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Copyright © 2002

ESCO Press

All rights reserved. Except as permitted under

The United States Copyright Act of 1976, no part

of this publication may be reproduced or distributed

In any form or means, or stored in a database

or retrieval system, without the prior written

permission of the publisher, ESCO Press.

ISBN 1-930044-13-5

This book was written as a general guide The authors and publisher have neither liability

nor can they be responsible to any person or entity for any misunderstanding, misuse, or

misapplication that would cause loss or damage f any kind, including loss of rights, material,

or personal injury, alleged to be caused directly or indirectly by the information contained in

this book.

Cover photo supplied by Honeywell International.

This image may not be reproduced ith ut written authorization from Honeywell. Genetron ® and AZ 20 ® are registered trademarks of Hon

eywell. Honeywell has no revi wed the material contained herein, and assumes no liability or responsibility for its use.

Printed in the United States of America

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Copyright © 2002

ESCO Press

All rights reserved. Except as permitted under

The United States Copyright Act of 1976, no part

of this publication may be reproduced or distributed

In any form or means, or stored in a database

or retrieval system, without the prior written

permission of the publisher, ESCO Press.

ISBN 1-930044-13-5

This book was written as a general guide The authors and publisher have neither liability




this book.

Cover photo supplied by Honeywell International.




7 6 5 4 3 2 1 Cop

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Press

Basic

Refrigeration and Charging Procedures

John Tomczyk

Mount Prospect, Illinois

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Table of Contents

Refrigerant Pressures States and Conditions

C ns n P ssur 1

Ev por n P e sur 1

R f ran St s n Cond ons 3

Vapor Pressures 3

Superheat 4

Subcooling 4

Basic Re ra ion Sys m 4

Compressor 5

Discharge Line 6

Condenser 6

Receiver 8

Liquid Line 8

Metering Device 8

Evaporator 8

Suction Line 10

Ap licati P e su s, a a Condit ns 11

Compressor Discharge 11

Condense Inlet 11

100% Satura ed Vapor Point 13

100% Saturated Liquid Point 13

Condenser Outlet 13

TXV Inlet 13

Middle of Evaporator 13

Saturated Vapor Point 14

Evaporator Outlet 14

Compressor Inlet 14

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Table of Contents

Subcooling and Superheating

Li u Su c 15

S b o lin Ca o s 15

Condenser Subcooling 15

Total Subcooling 19

S cooo N d d o Pr v n L q d L n a h 21

Pr s r Dr p 21

Friction Pressure Losses 21

Static Pressure Losses 23

How Much Su c o n s N d 24

Li u ressur Amp ic i n And Su a es o 26

Floating Head Pressures and LPA Advantages 30

Superheat Suppression 31

LPA/Superheat Suppression with Subcooling/Reheat Coil 32

Enviro a d M Re nt Con o Sy m 32

Principles of Operation 32

Determining the SPR Valve Setting 37

S p rh 38

Evaporato Superheat 38

Total Superheat 40

Metering Devices

C p ry T es 45

Sizing 46

High Heat Loads 49

Low Heat Loads 49

Service 49

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Table of Contents

e m s a i Expa sion Valve 52

Remote Bulb Pressure 54

Evaporator Pressure and Spring Pressure 56

Additional Pressure 57

Color Codes 57

Special Application TXVs 57

Externally Equalized Valves 58

Maximum Operating Pressure 58

Balanced Port TXVs 59

Selection Procedures 59

Au omat Expansi n Va v s AXVs) 64

System Charge

C ar in TXV/ e v r/S as R f o Sy t m 67

Charging Rules 68

Char in C p ary u Or Fix d Or f R ri a io Sy em 70

Charging from a Vacuum 70

C ar ing C p ary u o x d O c A Con on ng Sy m 73

Measuring Duct Velocity 79

Superheat Charging Curves 80

Superhea Curve Theory 81

Charging Capillary Tube — Cooling Mode Only 82

Superheat Method — Capillary Tube System 85 Copyri

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Refrigerant Pressures, States, and Conditions 1

Refrigerant Pressures,States, and Conditions

CHAPTERO N E

The typical vapor compression refrigerationsystem shown in Figure 1-1 can be divided intotwo pressures: condensing (high side) andevaporating (low side). These pressures are di-vided or separated in the system by the com-pressor discharge valve and the metering de-vice. Listed below are field service terms oftenused to describe these pressures:

Condensing EvaporatingPressure Pressure

High side pressure Low side p essureHead pressure Suction pressureDischarge pressure Back press re

CONDENSING PRESSURE

The condensing pres ure is the pressure atwhich the refrigeran changes state from a va-por to a liquid. This phase change is referred toas condensation. This pressure can be readdirect y from a pressure gauge connected any-where between the compressor discharge valveand the entrance to the metering device, as-suming there is negligible pressure drop. Inreality, line and valve friction and the weightof the liquid itself cause pressure drops fromthe compressor discharge to the metering de-vice. If a true condensing pressure is needed,the technician must measure the pressure as

close to the condens r as possible to avoid thesepressure drops This pressure is usually mea-sured on smaller systems near the compressorvalves, Figure 1-2. On small systems, it is notcritical where a technician places the pressuregauge (as long as it is on the high side of thesystem), because pressure drops are negligible.The pressure gauge reads the same no matterwhere it is on the high side of the system if lineand valve losses are negligible.

