MODULE 4

Contents
1. Application Of Refrigeration
• Domestic Refrigerators

• Water Coolers
• Ice Plants
• Cold Storages

• Food Preservation Methods- Plate Freezing , Quick-freezing.

2. Refrigeration System Components
• Compressors
• Condensers
• Expansion Devices
• Evaporators
3. Cooling Towers - Different Types And Their Application Fields
4. Refrigerant Leakage And Detection

5. Charging Of Refrigerant

6. System
. Controls
APPLICATIONS OF REFRIGERATION
 1.DOMESTIC REFRIGERATOR

• In a household refrigerator, the tubes in the freezer compartment, where

heat is absorbed by the refrigerant, serves as the evaporator. The coils
behind the refrigerator, where heat is dissipated to the kitchen air, serve as
the condenser

• Today’s refrigerators use much less energy as a result of using smaller and
higher- efficiency motors and compressors, better insulation materials,
larger coil surface areas, and better door seals.
• Despite the improvements made in several areas during the past 100 years
in household refrigerators, the basic vapor-compression refrigeration cycle
has remained unchanged. The alternative absorption refrigeration and
thermoelectric refrigeration systems are currently more expensive and less
efficient.
• Compressor used in domestic refrigerator is of reciprocating type and is
of hermetically sealed means compressor and electric motor are a single
unit enclosed in a container.
Parts of the Domestic Refrigerator
(1) Refrigerant (2) Compressor (3) Condenser (4) Expansive valve or the capillary tube (5)
Evaporator or chiller or freezer
(6)Drier(Crisper) : Kept between receiver and the evaporator to eliminate traces of moisture and
keeps vegetables and fruits fresh for longer time.
(7)Temperature control device or thermostat: To control the temperature inside the refrigerator
there is thermostat, whose sensor is connected to the evaporator. The thermostat setting can be
done by the round knob inside the refrigerator compartment. When the set temperature is
reached inside the refrigerator the thermostat stops the electric supply to the compressor and
compressor stops and when the temperature falls below certain level it restarts the supply
to the compressor.
(8)Defrost system: The defrost system of the refrigerator helps removing the excess ice from the
surface of the evaporator. The frost acts as insulation that impedes the HT to the evaporator. The
defrost system can be operated manually by the thermostat button or there is automatic defrost
system comprising of the electric heater and the timer.
(9)Starting Relay: Used to provide the necessary starting torque required to start the motor.
(10)Overload protector : To protect the compressor motor winding from damage due to excessive
current.
• Primary function of refrigerator is to provide food storage space maintained at low temperature for the
preservation of food.

• They are usually specified by the internal gross volume and the deep freezer’s volume.
• For specified external dimensions, a refrigerator is desired to have maximum food storage volume,
minimum energy consumption, and the lowest possible cost to the consumer.

• Refrigerant used are R-12 or R-22

• A household refrigerator is designed to maintain the freezer section at -18°C (0°F) and the refrigerator
section at 3°C (37°F). Lower freezer temperatures increase energy consumption without improving the
storage life of frozen foods significantly.

• Freezer provided bottom portion is more energy efficient (Since warm air rises, the top freezer
refrigerator uses more power to keep the temperature cooler) and time to cool products will be less.
• Different temperatures for the storage of specific foods can be maintained in the refrigerator section by

using special- purpose compartments.

• Practically all full-size refrigerators have a large air-tight drawer for leafy vegetables and fresh fruits to
seal in moisture and to protect them from the drying effect of cool air circulating in the refrigerator.
• The more expensive models come with an automatic ice maker located in the freezer section and can produce 2 to 3 kg of
ice per day.

• Household refrigerators consume from about 90 to 600 W of electrical energy when running and are designed to

perform satisfactorily in environments at up to 43°C (110°F).

• Refrigerator body is provided with good quality insulation (thick glass loos fill fibre or glass role)
• The size of the compressor and the other components of a refrigeration system are determined on the basis of the

anticipated heat load (or refrigeration load), which is the rate of heat flow into the refrigerator.

• The heat load consists of the

predictable part, such as heat transfer
through the walls and door gaskets
of the refrigerator, fan motors,
and defrost heaters and the
unpredictable part, which depends on
the user habits such as opening the
door, making ice, and loading the
refrigerator.
 Two types of home refrigerators are typically available in market.
1. DIRECT COOL REFRIGERATORS:
• These refrigerators are with or without crisper, ice making or frozen food storage compartment.
• Cooling of food is primarily obtained by natural convection within the refrigerator. However,
some refrigerators may have a fan to avoid internal condensation of water but are not claimed as
‘frost free’.
• Formation of frost/ice in the refrigerator reduces cooling. The ice built up on the surface of the
evaporator coil provides an additional resistance to heat transfer.
• Therefore these refrigerators need manual defrosting periodically.
2. FROST FREE REFRIGERATORS:
• These refrigerators cool the stored food through continuous internal movement of air that
restricts the formation of frost and sticking of food items with each other.
• A frost free freezer has three basic parts a timer, a heating coil and a temperature sensor. The
heating coil is wrapped around the freezer coils. Every six hour or so, the timer turns on the
heating coil and this melts the ice off the coil.
• When all the ice is removed, the temperature sensor senses the temperature rising above 0oC and
turns off the heating coil.
 2. FROST FREE REFRIGERATORS:
• These refrigerators cool the stored food through continuous
internal movement of air that restricts the formation of frost
and sticking of food items with each other.
• A frost free freezer has three basic parts a timer, a heating coil
and a temperature sensor. The heating coil is wrapped around
the freezer coils. Every six hour or so, the timer turns on the
heating coil and this melts the ice off the coil.
• When all the ice is removed, the temperature sensor senses the
temperature rising above 0oC and turns off the heating coil.
 DEFROST Hot refrigerant
To condenser
MECHANISM
OFF
ON 12:00am
6:00pm TIMER Hot refrigerant
bypass valve
ON
START
-105 OC Heating Coil wrapped
over Evaporator tube

TEMPERATURE
SENSOR

cold refrigerant
to expansion valve Hot refrigerant
From compressor
 2. WATER COOLERS
• To make water available at a constant temperature irrespective of ambient temperature.
• To produce cold water at about 70C to 130C.
• All coolers consists of basic parts that are the same as that of a refrigeration system such as compressor, condenser
(usually air cooled), expansion device (thermostatic expansion valve or capillary tube), provisions are provided for
water inlet and outlet.

Two types – Storage type and Instantaneous type

2.1 Storage type

• The basic parts being the compressor (usually a hermetically sealed compressor), condenser (usually air cooled

condenser), expansion device, and an evaporator (the space where water is to be cooled).
• The refrigerant flows from the compressor to the condenser where the high pressure refrigerant vapor is converted
into high pressure liquid refrigerant.
• From the condenser, the liquid refrigerant flows through the expansion device where the high pressure refrigerant is

converted into low pressure, low temperature liquid refrigerant.

• The liquid refrigerant absorbs the latent heat from the water in the evaporator and gets converted into vapor refrigerant
and flows to the compressor suction which completes one cycle.
Working Principle
• In this type of cooler, the evaporator coils are soldered on
to the outer surface of the walls of the storage tank. Water storage tank where
water is cooled. The
• The water level of the storage tank may be maintained evaporator coils are
soldered in between the
by a float valve. walls

• In this type of cooler, the disadvantage is that the time Cold water outlet
taken to bring the temperature down to the set value is
more ( i.e., the cooler will have to work for a long time
since the mass of water in the tank is more). Waste water tray
• The thermostat senses the temperature of water and
This area contains the
stops the machine when the set temperature has been compressor, condenser,
and cut out and cut in
achieved. switches (thermostat)
• When water is drawn from the cooler for drinking, an
equal amount of water is being admitted in to the tank.
• When the temperature of the water increases more than
the set point, the machine starts its cycle automatically.
• This type of cooler finds a variety of applications such as
in colleges, schools, hotels, etc.
2.2 Instantaneous type water coolers
• In general the instantaneous type of water coolers consists of two separate cylindrically wound coils.
• One coil is for the refrigerant and the other for water.
• They may be made of copper or stainless steel tubes. Usually both the coils are entwined together and bonded
together by soldering.

• The water is cooled by the refrigerant in the evaporator by conduction.

Three types
• Bottle type,
• Pressure type, and
• Self-contained remote type.
BOTTLE TYPE:
• The water that is to be cooled will be stored in a bottle or
reservoir.
• A faucet (push type water taps) is used to minimize the
wastage of water.
• The drip receptor receives water that is not used and sends it
to the drainage.
• When we operate the faucet, the water flows from bottle to
the water coil through flow regulator.
• Now as the water travels through the coil, it loses its latent
heat to the refrigerant in the evaporator coil there by
reduction in water temperature is achieved.
• A thermostat is placed at the end of the water coil to start and
stop the compressor according to the water temperature.

• This type of cooler may be used in hospitals, shops, home, etc.

