The Refrigeration Cycle - Lab- · PDF fileUsing the values in Table 15, draw the refrigeration cycle on a pressure-enthalpy diagram included at the end of this job sheet. Be sure to

© Festo Didactic 88271-20 97

In this job sheet, you will plot the refrigeration cycle on a pressure-enthalpy diagram using pressures and temperatures measured on your training system. You will also calculate the coefficient of performance (COP) of your refrigeration system in heating mode.

In the following steps, you will take the different temperature and pressure readings necessary to trace the compression cycle on a pressure-enthalpy diagram. In heating mode, you will measure the temperature at the inlet and outlet of the compressor, the temperature at the outlet of the forced-air evaporator, and the pressure on both sides of the compressor.

1. Perform the following settings on your training system:

Main power switch ............................................................................. Off

Thermostat ........................................................................ Heating mode

Temperature set point ....................... 5°C (9°F) above room temperature

Valve HV-1 ...................................................................................... Open

Valve HV-2 ...................................................................................... Open

Valve HV-3 ...................................................................................... Open

Valve HV-4 ...................................................................................... Open

Valve HV-5 ...................................................................................... Open

Valve HV-6 ...................................................................................... Open

Valve HV-7 ...................................................................................... Open

Valve HV-8 ................................................................................... Closed

Valve HV-9 ........................................................ No adjustments required

Valve HV-10 ................................................ Handle in horizontal position

Valve HV-11 .................................................................................... Open

Valve HV-12 .................................................................................... Open

Valve HV-13 .................................................................................... Open

Pressure gauge PI-1 selector switch ............................................... Right

Pressure gauge PI-2 selector switch ............................................... Right

Desuperheater On/Off switch ............................................................ Off

Priming tank three-way valves .....................................................

Air distribution register .................................................................... Open

The Refrigeration Cycle

Job Sheet 4

OBJECTIVES

PROCEDURE

Job Sheet 4 – The Refrigeration Cycle

98 © Festo Didactic 88271-20

2. Use the next figure to compare the refrigeration cycle with the heat pump diagram and determine which thermocouples are going to be read during this exercise.

Figure 69. Compression cycle.

3. Set the main power switch to On.



4. Measure the temperatures and pressures every four minutes after the compressor indicator light turns on. Complete Table 14.

Table 14. Compression cycle.

Time (min)

Temperature Pressure

Compressor inlet

( )

Compressor outlet

( )

Evaporator outlet

( ) LP HP

0

4

8

12

16

5. Set the thermostat operating mode to Off.

6. Using Figure 70, plot a graph showing TC-8, TC-9, and TC-11 temperatures as a function of time.

Figure 70. Temperature at various locations as a function of time in heating mode.

0

1

2

3

4

5

6

7

8

9

10

0 4 8 12 16

Time (min)

Tem

pera

ture



7. Using Figure 71, plot a graph showing LP and HP pressures as a function of time.

Figure 71. Pressure as a function of time in heating mode.

8. Using your graphs as a reference, observe a pressure and temperature stabilization after a transitional period of about ten minutes.

Using Table 14, copy your results taken after 16 minutes of operation into Table 15. Convert your pressure readings to absolute pressure values.

a The standard atmospheric pressure at sea level is 101.3 kPa (14.7 psia).

Table 15. Temperature and pressure after 16 minutes of operation.

Time (min)

Temperature Pressure

Gauge Absolute

Compressorinlet

( )

Compressoroutlet ( )

Evaporatoroutlet

( ) LP HP LP HP

16

9. Using the values in Table 15, draw the refrigeration cycle on a pressure-enthalpy diagram included at the end of this job sheet. Be sure to use the pressure-enthalpy diagram that corresponds to the system of units that you are using.

10. Identify the refrigerant conditions for points A to H shown in Figure 72. Label the points as subcooled, superheated, saturated liquid, saturated mixture, saturated vapor. Fill in the corresponding column in Table 16.

Find the enthalpy value corresponding to the different refrigerant conditions identified in Figure 72 and complete Table 16.

0

1

2

3

4

5

6

7

8

9

10

0 4 8 12 16

Pre

ssu

re

Time (min)



Figure 72. Pressure-enthalpy diagram.

Table 16. Refrigerant condition and enthalpy.

Point Refrigerant condition Enthalpy

A

B

C

D

E

F

G

H

11. Using your results from Table 16, complete Table 17.

Table 17. Refrigeration process.

Process name Equation

Refrigeration effect

Low-pressure superheat

Heat of compression

High-pressure superheat

Heat rejected by condenser

Subcooling

Expansion

12. Refrigeration devices are rated with a number called coefficient of performance (COP). The COP is the ratio of the refrigeration effect divided by the compression work.

(4-2)



Using the results from Equation (4-2), calculate the COP for your training system.

COP of your training system in heating mode: _____

13. If you had to select a heat pump based solely on the COP, which one would you select? Would you select the heat pump with the lowest or highest COP? Why?



14. Set the main power switch to Off.

Figure 73. Pressure-enthalpy diagram, SI units.



Figure 74. Pressure-enthalpy diagram, US customary units.

Name: _______________________________ Date: ____________________

Instructor's approval: ______________________________________________

The Refrigeration Cycle - Lab- · PDF fileUsing the values in Table 15, draw the refrigeration cycle on a pressure-enthalpy diagram included at the end of this job sheet. Be sure to

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