EVAPORATING PRESSURE

The evaporating pressure is the pressure atwhich the refrigerant changes state from a liq-uid to a vapor. This phase change is referred toas evaporation or vaporizing. A pressure gaugeplaced anywhere between the metering deviceoutlet and the compressor (including compres-sor crankcase) will read the evaporating pres-sure. Again, negligible pressure drops are as-sumed. In reality, there will be line and valvepressure drops as the refrigerant travels throughthe evaporator and suction line. The technicianmust measure the pressure as close to the evapo-rator as possible to get a true evaporating pres-sure. On small systems where pressure dropsare negligible, this pressure is usually measurednear the compressor (see Figure 1-2). Gaugeplacement on small systems is usually not criti-cal as long as it is placed on the low side of therefrigeration system, because the refrigerant

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2 Troubleshooting and Servicing Modern Air Conditioning and Refrigeration Systems

Figure 1-1. Typical compression refrigeration system

vapor pressure acts equally in all directions. Ifline and valve pressure drops become substan-tial, gauge placement becomes critical. In largermore sophisticated systems, gauge placementis more critical because of associated line and

valve pressure losses. If the system has signifi-cant line and valve pressure losses, the techni-cian must place the gauge as close as possibleto the component that requires a pressurereading.

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saturated vapor, respectively. Saturation occursin both the evaporator and condenser. At satu-ration, the liquid experiences its maximum tem-perature for that pressure, and the vapor expe-riences its minimum temperature. However,both liquid and vapor are at the same tempera-ture for a given pressure when saturation oc-curs. Saturation temperatures vary with differ-ent refrigerants and pressures. All refrigerantshave different vapor pressures. It is vapor pres-sure that is measured with a gauge.

Vapor Pressure

Vapor pressure is the pressure exerted on asaturated liquid. Any time saturated liquid andvapor are together (as in the condenser andevaporator), vapor pressure is generated. Va-por pressure acts equally in all directions andaffects the entire low or high side of a refrig-eration system.

As pressure increases, saturation temperatureincreases; as pressure decreases, saturation tem-perature decreases. Only at saturation are therepressure/temperature relationships for refriger-ants. Table 1-1 shows the pressure/temperaturerelationship at saturation for refrigerant 134a(R-134a). If one attempts to raise the tempera-ture of a saturated liquid above its saturationtemperature, vaporization of the liquid willoccur. If one attempts to lower the temperatureof a saturated vapor below its saturation tem-perature, condensation will occur. Both vapor-ization and condensation occur in the evapora-tor and condenser, respectively.

The heat energy that causes a liquid refrigerantto change to a vapor at a constant saturationtemperature for a given pressure is referred toas latent heat. Latent heat is the heat energythat causes a substance to change state withoutchanging the temperature of the substance.Vaporization and condensation are examples ofa latent heat process.

Figure 1-2. Semi-hermetic compressor showing pressure

access valves (Courtesy, Danfoss Automatic Controls,

Division of Danfoss, Inc.)

REFRIGERANT STATES AND CONDITIONS

Modern refrigerants exist either in the vapor orliquid state. Refrigerants have such low freez-ing points that they are rarely in the frozen orsolid state. Refrigerants can co-exist as vaporand liquid as long as conditions are right. Boththe evaporator and condenser house liquid andvapor refrigerant simultaneously if the systemis operating properly. Refrigerant liquid andvapor can exist in both the high or low pres-sure sides of the refrigeration system.

Along with refrigerant pressures and states arerefrigerant conditions. Refrigerant conditionscan be saturated, superheated, or subcooled.

SaturationSaturation is usually defined as a temperature.The saturation temperature is the temperatureat which a fluid changes from liquid to vaporor vapor to liquid. At saturation temperature,liquid and vapor are called saturated liquid and

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Temperature Pressure Temperature Pressure

(°F) (psig) (°F) (psig)

-10 1.8

-9 2.2

-8 2.6 30 25.6

-7 3.0 31 26.4

-6 3.5 32 27.3

-5 3.9 33 28.1

-4 4.4 34 29.0

-3 4.8 35 29.9

-2 5.3 40 34.5

-1 5.8 45 39.5

0 6.2 50 44.9

1 6.7 55 50.7

2 7.2 60 56.9

3 7.8 65 63.5

4 8.3 70 70.7

5 8.8 75 78.3

6 9.3 80 86.4

7 9.9 85 95.0

8 10.5 90 104.2

9 11.0 95 113.9

10 11.6 100 124.3

11 12.2 105 135.2

12 12.8 110 146.8

13 13.4 115 159.0

14 14.0 120 171.9

15 14.7 125 185.5

16 15.3 130 199.8

17 16.0 135 214.8

18 16.7

19 17.3

20 18.0

21 18.7

22 19.4

23 20.2

24 20.9

25 21.7

26 22.4

27 23.2

28 24.0

29 24.8

Table 1-1. R-134a saturated vapor/liquid pressure/

temperature chart

words, all of the liquid must be vaporized forsuperheating to occur; the vapor must be re-moved from contact with the vaporizing liquid.Once all the liquid has been vaporized at itssaturation temperature, any addition of heatcauses the 100% saturated vapor to start super-heating. This addition of heat causes the vaporto increase in temperature and gain sensibleheat. Sensible heat is the heat energy that causesa change in the temperature of a substance. Theheat energy that superheats vapor and increasesits temperature is sensible heat energy. Super-heating is a sensible heat process. Superheatedvapor occurs in the evaporator, suction line,and compressor.

SubcoolingSubcooling always refers to a liquid at a tem-perature below its saturation temperature for agiven pressure. Once all of the vapor changesstate to 100% saturated liquid, further removalof heat will cause the 100% liquid to drop intemperature or lose sensible heat. Subcooledliquid results. Subcooling can occur in both thecondenser and liquid line and is a sensible heatprocess. Another method of subcooling liquid,

called liquid pressure amplificationTM, is cov-ered in Chapter Two. This method increasesthe pressure on subcooled liquid, causing it tobe subcooled even more. This creates a liquidwith a temperature below its new saturationtemperature for the new higher pressure.