PRESSURE TYPE:
• In this type of cooler, water is supplied under pressure.
The city water enters the cooler at the rear of the cooler.
• It is cooled initially in a pre-cooler.
• The waste water passing through the drainage line is
also cooled; hence this drainage pipe is wrapped
around the fresh water pipe for pre- cooling thus
reducing the cooling load for the cooler.
• The pre-cooled water is then taken to the storage
chamber, where the refrigerant gains heat from the
water.
• The outlet for water is taken from the bottom of the
storage tank which may be a bubbler or a self-closing
valve.
• A thermostat is used to control the temperature of water
in the pipe to maintain a particular set point. 15
SELF-CONTAINED REMOTE TYPE:
• This system consists of a mechanical refrigeration
system, the water being cooled by the cooler which is
remote from the desired drinking place.
• This remote cooler supplies cold water to the desired
drinking place.
• The thermostat is clamped onto water pipe at its
outlet in an instantaneous type water cooler.
• The flow rate must be adjusted to match its capacity. If
rate of flow is more, the cooler will not bring down
the temperature of water to the set point and also it
results in high evaporator temperature which in turn
leads to high suction pressure of the compressor
which may adversely affect the compressor motor.
• This type doesn't require extra space near the place of
work.
 3. ICE PLANT
It basically consists of three main circuits.
• Refrigeration Circuit (Working fluid, Ammonia, Primary refrigerant)
• Cooling Water Circuit (Cooling water)
• Brine Circuit (Brine solution)

17
• It consists an ice box having heavy insulation.
• The size depends on the capacity of ice plant.
• Should contain sufficient no. of cans for ice harvest.
• The ice cans are usually tapered around 10 to 20 mm per meter depth.
• Water level in the can should be around 20 to 30 mm below the brine level.
• Provided piping for air blowing into ice cans for air agitation. It helps form
ice in the whole of can otherwise a small amount of water remains at the
center.
• Heat transfer between water and brine is either by free convection or forced
convection(caused by suitable no. of agitators).
• The brine solution is maintained by refrigeration plants at -100C to -
110C
• Ammonia gas is used as refrigerant because of (i) Excellent thermal
properties (ii) High refrigeration effect per kg of refrigerant (iii) Low
specific volume.
• The high temperature, high pressure ammonia vapors are condensed in a
condenser (shell and tube type).
• The condensed liquid ammonia is collected in the receiver and then expanded
through the expansion valve.
• It then passes through the evaporator coils surrounding a brine tank in which
brine solution is filled.
• The low pressure ammonia absorbs heat from the brine solution, equivalent to
its latent heat of vaporization, gets converted to vapor state and is once again
fed to compressor to complete cycle.
• Note : Brine solution circulates itself from brine tank to evaporator and cools the
water kept in ice-can below zero degree centigrade to make it in ice form. Here,
brine solution is also a refrigerant but as it does change the phase during heat
transfer between water and evaporator, it is called secondary refrigerant. On the
other hand, Ammonia is primary refrigerant as it undergoes phase change during
cooling process.
 4. COLD STORAGES
• Cold storages are meant to preserve the perishable commodities of food items for a longer period with retention of
the original color, flavor and taste. (it doesn't improve the quality of food products but slows down its deterioration)
• They are specially designed and built of concrete, stone or brick in order to prevent the leakage or cold leakage. Its floors
ceilings, walls and doors are properly insulated with special insulating materials with low thermal conductivity.
• Vegetable require 00C to 50C with
RH 80 - 90%
• For milk processing - 250C to - 300C
• For fish -200C to - 450C
Working of cold storage plant:
• Works on the 'Vapor Compression Refrigeration' cycle.
• The compressor compresses vaporized refrigerant (Ammonia) to high pressure and high temperature to raise
the boiling point of refrigerant.
• The condenser then liquefies the vaporized refrigerant to high pressure and high temperature state. Thus,
heat rejection takes place.
• The condensate from the condenser is collected in reservoir and allow to pass through expansion valve where
its pressure and temperature decrease from earlier state.

• The low pressure liquid refrigerant then allow to pass through refrigerated space where by heat of hot air of

refrigerated space starts evaporating the liquid refrigerant hence, heat in the atmosphere decrease and

cooling is produced.
• Blowers circulates the chilled air to stored fruits and vegetables.
• For most product, a high but not saturated, relative humidity is required (85% - 95%)
• Pre - cooling of product prior to refrigerated storage is strongly recommended since rapid removal of field heat
and cooling the product to the storage temperature before placing it in the refrigerated storage will
substantially increase the storage life.
 Food Preservation Methods
Plate Freezing &Quick-freezing

VINAY VN, ASST. PROF. MITS

17
1. PLATE FREEZING
• They are commonly used for freezing brick-shaped packaged products.
• In plate freezers, refrigerant is allowed to circulate inside thin channels within the plates. The packaged
products are firmly pressed between the plates. High rates of heat transfer can be obtained between the
packaged product and the refrigerant plates.
• Plate freezers can be arranged with the plates horizontal to form a series of shelves and called as horizontal
plate freezers (HPF). When the plates are arranged in a vertical plane they form a series of bins and in this
form they are called vertical plate freezers (VPF)

a. Vertical Plate Freezers

• Vertical plate freezers are usually applied for freezing of large quantities
of fish or meat. In general Ammonia, CO2 or synthetic refrigerants are
used. With the use of CO2, a temperature of -500C is possible inside the
plates, achieving a significantly shorter freezing time of the product,
consequentially increasing the capacity of the plates freezer (minimum
25%).
• Products are simply placed or poured into vertical pockets between
aluminium freezing plates. Symmetrical frozen blocks stack easily,
maximizing on amount of available storage space
• Minimal energy consumption, easy installation and low capital and
maintenance costs. Rapid freezing preserves products quality and minimizes
production time. 18
24
b. Horizontal Plate freezers
• It consists of a number of horizontal plates, through which a cold refrigerant runs. The
products which are frozen in horizontal plates freezers are usually pre-packed in a carton or
an aluminium tray before the product is put in the horizontal plate freezer.
• It is used in meat processing, food processing, poultry and many more industries.
• The horizontal contact plate freezer is ideal for block freezing and preserving portioned
products.
• Frozen blocks, flat and uniform, are easily stacked and stored.
• Minimal energy consumption, easy installation and low capital and maintenance costs.
• Rapid freezing preserves products quality and minimizes production time.
• Efficient and high performance - minimizing retention time for the food products to be
frozen and reducing weight loss to generate a higher yield.
• Flexible design - Low floor space can be used.
• Quick to install - This reduces the installation time to an absolute minimum and helps to
save money. 25
Advantages for plate freezer:
• Fast temperature reduction and freezing time
• Safe freezing, greater protection against dehydration
• The best quality product, no damages to the products
• High efficiency of heat exchange and refrigeration
• Quality material, guaranteed hygiene
2. Quick-freezing
• Quick freezing is Rapid freezing of food by exposure to a blast of air at a very low temperature. Unlike slow
freezing, very small crystals of ice are formed which do not rupture the cells of the food and so the structure is
relatively undamaged.
• During Quick Freezing, chilled air is sent to the freezer compartment to freeze items at a rapid rate. By placing food
on the Aluminum Tray, food chills faster due to quick conductivity of the metal
• By quickly going past the maximum ice crystal formation zone where moisture in food items freezes, the growth of

ice crystals will be inhibited. Damage to food cells is prevented, reducing the dripping during defrosting.

• A quick-frozen food is commonly defined as one that has been cooled from a temperature of 0°C to −5°C or lower, in

a period of not more than 2 hours, and then cooled to −18 °C.

• Thus the products treated retain their freshness, textures and

flavors keeping their essential nutrients and vitamins.

• Quick freezing can cause serious food poisoning if the process

is not performed correctly, it is therefore necessary to take
numerous precautions to avoid this and to preserve the
original quality of the products.
Applications of Refrigeration and Air Conditioning
1. Air Conditioning of Residential and Official Buildings
Air conditioning of building is required in all climates. In the summer, living/working spaces
have to be cooled and in the winter the same have to be heated. Even in places where
temperature remains normal, cooling of the building is required to remove the heat generated
internally by people, lights, mechanical and electrical equipment. Further in these buildings, for
the comfort, humidity and cleanliness of air has to be maintained. In hospitals and other
medical buildings, conditions on cleanliness and humidity are more stringent. There ventilation
requirements often specify the use of 100 percent outdoor air, and humidity limits.
2.Industrial Air Conditioning
The term industrial air conditioning refers to providing at least a partial measure of comfort for
workers in hostile environments and controlling air conditions so that they are favorable to
processing some objects or materials. Some examples of industrial air conditioning are the
following:
a) Spot Heating
In a cold weather it may be more practical to warm a confined zone where a worker is located.
One such approach is through the use of an infrared heater. When its surfaces are heated to a high
temperature by means of a burner or by electricity, they radiate heat to the affected area.
b) Spot Cooling
If a specific area has to be cooled, it will be unwise to cool entire room or factory. In this case,
conditions may be kept tolerable for workers by directing a stream of cool air onto occupied areas.
c) Environmental Laboratories
The role of air conditioning may vary from one laboratory to the other. In one laboratory, a very low
temperature, say – 40 oC must be maintained to test certain equipment at low temperatures, and in
another, a high temperature and humidity may be required to study behavior of animals in tropical
climates.
d) Printing
In printing industries, control of humidity is a must. In some printing processes the paper is run
through several different passes, and air conditioning must be maintained to provide proper
registration. If the humidity is not properly maintained the problems of static electricity, curling or
buckling of paper or the failure of the ink to dry arise.
e) Textiles
Like paper, textiles are sensitive to changes in humidity and to a lesser extent changes in temperature.
In modern textile plants, yarn moves at very high speeds and any changes in flexibility and strength of
the yarn because of the change in humidity and temperature will thus affect the production.
24
f) Precision Parts and Clean Rooms
In manufacturing of precision metal parts air conditioning helps to (a) keep the temperature uniform
so that the metal will not expand and contract, (b) maintain a humidity so that rust is prevented and
(c) filter the air to minimize dust.
g) Photographic Products
Raw photographic materials deteriorate fast in high humidity and temperatures. Other materials
used in coating film also require a careful control of temperature. Therefore, photographic-products
industry is a large user of refrigeration and air conditioning.
h) Computer Rooms
In computer rooms, air conditioning controls temperature, humidity and cleanliness of the air. Some
electronic components operate in a faulty manner if they become too hot. One means of preventing
such localized high temperature is to maintain the air temperature in the computer room in the
range of 20 to 230C. A relative humidity of about 65% is maintained.
i) Food Storage and Distribution
Many meats, fish, fruits and vegetables are perishable and their storage life can be extended by
refrigeration. Fruits, many vegetables and processed meat, such as sausages, are stored at
temperatures just slightly above freezing to prolong their life. Other meats, fish, vegetables and
fruits are frozen for many months at low temperatures until they are defrosted and cooked by
consumer.
REFRIGERATION SYSTEM COMPONENTS
PREFACE
• The functions of the condenser are to de-superheat the high pressure gas, condense it and also sub-cool the
liquid.
• Heat from the hot refrigerant gas is rejected in the condenser to the condensing medium-air or water.
• Air and water are chosen because they are naturally available. Their normal temperature range is satisfactory
for condensing refrigerants.
• The selection of a condenser depends upon the capacity of the refrigerating system, the type of refrigerant
used and the type of cooling medium available.
1. Process(2-3)- First of all the superheated vapor is cooled to saturation temperature (called de-
superheating) corresponding to the pressure of the refrigerant. The de-superheating occurs in the
discharge line and in the first few coils of the condenser.
2. Process (3-4) - Now, the saturated vapor refrigerant gives up its latent heat and is condensed to a
saturated liquid refrigerant. Process is called condensation.
3. Process (4-5) - The temperature of the liquid refrigerant is reduced below its saturation temperature

(sub cooled) in order to increase the refrigeration effect.

