge port to the suction side near to the protector when the
discharged gas reaches a critical temperature.
The hot gas then causes the motor protector to trip shutting down
the compressor.
1. Temperature Operated Disk (TOD) – A bi-metallic disk that
senses compressor discharge temperature & opens at 270
degrees F.
2. Internal Pressure Relief (IPR) – Opens at approximately 400+/-
50 psi differential bet. High and Low side pressures.
3. Floating Seal – Separates the high side from the low side. Also
prevents the compressor from the drawing into a deep vacuum
& damaged (shorting) the fusire electrical terminal.
4. Internal Motor Protection – An inherent protector sensing both
internal temperatures & amperages.
OIL SEPARATORS
A Oil Separator is a separation chamber for oil and discharge gas. It is installed on the
discharge line between the compressor and the condenser. By using baffles and reducing the
gas velocity, the oil separated from refrigerant and returned to the crankcase of the
compressor by means of a float valve and connecting tube.
Hot Gas Defrost Check Valve
The ORD valve is a pressure differential valve that responds to changes in the pressure
differences across the valve. The valve designation stands for (Open on Rise of Differential
pressure.)therefore, the ORD is dependent on some other control valve or action for its
operation.
When defrost system is initiated, liquid line SOLENIOD VALVES on plate, one is energized, the
other valve de-energized , check the valve responds to changes in pressure differential.
AIR COOLED CONDENSER
The condenser reverses the evaporator process. It changes high
temperature, high pressure refrigerant vapor into refrigerant
liquid. To drop the temperature of the vapor, an externa device
must be used to exact heat. Some system are water-cooled and
other are air-cooled. A water cooled system can be more
desirable if low cost condensing water is available. To cool the
refrigerant cold water is fed through the condensing coils to
absorb heat.
FAN CYCLE SWITCH CONDESING
TEMPERATURE CONTROL
Condensing temperature must be controlled to maintain condensing pressure a guarantee
proper system operation. The condensing temperature must be controlled so that liquid
sub cooling and liquid flash gas can be maintained, adequate pressure at the inlet side of
thermos valve to obtain sufficient pressure drop across the valve port is provided, and
system with hot gas defrost can operate properly. Condensing temperature is controlled by
fan cycling and head-pressure regulator valves.
Fan cycle switch in this case is hard piped with the following non-adjustable settings:
Cut-out 185 + or - 10 psig
Cut-out 235 + or - 10 psig
HIGH PRESSURE CONTROL SWICTH
The high pressure safety switch is installed (in Condenser box) inside electric
box next to the fan cycle switch as a precaution to shut off compressor motor
when discharge pressure reaches 440 PSI to avoid damage to compressor.
LIQUID RECEIVER TANK
A receiver is primarily a liquid storage tank for refrigerant which is not an
circulation. All air cooled units equipped with expansion valves require a
separate receiver to allow for the wide swings in ambient temperatures. A
valve at the receiver outlet is required in order to pump the refrigerant charge
into the receiver, an operation commonly called “ pumping the system down
“.
LIQUID SOLENIOD VALVE
• A solenoid valve is an electrically controlled refrigerant flow control valve.
• A solenoid valve is made up of body , a plunger with an iron core that scats the valve
orifice and an electrical solenoid.
• A solenoid valve is closed when the coil is de-energized and the plunger is seated.
• A solenoid valve are used to trap the liquid refrigerant in the receiver tank and also for
pump down purposes when servicing system.
• A solenoid valve are also used on hot gas auto defrost systems, two on each plate, one
normally open and the other normally closed.
• There are two types, “normally open “ and “normally closed”
FILTER-DRIER
Filter-driers are used to protect the
compressor from contamination, particularly
moisture, left in the system at the time of
installation and keep the system free of
impurities during operation, such as motor
burn byproducts.
HEAT EXCHANGERS
Heat exchanges are specifically designed for application on refrigeration system to
transfer heat between liquid refrigerant leaving the condenser on the high pressure
side of the system and refrigerant vapor leaving the evaporator on the low pressure
side of the system.
Heat transfer may be desirable for several reasons:
To raise the vapor temperature to prevent frosting or condensation on the suction
line.
To evaporate any remaining liquid in the vapor stream prevent possible
compressor damage.
To sub cool the liquid to prevent flash gas in the liquid line.
To increase system refrigerating capacity.
SLIGHT GLASS AND HERMETIC MOISTURE INDICATORS
The HMI was designed to provide an accurate method of determining the moisture content
of a system’s refrigerant. Unique 3%of high accuracy moisture indicate.
THERMOSTATIC EXPANSION VALVES
The most commonly used for controlling the flow of refrigerant is the thermostatic expansion valve.
Temperature of the vapor leaving the evaporator controls the flow leaving the expansion valve. The flow is
controlled by a needle and diaphragm in the valve.
The diaphragm is subject to three forces:
Evaporator pressure, the Super heat spring & pressure exerted buy the charge in the Thermal bulb.
EVAPORATOR (PLATE)
The evaporator is main part of the pressure side of the
refrigeration system. In the evaporator, liquid refrigerant boils and
evaporates. As the liquid refrigerator changes to vapor, the heat is
absorbed in the evaporator and freezes the eutectic solution to
desired temperature.
Evaporator it is a device used to turn the liquid form of a chemical
into its gaseous form.
The refrigerant feed for air and liquid coolers and ice makers can be
classified mainly into the following three types:
Dry-expansion or direct-expansion (DX) – In evaporators with dry- or direct-expansion
refrigerant feed, liquid refrigerants is fed through an the evaporator, and is completely
vaporized and superheated to a certain degree before reaching the exit of the evaporator.