A thorough understanding of pressures, states,and conditions of the basic refrigeration sys-tem enables the service technician to be a goodsystematic troubleshooter. It is not until thenthat a service technician should even attemptsystematic troubleshooting.

BASIC REFRIGERATION SYSTEM

Figure 1-3 illustrates a basic refrigeration sys-tem. The basic components of this system arethe compressor, discharge line, condenser, re-ceiver, liquid line, metering device, evaporator,and suction line. Mastering the function of eachindividual component can assist the refrigera-

SuperheatSuperheat always refers to a vapor. A super-heated vapor is any vapor that is above itssaturation temperature for a given pressure. Inorder for vapor to be superheated, it must havereached its 100% saturated vapor point. In other

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Figure 1-3. Basic refrigeration system

tion technician with analytical troubleshootingskills, saving time and money for both techni-cian and customer.

CompressorOne of the main functions of the compressor isto circulate refrigerant. Without the compres-

sor as a refrigerant pump, refrigerant could notreach other system components to perform itsheat transfer functions. The compressor alsoseparates the high pressure from the low pres-sure side of the refrigeration system. A differ-ence in pressure is mandatory for fluid (gas orliquid) flow, and there could be no refrigerantflow without this pressure separation.

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Another function of the compressor is to el-evate or raise the temperature of the refrigerantvapor above the ambient (surrounding) tempera-ture. This is accomplished by adding work, orheat of compression, to the refrigerant vaporduring the compression cycle. The pressure ofthe refrigerant is raised, as well as its tempera-ture. By elevating the refrigerant temperatureabove the ambient temperature, heat absorbedin the evaporator and suction line, and any heatof compression generated in the compressionstroke can be rejected to this lower temperatureambient. Most of the heat is rejected in thedischarge line and the condenser. Remember,heat flows from hot to cold, and there must bea temperature difference for any heat transferto take place. The temperature rise of the re-frigerant during the compression stroke is ameasure of the increased internal kinetic en-ergy added by the compressor.

The compressor also compresses the refriger-ant vapors, which increases vapor density. Thisincrease in density helps pack the refrigerantgas molecules together, which helps in the con-densation or liquification of the refrigerant gasmolecules in the condenser once the rightamount of heat is rejected to the ambient. Thecompression of the vapors during the compres-sion stroke is actually preparing the vapors forcondensation or liquification.

Discharge LineOne function of the discharge line is to carrythe high pressure superheated vapor from thecompressor discharge valve to the entrance ofthe condenser. The discharge line also acts asa desuperheater, cooling the superheated va-pors that the compressor has compressed andgiving that heat up to the ambient (surround-ings). These compressed vapors contain all ofthe heat that the evaporator and suction linehave absorbed, along with the heat of compres-sion of the compression stroke. Any generatedmotor winding heat may also be contained inthe discharge line refrigerant, which is why thebeginning of the discharge line is the hottestpart of the refrigeration system. On hot dayswhen the system is under a high load and mayhave a dirty condenser, the discharge line can

reach over 400°F. By desuperheating the re-frigerant, the vapors will be cooled to the satu-ration temperature of the condenser. Once thevapors reach the condensing saturation tempera-ture for that pressure, condensation of vapor toliquid will take place as more heat is lost.

CondenserThe first passes of the condenser desuperheatthe discharge line gases. This prepares the highpressure superheated vapors coming from thedischarge line for condensation, or the phasechange from gas to liquid. Remember, thesesuperheated gases must lose all of their super-heat before reaching the condensing tempera-ture for a certain condensing pressure. Oncethe initial passes of the condenser have rejectedenough superheat and the condensing tempera-ture or saturation temperature has been reached,these gases are referred to as 100% saturatedvapor. The refrigerant is then said to havereached the 100% saturated vapor point, Figure1-4.

One of the main functions of the condenser isto condense the refrigerant vapor to liquid.Condensing is system dependent and usuallytakes place in the lower two-thirds of the con-denser. Once the saturation or condensing tem-perature is reached in the condenser and therefrigerant gas has reached 100% saturatedvapor, condensation can take place if more heatis removed. As more heat is taken away fromthe 100% saturated vapor, it will force the vaporto become a liquid or to condense. When con-densing, the vapor will gradually phase changeto liquid until 100% liquid is all that remains.This phase change, or change of state, is anexample of a latent heat rejection process, asthe heat removed is latent heat not sensible heat.The phase change will happen at one tempera-ture even though heat is being removed. Note:An exception to this is a near-azeotropic blendof refrigerants where there is a temperatureglide or range of temperatures when phasechanging (see Chapter Eight on blend tempera-ture glide). This one temperature is the satura-tion temperature corresponding to the satura-tion pressure in the condenser. As mentionedbefore, this pressure can be measured anywhere

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Figure 1-4. Basic refrigeration system showing 100% saturated vapor and liquid points

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on the high side of the refrigeration system aslong as line and valve pressure drops and lossesare negligible.

The last function of the condenser is to subcoolthe liquid refrigerant. Subcooling is defined asany sensible heat taken away from 100% satu-rated liquid. Technically, subcooling is definedas the difference between the measured liquidtemperature and the liquid saturation tempera-ture at a given pressure. Once the saturatedvapor in the condenser has phase changed tosaturated liquid, the 100% saturated liquid pointhas been reached. If any more heat is removed,the liquid will go through a sensible heat rejec-tion process and lose temperature as it losesheat. The liquid that is cooler than the saturatedliquid in the condenser is subcooled liquid.Subcooling is an important process, because itstarts to lower the liquid temperature to theevaporator temperature. This will reduce flashloss in the evaporator so more of the vaporiza-tion of the liquid in the evaporator can be usedfor useful cooling of the product load (seeChapter Two on the importance of liquidsubcooling).

