Module No. 14 : Refrigeration Unit No. 2- Refrigeration trainer Page 1/11
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UNITS IN THIS COURSE
UNIT 1 INTRODUCTION TO REFRIGERATION
UNIT 2 THE REFRIGERATION TRAINER
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TABLE OF CONTENTS
Para Page
2.0 OBJECTIVES 3
2.1 INTRODUCTION 4
2.2 GENERAL DESCRIPTION OF THE REFRIGERATION TRAINER 4
2.3 THERMAL EXPANSION VALVE 7
2.4 OPERATION 8
2, 4 1 Pre-start Checks 8
2.4.2 Start-up 8
2.4.3 Running Checks 9
2.4.4 Readings 9
2.4.5 Changeover to TEV 10
2.4.6 Changing back to MEV 10
2.4.7 Shutting Down 10
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2.0 OBJECTIVES
The trainee will be able to:
Identify and explain the use and operation of the refrigeration trainer components.
Explain the operating sequence of the refrigeration trainer and demonstrate the ability to perform pre-start, start and operational checks.
Demonstrate the ability to control refrigerant flow rate and temperature control on the refrigeration trainer.
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2.1 INTRODUCTION
This is Unit 2 of the Operator Training Course OP1 9, Refrigeration, In Unit 2, The Refrigeration Trainer, you will see the refrigeration cycle at work and develop an understanding of how it can remove heat from an area. You will also learn to control the refrigeration cycle by use of the Manual Expansion Valve (MEV) and the Thermostatic Expansion Valve (TEV ).
2.2 GENERAL DESCRIPTION OF THE REFRIGERATION TRAINER
1 The refrigeration trainer, made by the Hampden 'Engineering Corp., is a panel-mounted device holding the various components of a simple refrigeration system. Some of the components are transparent so that you can easily follow the flow of refrigerant through the system during operation, All the components are clearly labeled for easy identification. The components are the same ones that are used working refrigeration units, although they are much smaller,
The compressor, evaporator fan and condenser fan are each driven by an electric motor and started and stopped from a bank of four control switches mounted on the main panel. One of the switches is not used. The switch panel is shown in Figure 2-1.
Figure 2-1. Control Switches
Figure 2-2 shows the layout of the refrigeration trainer.
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Figure 2-2. Refrigeration Trainer Layout
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The refrigeration trainer has a total of 7 valves, 5 temperature measurement points and 2 pressure gauges. These are all numbered and have the following functions.
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2.3 THERMAL EXPANSION VALVE
Figure 2-3 Thermal Expansion Valve
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In a large refrigeration System the Thermal Expansion Valve (TEV) lets only the correct amount of liquid refrigerant into the evaporator. Because the refrigeration trainer is only small the TEV fitted on the trainer works only fully open or fully closed.
The refrigerant temperature at the evaporator outlet is monitored by a sealed sensing bulb connected to the TEV by a capillary tube. The bulb and tube are filled with a liquid/vapour mixture.
Figure 2-3 shows that there are two pressures or forces which affect the TEV. One of the pressures is from the calibrated spring, which pushes upward on the diaphragm to close the valve. The tension of the spring is usually set at The factory. The other pressure is from the temperature sensing bulb. It pushes downward on the top of the diaphragm to open The valve. The higher the evaporator outlet temperature, the more the valve opens. The more the valve opens, the more refrigerant passes to the evaporator and The more cooling takes place.
2.4 OPERATION
2.4.1 Pre-start Checks
1. . Make sure that the three electric switches are all in the OFF position.
2. Check that the trainer is plugged into an electrical supply and the supply is switched on.
3. Make sure valves V1, V2, V3, V4, V5 and the MEV are all closed.
4. Look at the HP receiver and check that there is liquid refrigerant in it.
5. Take a set of pre-start readings at all the temperature points (T1 to T5) and at the two pressure points P1 1 and P1 2. Enter your readings on the Log Sheet at the end of this Unit.
2.4.2 Start-up
1. Open condenser outlet stop valve V2.
2. Open HP receiver outlet stop valve V3.
3. Check that the MEV is closed.
4. Check that TEV isolation valve V4 is closed.
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5. Open evaporator outlet stop valve V5.
6. Make sure that the HP cut out switch is working correctly by starting the com- pressor with the compressor discharge valve (V 1 ) closed. When the compressor cuts out, switch the electrical supply to OFF at the electric switch panel. The HP cut out switch will reset automatically.
7. Open compressor discharge stop valve V1 .
8. At the switch panel Start the evaporator fan by moving the evaporator fan switch to the ON position. Look at the evaporator fan and make sure it is running.
9. At the switch panel start the condenser fan by moving the condenser fan switch to the ON position. Look at the condenser fan and make sure it is running.
10 .At the switch panel start the compressor by moving the compressor switch to the ON position. You will hear the compressor start to run.
11 Look at the flowmeter and slowly start to open the MEV.
12. Continue to slowly open the MEV until the flowmeter indicates a flow of 40.
The refrigeration trainer is now operational.
2.4.3 Running Checks
1. . Check the flow of refrigerant throughout the system. In particular, look at the sight glass and make sure the refrigerant at this point is a gas with no trace of liquid.
2.4.4 Readings
Make a note of the following readings on the Log Sheet at the end of this Unit.
1. Flowmeter.
2. Compressor discharge pressure (PI 1 ) in psig.
3. Compressor suction pressure (PI 2) in inches of mercury (in Hg).
4. Temperatures at points TI to T5.
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2.4.5 Changeover to TEV
The T EV can be brought into service without shutting down the compressor as follows.
1. . Slowly open the TEV isolation valve V4.
2. When V4 i's fully open, close the MEV.
The refrigeration trainer is now running under the control of
2.4.6 Changing back to MEV
1. I Open the MEV two turns.
2. Close the TEV Isolation wave V4.
3. Set up the flow to read 40 on the flow meter using the MEV.
2.4.7. Shutting Down
There are two levels of shutdown called short term shutdown and Iong term shutdown. A short term shutdown is a shutdown for less than one hour. A long term shutdown is a shutdown of more than one hour.
Short Term Shutdown
1. .Stop the compressor by moving the compressor switch on the switch panel to the OFF Position.
2. Close the compressor discharge stop valve V1 .
Long Term Shutdown
1. . Stop the compressor by moving the compressor switch on the switch panel to the OFF position.
2. Close all five valves on the refrigeration trainer.
3. Stop the condenser fan and the evaporator fan by moving the condenser fan switch and the evaporator fan switch on the switch panel to the OFF position
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LOG SHEET
READINGS
STATE OF REFRIGERANT
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