4. TRANSPORT REFRIGERATION SYSTEMS
There are four types of refrigeration systems and they are:
i. Mechanical- Compression Refrigeration Systems
The most used refrigeration cycle is the mechanical- compression. It has applications in both air
conditioning, commercial and industrial refrigeration.
These types of systems transfer heat by mechanically compressing refrigerant into a low-pressure,
cold liquid and expanding it into a high-pressure, hot gas. Refrigerants are substances that can boil
at a wide range of temperatures with the application or removal of pressure.
Like all liquids, they absorb heat when they boil into a gas and release it when they condense back
into a liquid.
The basics of the process deal with moving the refrigerant from the low-pressure side of the closed
system to the high-pressure side. The liquid refrigerant boils at 40°F (4.44 °C) on the low-pressure
side and absorbs heat from the warm indoor air.
On the high-pressure side of the system, the heat travels from the 110°F (43.33 °C) vapor
refrigerant to the cooler outdoor air, and the process repeats.
ii. Absorption Refrigeration
Heat is also transferred by absorption refrigeration systems through compressing and expanding
refrigerant. These systems rely on the process of absorption and heat, instead of an electrically
powered mechanical compressor, to move the refrigerant from the low-pressure side to the highpressure side.
Unlike mechanical-compression refrigeration systems, which typically use R-22 and R-410A for
refrigerants, absorption refrigeration systems use refrigerants that other substances are attracted to
and absorb.
For example, residential HVAC chillers often use ammonia as the refrigerant and water as the
absorbent. The water is located in a component called the absorber, where it sucks ammonia from
the low-pressure side of the system and removes heat while absorbing it. A pump sends the waterammonia solution to a generator, which boils it, separating the ammonia from the water before
sending it to the high-pressure side.
In addition to the process of absorption, heat is also used to move the refrigerant throughout the
system. The heat can be derived from hot water, steam, natural gas or other fuel sources.
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iii. Evaporative Cooling
Unlike the mechanical-compression and absorption refrigeration systems above, evaporative
cooling doesn’t use the traditional refrigeration cycle. Instead, these units, often called swamp
coolers, cool warmer outdoor air by blowing it over water-soaked pads as it enters the home.
The water absorbs the heat from the air and evaporates. The cooler air is channeled into the home
and the warm air out of it. Evaporative coolers can reduce air temperature by 15° ( -9.4°C) to 40°F
(4.44°C) but are best suited for dry climates, such as those in the southwestern U.S. They’re also
less costly to install and use about a quarter of the energy of central air conditioners.
iv. Thermoelectric Refrigeration
This system is unique from the three other types of refrigeration in that no refrigerant or water is
used. It uses an electric current and a thermocouple.
A thermocouple is made up of two different metal wires that are joined at both ends. Insulation
separates the rest of the wires from each other. When the current is directed on the thermocouple,
one end will become hot and the other cool.
Reversing the current’s direction has the effect of swapping the cold and hot junctions. The hot
end will typically be placed outside of the area to be cooled with a heat sink attached to it to keep
it the same temperature as the surrounding air.
The cold side, which is below room temperature, is placed in the area to be cooled, attracting heat
out of the air. This type of refrigeration is generally used for small cooling loads that can be
difficult to access, such as electronic systems.
1. Identify the various types of transport systems such as trucks, trailers, containers, trains.
Refrigerated transport is a method of transporting shipments with specially designed
temperature-controlled trucks. The transporting trucks has a built-in refrigeration system which
cools the shipments at a regulated temperature all through the process of shipping.
Fig: A refrigerator truck is a vehicle or truck designed to carry perishable commodities at
specific temperatures
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How are refrigerated foods transported?
In reality, the most important way to properly transport food that needs to be refrigerated is to
pack it properly before even beginning to move it. To do this, you should carefully package all
of the food into containers that are large enough to safely fit the products without potential damage.
What are refrigerated trucks used for?
Companies use refrigerated trucks to transport foods and drinks, pharmaceuticals, floral
arrangements and any other product that needs to stay a certain temperature when being moved.
Refrigerated trucks do, in fact, have an onboard, built-in refrigerator or freezer, however, these
units operate seamlessly with the vehicle's electrical and charging system. An engine-mounted
compressor paired with a skirt-mounted condenser gets things cold, while fans direct air to each
and every part of the unit.
Typically, reefer trailers come in standard lengths between 28 and 53 feet, and do not exceed
13.5 feet in height. The load on a reefer truck should never exceed 44,000 pounds. Refrigerated
trucks are made from fibre glass and polyurethane foam panel with internal ribbing using
Steel sub-frame. These trailers maintain temperatures between 55 deg Fahrenheit (12.78 °C) to
-20 deg Fahrenheit (-28.89 °C), allowing them to carry a wide variety of cargo.
A Reefer Trailer refers to a refrigerated trailer that gets attached to a semi-truck in order to
transport perishables and other temperature-sensitive goods. It was originally the ice cream
industry as shown in the diagram below.