Flooded refrigerant feed – In evaporators with flooded refrigerant feeds, liquid
refrigerant is fed through a throttling device and vaporizes outside the tubes within a
shell.
Liquid overfeed – In liquid overfeed evaporators, liquid refrigerant is fed by a
mechanical or gas pump and is then overfeed to each evaporator.
SUCTION LINE ACCUMULATOR
A suction accumulator is used to prevent liquid flood-back.
It intercepts liquid refrigerant before it can reach the
compressor crank case.
It is located in the compressor suction line between the
compressor and the evaporator.
CPR VALVE
The crankcase pressure regulator valve (CPR)
regulates suction pressure at the compressor to
prevent overloading on the compressor motor.
The valve setting is determined by a pressure
spring and the valve modulates from fully open to
fully close in response to the pressure. Located
between the evaporator and the condenser,
The CPR valve is normally used to prevent motor
overloading during pull-down cycle.
THE PTC START ASSISTANCE
The positive temperature coefficient (PTC)
resistor is used for application where high
starting torque is not required.
The PTC resistor is connected in parallel
with the run capacitor, placing it in series
with the start winding.
The PTC has a low resistance when it is
cold.
RUN CAPACITOR
Ran capacitor are used on compressor to
improve efficiency, raise the motor’s power
factor, and lower noise. Run capacitors are
continuously in the operating circuit and
are normally of the metallized film type.
They are manufactured in oval or around
cans.
OPERATION AND MAINTENANCE
OF CHILLERS
Chillers these are the machine that removes heat from a liquid via a
vapor-compression or absorption or absorption refrigeration cycle.
Chillers are a key component of air conditioning system for large
buildings. They produce cold water to remove heat from the air in the
building.
As with other types of air conditioning systems, most Chillers extract heat
from water by mechanically compressing a refrigerant.
Chillers are complex machine that are expensive to purchase and operate.
Chillers commonly use more energy than any other piece of equipment
large buildings.
TYPES OF CHILLERS
Mechanical Compression
During the compression cycle, the refrigerant passes through four major components
within the chiller the evaporator, the compressor, the condenser, and a flow- metering
device such as an expansion valve. The evaporators is the low-temperature (cooling) side
of the system and the condenser is the high temperature (heat-rejection) side of the system.
Mechanical Compressor Chiller
Mechanical compression chillers are classified by compressor type reciprocating,
rotary screw, centrifugal and frictionless centrifugal.
RECIPROCATING
Similar to a car engine with multiple positions, a crankshaft is turned by
an electric motor the position compress the gas, heating it in the process.
The hot gas is discharged to the condenser instead of being exhausted out
a tailpipe.
The pistons have intake and exhaust valve that can be opened on
demand to allow the piston to idle, which reduces the chiller capacity as the
demand for chilled water is reduced.
Capacities range from 20to 125 tons.
ROTARY SCREW
The screw or helical compressor has two mating
helically grooved rotors in a stationary housing.
As helical rotors rotate, the gas is compressed by
direct volume reduction between the two rotors.
Capacity is controlled by a sliding inlet valve or
variable speed drive (VSD) on the motor.
Capacities range from 20 to 450 tons.
TYPES OF RECIPROCATING REFRIGERATION
SYSTEM
• Air-Cooled Reciprocating DX Cooler – In the DX system, a direct-expansion
coil is used as the evaporator, and HCFC-22 and HFC134a are the primary
refrigerants used in new and retrofit projects. The air-cooled condenser is
often combined with the reciprocating compressor to form a unit called
the conditioning unit.
• Air-Cooled Reciprocating Chiller – This kind of reciprocating refrigeration
system consists of a direct-expansion shell-and-tube liquid cooler as
compressor, accessories, and controls.
RECIPROCATING COMPRESSOR
a single-acting in a cylinder is driven by a crankshaft via a connecting rod.
• CYCLINDER BLOCK AND PISTON – is integrated with the crankcase and
forms a single casting. The crankcase and the cylinder block are usually made of high-
grade cast iron. Piston are generally made of aluminum, aluminum alloy, or cast iron.
• SUCTION AND DISCHARGE VALVES – The suction valve controls the vapor
refrigerants entering the cylinder, another discharge valves controls the hot gas
discharging from the cylinder. Suction and Discharge valves are usually made of high
carbon-alloy steel or stainless steel.
• OIL LUBRICATION – is necessary to form a fluid film separating the moving
surfaces to protect them from wear and corrosion. Oil is also used as a coolant to carry
heat away and cools the refrigerants. Oil provides an oil seal between the piston and
cylinder and between the valve and valve plates.
• CRANKCASE HEATER – is often installed to keep the oil temperature in the
crankcase 15 to 25 F 9 (8.3 to 13.9 C) higher than that in the rest of the system and this
prevent refrigerant migration.
ACCESSORIES
LIQUID RECEIVER – is not necessary when an evaporative condenser is used, a liquid receiver is often
installed to supplement its small strong capacity.
There Are Two Types Oil Receiver:
Through-type receiver – the liquid flows from the condenser to the receiver, and the pressure in the receiver
is always lower than that at the condenser outlet.
Surge-type receiver – its purpose is to allow liquid to flow directly to the expansion valve and remain
subcooled.
LIQUID- SUCTION HEAT EXCHANGER – is usually mounted across the suction and liquid lines when
the hot-gas discharge temperature of the refrigerant (such as HFC-134a) does not damage the lubrication oil or
discharge valves.
SIGHT GLASS
is a small glass port used to
observe the condition of
refrigerant flow in the liquid line.
THANK YOU SO MUCH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
PREPARED BY:
JONA D. PAGANGPANG
BTLED- HOME ECONOMICS