ReceiverThe receiver acts as a surge tank. Once thesubcooled liquid exits the condenser, the re-ceiver receives and stores the liquid. The liquidlevel in the receiver varies depending onwhether the metering device is throttling openedor closed. Receivers are usually used on sys-tems in which a thermostatic expansion valve(TXV or TEV) is used as the metering device.The subcooled liquid in the receiver may loseor gain subcooling depending on the surround-ing temperature of the receiver. If the subcooledliquid is warmer than receiver surroundings, theliquid will reject heat to the surroundings andsubcool even more. If the subcooled liquid iscooler than receiver surroundings, heat will begained by the liquid and subcooling will belost.

A receiver bypass is often used to bypass liq-uid around the receiver and route it directly tothe liquid line and filter drier. This bypass pre-vents subcooled liquid from sitting in the re-

ceiver and losing its subcooling. A thermostatwith a sensing bulb on the condenser outletcontrols the bypass solenoid valve by sensingliquid temperature coming to the receiver, Fig-ure 1-5. If the liquid is subcooled to a predeter-mined temperature, it will bypass the receiverand go to the filter drier.

Liquid LineThe liquid line transports high pressuresubcooled liquid to the metering device. Intransport, the liquid may either lose or gainsubcooling depending on the surrounding tem-perature. Liquid lines may be wrapped aroundsuction lines to help them gain more subcooling,Figure 1-6. Liquid/suction line heat exchangerscan be purchased and installed in existing sys-tems to gain subcooling. The importance ofliquid subcooling will be covered more exten-sively in Chapter Two.

Metering DeviceThe metering device meters liquid refrigerantfrom the liquid line to the evaporator. Thereare several different styles and kinds of meter-ing devices on the market with different func-tions. Some metering devices control evapora-tor superheat and pressure, and some even havepressure limiting devices to protect compres-sors at heavy loads.

The metering device is a restriction that sepa-rates the high pressure side from the low pres-sure side in a refrigeration system. The com-pressor and the metering device are the twocomponents that separate pressures in a refrig-eration system. The restriction in the meteringdevice causes liquid refrigerant to flash to alower temperature in the evaporator because ofits lower pressure and temperature.

EvaporatorThe evaporator, like the condenser, acts as aheat exchanger. Heat gains from the productload and outside ambient travel through thesidewalls of the evaporator to vaporize any liq-uid refrigerant. The pressure drop through themetering device causes vaporization of some

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Basic

Refrigeration and Charging Procedures

John Tomczyk

Mount Prospect, Illinois

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John Tomczyk

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Table of Contents

Refrigerant Pressures States and Conditions

C ns n P ssur 1

Ev por n P e sur 1

R f ran St s n Cond ons 3

Vapor Pressures 3

Superheat 4

Subcooling 4

Basic Re ra ion Sys m 4

Compressor 5

Discharge Line 6

Condenser 6

Receiver 8

Liquid Line 8

Metering Device 8

Evaporator 8

Suction Line 10

Ap licati P e su s, a a Condit ns 11

Compressor Discharge 11

Condense Inlet 11

100% Satura ed Vapor Point 13

100% Saturated Liquid Point 13

Condenser Outlet 13

TXV Inlet 13

Middle of Evaporator 13

Saturated Vapor Point 14

Evaporator Outlet 14

Compressor Inlet 14

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Compressor Discharge

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Condense Inlet

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100% Satura ed Vapor Point

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Table of Contents

Subcooling and Superheating

Li u Su c 15

S b o lin Ca o s 15

Condenser Subcooling 15

Total Subcooling 19

S cooo N d d o Pr v n L q d L n a h 21

Pr s r Dr p 21

Friction Pressure Losses 21

Static Pressure Losses 23

How Much Su c o n s N d 24

Li u ressur Amp ic i n And Su a es o 26

Floating Head Pressures and LPA Advantages 30

Superheat Suppression 31

LPA/Superheat Suppression with Subcooling/Reheat Coil 32

Enviro a d M Re nt Con o Sy m 32

Principles of Operation 32

Determining the SPR Valve Setting 37

S p rh 38

Evaporato Superheat 38

Total Superheat 40

Metering Devices

C p ry T es 45

Sizing 46

High Heat Loads 49

Low Heat Loads 49

Service 49

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Principles of Operation

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Principles of Operation

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Determining the SPR Valve Setting

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Determining the SPR Valve Setting

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Evaporato Superheat

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Total Superheat

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Floating Head Pressures and LPA Advantages

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Table of Contents

e m s a i Expa sion Valve 52

Remote Bulb Pressure 54

Evaporator Pressure and Spring Pressure 56

Additional Pressure 57

Color Codes 57

Special Application TXVs 57

Externally Equalized Valves 58

Maximum Operating Pressure 58

Balanced Port TXVs 59

Selection Procedures 59

Au omat Expansi n Va v s AXVs) 64

System Charge

C ar in TXV/ e v r/S as R f o Sy t m 67

Charging Rules 68

Char in C p ary u Or Fix d Or f R ri a io Sy em 70

Charging from a Vacuum 70

C ar ing C p ary u o x d O c A Con on ng Sy m 73

Measuring Duct Velocity 79

Superheat Charging Curves 80

Superhea Curve Theory 81

Charging Capillary Tube — Cooling Mode Only 82

Superheat Method — Capillary Tube System 85 Copyri

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Measuring Duct Velocity

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Measuring Duct Velocity

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Superheat Charging Curves

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Superheat Charging Curves

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Superhea Curve Theory

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Superhea Curve Theory

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Charging Capillary Tube — Cooling Mode Only Copyri