Fig: a reefer trailer
The truck can be plugged to electrical power mains in your refrigerated vehicles to allow the reefer
unit operate on electric power in addition to the limited fuel supply in the fuel tank.
UNDERSTANDING THE METHOD OF CONTAINER BODY INSULATION AND AIR
CIRCULATION
The main insulation materials commonly used in refrigerated and thermal insulation truck
are polystyrene foam, polyurethane foam and extruded polystyrene foam.
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Refrigerated trailers' insulation capability degrades around 3 to 5 percent per year. This causes
higher fuel consumption, as the equipment needs to run more hours to maintain freight temperature
requirements. In addition, corrosion is one of the top reasons trailer life is limited.
Insulation is essential for trucks transporting temperature sensitive goods
Good insulation is important for refrigerated trucks to be fuel-efficient, cost-efficient and reliable.
Good insulation is also essential for unrefrigerated trucks carrying goods and materials, which are
sensitive to temperature fluctuations like flowers and chocolates. Polyurethane spray foam
insulation is perfect for this purpose.
Protection against heat radiating down from the hot metal roof
The foam can be sprayed directly to the underside of the roof of either held tight. It greatly reduces
the heat, which would normally radiate down from the hot metal roof. This protection is essential
for trucks carrying flowers as it prevents them from becoming limp or scorching under the heat.
Protection against heat rising from road surfaces
The foam is also a valuable addition to the underside of the floor of the truck body, for both
refrigerated and non-refrigerated trucks. It eliminates the heat load created by the heat rising from
the road surface and improves the efficiency of the refrigeration plant.
Polyurethane foam insulation offers several key benefits when used to insulate truck bodies:
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Excellent thermal insulation properties
Strong and light
Seals tight against water, moisture and air
Quick and efficient to install into any truck body
The most effective thermal insulation material
Polyurethane boasts as the most effective thermal insulation properties of any commerciallyavailable insulation material in the world. It has the highest R-value, which means it has the lowest
heat/cold transfer rate across each unit of thickness.
Long-lasting durability
Choosing polyurethane means your investment will last, unlike other types of insulation,
polyurethane is immune to damage and deterioration from water. It also holds its shape and won’t
pat down or sag, which means it maintains its effectiveness for many years after it is installed.
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Other qualities of polyurethane
The polyurethane insulation installation process is quick, efficient and versatile. Polyurethane
foam can be sprayed, poured or injected onto any surface or cavity. Truck insulation can be
installed with minimal disruption and minimal vehicle downtime.
How do you circulate air in a shipping container?
Fitting Vents- The cheapest and easiest way to improve airflow is to fit vents into your container.
Simple vent openings fitted into opposite walls create cross ventilation, allowing air to flow into,
through and out of the refrigerated space.
How much ventilation does a shipping container need?
For a 20ft container, we recommend installing 2 to 4 vents the air flow will be much more effective
with a minimum 2 vents.
Do shipping containers need ventilation?
While shipping containers/ storage containers are built with small pressure vents that allow the
unit to breathe, they are not sufficient to create functional ventilation inside the container. For this
reason, ensuring that you have adequate ventilation is essential.
What are ventilated containers used for?
The Ventilated containers are generally used to transport cargo with good moisture contents
which requires ventilation while in transit. Cargo like coffee beans, cocoa beans etc. are
transported in ventilated container.
Are shipping containers air tight?
In many cases yes. Most new shipping containers are manufactured with durable rubber seals
around their doors that prevent any water or moisture from entering the container. However, not
all containers you'll see on the market are watertight.
Fig: doors of container showing seals to prevent inflow of moisture
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Before you go on to choose the holder, do notice if the things you are shipping have moisture
content or not. Because if it ha it in them, then the ventilated containers would be the most suitable
option.
Ventilation in the ‘Ventilated containers’ or ‘coffee containers’ is given by ventilation openings in
the top and lower side rails. The Ventilated containers are commonly used to move freight with a
great moist content which requires ventilation through the transit to keep the Cargo from
deteriorating.
The ordinary dry container is used to ship dry freight. Load like Coffee beans, Cocoa beans and
so on is move in a ventilated vessel. For instance, the openings don’t allow in spray to prevent the
freight by rain or shower.
Ventilated containers, barely vary from standard containers in appearance. The significant
difference between the general dry cargo container and the ventilated container is that
the ventilated containers have ventilation systems whilst dry containers don’t have.
Special hardware equipment are used to ensure that moisture is kept from developing inside the
container. There are two essential methods:
Natural Ventilation:
For air ventilation, containers with natural ventilation use pressure difference between the vessel’s
interior and exterior air. Warm air ascends in the compartment and ways out at the top through the
rooftop ventilation strips. Cooler outer air at that point makes its way into the container through
the floor ventilation strips.