There are three types of condensers, viz.

(a) Air- cooled,
(b) Water-cooled and
(c) Evaporative.
As their names imply, air-cooled condensers use air as the cooling medium, water-cooled condensers use
water as the medium and the evaporative condenser is a combination of the above, i.e. uses both water
and air.
Factors Affecting the Condenser Capacity
The condenser capacity is the ability of the condenser to transfer heat from the hot vapor refrigerant to
the condensing medium. The heat transfer capacity of a condenser depends upon the following factor.
Material
Different materials have different abilities of heat transfer, therefore the size of a condenser of a
given capacity can be varied by selecting the right material. It may be noted that higher the ability
of a material to transfer heat, the smaller will be the size of condenser.
Amount of contact
The condenser capacity may be varied by controlling the amount of contact between the
condenser surface and the condensing medium, this can be done by varying the surface area of the
condenser and the rate of flow of the condensing medium over the condenser surface. The amount
of liquid refrigerant level in the condenser also affects the amount of contact between the vapor
refrigerant and the condensing medium.
Temperature Difference
The heat transfer capacity of a condenser greatly depends upon the temperature difference
between the condensing medium and the vapor refrigerant. As the temperature difference
increases, the heat transfer rate increases and therefore the condenser capacity increases.
1. Air-Cooled Condensers
The refrigerant rejects heat to air flowing over the condenser.

Air-cooled condensers can be further classified into Natural convection type or Forced convection type.
1.1 Natural Convection Condenser
• Air movement over the surface of condenser tubes is by natural convection. As air comes in contact with the warm-
condenser tubes, it absorbs heat from the refrigerant and thus the temperature of the air increases. Warm air rise up
and in its place, cooler air from below rises to take away the heat from the condenser. This cycle goes on.
• Not capable of rejecting heat rapidly, Since air moves very slowly by natural convection. A relatively large surface area of
the condenser is required.
• Use of this type of condenser limited to very small units such as domestic refrigerators, freezers, water coolers, room air
AC.
• In the small units, the condenser is fixed at the rear of the refrigerator cabinets. Generally, steel tubes are used. To

increase the heat-transfer area, wires are welded to the condenser tubes. In certain designs, widely-spaced fins are
used.
• Another design is the plate-type. The condenser coil is fastened to a plate. The plate being in contact with the condenser
tubes, the surface area of the condenser is increased. The plate-type condenser is mounted on the back of the
refrigerator cabinet with a small gap between the cabinet and the plate. This gap facilitates better natural convection air
currents.
Fig.1 Natural convection
thin wires are welded
to the condenser tube coil

Fig.2 Forced convection plate fin and

tube condenser
1.2 Forced-air Circulation Condenser
• This type employs a fan or blower (propeller or centrifugal) to move air over the condenser coil at a certain
velocity.
• The condenser coil is of the finned type. Fins in such coils are closely spaced (ranging between 8 and 17 fins
per inch). The fins are usually of aluminum and tubes are made of copper.
• The space between the fins gets choked with dirt,therefore to obtain optimum capacity, the fins should be
kept clean.
• For circulating air over the condenser, fans are mounted on the shaft/pulley of the compressor motor.
• For bigger-capacity plants a separate motor is used to drive the fan or blower as also for hermetic-
compressor units.
• Forced convection type condensers are commonly used in window air conditioners, water coolers and
packaged air conditioning plants.
• It is divided into (a) Base mounted air cooled condensers (b) Remote air cooled condensers
• Base mounted air cooled condensers – Propeller fans are mounted on the same base of compressor, motor,
receiver and other controls. The entire arrangement is called a condensing unit. Used for refrigeration system
of 10 tonnes or less.
• Remote air cooled condensers – Used on systems above 10 tonnes and are available up to 125 tonnes. These
condenser may be horizontal or vertical. These condensers use propeller fans or centrifugal fans depending
on the location of condenser.
2. Water Cooled Condensers
• In water cooled condensers water is the external fluid (condensing medium).
• Used in commercial and industrial refrigerating units.
There are three types of condensers which fall under this category:
(a) Tube-in-tube or double pipe,
(b) Shell-and-coil, and
(c) Shell-and-tube.
2.1. Tube-in-Tube or Double Pipe Condenser
• In this type, a smaller diameter pipe inserted inside a bigger diameter pipe and is bent to the desired form.
• Water flows through the inner tube and the refrigerant through the annular space between the two tubes. The
flow of refrigerant and water being arranged in opposite direction (Counter) to get the maximum benefit of heat
transfer.
• Due to the impurities present in water, scales can form on the water-side of the tube which can impede the heat
transfer. Therefore it becomes necessary to periodically clean the water tube. But in the tube-in-tube system,
cleaning is not easy, unless a removable header is provided to connect all the tubes. Headers are used at both the
ends to make the length of the condenser small and reduce pressure drop.

• Double pipe condensers are normally used up to 10 TR capacity.

Tube in Tube or Double pipe Shell and Coil
2.2 Shell-and-Coil Condenser
• These condensers are used in systems up to 50 TR capacity.
• It consists of a welded-steel shell containing a coil of finned tubing to increase the heat transfer coefficient.
• Water flows in the coil, the refrigerant being in the shell.
• Coiled tubing is free to expand and contract with temperature changes because of its spring action and can
withstand any strain caused by temperature changes.
• When water flows through the coils, cleaning is done by circulating suitable chemicals through the coils.
2.3 Shell-and-Tube Condenser
• Used in systems from 2 TR upto 1000 TR capacity. The most common type is horizontal shell type.
• The refrigerant flows through the cylindrical shell while water flows through the straight tubes in single to
four passes.
• The condensed refrigerant collects at the bottom of the shell. The liquid refrigerant is drained to the
receiver through a vent connecting the receiver to the condenser.
• Vertical shell-and-tube type condensers are usually used with ammonia in large capacity systems so that
cleaning of the tubes is possible from top while the plant is running.

• A fusible plug or safety pressure relief valve is fixed on the shell of the condenser to protect the high side of
the refrigeration system against excessive pressures.
Care should be taken not to overcharge the system with the refrigerant. This is because an excessive
accumulation of liquid in the condenser tends to cover too much of the water tubes and reduce the heat-
transfer surface available for condensing the high-pressure gas. This result in increasing the head pressure
and condensing temperature, also excessive overcharge can create hydraulicpressures.
 Air cooled Condenser Water Cooled Condenser
Simple construction, less initial and maintenance Complicated construction, more initial and
cost maintenance cost
No handling problems Difficult to handle
Doesn’t require piping arrangement for carrying Pipes are required to take water to and from the
air condenser
Problem in disposing used air unless a
No problem in disposing of used air
recirculation system is provided

No corrosion – Low fouling effect Corrosion occurs – Fouling effects are high

Low heat transfer capacity due to low “K” High heat transfer capacity due to high “K”

Used for low capacity plants (< 5 TR) Used for large plants

There is fan noise There is no fan noise

Non uniform distribution of air on condenser Even distribution of water on the condenser surface

High flexibility Low flexibility

3. Evaporative Condenser
• Use both air and water as a condensing medium.
• Water is pumped from the sump of the
evaporative condenser to a spray header and
sprayed through the nozzle over the condenser
coil through which the hot vapor refrigerant
from the compressor is passing.
• Heat transfers from the refrigerant through the
condensing tube walls and into the water that is
wetting the outside surface of the tubes.
• A fan draws air from the bottom-side of the
condenser and discharges it out at the top of the
condenser. The spray water coming in contact
with the condenser tube surface evaporates into
the air stream.
SUMP
• The heat for vaporizing the water is taken from
the refrigerant, thereby condensing the
refrigerant in tube.
• The evaporative condenser combines the functions of the water-cooled condenser and the cooling tower.
• The cold water that drops down into a sump is recirculated. In order to make up the deficiency caused by the
evaporated water, additional water is supplied to the sump. A float valve in the sump controls the make up
supply.
• An eliminator is provided above the spray header to stop particles of water from escaping along with the
discharge air.
• It occupies less space and moreover, it needs less power than a water-cooled condenser.
• The heat transfer coefficient for evaporative cooling is very large.
• The required air flow rates are in the range of 350 to 500 m/h per TR of refrigeration capacity.
• Most troublesome point about the evaporative condenser is the difficulty in keeping the surface of the
condenser coil clean.
• The condenser coil being both hot and wet in operation, the dirt carried along with the air stream forms a hard
layer on the condenser.

• Scale also forms a hard layer if hard water is used. Once these hard layers are allowed to form, it is never
possible to effectively clean the coil.
• So the capacity of the condenser gets substantially affected, because of this maintenance problem.
• Evaporative condensers are not much in favor.
INTRODUCTION
• Also known as throttling device, metering device.
• Expansion device used with dry expansion evaporators – expansion valves
• Expansion device used with flooded evaporators – float valves
• The basic functions of an expansion device used in refrigeration systems are to:
1. Reduce pressure from condenser pressure to evaporator pressure, and
2. It maintains the desired pressure difference between the high and low pressure sides of the system, so
that the liquid refrigerant vaporizes at the designed pressure in the evaporator.

