deisgned topics under refrigeration and air conditioning system

1. REFRIGERATION & AIR CONDITIONING SYSTEM
Topic: Introduction to basic refrigeration cycle
Week 1-6
Bello .A. A NCE(Tech), BSc(Ed), MSc(Ed)

2. Learning Outcomes:
At the end of this lesson, learners should be able to:
 understand the concept of basic refrigeration cycle,
 list the four key components in a basic refrigeration cycle,
 identify and state the functions of each component,
 analyze the basic operation of refrigeration cycle.

3. Understanding the Refrigeration cycle
 The refrigeration cycle basically involves the movement of refrigerant
from one place to the next and in different forms with the ultimate goal
of pulling down temperatures whether in a cabinet, counter or even
cold room format.
 The refrigeration cycle starts and ends with the compressor. The
refrigerant flows into the Compressor where it is compressed and
pressurized. At this point, the refrigerant is a hot gas. The refrigerant is
then pushed to the Condenser which turns the vapour into liquid and
absorbs some of the heat. The refrigerant then proceeds to
the Expansion Valve where it expands, losing pressure and heat.

4. Understanding the Refrigeration cycle
 The refrigerant coming out of the expansion valve is cold
and slow due to the loss of pressure. It enters
the Evaporator in a liquid state where the exchange of heat
takes place thus cooling the load inside the refrigerator. As
the gas cools down the load, it absorbs the heat which turns
it into a gas. The gas is then pushed back into
the Compressor where it can start the cycle again.
 During the refrigeration cycle, a build-up of ice around the
evaporator may occur. Both commercial fridges and freezers
will combat this build-up with some form of defrost system.

5. Components of a basic refrigeration cycle

6. Compressor

7. Condenser

8. Metering devices

9. Metering devices:

10. Evaporator

11. Refrigeration Cycle Recap

12. Basic refrigeration cycle

13. Animation of refrigeration components

14. Evaluation (Assessment)
 What do you understand by the concept ‘basic
refrigeration’?
 List the four key components of a basic refrigeration
cycle
 State the functions of each component
 Analyze the operation of a basic refrigeration cycle

15. Assignment
 Draw a neat diagram of a basic refrigeration cycle and
analyze how the process works.

16. Topic: Introduction to Evaporator
Learning Outcomes:
By the end of this lesson, learners should be able to:
 define evaporator,
 State the function of an evaporator,
 Mention the types of evaporator
 Differentiate the various types of evaporator
constructions

17. What is an Evaporator?
An evaporator is an important component together with
other major components in a refrigeration and air
conditioning system such as compressor, condenser and
expansion device.

18. What refrigeration evaporator looks
like

19. How an evaporator works
 This is the part of the refrigeration system that is doing
the actual cooling. Because its function is to absorb
heat into the refrigeration system (from where you
don't want it), the evaporator is placed in the area to
be cooled. The refrigerant is let into and measured by a
flow control device, and eventually released to the
compressor. The evaporator consists of finned tubes,
which absorbs heat from the air blown through a coil
by a fan.

20. Evaporators

21. Operation of an evaporator

22. Diagram showing heat flowing in from the region to be
cooled inside the evaporator

23. There are two types of evaporator:
 Forced Convection Type uses a fan or pump to
force the liquid being cooled over the evaporator.
 Natural Convection Type has the liquid being
cooled flows naturally to the evap. due to the
density differences of the chilled and warm liquid.
TYPES OF EVAPORATORS

24. Types of evaporator (continuation)
Different types of evaporators are used in different
types of refrigeration applications and accordingly
they have different designs. The evaporators can be
classified in various ways depending on the
construction of the evaporator, the method of
feeding the refrigerant, the direction of circulation
of the air around the evaporator, etc. Here we have
classified the evaporators based on their
construction.

25. Classification of the Evaporators Based on the
Construction
 The evaporators used for the refrigeration and the
air conditioning applications have different types of
construction depending on the application. Based
on their construction the various types of
evaporators are:
 Bare Tube Evaporators
 Plate Type of Evaporators
 Finned Evaporators
 Shell and Tube types of Evaporators

26. Bare Tube Evaporators
The bare tube evaporators are made up of copper tubing or steel
pipes. The copper tubing is used for small evaporators where the
refrigerant other than ammonia is used, while the steel pipes are used
with the large evaporators where ammonia is used as the refrigerant.
The bare tube evaporator comprises of several turns of the tubing,
though most commonly flat zigzag and oval trombone are the most
common shapes. The bare tube evaporators are usually used for
liquid chilling. In the blast cooling and the freezing operations the
atmospheric air flows over the bare tube evaporator and the chilled
air leaving it used for the cooling purposes. The bare tube
evaporators are used in very few applications, however the bare tube
evaporators fitted with the fins, called as finned evaporators are used
very commonly.

27. Bare tube evaporator

28. Plate Type of Evaporators
 In the plate type of evaporators the coil usually made up of
copper or aluminum is embedded in the plate so as so to
form a flat looking surface. Externally the plate type of
evaporator looks like a single plate, but inside it there are
several turns of the metal tubing through which the
refrigerant flows. The advantage of the plate type of
evaporators is that they are more rigid as the external plate
provides lots of safety. The external plate also helps
increasing the heat transfer from the metal tubing to the
substance to be chilled. Further, the plate type of
evaporators are easy to clean and can be manufactured
cheaply.