Forced Ventilation:
For the required air, forced ventilation containers use fans, air channels and ventilation flaps.
Container vent spaces or air openings are regularly built like a web to prevent infiltration
precipitation.
Frequently, there are openings in the base and top side rails, which form ordinary air ducts.
Sometimes small perforated walls are introduced on the outer side.
Cocoa beans and other natural products with high moisture content can be responsible for the
container’s products’ deterioration. As a result, it is necessary to guarantee that you have
satisfactory ventilation.
Proper ventilation is relevant if containers are used in a climates where temperatures change
definitely or in cases where the cargo is sensitive to temperature or humidity.
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Fig: a ventilated container
How can I ventilate a room without ventilation?
How To Improve Air Circulation In A Room Without Windows
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Use portable fans.
Simply leave the door open.
Add a ceiling fan to the room.
Turn on the HVAC.
Add a wall air conditioner.
Install a swamp cooler.
Install a mini-split ductless air conditioner.
Understand the refrigeration systems used such as liquid refrigerant, eutectic and mechanical
system
Refrigeration systems that use one, two, three or four stages of compression have been successfully
operated in many applications. The number of levels of refrigeration depends upon the number of
compression stages required; interstage heat loads, economics and the type of compression.
Four Types of Refrigeration Systems
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Evaporative Cooling. Evaporative cooling units are also referred to as swamp coolers.
Mechanical-Compression Refrigeration Systems. Mechanical compression is used in
commercial and industrial refrigeration, as well as air conditioning.
Absorption.
Thermoelectric.
Which liquid is used as a refrigerant in refrigerator?
Modern refrigerators use a refrigerant called HFC-134a which does not deplete the ozone layer,
unlike Freon.
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What is the work of the liquid refrigerant?
The fluid used for heat transfer in a refrigeration system which absorbs heat at a low
temperature and low pressure and rejects heat at a higher temperature and a higher pressure.
What are the 3 main types of refrigeration systems that are used in commercial HVAC building
systems?
Three of the most commonly used systems for commercial buildings are: Variable-Air-Volume
(VAV) systems with a packaged rooftop unit. Chiller, cooling tower and boiler
systems. Water-source heat pump systems with a cooling tower and boiler.
What is a chiller system?
A chiller (cooling water circulation device) is a term for a device that controls the temperature
by circulating a liquid such as water or heat medium as a cooling liquid whose temperature was
adjusted by the refrigerant cycle. It is referred to as a “chiller” because it is often used for cooling.
Which refrigerant is used in chillers?
Ammonia (R717) is a type of refrigerant that belongs to the class of halogen-free chemicals. This
is the most popular refrigerant used in chiller plants.
What is a refrigerant chiller?
A chiller uses a vapor compression mechanical refrigeration system that connects to the
process water system through a device called an evaporator. Refrigerant circulates through an
evaporator, compressor, condenser and expansion device of a chiller. The refrigerant returns to a
liquid state at the condenser.
What is HVAC used for?
HVAC systems are used for moving air between indoor and outdoor areas, along with heating
and cooling both residential and commercial buildings. They are the systems that keep you warm
and cozy in the winter and feeling cool and fresh in the summer.
Which refrigerant is used in ice plant?
Liquid ammonia acts as a refrigerant in ice plants where evaporation of a liquid needs heat
energy. When liquid ammonia vaporizes, it absorbs large quantities of heat without changing its
temperature. For these reasons, ammonia is widely used as a refrigerant.
Is chilled water a refrigerant?
It is used as a refrigerant to remove heat from the building. The chilled water circulates through
a chilled water loop and through coils located in air handlers. Chilled water systems include other
HVAC equipment designed to exchange heat such as computer room air conditioners.
What is the difference between HVAC and chiller?
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Industrial chillers are built to handle the cooling of various manufacturing processes (brewery
cooling, hydroponic cooling, plastics cooling) directly. Conventional HVACs are built to regulate
the environmental temperatures within designated spaces.
Why secondary refrigerant is used in ice plant?
Secondary refrigerants are usually liquids, and are used to transfer heat from the substance
being cooled to a heat exchanger where the heat is absorbed by a primary refrigerant. ...
Large refrigeration plants often use secondary refrigerants to transport the cooling capacity from
the plant room to the point of use.
Why liquid ammonia is used as a refrigerant?
Liquid ammonia takes a lot of energy to vaporize. This heat is taken from the surrounding bodies
which are consequently cooled down. Thus it is used as a refrigerant in ice plant.
Where is primary and secondary refrigerant used?
When used in compression or absorption systems, these fluids provide refrigeration by
undergoing a phase change process in the evaporator. As the name implies, secondary refrigerants
are those liquids, which are used for transporting thermal energy from one location to other.
Which method is used for cooling is used in ice plant?
Brine solution takes heat from water in secondary circuit and delivers the heat to ammonia in
primary circuit. Thus, the indirect method of cooling is used in ice plant.
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