3. It controls the flow of refrigerant according to the load on the evaporator.

• There are different types of expansion or throttling devices. The most commonly used are:
(a)Capillary tube
(b)Constant pressure expansion valve
(c) Solenoid valve
(b) Float valves
(c) Thermostatic expansion valve
(d)Electronic Expansion Valve
 Types
FIXED OPENING TYPE VARIABLE OPENING TYPE
• The flow area • The flow area changes with changing mass
remains fixed. flow rates.
1. Hand (manual) expansion valves
2. Constant pressure or Automatic
1. Capillary Tube Expansion Valve (AEV)
3. Thermostatic Expansion Valve (TEV)
2. Orifice
4. Float type Expansion Valve
a) High Side Float Valve
b) Low Side Float Valve
5. Electronic Expansion Valve
 1. Capillary Tube
• The capillary is a small diameter tubing that offers the restricted flow of the refrigerant.
• Its internal diameter ranges from 0.5mm to 3mm and the length ranges from 1.0m to 6m depending upon the
capacity of the refrigerating or air-conditioning system.
• A fine mesh screen is provided at the inlet of the tube in order to protect it from contaminants. A small filter
drier is used to provide additional freeze up application.
• The pressure drop attained through the capillary depends upon its diameter and length.
• The longer the capillary tube and/or the smaller the inside diameter of the tube, greater is the pressure
drop it can create in the refrigerant flow.
• Capillary tubing made of copper is most commonly used.
• Capillary tubing is used for small refrigerating and air-conditioning systems like household refrigerators,
water coolers, deep freezers, window air-conditioners, split air-conditioners, small packaged air-conditioners etc.
• The capillary tube is not self-adjusting. If the condition changes, such as an increase in the
discharge/condenser pressure due to a rise in the ambient temperature, reduction in evaporator pressure,
etc. the refrigerant flow-rate will also change.
• Therefore a capillary tube, selected for a particular set of conditions and load will operate somewhat less
efficiently at other conditions.
The pressure reduction occurs due to:
1. The refrigerant has to overcome the frictional resistance offered by tube walls. This leads to some
pressure drop.
2. The liquid refrigerant flashes (evaporates) as its pressure reduces. So the average density
decreases. The mass flow rate and tube diameter (hence area) being constant, the velocity of
refrigerant increases. This requires pressure drop.
• Its mass flow rate is totally dependent upon the pressure difference across it; it cannot adjust itself to
variation of load effectively.
• The balance point : The compressor and the capillary tube, under steady state must arrive at some
suction and discharge pressures, which allows the same mass flow rate through the compressor and
the capillary tube.
• Mass flow rate through the compressor decreases with increase in pressure ratio since the
volumetric efficiency of the compressor decreases with the increase of pressure ratio.
• Mass flow rate through the capillary tube increases with increase in pressure difference across it.
• Hence, for a given value of condenser pressure, there is a definite value of evaporator pressure at
which the mass flow rates are the same.
• This pressure is the balance point that the system will acquire in steady state.
• It is observed that the evaporator temperature at balance point increases with increase of condenser
temperature.
Variation of refrigerant mass flow with evaporator
temperatures
Advantages:
• It is inexpensive.
• It does not have any moving parts hence it does not require maintenance.
• Open connection - during off-cycle, pressure equalization occurs between
condenser and evaporator. This reduces the starting torque requirement of the
motor. Hence, a motor with low starting torque (squirrel cage Induction motor) can be
used.
Disadvantages:
• It cannot respond to daily and seasonal variation in ambient temperature and load -
COP low under off design conditions.
• It is susceptible to clogging because of narrow bore of the tube. A filter-drier should
be used ahead of the capillary to prevent entry of moisture or any solid particles.
• During off-cycle liquid refrigerant flows to evaporator because of pressure
difference. The evaporator may get flooded and the liquid refrigerant may flow to
compressor and damage it when it starts. So it is used only with hermetically sealed
compressors where refrigerant does not leak.
 2. Automatic Expansion Valve (AEV)
• Also known as a constant pressure expansion valve -
maintain a constant pressure and thereby a constant
temperature in the evaporator no matter what the
refrigeration load inside the evaporator is.
• When the load on evaporator is high it won’t allow more flow
of the refrigerant as per the requirement. Similarly, when the
load is lesser, it won’t allow reduction of the flow of the
refrigerant as per the requirement.
• It is used with dry expansion evaporators where the load is
relatively constant.
• The automatic expansion valve consists of a needle valve and a
seat (which forms an orifice), a metallic diaphragm, spring,
and an adjusting screw.
• The adjustment spring is usually set such that during off-cycle
the valve is closed.
• During the off-cycle, the refrigerant remaining in the
evaporator will vaporize but will not be taken out by the
compressor – so the evaporator pressure rises.
• The opening and closing of the valve with respect to the seat depends upon the following two opposing forces
acting on the diaphragm

1. The spring pressure and atmospheric pressure acting on the top of the diaphragm, and
2. The evaporator pressure and spring pressure acting below the diaphragm.
• When the compressor is running, the valve maintains an evaporator pressure in equilibrium with the spring
pressure and the atmospheric pressure.
• The spring pressure can be varied by adjusting the tension of the spring with the help of spring adjusting
screw.
• Once the spring is adjusted for a desired evaporator pressure, then the valve operates automatically to
maintain constant evaporator pressure by controlling the flow of refrigerant to the evaporator.
• When the evaporator pressure falls down, the diaphragm moves downwards to open the valve and allows
more liquid refrigerant to enter into the evaporator, thus ensuring the desired evaporator pressure.
• When the evaporator pressure rises, the diaphragm moves upwards to reduce the opening of the valve and
decreases the flow of liquid refrigerant into the evaporator, thus ensuring the desired evaporator pressure.
• When compressor stops, the refrigerant continues to flow into the evaporator and increases the pressure in
evaporator, which causes the diaphragm to move upward and the valve is closed. It remains closed until
compressor starts again and reduces the pressure in the evaporator.
 3.Float valves
• Normally used with flooded evaporators in large capacity refrigeration systems.
• It opens or closes depending upon the liquid level as sensed a float(a hollow metal or plastic ball)
• The float valve always maintains a constant liquid level in a chamber called as float chamber.
• Depending upon the location of the float chamber, two types are:
a) Low-side float valve b) High-side float valve.
3.1 Low-side float valve
• The low-side float valve is located at the low pressure side of the system ie., connected to the
evaporator.
• It maintains a constant liquid level in a flooded evaporator or a float chamber attached to the
evaporator.
• The float of the low side float valve is placed in the evaporator.
• The valve assembly comprises of the hollow ball, a float arm, needle valve and the seat.
• The movement of the float ball (rise or fall) is transmitted to the needle valve by the float arm which
closes or opens the flow of liquid refrigerant.
• The hollow ball is connected to the needle and valve seat via the float arm.
• The needle valve being located at the inlet of the float chamber.
• When the load increases, more amount of refrigerant evaporates from the evaporator.
• As a result, the refrigerant liquid level in the evaporator or the low-side float chamber drops.
• The float then moves such that the valve opening is increased and more amount of refrigerant flows
into the evaporator and the liquid level is restored.
• When the load falls, the float reduces the opening of the valve and less amount of refrigerant flows
into the evaporator.
3.2. High Side Float Valve
• Maintains the liquid level constant in a float chamber
connected to the condenser on the high pressure side.
• The liquid condensed in the condenser flows down to the float
chamber.
• The needle and seat of the valve are at the outlet of the
float chamber.
• As the liquid level rises in the chamber, the float ball also rises,
thereby opening the needle valve.
• As the liquid level falls in the chamber, thereby closing the
needle valve.
• It is noted that refrigerant vapor is condensed in the
condenser at the same rate at which the liquid vaporizes in the
• evaporator; the float chamber receives and feeds liquid to the
evaporator at the same rate.
• Since the rate of vaporization of the liquid in the evaporator is
according to the load, the high-side float obviously works as
per the load.
• When the load increases, more amount of refrigerant evaporates and condenses.
• As a result, the liquid level in the float chamber rises momentarily. The float then opens the valve more to
allow a higher amount of refrigerant flow so the liquid level drops back to the original level.
• It allows only a fixed amount of refrigerant on the high pressure side(condenser), the bulk of the
refrigerant is stored in the low-pressure side (evaporator).
• The refrigerant liquid level in a high float valve is critical. Too much liquid refrigerant causes flooding
of the suction line followed by compressor slugging and too little liquid refrigerant causes a low
evaporator level resulting in low capacity of the refrigerating system.

• A high-side float valve can be used with both flooded as well as direct expansion type evaporators.
• Refrigerant feed/throttling devices for flooded chillers are usually the low- side or high-side float
valve. For example, in centrifugal plants, the chiller is of the flooded type and generally high-side
float valves are used as throttling devices. In a flooded chiller working in conjunction with a
reciprocating compressor, a low-side float valve is used as the throttling and refrigerant liquid flow
control.
Refrigeration system with Low Side Float Valve Refrigeration system with High Side Float Valve
 4. Thermostatic expansion valve
• Most commonly used device in both commercial and
industrial refrigeration system.
• Also known as constant superheat valve – it maintains
a constant superheat of the vapor refrigerant at the
end of evaporator coil - prevent the slugging of the
compressors.
• It consist of a needle valve, seat, metallic diaphragm, spring, an adjusting screw, a feeler or thermal bulb (mounted
on suction line near the outlet of the evaporator coil).
• The feeler bulb is connected to the top of the bellows by a capillary tube. The feeler bulb and the capillary tube contain
some fluid called power fluid.
• The power fluid is the same as the refrigerant or it may be different fluid(TEV is called TEV with cross charge).

• The opening and closing of the valve depends on the following forces acting on the diaphragm
1. The spring force (PS) acting on the bottom of the diaphragm
2. The evaporator pressure (PE) acting on the bottom of the diaphragm
3. The feeler bulb pressure (PB) acting on the top of the diaphragm
• Feeler bulb will be at same temperature as the refrigerant at the exit of evaporator. Any change in temperature of
the refrigerant will cause a change in pressure in the feeler bulb which will be transmitted to the top of the
diaphragm.