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Charging Capillary Tube — Cooling Mode Only Copyri

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Superheat Method — Capillary Tube System Copyri

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Superheat Method — Capillary Tube System

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System Charge

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System Charge

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Refrigerant Pressures,States, and Conditions

CHAPTERO N E

The typical vapor compression refrigerationsystem shown in Figure 1-1 can be divided intotwo pressures: condensing (high side) andevaporating (low side). These pressures are di-vided or separated in the system by the com-pressor discharge valve and the metering de-vice. Listed below are field service terms oftenused to describe these pressures:

Condensing EvaporatingPressure Pressure

High side pressure Low side p essureHead pressure Suction pressureDischarge pressure Back press re

CONDENSING PRESSURE

The condensing pres ure is the pressure atwhich the refrigeran changes state from a va-por to a liquid. This phase change is referred toas condensation. This pressure can be readdirect y from a pressure gauge connected any-where between the compressor discharge valveand the entrance to the metering device, as-suming there is negligible pressure drop. Inreality, line and valve friction and the weightof the liquid itself cause pressure drops fromthe compressor discharge to the metering de-vice. If a true condensing pressure is needed,the technician must measure the pressure as

close to the condens r as possible to avoid thesepressure drops This pressure is usually mea-sured on smaller systems near the compressorvalves, Figure 1-2. On small systems, it is notcritical where a technician places the pressuregauge (as long as it is on the high side of thesystem), because pressure drops are negligible.The pressure gauge reads the same no matterwhere it is on the high side of the system if lineand valve losses are negligible.

EVAPORATING PRESSURE

The evaporating pressure is the pressure atwhich the refrigerant changes state from a liq-uid to a vapor. This phase change is referred toas evaporation or vaporizing. A pressure gaugeplaced anywhere between the metering deviceoutlet and the compressor (including compres-sor crankcase) will read the evaporating pres-sure. Again, negligible pressure drops are as-sumed. In reality, there will be line and valvepressure drops as the refrigerant travels throughthe evaporator and suction line. The technicianmust measure the pressure as close to the evapo-rator as possible to get a true evaporating pres-sure. On small systems where pressure dropsare negligible, this pressure is usually measurednear the compressor (see Figure 1-2). Gaugeplacement on small systems is usually not criti-cal as long as it is placed on the low side of therefrigeration system, because the refrigerant

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ghtEvaporating

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ghtHigh side pressure Low side p essure

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ghtHigh side pressure Low side p essure

Suction pressure

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Suction pressureDischarge pressure Back press re

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Discharge pressure Back press re

P

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PRES

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RESSURE

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SURE

The condensing pres ure is the pressure at

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The condensing pres ure is the pressure atwhich the refrigeran changes state from a va-

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which the refrigeran changes state from a va-por to a liquid. This phase change is referred to

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por to a liquid. This phase change is referred tocondensationCop

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. This pressure can be readCopyri

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. This pressure can be readdirect y from a pressure gauge connected any-Cop

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direct y from a pressure gauge connected any-where between the compressor discharge valveCop

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where between the compressor discharge valveand the entrance to the metering device, as-Cop

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and the entrance to the metering device, as-

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sured on smaller systems near the compressor

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sured on smaller systems near the compressorvalves, Figure 1-2. On small systems, it is not

Escovalves, Figure 1-2. On small systems, it is not

Escocritical where a technician places the pressure

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Escosystem), because pressure drops are negligible.

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The pressure gauge reads the same no matterwhere it is on the high side of the system if line

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where it is on the high side of the system if lineand valve losses are negligible.Esc

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Press

Refrigerant Pressures,

Press

Refrigerant Pressures,es, and Conditions

Presses, and Conditions

Press

close to the condens r as possible to avoid these

Press

close to the condens r as possible to avoid thesepressure drops This pressure is usually mea-Pres

spressure drops This pressure is usually mea-sured on smaller systems near the compressorPres

ssured on smaller systems near the compressorvalves, Figure 1-2. On small systems, it is notPres

svalves, Figure 1-2. On small systems, it is not



vapor pressure acts equally in all directions. Ifline and valve pressure drops become substan-tial, gauge placement becomes critical. In largermore sophisticated systems, gauge placementis more critical because of associated line and

valve pressure losses. If the system has signifi-cant line and valve pressure losses, the techni-cian must place the gauge as close as possibleto the component that requires a pressurereading.

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saturated vapor, respectively. Saturation occursin both the evaporator and condenser. At satu-ration, the liquid experiences its maximum tem-perature for that pressure, and the vapor expe-riences its minimum temperature. However,both liquid and vapor are at the same tempera-ture for a given pressure when saturation oc-curs. Saturation temperatures vary with differ-ent refrigerants and pressures. All refrigerantshave different vapor pressures. It is vapor pres-sure that is measured with a gauge.

Vapor Pressure

Vapor pressure is the pressure exerted on asaturated liquid. Any time saturated liquid andvapor are together (as in the condenser andevaporator), vapor pressure is generated. Va-por pressure acts equally in all directions andaffects the entire low or high side of a refrig-eration system.

As pressure increases, saturation temperatureincreases; as pressure decreases, saturation tem-perature decreases. Only at saturation are therepressure/temperature relationships for refriger-ants. Table 1-1 shows the pressure/temperaturerelationship at saturation for refrigerant 134a(R-134a). If one attempts to raise the tempera-ture of a saturated liquid above its saturationtemperature, vaporization of the liquid willoccur. If one attempts to lower the temperatureof a saturated vapor below its saturation tem-perature, condensation will occur. Both vapor-ization and condensation occur in the evapora-tor and condenser, respectively.