29. Plate type of evaporator

30. Finned Evaporators
 The finned evaporators are the bare tube type of
evaporators covered with the fins. When the fluid (air or
water) to be chilled flows over the bare tube evaporator lots
of cooling effect from the refrigerant goes wasted since
there is less surface for the transfer of heat from the fluid to
the refrigerant. The fluid tends to move between the open
spaces of the tubing and does not come in contact with the
surface of the coil, thus the bare tube evaporators are less
effective. The fins on the external surface of the bare tube
evaporators increases the contact surface of the of the
metallic tubing with the fluid and increase the heat
transfer rate, thus the finned evaporators are more effective
than the bare tube evaporators.

31. Finned Evaporators

32. Shell and Tube types of Evaporators
 The shell and tube types of evaporators are used in the large
refrigeration and central air conditioning systems. The
evaporators in these systems are commonly known as the
chillers. The chillers comprise of large number of the tubes that
are inserted inside the drum or the shell. Depending on the
direction of the flow of the refrigerant in the shell and tube type
of chillers, they are classified into two types: dry expansion type
and flooded type of chillers. In dry expansion chillers the
refrigerant flows along the tube side and the fluid to be chilled
flows along the shell side. The flow of the refrigerant to these
chillers is controlled by the expansion valve. In case of the
flooded type of evaporators the refrigerant flows along the shell
side and fluid to be chilled flows along the tube. In these chillers
the level of the refrigerant is kept constant by the float valve that
acts as the expansion valve also.

33. Shell and Tube types of Evaporators

34. Evaluation (Assessment)
 What is the purpose of an evaporator in refrigeration
system?
 Mention the types of evaporator
 Differentiate between the finned type of evaporator and
plate type of evaporator construction
 Which of the construction is most suitable for commercial
use and state why?

35. Assignment
 Draw neatly a finned construction type of evaporator
to its difference from plate construction type of
evaporator

36. Learning outcomes:
By the end of this lesson, learners should be able to:
 understand the concept of repair and maintenance
 analyze the steps to be taken when repairing a refrigeration
system

37. Repair and maintenance of an evaporator
 Repair
A refrigerator uses refrigerant evaporation to cool air
blown across an evaporator coil. A compressor pulls the
refrigerant vapor back and condenses it to a high-pressure
high-temperature vapor. This vapor cools and condenses
back to a liquid as it passes through a fan cooled
condensing coil. Then high pressure liquid travels back to
an orifice at the start of the evaporator coil where the
process starts over. Residential refrigerators should have
the freezer set at 0 degrees Fahrenheit and the
refrigerator set at 37 degrees Fahrenheit.

38. Steps
Step 1
 Remove the panel covering the evaporator coil. This panel, found in the
freezer compartment, will need either a Phillips screwdriver or a 1/4-
inch nut driver to remove the holding screws.
Step 2
 Remove the hold-down clamps on the evaporator coil with either a
Phillips screwdriver or a 1/4-inch nut driver. Hold-down clamps prevent
the coil from vibrating when the refrigerator runs and screw directly to
the refrigerator body.
Step 3
 Find the leaks in the evaporator coil. Look for rubbed areas, oily spots
and heavily oxidized areas. Pay extra attention to the bends in the coil
tubing.

39. Steps (continuation)
Step 4
 Clean the leak area with sand paper. Completely remove all loose
material and debris, especially refrigerant oil. Avoid pushing debris into
the hole. Wipe all sanding dust off of the leak area with a clean rag.
Step 5
 Connect a vacuum pump to the refrigerator's refrigerant service valve,
found near the compressor. The service valve looks like a over-sized
valve found on a tire, except its made of metal. A hand-held automotive
vacuum pump will work on a refrigerator.
Step 6
 Pull a vacuum with the vacuum pump. Try to create a vacuum of at least
10 inches of mercury. Large leaks in the evaporator coil may prevent
this. A vacuum will pull the patch into the leak, creating a better bond.

40. Steps (continuation)
 Step 7
 Knead a 1 inch section of epoxy putty with your hands. Continue to mix
the putty until it has a uniform color and texture.
 Step 8
 Press the epoxy putty over the leaking area. Wrap the putty around the
pipe. The patch should extend about 1/2-inch on each side of the leak.
Finish applying the epoxy putty within 3 minutes of mixing.
 Step 9
 Check the vacuum gauge. Pull a 10 inches of mercury vacuum on the
refrigerant system. Disconnect the vacuum pump.
 Step 10
 Check the vacuum reading after 24 hours. A leak still exists if the
vacuum reading has dropped. Perform a leak test and repair as
necessary.

41. Maintenance
 1. Prevent the dreaded emergency breakdown.
 2. Avoid mold and contaminated ice.
 3. Reduce energy bills.
 4. Extend the life of your commercial refrigerators and
freezers.
 5. Take good care of your commercial refrigeration
equipment, and it will take good care of you.
 6. Waste not, want not.

42. Evaluation (Assessment)
 define maintenance and repair in your understanding
 analyze the steps to be when repairing an evaporator

43. Assignment
 What recommendation would you give to someone
who tells you his freezer is not freezing as expected?

44. The End