• At normal operating condition feeler bulb pressure acting at the top of diaphragm is balanced by the evaporator
and spring force pressure.
• The force tending to open the valve depends upon spring pressure and evaporator pressure
which in turn depends upon the saturation temperature of the refrigerant in the evaporator coil.
• The force tending to close the valve depends upon feeler bulb pressure which in turn depends
upon the temperature of the power fluid in the bulb.
• Operation of valve is controlled by the difference between the two temperatures (saturation
temperature and feeler bulb temperature)
• If the load on the evaporator increases, it causes liquid refrigerant to boil off faster in the evaporator
coil, thus the feeler bulb temperature and pressure increases which is transmitted through the
capillary tube to the diaphragm.
• At this stage Diaphragm moves downward – Opens the valve – Admitting more quantity of
refrigerant to evaporator - Continues till the pressure equilibrium on the diaphragm is reached.
• If the load on the evaporator decreases, it causes less liquid refrigerant to evaporate, the excess
refrigerant flows towards the evaporator outlet which cools the feeler bulb – pressure reduces
due to decrease in its temperature – low feeler bulb pressure is transmitted through the capillary
tube to the diaphragm.
• Diaphragm moves upward – reduces the opening of the valve, and thus the flow of the refrigerant to
evaporator. Evaporator pressure reduces and continues till the evaporator and spring force pressure
maintain equilibrium with the feeler bulb pressure.
• Thus the TEV maintains the flow of the
refrigerant inside the evaporator as per the
refrigeration or air conditioning load.
• The TEV constantly modulates the flow to
maintain the superheat for which it has been
adjusted by the spring.
• Most TEV are set for 50C of superheat.
• This leads to highly efficient working of the
compressor and the whole refrigeration and the
air conditioning plant.
• It is commonly used in the industrial refrigeration
plants, high capacity split air conditioners,
packaged air conditioners, central air
conditioners and many other systems.
Advantages of the Thermostatic Expansion Valve
• The TEV maintains the flow of the refrigerant to the evaporator as per the load inside. Thus
the refrigeration or the air conditioning plant can run to the optimum capacity as per the
requirements.
• The TEV keeps the evaporator fully active and helps getting the optimum cooling effect from it.
• Since the entire refrigerant in the evaporator gets vaporized the chances of the liquid refrigerant
particles going to the compressor are reduced. This reduces the chances of the breakdown of
the compressor due to compression of the liquid.
• The compressor can also work at the optimum capacity as per the refrigeration load on the
system. If the load is lesser it has to compress refrigerant and work on lesser capacity thus
absorbing lesser electric power. If the load is higher it can work at higher capacities.
Disadvantages of the Thermostatic Expansion Valve
• TEV is more expensive and proper precautions should be taken at the installation.
• The use of TEV depends upon degree of superheat. Hence, in applications where a close
approach between the fluid to be cooled and evaporator temperature is desired, TEV cannot be
used since very small extent of superheating is available for operation.
5.Electronic Type Expansion Valve
• The needle moves up and down in response to magnitude of current in the heating
element.
• A small resistance allows more current to the heater, hence the valve opens wider.
• A thermistor is placed in series with the heater.
• The heater current depends upon the thermistor resistance that depends upon the
refrigerant condition.
• Superheated vapour lowering the thermistor resistance and increasing the heater
current.
• This opens the valve wider and increases the mass flow rate.
• This continues until the vapour becomes saturated and some liquid refrigerant droplets
appear.
• The liquid refrigerant cool the thermistor and increase its resistance, so it allows a small
current to flow through the heater making the valve opening narrower.
• The control of this valve is independent of refrigerant and refrigerant pressure; hence it
works in reverse flow direction also.
• It is convenient to use it in year-round-air-conditioning systems, which serve as heat
pumps in winter with reverse flow.
 6. Solenoid valve
• A solenoid valve is an electromechanical valve frequently used to control the flow of liquid or gas.
• Solenoid valves are found in many applications and are commonly used in refrigeration and air
conditioning systems.
• Their function is simply to turn refrigerant flow on and off.
• Solenoid valves offer fast and safe switching, reliability, long life and compact design.
• The valve is commonly used to replace a manual valve or where remote control is desirable.
• A solenoid is operated by opening and closing an orifice in a valve body that permits or prevents flow
through the valve.
• The orifice is opened or closed through the use of a plunger that is raised or lowered within a sleeve tube by
energizing the coil.
• The bottom of the plunger contains a compatible sealing material, which closes off the orifice in the body,
stopping flow through the valve.
Diagram of solenoid valve

Operation

The solenoid assembly consists of a coil, plunger, and sleeve assembly. In a normally closed valve, a plunger
return spring holds the plunger against the orifice, preventing flow through the valve. When the coil is
energized, a magnetic field is produced, raising the plunger and allowing flow through the valve. In a
normally open valve, when the coil is energized, the plunger seals off the orifice, stopping flow through the
valve.
• In an evaporator, the refrigerant boils or evaporates and in doing so absorbs heat from the surrounding location
or medium which is to be cooled.

• The temperature of the boiling refrigerant in the evaporator must always be less than that of surrounding
medium.
• It is also called a cooling coil, chilling coil, freezing coil.
• Point 5 – Entry of liquid refrigerant into expansion valve. Liquid refrigerant is sub-cooled
ensuring that expansion valve receives pure liquid refrigerant with no vapors.
• Point 6 – Low pressure liquid refrigerant passes through the evaporator coil, and

continually absorbs heat through the coil walls, from the medium being cooled.
• Point 1’ – All liquid refrigerant has evaporated and only vapor refrigerant remains in the
evaporator coil.
• Since at point 1’ vapor refrigerant is still colder than the medium being cooled, therefore
the vapor refrigerant continues to absorb heat. This heat absorption causes an increase
in the sensible heat(or temperature) of the vapor refrigerant.
• The vapor temperature continues to rise until the vapor leaves the evaporator to the
suction line at point 1.
• At this point, the temperature of the vapor is above the saturation temperature and the
vapor refrigeration is superheated.
Classification of evaporators
1. According to the type of construction
• Bare tube coil evaporator
• Finned tube evaporator
• Plate evaporator
• Shell and tube evaporator
• Shell and coil evaporator
• Tube in tube evaporator
2. According to the manner in which liquid refrigerant is fed
• Flooded type evaporator
• Dry expansion evaporator
3. According to the mode of heat transfer
• Natural convection evaporator
• Forced convection evaporator
4. According to the operating conditions
• Frosting, Non frosting, Defrosting evaporator
• The process of heat removal from the substance to be cooled or refrigerated is done in the evaporator.
The liquid refrigerant is vaporized inside the evaporator (coil or shell) in order to remove heat from a
fluid such as air, water etc.
• Evaporators are manufactured in different shapes, types and designs to suit a diverse nature of cooling requirements.
• The terms dry expansion and flooded indicate the manner in which the liquid refrigerant is fed into the
evaporator and circulated, the terms natural convection and forced convection describe the way in which
the fluid (air or liquid) is cooled/circulated around the evaporator.

Heat Transfer in Evaporators

The three heat-transfer resistances in evaporatorsare:
(a) Refrigerant side for the transfer of heat from solid surface to the liquid refrigerant.
(b) Metal wall.
(c) Cooled-medium side which could be due to air, water, brine or any other fluid or a wetted surface on acooling and
dehumidifying coil.
• The heat transfer from solid surface to the evaporating refrigerant is of primary interest here. However, the mechanism
of boiling is so complex because of the influence of such factors as surface tension, saturation temperature, latent heat
and nature of the solid surface, in addition to the usual transport properties, that it is very difficult to predict the heat-
transfer coefficientanalytically.
• In commercial equipment, the boiling process occurs in two types of situations: one, of pool boiling as in flooded
evaporators with refrigerant boiling the shell - side and the other, of flow or forced convection boiling as in direct-
expansion evaporators with refrigerant on thetube-side.
 1. Natural convection evaporator
• Natural convection coils are very useful when low air velocities and minimum dehydration of the product is required.
• Mainly used in domestic refrigerators, cold storages, small freezers and water coolers.
• The liquid refrigerant evaporates inside the cooling coil and cools the air whose density increases. The high-density air
flows downwards through the product in the cold storage and cools down. (evaporator should be placed as high as
possible)
• The circulation of air over the cooling coil by natural convection is a function of the temperature difference
between evaporator (greater the difference greater the rate of air circulation) and the space and location.

• Sufficient space should be provided between evaporator and ceiling to permit the air circulation over the top of the
coil.
• Baffles are also provided to separate the warm air and cold air plumes to ensure good air circulation.
• For rooms with larger width more evaporator coils are used.
• The refrigerant tubes are made of steel or copper. Steel tubes are used for ammonia and in large capacity systems.
• The advantages are that the coil takes no floor space and it also requires low maintenance cost.

• It can operate for long periods without defrosting the ice formed on it and it does not require special skills to fabricate
it.
• Defrosting can be done easily (e.g. by scraping) even when the plant is running.
• Disadvantage is that natural convection heat transfer coefficient is very small hence very long length are required,
which in turn requires larger quantity of refrigerants.
 2.Flooded evaporators
• Used in the chemical and food processing industries.
• Used in comfort and process air cooling installations.
• Used in cold storage boxes and freezers
• In a flooded-type evaporator a constant refrigerant liquid level is maintained.
• A float valve is used as the expansion device which maintains a constant liquid level in the evaporator.
• The liquid refrigerant from the receiver passes through a low side float control valve and accumulator before
entering the evaporator coil.
• The accumulator (surge drum or surge tank) serves as a storage tank for the liquid refrigerant and It maintains
a constant liquid level in the evaporator and helps to separate the liquid refrigerant from the vapor returning
to the compressor.
• Due to the heat supplied by the substance to be cooled, the liquid refrigerant in the evaporator coil vaporizes
and thus the liquid level falls down.
• The accumulator supplies more liquid to the evaporator in order to keep the liquid refrigerant in the

evaporator at proper level.

• In this way, the level of liquid refrigerant in the accumulator also falls down. Since the float within float
chamber rests on liquid refrigerant at the same level as that in the accumulator, therefore the float also floats
down and open the float control valve.
• Now the liquid refrigerant from the receiver is admitted into the accumulator. As the liquid level in the
accumulator rises and reaches to the constant level , the float also rises with it until the float control valve
closes.
• Since the evaporator is almost completely filled with the liquid refrigerant, therefore the vapor
refrigerant from the evaporator is not superheated but it is in a saturated condition.
• In order to prevent liquid refrigerant to enter into the compressor, an accumulator is generally used
with the flooded evaporator.
• The liquid refrigerant trapped in the accumulator is recirculated through the evaporator.
• The evaporator coil is connected to the accumulator and the liquid flow from the accumulator to the
evaporator coils is by gravity.
• The vapor formed by vaporizing the liquid in the coil been lighter, rises up and passes on to the
top of the accumulator from where it is supplied to the suction side of the compressor.
• The baffle plate arrests any liquid present in the vapor.
• Advantage is that the whole surface of the evaporator coil is in contact with the liquid refrigerant
under all load conditions.
• High heat transfer rates.
• Disadvantages are more expensive and more refrigerant charge is required.
 3.Direct expansion coils or Dry expansion evaporators
• In these evaporators the amount of refrigerant fed by the flow control device is just enough so that all
evaporates before it leaves the evaporator. Aslo known as Direct expansion evaporators
• At the inlet of the evaporator, the refrigerant is predominantly in the liquid form with a small amount of vapor
formed (flash gas is formed which causes bubbles in evaporator) at the expansion valve. The vapour leaving
the evaporator is usually slightly superheated to ensure that there is no risk of any refrigerant liquid reaching
the compressor.