The heat energy that causes a liquid refrigerantto change to a vapor at a constant saturationtemperature for a given pressure is referred toas latent heat. Latent heat is the heat energythat causes a substance to change state withoutchanging the temperature of the substance.Vaporization and condensation are examples ofa latent heat process.

Figure 1-2. Semi-hermetic compressor showing pressure

access valves (Courtesy, Danfoss Automatic Controls,

Division of Danfoss, Inc.)

REFRIGERANT STATES AND CONDITIONS

Modern refrigerants exist either in the vapor orliquid state. Refrigerants have such low freez-ing points that they are rarely in the frozen orsolid state. Refrigerants can co-exist as vaporand liquid as long as conditions are right. Boththe evaporator and condenser house liquid andvapor refrigerant simultaneously if the systemis operating properly. Refrigerant liquid andvapor can exist in both the high or low pres-sure sides of the refrigeration system.

Along with refrigerant pressures and states arerefrigerant conditions. Refrigerant conditionscan be saturated, superheated, or subcooled.

SaturationSaturation is usually defined as a temperature.The saturation temperature is the temperatureat which a fluid changes from liquid to vaporor vapor to liquid. At saturation temperature,liquid and vapor are called saturated liquid and

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Modern refrigerants exist either in the vapor or

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liquid state. Refrigerants have such low freez-

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ghtliquid state. Refrigerants have such low freez-

ing points that they are rarely in the frozen or

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ing points that they are rarely in the frozen orsolid state. Refrigerants can co-exist as vapor

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solid state. Refrigerants can co-exist as vaporand liquid as long as conditions are right. Both

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and liquid as long as conditions are right. Boththe evaporator and condenser house liquid and

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the evaporator and condenser house liquid andvapor refrigerant simultaneously if the system

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vapor refrigerant simultaneously if the system

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is operating properly. Refrigerant liquid and

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is operating properly. Refrigerant liquid andvapor can exist in both the high or low pres-

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vapor can exist in both the high or low pres-sure sides of the refrigeration system.

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sure sides of the refrigeration system.

Along with refrigerant pressures and states are

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Along with refrigerant pressures and states are

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affects the entire low or high side of a refrig-

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Escoeration system.

As pressure increases, saturation temperature

EscoAs pressure increases, saturation temperature

increases; as pressure decreases, saturation tem-

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perature decreases. Only at saturation are there

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perature decreases. Only at saturation are therepressure/temperature relationships for refriger-

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pressure/temperature relationships for refriger-ants. Table 1-1 shows the pressure/temperatureEsc

oants. Table 1-1 shows the pressure/temperaturerelationship at saturation for refrigerant 134aEsc

orelationship at saturation for refrigerant 134a

Press

have different vapor pressures. It is vapor pres-

Press

have different vapor pressures. It is vapor pres-sure that is measured with a gauge.

Presssure that is measured with a gauge.

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Press

Vapor pressure is the pressure exerted on asaturated liquid. Any time saturated liquid and

Press

saturated liquid. Any time saturated liquid andvapor are together (as in the condenser and

Press

vapor are together (as in the condenser andevaporator), vapor pressure is generated. Va-Pres

sevaporator), vapor pressure is generated. Va-por pressure acts equally in all directions andPres

spor pressure acts equally in all directions andaffects the entire low or high side of a refrig-Pres

saffects the entire low or high side of a refrig-


Temperature Pressure Temperature Pressure

(°F) (psig) (°F) (psig)

-10 1.8

-9 2.2

-8 2.6 30 25.6

-7 3.0 31 26.4

-6 3.5 32 27.3

-5 3.9 33 28.1

-4 4.4 34 29.0

-3 4.8 35 29.9

-2 5.3 40 34.5

-1 5.8 45 39.5

0 6.2 50 44.9

1 6.7 55 50.7

2 7.2 60 56.9

3 7.8 65 63.5

4 8.3 70 70.7

5 8.8 75 78.3

6 9.3 80 86.4

7 9.9 85 95.0

8 10.5 90 104.2

9 11.0 95 113.9

10 11.6 100 124.3

11 12.2 105 135.2

12 12.8 110 146.8

13 13.4 115 159.0

14 14.0 120 171.9

15 14.7 125 185.5

16 15.3 130 199.8

17 16.0 135 214.8

18 16.7

19 17.3

20 18.0

21 18.7

22 19.4

23 20.2

24 20.9

25 21.7

26 22.4

27 23.2

28 24.0

29 24.8


temperature chart

words, all of the liquid must be vaporized forsuperheating to occur; the vapor must be re-moved from contact with the vaporizing liquid.Once all the liquid has been vaporized at itssaturation temperature, any addition of heatcauses the 100% saturated vapor to start super-heating. This addition of heat causes the vaporto increase in temperature and gain sensibleheat. Sensible heat is the heat energy that causesa change in the temperature of a substance. Theheat energy that superheats vapor and increasesits temperature is sensible heat energy. Super-heating is a sensible heat process. Superheatedvapor occurs in the evaporator, suction line,and compressor.

SubcoolingSubcooling always refers to a liquid at a tem-perature below its saturation temperature for agiven pressure. Once all of the vapor changesstate to 100% saturated liquid, further removalof heat will cause the 100% liquid to drop intemperature or lose sensible heat. Subcooledliquid results. Subcooling can occur in both thecondenser and liquid line and is a sensible heatprocess. Another method of subcooling liquid,

called liquid pressure amplificationTM, is cov-ered in Chapter Two. This method increasesthe pressure on subcooled liquid, causing it tobe subcooled even more. This creates a liquidwith a temperature below its new saturationtemperature for the new higher pressure.