• The refrigerant, by the time it reaches the end of the evaporator, is purely in the vapor state and that too
superheated. It may be noted that in this type, the refrigerant doesn't recirculate within the evaporator as in
flooded evaporator.
• Thus the evaporator in its length is filled with a varying proportion of liquid and vapor. The inside of the
evaporator is far from ‘dry’ but wetted with liquid.
• Refrigerant supply to the evaporator is through a thermostatic expansion valve, which maintain automatically
a moderate level of superheating of the vapour drawn off.
• Mostly used in producing refrigeration and having capacity below 150 tonnes of refrigeration. The direct
expansion coil is preferred for air conditioning purposes.
• They are simpler in design, more compact and require less refrigerant and have less problems with oil return,
and are cheaper than flooded or refrigerant circulates evaporators.
When the cooling load is light, quantity of liquid When the cooling load is heavy, it allows a larger quantity of
refrigerant in the evaporator is small. When liquid liquid refrigerant into the evaporator coil. In this case the

refrigerant passes through the expansion valve, some liquid and vapor separates. The liquid refrigerant flows along
vapor (flash gas) is formed. The flash gas causes bubbles in the bottom of the coil and vapor rises towards the top. Thus
the evaporator. If the coil diameter is small, the bubbles evaporator efficiency increases. This efficiency depends upon

can cause dry areas on the interior walls of the coil which the diameter of evaporator tubes, quantity in the evaporator
reduce the rate of heat transfer. Thus evaporator and quantity in the evaporator and the velocity of the liquid
efficiency decreases as dry area increase. refrigerant within the evaporator coil.
INTRODUCTION
• A compressor is the most important and often the costliest component (typically 30 to 40 percent of total cost) of any
vapor compression refrigeration system (VCRS).
• The function of a compressor in a VCRS is to continuously draw the refrigerant vapor from the evaporator, so that a low
pressure and low temperature can be maintained in the evaporator at which the refrigerant can boil, extracting heat
from the refrigerated space.

• The compressor then has to raise the pressure of the refrigerant to a level at which it can condense by rejecting heat to
the cooling medium in the condenser.

• Compressors used in refrigeration systems based on the working principle can be classified in several ways:
Positive displacement machines
• Reciprocating Compressors
• Rotary Compressors
• Scroll Compressors
• Screw Compressors
Non positive machines
• Centrifugal Compressors
• In positive displacement type compressors, compression is achieved by trapping a refrigerant vapor into an enclosed space
and , its pressure rises and then reducing its volume.

• When the pressure rises to a level that is slightly higher than the condensing pressure, then it is expelled from the

enclosed space and a fresh charge of low-pressure refrigerant is drawn in and the cycle continues.
• Since the flow of refrigerant to the compressor is not steady, the positive displacement type compressor is a pulsating flow
device and are prone to high wear, vibration and noise level.
• In non positive displacement compressors, the pressure rise of refrigerant is achieved by imparting kinetic energy to a
steadily flowing stream of refrigerant by a rotating mechanical element and then converting into pressure as the
refrigerant flows through a diverging passage.

• These compressors are steady flow devices, hence are subjected to less wear and vibration.
• The reciprocating and screw compressors used with refrigerants which require a relatively small displacement and
condense at relatively high pressure, such as R-12, R-22, Ammonia, etc.
• The centrifugal compressors are suitable for handling refrigerants that require large displacement and operate at low
condensing pressure, such as R-11, R-113, etc.

• The rotary compressor is most suited for pumping refrigerants having moderate or low condensing pressures, such as R-
21 and R-114; this is mainly used in domestic refrigerators.
 1. Reciprocating compressor
• Vapor refrigerant is compressed by the reciprocating (i.e. back and forth) motion of the piston.
• These compressors are used for refrigerants which have comparatively low volume per kg and a large differential pressure,

such as ammonia, R-40 ,R-12, R-22, etc.

• Sizes : 1/12 kW used in domestic refrigerator and up to 150kW for large capacity.

• Types: Single acting vertical compressors and double acting horizontal compressors.
• Modern day reciprocating compressors are high speed (≈ 3000 to 3600 rpm), single acting, single or multi-cylinder (Upto 16
cylinders) type.

1.1 Single stage reciprocating compressor

Operating principle
• Reciprocating compressors consist of a piston moving back and forth in a cylinder, with suction and discharge valves to
achieve suction and compression of the refrigerant vapor.
• Its construction and working are somewhat similar to a two-stroke engine, as suction and compression of the refrigerant
vapor are completed in one revolution of the crank.

• The suction side of the compressor is connected to the exit of the evaporator, while the discharge side of the compressor is
connected to the condenser inlet.
 1.2 Multi stage reciprocating compressor
• To deliver vapor refrigerant at a very pressure as in the case of low temperature refrigerating systems.

• Vapor refrigerant is compressed in two or more cylinders in series with intercooling between them
Drawbacks in single stage compression
• Size of the cylinder is too large
• Difficult to reject heat from the refrigerant in the small time available for the compression due to high temperature.

• Sometimes heats up the cylinder head or burn the lubricating oil due to high temperature.
• The friction losses and running cost is high
• Volumetric efficiency is low

Advantages of Multi-stage compression

• Work done per kg of refrigerant is reduced
• Volumetric efficiency improves
• Reduces leakage loss considerably
• Gives more uniform torque, and hence a smaller size flywheel is required.
• Provides effective lubrication because of lower temperature range.
• Reduces the cost of compressor.
Two stage reciprocating compressor with intercooler

Fig 1
• The vapor refrigerant from the evaporator at pressure p1 and temperature T1 sucked by the LPC at point 1 during its suction
stroke.

• After compression it is delivered at point 2 to the intercooler at pressure p2 and T2.

• in the intercooler, the compressed refrigerant is cooled from temperature T2 to T3 at constant pressure p2.
• Thus cooled refrigerant is now sucked by the HPC at point 3 during its suction stroke.
• Finally the refrigerant after compression in the HPC (second stage) is delivered at point 4 to a condenser at pressure p3
and temperature T4
 2. Screw Compressor
• Rotary screw compressors are positive displacement compressors

• The machine consists of two helically- grooved rotors which rotate in a housing.
• The male rotor consists of lobes and is normally the driving rotor. The female rotor has gullies and is normally the driven rotor.
A four-lobe male rotor will drive a six-gully female rotor at two-thirds of its speed.

• At 3600 rpm the number of compressed gas discharges of a four-lobe rotor will he 4 x 3600 = 14,400 per minute.

• In a positive displacement machines, there are three basic phases – suction, compression and discharge.
• When the male rotor turns clockwise, an inter-lobe space between a pair and housing nearest to the suction end, opens
and is filled with the gas. There are four such pairs to be filled during one revolution in a four-lobe rotor and the suction

periods overlap one another.

• When re-meshing starts, the volume decreases and the pressure rises. The charge is moved helically and compressed until
the trapped volume reaches the discharge end. The compression ratio is thus fixed.
• Further rotation simply empties the rotors of the high pressure gas until the last traces of the gas are squeezed out,
irrespective of the pressure in the condenser.

• On completion of the discharge phase, there is no residual gas remaining in the rotors. As a result, there is no expansion of
clearance gases. The compressor has no suction and discharge valves.
• There are leakage paths in a screw compressor mainly across the line of mesh between the rotors and across the clearance
between the rotors and the housing.
• To eliminate leakage, oil is injected in a number of small jets directed towards the mesh. Oil injection also serves the

purpose of cooling and lubricating along with that of sealing the leakage paths.
• A slide valve, closely following the shape of the rotors is used for capacity control. At full load the valve is closed. At part
load, the valve opens enabling a return flow passage to be formed so that a part of the gas drawn into the inter-lobe spaces

can flow back to the suction side.

• The screw compressor combines many advantageous features of both centrifugal and compressors, along with some of its
own. As it is a positive displacement machine, high pressure refrigerants, such as R-22 and ammonia are used in it. As it is
a high speed rotary machine, a large volume can be handled by it. It is, therefore, found extremely suitable for large capacity
low temperature applications such as in food refrigeration.
• Like reciprocating compressors, it has no surging problems. It has small pipe dimensions and positive pressures due to the
use of high pressure refrigerants.
• Like centrifugal compressors, it has high compression efficiency, continuous capacity control, unloaded starting and no
balancing problems. Also, the compressor is suitable for large capacity installations.
 3. Vane type compressors or Rotary compressor
• They are positive displacement, direct-drive machines

• There are essentially two designs of this compressor:

(a) Rolling piston type
(b) Rotating vane type
• In the rolling piston type, the roller is mounted on an eccentric shaft with a single stationary blade, which is always in
contact with the roller by means of a spring.

• A blade is set into the slot of a cylinder in such a manner that it maintains contact with the roller by means of spring.
• The blades separates suction and discharge ports and moves in and out of the slot to follow the rotor when it rotates
• The theoretical piston displacement is

Where A and B are respectively the diameters of the cylinder and rolling piston and H the length of the cylinder.
• When the roller rotates, the vapor refrigerant ahead of the the roller is being compressed and the new intake from the

evaporator is drawn into the cylinder.

• As the roller turns towards the mid position, more vapor refrigerant is drawn into the cylinder while the compressed
refrigerant is discharged to the condenser.
• At the end of the compression stroke , most of the compressed vapor refrigerant is passed through the discharge port to the
condenser.

• In this way low pressure and temperature vapor refrigerant is compressed gradually to a high pressure and temperature
• In the rotating vane type, its having four vanes, the rotor is concentric with the shaft. The vanes slide within the
rotor but keep contact with the cylinder.

• The center of the rotor is eccentric with the center of the cylinder.
• The blades are forced against the cylinder wall by the centrifugal action during the rotation of the motor.
• The low pressure and temperature vapor refrigerant from the evaporator is drawn through the suction port (In)
• As the rotor turns, the suction vapor refrigerant entrapped between the two adjacent blades is compressed.
• Compressed refrigerant at high pressure & temperature is discharged through the discharge port (Out) to the
condenser
• In both designs, the whole assembly is enclosed in a housing (not shown in the figures), filled with oil and
remains submerged in oil. When the compressor is working, oil film forms the seal between the high-pressure and
the low- pressure sides. When the compressor stops, this seal is lost and high pressure vapor refrigerant flow into
low pressure side
• Rotary compressors have high volumetric efficiencies due to negligible clearance. They are normally used in a
single stage up to a capacity of 5 TR with R-114. Large rotary compressors are used in low-temperature fields,
such as in chemical and industrial processing, cold storages and freezing, as high displacement. low- stage or
booster compressors at -90 to -l00°C evaporator temperature with R-12, R-22 and ammonia.
• They are available in 10 to 600 hp sizes with 2 to 120 cubic metres per minute displacement in one unit.
Based on arrangement of compressor motor or external drive, the different type of
reciprocating compressors are;

1. Open type refrigeration compressors

2. Hermetic and
3. Semi hermetic
OPEN TYPE COMPRESSOR

Advantages of open compressor

• They can be driven from a non-electric power source such as turbine, IC engine
• Compressor and motor are accessible to repair in case of failure.

• Servicing is easy and cheap

Disadvantages of open compressor
• Noisy operation
• Not leak proof they need shaft seals to prevent leakage lubrication required at
sealing to maintain Pressure.

• They are not compact.

Open type refrigeration compressors…..
• In open type compressors the rotating shaft of the compressor extends through a seal in the crankcase for an
external
drive.
• The external drive may be an electrical motor or an engine (e.g. diesel engine).
• The compressor may be belt driven or gear driven.
• Open type compressors are normally used in medium to large capacity refrigeration system for all refrigerants and
for ammonia (due to its incompatibility with hermetic motor materials).
• Open type compressors are characterized by high efficiency, flexibility, better compressor cooling and serviceability.
• Disadvantage: The shaft has to extend through the seal, refrigerant leakage from the system cannot be eliminated
completely.
• Hence refrigeration systems using open type compressors require a refrigerant reservoir to take care of the
refrigerant leakage for some time, and then regular maintenance for charging the system with refrigerant,
changing of seals, gaskets

etc.
 Hermetic compressor

• Used in household refrigerators, deep freezers, window air conditioners, split air conditioners, most of the packaged air
conditioners.
• The hermetically sealed reciprocating compressor is very easy to handle, and requires low maintenance. They are used with
motor power requirements from 1/20 to 7.5 hp.
• In hermetically sealed compressor, the compressor and the motor are enclosed in the welded steel casing and the two are
connected by a common shaft. This makes the whole compressor and the motor a single compact and portable unit that can
be handled easily and prevent refrigerant leakage.(eliminate the use of crankshaft seal)
• The housing has welded connections for refrigerant inlet and outlet and for power input socket.
• All motors reject a part of the power supplied to it due to eddy currents and friction, that is, inefficiencies. Similarly the
compressor also gets heated-up due to friction and also due to temperature rise of the vapor during compression.
• In Open type, both the compressor and the motor normally reject heat to the surrounding air for efficient operation. In

hermetic compressors heat cannot be rejected to the surrounding air since both are enclosed in a shell.
• Hence, the cold suction gas is made to flow over the motor and the compressor before entering the compressor. This keeps
the motor cool.
• The motor winding is in direct contact with the refrigerant hence only those refrigerants, which have high dielectric strength,
can be used in hermetic compressors.

• The hermetically sealed compressor is very different from the traditional open type of compressors in which the
compressor and the motor are different entities and the compressor is connected to the motor by coupling or belt.
• The cooling rate depends upon the flow rate of the refrigerant, its temperature and the thermal properties of the
refrigerant.
• If flow rate is not sufficient and/or if the temperature is not low enough the insulation on the winding of the motor can burn
out and short-circuiting may occur.

• Hence, hermetically sealed compressors give satisfactory and safe performance over a very narrow range of design

temperature and should not be used for off-design conditions.

• The COP of the hermetic compressor based systems is lower than that of the open compressor based systems since a part of
the refrigeration effect is lost in cooling the motor and the compressor.
• However, hermetic compressors are almost universally used in small systems such as domestic refrigerators, water coolers,
air conditioners etc, where efficiency is not as important as customer convenience (due to absence of continuous
maintenance).
• They are normally not serviceable and are not flexible as it is difficult to vary their speed to control the cooling capacity.
Advantages of the Hermetically Sealed Compressor
1) Can be moved easily from one place to the other place, they are highly portable. One does not have to disassemble the

compressor from the motor and no coupling, belt and pulley arrangement is involved.
2) Since no coupling, belt or pulley is involved, the maintenance is lesser.
3) The lubrication system of the hermetically sealed compressor is inherent and no external lubrication is required, unless the
fresh gas charging is done.
4) The installation of the hermetically sealed compressor is very easy. The suction and discharge connections and the electrical
connections are available externally.

5) Have very long life, the companies offer warranty period of up to seven years for these compressors.

Disadvantages:
1) Maintenance is not easy because the moving parts are inaccessible.
2) A separate pump is reqd. for evacuation and charging of refrigerant.
3) Burnout winding can contaminate entire system.
4) Only electric power sources can run this unit.
 Semi hermetic
• In some (usually larger) hermetic units, the cylinder head is usually removable so that the valves and the piston can be serviced.
This type of unit is called a semi-hermetic (or semi-sealed) compressor.

Advantages
• Due to the semi-hermetic design such compressors are very compact and occupy less space compared to open type machines
thus saving expensive building and plant room costs.
• The foot print and weight of a semi-hermetic machine is 70% of that of the corresponding open type machine. These

compressors are hence easier to handle and do not require heavy foundations like open type machines.
• The common problem of refrigerant leakage through the shaft seal is not facing with the semi-hermetic compressor because
the motor is directly mounted on the compressor crankshaft.
• Semi-hermetic compressors do not require any pulleys and belts and have no alignment problems and no wear and tear
problem of the d rive elements.

• Such compressors are also quieter and produce less vibration compared to the open type. This reason alone makes them the

ideal choice for roof-top applications.

Cooling Tower: They are special type of heat exchanger that allows water and air to come in contact with each other to lower the
temperature of the hot water. During the cooling tower working process, small volumes of water evaporate, lowering the
temperature of the water that’s being circulated throughout the cooling tower.
In a short summary, a cooling tower cools down water that gets over heated by industrial equipment andprocesses.

The hot water is usually caused by air conditioning condensers or other industrial processes. That water is pumped through pipes
directly into the cooling tower. Cooling tower nozzles are used to spray the water onto to the “fill media”, which slows the water
flow down and exposes the maximum amount of water surface area possible for the best air-water contact. The water is exposed
to air as it flows throughout the cooling tower. The air is being pulled by an motor-driven electric “cooling tower fan”.

When the air and water come together, a small volume of water evaporates, creating an action of cooling. The colder water gets
pumped back to the process/equipment that absorbs heat or the condenser. It repeats the loop over and over again to constantly
cool down the heated equipment or condensers.

The make-up water source is used to

replenish water lost to evaporation
Types of cooling tower on basis of methods by air-to-water flow
1. Cross flow:
• The water vertically flows through the fill media while the air horizontally flows
across the falling water. That’s why they call it “crossflow” because the air and water
cross paths or flows. Because of the crossing of flows, the air doesn’t need to pass
through the distribution system.
• Hot water flow via gravity and distribution basins on the top of the tower right
above the fill media.
• Generally a larger plan area but lower height, better access formaintenance.
• Risk of recirculation higher due to reducedheight.
2. Counter flow cooling towers:
• The air vertically flows upwards, counter to the water flow in the fill media. Due to
the air flowing vertically, it’s not possible to use the basin’s gravity-flow like in
crossflow towers.
• As a substitute, these towers use pressurized spray systems, usually pipe-type,to
spray the water on top of the fillmedia.
• The pipes and cooling tower nozzles are usually spread farther apart so they will not
restrict any air flow.
• Common in HVAC&R applications.
3. Hyperbolic
• Hyperbolic towers are structurally strong and use a minimum of
materials, while handling large projects like nuclear or coal-fired

power plants.
• Hyperbolic towers operate through a chimney, or stack, effect; when
the air outside the cooling tower is cooler than the air inside the

tower, the air outside forces the humid, inside air to travel upwards.
• Fill is placed around the lower portion of the tower, water is sprayed
over it, and the water is cooled by the natural draft of the air moving

up through the tower.