A thorough understanding of pressures, states,and conditions of the basic refrigeration sys-tem enables the service technician to be a goodsystematic troubleshooter. It is not until thenthat a service technician should even attemptsystematic troubleshooting.

BASIC REFRIGERATION SYSTEM

Figure 1-3 illustrates a basic refrigeration sys-tem. The basic components of this system arethe compressor, discharge line, condenser, re-ceiver, liquid line, metering device, evaporator,and suction line. Mastering the function of eachindividual component can assist the refrigera-

SuperheatSuperheat always refers to a vapor. A super-heated vapor is any vapor that is above itssaturation temperature for a given pressure. Inorder for vapor to be superheated, it must havereached its 100% saturated vapor point. In other

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26 22.4

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27 23.2

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28 24.0

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29 24.8

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29 24.8

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Table 1-1. R-134a saturated vapor/liquid pressure/Copyri

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temperature chartCopyri

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temperature chart

Esco

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perature below its saturation temperature for a

Esco

perature below its saturation temperature for agiven pressure. Once all of the vapor changes

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state to 100% saturated liquid, further removal

Escostate to 100% saturated liquid, further removal

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Escoof heat will cause the 100% liquid to drop in

temperature or lose sensible heat. Subcooled

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liquid results. Subcooling can occur in both thecondenser and liquid line and is a sensible heat

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condenser and liquid line and is a sensible heatprocess. Another method of subcooling liquid,Esc

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a change in the temperature of a substance. The

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sperature below its saturation temperature for agiven pressure. Once all of the vapor changesPres

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Figure 1-3. Basic refrigeration system

tion technician with analytical troubleshootingskills, saving time and money for both techni-cian and customer.

CompressorOne of the main functions of the compressor isto circulate refrigerant. Without the compres-

sor as a refrigerant pump, refrigerant could notreach other system components to perform itsheat transfer functions. The compressor alsoseparates the high pressure from the low pres-sure side of the refrigeration system. A differ-ence in pressure is mandatory for fluid (gas orliquid) flow, and there could be no refrigerantflow without this pressure separation.

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Figure 1-3. Basic refrigeration systemCopyri

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Figure 1-3. Basic refrigeration systemCopyri

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tion technician with analytical troubleshootingskills, saving time and money for both techni-

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skills, saving time and money for both techni-

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Another function of the compressor is to el-evate or raise the temperature of the refrigerantvapor above the ambient (surrounding) tempera-ture. This is accomplished by adding work, orheat of compression, to the refrigerant vaporduring the compression cycle. The pressure ofthe refrigerant is raised, as well as its tempera-ture. By elevating the refrigerant temperatureabove the ambient temperature, heat absorbedin the evaporator and suction line, and any heatof compression generated in the compressionstroke can be rejected to this lower temperatureambient. Most of the heat is rejected in thedischarge line and the condenser. Remember,heat flows from hot to cold, and there must bea temperature difference for any heat transferto take place. The temperature rise of the re-frigerant during the compression stroke is ameasure of the increased internal kinetic en-ergy added by the compressor.

The compressor also compresses the refriger-ant vapors, which increases vapor density. Thisincrease in density helps pack the refrigerantgas molecules together, which helps in the con-densation or liquification of the refrigerant gasmolecules in the condenser once the rightamount of heat is rejected to the ambient. Thecompression of the vapors during the compres-sion stroke is actually preparing the vapors forcondensation or liquification.

Discharge LineOne function of the discharge line is to carrythe high pressure superheated vapor from thecompressor discharge valve to the entrance ofthe condenser. The discharge line also acts asa desuperheater, cooling the superheated va-pors that the compressor has compressed andgiving that heat up to the ambient (surround-ings). These compressed vapors contain all ofthe heat that the evaporator and suction linehave absorbed, along with the heat of compres-sion of the compression stroke. Any generatedmotor winding heat may also be contained inthe discharge line refrigerant, which is why thebeginning of the discharge line is the hottestpart of the refrigeration system. On hot dayswhen the system is under a high load and mayhave a dirty condenser, the discharge line can

reach over 400°F. By desuperheating the re-frigerant, the vapors will be cooled to the satu-ration temperature of the condenser. Once thevapors reach the condensing saturation tempera-ture for that pressure, condensation of vapor toliquid will take place as more heat is lost.

CondenserThe first passes of the condenser desuperheatthe discharge line gases. This prepares the highpressure superheated vapors coming from thedischarge line for condensation, or the phasechange from gas to liquid. Remember, thesesuperheated gases must lose all of their super-heat before reaching the condensing tempera-ture for a certain condensing pressure. Oncethe initial passes of the condenser have rejectedenough superheat and the condensing tempera-ture or saturation temperature has been reached,these gases are referred to as 100% saturatedvapor. The refrigerant is then said to havereached the 100% saturated vapor point, Figure1-4.