• High initial cost
• Large space due to height and width
• Cheap to operate
• Self supported structure and withstand wind velocity 150km/hr.
Types of cooling tower on basis of methods of air flow generation
1. Natural Draught Cooling Tower:
• In this type of cooling tower, fan is not used for circulating air but here, by enclosing the heated air in the chimney and it will
create pressure difference between heated air and surrounding air. Because of this pressure difference air enters in to the
cooling tower. Air movement depends on induction forces.
• It utilises the principle of buoyancy to achieve the desiredeffect
• Fluid movement is parallel or crossflow.
• Less efficient in providing cooling
• Large space required for installation
• Energy consumption is low
• Safe operation and used for high capacity plants
• Low maintenance as no moving parts.
• No recirculation of air occurs.
• Performance depends on prevailing wind velocity and direction.
• It requires large hyperbolic tower, so capital cost is high but operating
cost is low because of absence of electrical fan.
• Rarely used in HVAC & R systems due to huge area and heavy usage
2) Mechanical or Forced Draught Cooling Tower:
• In this type of cooling tower, fan is used to circulate the air. When power plant runs on peak load, it requires a very high rate of cooling
water. To rotate fan, it uses motor with speed around 1000 rpm. Working principle is same as natural draught cooling tower, only
difference is that here fan is mounted on thecooling tower.
• There are two types; Induced and forced draught coolingtower.
• If fan is mounted on the top of the tower is called as induced draught
cooling tower which pulls air through the tower, is most popular for very
large capacity installation and requires large capacity of fan.
• The water is sprayed and broken into droplet and is cooled byair.
• It has a powerful fan unit at the top. When turned on this powerful
exhaust fan pulls the hot moist air out of the system and into the
atmosphere.
• The exit velocity of air, in this case, is quite high when compared to the
entry velocity hence eliminating the risk of recirculation.
• Can operate with or without fill, low cost and powerconsumption
• Water circulation needs pump of small capacity
• Fan size is limited by weight of tower
• Vibration and noise level is high Induced draught cooling tower
• Forced draught cooling tower contains horizontal shaft for the fan
(situated at air intake) and it is placed at bottom of the tower. Hot water
coming from the condenser enters the unit from the top and gets
sprayed through the nozzles. Water droplets falling downward meet the
air.
• Here the entry velocity of the air is quiet high in comparison to the exit
velocity.
• More efficient and safe
• Generally incorporate fill and minimum noise and vibrations
• Fan, drive and motor located in dry air stream so less maintenance and
corrosion is likely
• Ideal for applications where cooling and pressuring are both desired.
• Blade erosion is less Forced draught cooling tower

• Fan size is limited by size of tower,

• Good air distribution but may be susceptible to recirculation
• Pump required for water circulation has to be highcapacity
• Common in HVAC&R applications.
Types Of Cooling Towers On The Basis Of Heat Transfer methods used

1. Dry Cooling Towers:

• In this type of cooling tower, the working fluid is channelled through
tubes which collects the ambient heat and then this heat is exchanged
with atmosphere using air as a medium. No liquid or water is hence
used for cooling in this type of setup.
• It operate by heat transfer through a surface that separates the
working fluid from ambient air utilizing convective heat transfer. They
do not use evaporation.

2. Wet Cooling towers:

• It is also known as open circuit cooling towers.

• The working principle of wet cooling towers is evaporative cooling
and in this case the working fluid or the fluid used for heat exchange
and the fluid that is actually evaporating is the same i.e. water.
3. Fluid Coolers: Also known as closed circuit cooling towers.
• Aclosed circuit cooling tower in which the process fluid does not contact
the cooling air.
• Hybrid in nature and combine the best of both dry and wet cooling
systems.
• Different types of fluids can be cooled including water, plating solutions,
quenching oils, chemical solutions, gases, refrigerants and air.
• Can be natural, forced or induced draft.
• Reduced water treatment and corrosion.
• Reduced pumping requirement.
• Common in industrial applications and HVAC
Refrigerant leaks and their detection
• Leakage of refrigerant from a refrigeration system affects the performance of a sealed system (systems with hermetic
compressors) adversely.
• Due to refrigerant leakage, the running time of the system increases continuously. Both suction as well as discharge
pressures reduce due to loss of refrigerant.

• There will be less liquid and more flash gas, which has negative effect on several components of the system.
• If the suction pressure due to refrigerant leakage falls below atmospheric pressure, then there is a possibility of air leaking
into the system. This will bring moisture into the system and the presence of moisture affects the system

adversely.
Leak detection:
• Bubble Solutions. The oldest method of leak detection is the bubble solution. Soap solution is applied at suspected leak
points, usually with a squeeze bottle, brush, or dauber. Theoretically, the escaping refrigerant will produce bubbles at the
leak sites. However, very small leaks or windy conditions may make this method ineffective.
• Halide Torches. Halide torches are more sophisticated than bubble solutions. This method is based on the fact that the

torch’s flame will turn green when exposed to refrigerants containing chlorine atoms (CFCs and HCFCs). However, not all
refrigerants contain chlorine atoms.
Electronic leak detector
• All electronic leak detectors use an element that is sensitive to halogenated gases.

• An audible and/or visual alarm signals when a leak has been detected.
• HFCs, CFCs, HCFCs and HCFC-based refrigerant blends can be detected easily
• Most commonly used due to accuracy and ease of use.
• This detector has a filter that prevent contaminants and water from entering it.

Ultrasonic Leak Detector

• The system must be highly pressurized for this detector to work.
• This refrigerants leak detector uses an electronic amplification system that is able to detect the high frequency sound of

the leak.
• A microphone and earphones are used as input and output of the system.
Detecting Ammonia
• Ammonia can be detected by the use of phenolphthalein paper where the moistened paper will turn pink (small amount)
or scarlet (bigger amount) when in contact with this gas.

• The other method is by using a lighted sulfur candle which will give a thick white smoke when it encounters the ammonia
gas.
CHARGING OF REFRIGERANT
• The schematic arrangement for the charging of a refrigerant unit shownbelow.
• The refrigerant charging tube is flexible, the main refrigerant pipe is rigid and these are joined by a connector.

The sequence of operation is

1.Before charging the air has to be removed from the refrigerant
equipment and for that
a. Shut down the output from the compressor by closing valve
V1
b. Close the refrigerant inlet valve V2
c. Open the valve V3 (output from evaporator tubing) and
valve V2 (input to receiver)
d. Start the compressor motor
The air from the condenser, receiver and evaporator is purged out
through open valve V5. After air removal vacuum is produced in the
system. If the vacuum is retained for about 30 mins, it can be
concluded that system is free fromair.
e. After purging air from the system, the connections are
tightened and the valves V3 and V4 are closed.
2. For charging the refrigerant,
a. Open the cylinder valve V6 and the compressor suction valve V2
b. Stop the compressor motor when sufficient quantity of refrigerant has entered the system
c. Close the valve V2 and V6.That will disconnect the charge cylinder from the system

• The quantity of the refrigerant charged in the system is observed by noting the difference in weight of the refrigerant

cylinder. The amount of the refrigerant to be charged is dependent on the size and type of insulation.
• For small installation like water cooler, room cooler the exact quantity is prescribed by the manufacturer. if the
recommended weight of the refrigerant is not known, the refrigerant is charged in the system till no flashing or
bubbles are visible in the sight glass in the liquid line.
• The proper charging of the refrigerant is essential for smooth functioning of the system.

• Overcharging results in high temperature and pressure in the system and may lead to damage in compressor.
• Undercharging results in insufficient cooling and frequent tripping of the compressor motor.
REFRIGERATION CONTROLS SYSTEM
These are devices used to control the flow of refrigerant at various points throughout the refrigerant cycle. There are six basics
types of refrigerant flow controls.
1. Automatic Expansion Valve (Study)
2. Thermostatic Expansion valve (Study)
3. Capillary Tube (Study)
4. Low side Float (Study)
5. High Side Float (Study)
There are also secondary controls which, in some systems, ensure that other important activities are carried out
properly. Examples are defrost control and head pressure control.
Control Systems Offer Many Advantages
• Energy efficiency
• Reduced maintenance costs and extended equipment life
• Operator convenience
• Equipment redundancies
• Ice quality
• Reduced downtime and Reduced liability
1. THE THERMOSTAT - THERMOSTATIC EXPANSION VALVE (TXV)
• Thermostats allow refrigeration systems to bring product down to a predetermined temperature, but no lower than that
temperature.
• Thermostats typically are located inside the fridge behind the interior walls, with a sensor extending into the cooling
compartment.
• Refrigeration thermostats are similar to room thermostats in that they use a bimetallic strip to sense temperature Thermostats
don’t often fail completely, but their internal calibration sometimes changes, and other factors can affect their accuracy.
• Thus, it is not safe to assume that the temperature indicated on the thermostat dial is the actual temperature in the
refrigerated space. An accurate thermometer should be used to monitor spacetemperature.
2. DEFROST CONTROL
• Where cooling (not freezing) is the refrigeration goal, special defrosting equipment and controls may not be needed.
• Because the refrigerated space temperature is above freezing, allowing the evaporator fans to run when the compressor is
off may be all that is needed to remove the frost.
• Where freezing is the goal, however, heat from some source must be periodically applied to the evaporator coil to melt the
accumulated frost.
• Defrost cycles are often initiated by timers. This is appropriate. But using a timer to establish the duration of the defrost
period tends to waste energy. Evaporator temperature is a better indicator of when to stopdefrosting.
3. HEAD PRESSURE CONTROL
• Head pressure refers to the pressure in the high pressure side of a refrigeration system – the condenser.
• It may also be referred to as the discharge or condensing pressure. The temperature at which refrigerant condenses in the

condenser is known as the condensing temperature.

• Lowering head pressure reduces the temperature at which the condenser operates and increases the efficiency of your

refrigeration system.
• By minimising the head pressure, we can maximise system’s cooling capacity and minimise energy costs.
• When head pressure is higher than necessary, the compressor has to do more work. It will therefore

use more power and its efficiency and cooling capacity will decrease.
• The compressor has to run for longer to provide the required cooling and, in extreme cases, won’t be able to provide
enough cooling to achieve the required process or storage temperature.

• So minimising head pressure saves energy, and also maximises the cooling capacity of the refrigeration system, often

resulting in better temperature control

• If the refrigeration system has head pressure controls, we may be able to lower the head pressure by reducing the set
point, especially in cooler weather. In all cases the head pressure was controlled by on/off switching of the condenser fans.
4. SOLENOID VALVE
• A solenoid valve uses an electromagnet to control the flow of liquids or gases, mainly refrigerants in HVAC systems. Their
function is simply to turn refrigerant flow on andoff
• In these valves, an electrified coil becomes magnetized and causes a plunger to stop the flow through the valve; when it's
demagnetized, the flow resumes.
• The orifice is opened or closed through the use of a plunger that is raised or lowered within a sleeve tube by energizing the
coil.
• The bottom of the plunger contains a compatible sealing material, which closes off the orifice in the body, stopping flow
through the valve.
• This flow can be controlled by a simple switch on the device. These valves are fast, reliable and sturdy, but their main
advantage is that they can be placed in remote locations on a device, making them a compact and easy fit.
• Solenoid valves are two types: Direct acting and Pilot operated
• Solenoid valve are widely used in refrigerant, water and brine lines in place of manually operated stop valves to provide
automatic operation.