One of the main functions of the condenser isto condense the refrigerant vapor to liquid.Condensing is system dependent and usuallytakes place in the lower two-thirds of the con-denser. Once the saturation or condensing tem-perature is reached in the condenser and therefrigerant gas has reached 100% saturatedvapor, condensation can take place if more heatis removed. As more heat is taken away fromthe 100% saturated vapor, it will force the vaporto become a liquid or to condense. When con-densing, the vapor will gradually phase changeto liquid until 100% liquid is all that remains.This phase change, or change of state, is anexample of a latent heat rejection process, asthe heat removed is latent heat not sensible heat.The phase change will happen at one tempera-ture even though heat is being removed. Note:An exception to this is a near-azeotropic blendof refrigerants where there is a temperatureglide or range of temperatures when phasechanging (see Chapter Eight on blend tempera-ture glide). This one temperature is the satura-tion temperature corresponding to the satura-tion pressure in the condenser. As mentionedbefore, this pressure can be measured anywhere

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One function of the discharge line is to carry

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the high pressure superheated vapor from thecompressor discharge valve to the entrance of

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compressor discharge valve to the entrance ofthe condenser. The discharge line also acts as

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the condenser. The discharge line also acts asa desuperheater, cooling the superheated va-

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a desuperheater, cooling the superheated va-pors that the compressor has compressed and

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pors that the compressor has compressed andgiving that heat up to the ambient (surround-

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sion of the compression stroke. Any generated

Esco

densation or liquification of the refrigerant gas

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densation or liquification of the refrigerant gasmolecules in the condenser once the right Esc

omolecules in the condenser once the right

ture or saturation temperature has been reached,

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ture or saturation temperature has been reached,these gases are referred to as 100% saturated

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Esco1-4.

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Esco

One of the main functions of the condenser isto condense the refrigerant vapor to liquid.Esc

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otakes place in the lower two-thirds of the con-

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the discharge line gases. This prepares the high

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the discharge line gases. This prepares the highpressure superheated vapors coming from the

Presspressure superheated vapors coming from the

discharge line for condensation, or the phase

Pressdischarge line for condensation, or the phase

change from gas to liquid. Remember, these

Presschange from gas to liquid. Remember, these

superheated gases must lose all of their super-

Press

superheated gases must lose all of their super-heat before reaching the condensing tempera-

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heat before reaching the condensing tempera-ture for a certain condensing pressure. Once

Press

ture for a certain condensing pressure. Oncethe initial passes of the condenser have rejectedPres

sthe initial passes of the condenser have rejectedenough superheat and the condensing tempera-Pres

senough superheat and the condensing tempera-ture or saturation temperature has been reached,Pres

sture or saturation temperature has been reached,these gases are referred to as 100% saturatedPres

sthese gases are referred to as 100% saturated


Figure 1-4. Basic refrigeration system showing 100% saturated vapor and liquid points

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on the high side of the refrigeration system aslong as line and valve pressure drops and lossesare negligible.

The last function of the condenser is to subcoolthe liquid refrigerant. Subcooling is defined asany sensible heat taken away from 100% satu-rated liquid. Technically, subcooling is definedas the difference between the measured liquidtemperature and the liquid saturation tempera-ture at a given pressure. Once the saturatedvapor in the condenser has phase changed tosaturated liquid, the 100% saturated liquid pointhas been reached. If any more heat is removed,the liquid will go through a sensible heat rejec-tion process and lose temperature as it losesheat. The liquid that is cooler than the saturatedliquid in the condenser is subcooled liquid.Subcooling is an important process, because itstarts to lower the liquid temperature to theevaporator temperature. This will reduce flashloss in the evaporator so more of the vaporiza-tion of the liquid in the evaporator can be usedfor useful cooling of the product load (seeChapter Two on the importance of liquidsubcooling).

ReceiverThe receiver acts as a surge tank. Once thesubcooled liquid exits the condenser, the re-ceiver receives and stores the liquid. The liquidlevel in the receiver varies depending onwhether the metering device is throttling openedor closed. Receivers are usually used on sys-tems in which a thermostatic expansion valve(TXV or TEV) is used as the metering device.The subcooled liquid in the receiver may loseor gain subcooling depending on the surround-ing temperature of the receiver. If the subcooledliquid is warmer than receiver surroundings, theliquid will reject heat to the surroundings andsubcool even more. If the subcooled liquid iscooler than receiver surroundings, heat will begained by the liquid and subcooling will belost.

A receiver bypass is often used to bypass liq-uid around the receiver and route it directly tothe liquid line and filter drier. This bypass pre-vents subcooled liquid from sitting in the re-

ceiver and losing its subcooling. A thermostatwith a sensing bulb on the condenser outletcontrols the bypass solenoid valve by sensingliquid temperature coming to the receiver, Fig-ure 1-5. If the liquid is subcooled to a predeter-mined temperature, it will bypass the receiverand go to the filter drier.

Liquid LineThe liquid line transports high pressuresubcooled liquid to the metering device. Intransport, the liquid may either lose or gainsubcooling depending on the surrounding tem-perature. Liquid lines may be wrapped aroundsuction lines to help them gain more subcooling,Figure 1-6. Liquid/suction line heat exchangerscan be purchased and installed in existing sys-tems to gain subcooling. The importance ofliquid subcooling will be covered more exten-sively in Chapter Two.

Metering DeviceThe metering device meters liquid refrigerantfrom the liquid line to the evaporator. Thereare several different styles and kinds of meter-ing devices on the market with different func-tions. Some metering devices control evapora-tor superheat and pressure, and some even havepressure limiting devices to protect compres-sors at heavy loads.

The metering device is a restriction that sepa-rates the high pressure side from the low pres-sure side in a refrigeration system. The com-pressor and the metering device are the twocomponents that separate pressures in a refrig-eration system. The restriction in the meteringdevice causes liquid refrigerant to flash to alower temperature in the evaporator because ofits lower pressure and temperature.

EvaporatorThe evaporator, like the condenser, acts as aheat exchanger. Heat gains from the productload and outside ambient travel through thesidewalls of the evaporator to vaporize any liq-uid refrigerant. The pressure drop through themetering device causes vaporization of some

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