1

Principles of Refrigeration

MAE 554Professor H. Ezzat Khalifa

Syracuse University

P-h Chart for R134a (SI Units)

2

Psychrometric Chart (ASHRAE)

Psychrometric Processes

Cool Heat

Humidify

Dehumidify

Cool & Dehumidify

Air Conditioning Systems Cool & Dehumidify Air

3

A/C System Psychrometric Processes

Room Condition Line

Coil temperature must be cooler than room dew point (DP) to dehumidify the air Coil Inlet

Room Return Air

Outdoor Air

Room DP

Coil Exit

Reversed Carnot Cycle

s

T

TC

TH

4

0.0

5.0

10.0

15.0

20.0

25.0

30.0

-40.0 -35.0 -30.0 -25.0 -20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0

Cold-Side Temperature - TC, C

CO

P c

20.030.040.050.060.070.0

Carnot Cycle Performance

Sat Cond T, °C

Reversed Carnot Vapor Compression Cycle

s

T

TC

TH

5

Reversed Rankine Vapor Compression Cycle

s

T

TC

TH

Superheat HornIncreased Work

Ideal Practical Vapor Compression Cycle

s

T

TC

TH

Superheat HornIncreased Work

Throttling Lossin Refrigeration

Throttling LossIn Work

6

1

3 2

4

Simple Vapor Compression Cycle

Single-Stage Vapor Compression Cycle

ΔhWΔhE h

P

PE

PC

ΔTSC

ΔhWo

ΔTSH

7

Ideal VCC Performance

0

2

4

6

8

10

-40.0 -30.0 -20.0 -10.0 0.0 10.0

Evap. Sat. Temp., C

CO

P C

0

5

10

15

20

25

Cap

acity

, kW 35.0 COP

50.0 COP

35.0 Q

50.0 Q

Cond. Sat. Temp., ºC

R22Ideal VCC10 CFM

Compressor

Comparison of Ideal VCC with Carnot Cycle

0.5

0.6

0.7

0.8

0.9

1.0

-40.0 -30.0 -20.0 -10.0 0.0 10.0

Evap. Sat. Temp., C

Rel

ativ

e C

OP

0.5

0.6

0.7

0.8

0.9

1.0

35.0

50.0

Cond. Sat. Temp., ºC

8

h

P

PE

PC

PS

PD

11b

1a

2d

1c

3 2

4

P-h Diagram for Real Vapor Compression Cycle

Effect of the Gas Specific Heat Ratio, γ

9

1

23

4

6

7 8

5

Two-Stage VCC with Flash Economizer

ΔhE h

P

PE

PC

ΔTSC

ΔhW1

ΔTSH

1

23

45

6

7

8

ΔhW2

PI

P-h Diagram for 2-Stage VCC with Flash Economizer

10

1

23

45

6

7 8

5

Two-Stage VCC with Subcooler Economizer

ΔhE h

P

PE

PC

ΔTSC

ΔhW1

ΔTSH

1

23

45

6

7

8

ΔhW2

PI

P-h Diagram for 2-Stage VCC with Subcooler

11

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

-40 -30 -20 -10 0 10 20 30 40 50

Intermediate Sat. Temp., C

CO

PC, C

OP C

r

COPC

COPCr

Geometric-MeanIntermediate

Optimum Intermediate Temperature for 2-Stage VCC

0

2

4

6

8

10

-40.0 -30.0 -20.0 -10.0 0.0 10.0

Evap. Sat. Temp., C

CO

PC

35/COP 1

50/COP 1

35/COP 2

50/COP 2

Cond. Sat. Temp., ºC

R22Ideal VCC

Comparison of Two-Stage and Single-Stage VCCs

12

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

1 2 3 4

Number of Stages

Rel

ativ

e C

OP

C a

nd C

apai

ty

Rel. COPRel. Capacity

R22Ideal VCC

Performance of Multi-stage VCCs

14

Cascade System

High-Temperature Refrigerant

Low-Temperature Refrigerant

13

Desirable Characteristics of Refrigerants

• Thermally stable• Safe (toxicity and flammability)• Low cost and widely available• Compatible with materials of construction• High performance

– High latent heat– Low compression superheat– Low throttling losses– High heat transfer properties

• Environmentally benign (ODP and GWP)

Refrigerant Classification

Refrigerants

MixturesPure

Zeotropes Azeotropes

R502

R507

R410A*

R404A*

R407C

Natural CFC HCFC HFC

Ammonia

Propane

R12

R114

R11

R22

R123

R134a

R32

R125

R143a

Iso-Butane

R290-R600a

*Near-Azeotropes

CO2

Used in or considered for Refrigeration

Propane/Iso-Butane

14

Mixture Phase Diagrams

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Mole Fraction, x

Sat.

Tem

pera

ture

Tsat

Liquid Mole-Fraction Vapor Mole-Fraction

P1

P2

Mixture Phase Diagrams

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Mole Fraction, x

Sat.

Tem

pera

ture

Tsat

Liquid Mole-Fraction Vapor Mole-Fraction

P1

P2

Azeotrope

15

NIST Refrigerant Properties

ASHRAE Refrigerant Safety Classification

B3R1140

A3R170, R290, R600a, R1150

High Flammability

B2NH3

A2R32, R142b, R143a, R152a

Low Flammability

B1R123, R764, R21

A1R11, R12, R22, R125, R134a, R407C,

R507, R404A, R410A, R744No Flammability

High ToxicityLow/No Toxicity

Refrigerants marked in Red are ozone depleting substances that are no longer used in new equipment.Refrigerants marked in Green are natural refrigerants that have low GWP,as well as no ODP.

16

Refrigerants: Methane Group

Refrigerants: Ethane Group

17

ODP and GWP for Various Refrigerants

Refrigerant ODP GWP Refrigerant ODP GWP

CFC-11 1.0 1.0 HFC-125 0.0 0.84 CFC-12 1.0 3.05 HFC-134 0.0 0.25 CFC-13 N/A N/A HFC-134a 0.0 0.25 HCFC-22 0.051 0.370 HFC-143a 0.0 1.2 HFC-23 0.0 N/A HFC-152a 0.0 0.029 HFC-32 0.0 0.130 R500 0.78 2.39 CFC-113 0.87 1.300 R502 0.245 5.10 CFC-114 0.74 4.150 R503 N/A N/A HCFC-123 0.016 0.019 R410A 0.0 0.49 HCFC-123a 0.016 0.019 R507 0.0 0.96 HCFC-124 0.018 0.095

ODP (Ozone Depletion Potential), and GWP (Greenhouse Warming Potential) are calculated relative to CFC R11.

Refrigerant Comparison

(1.0) means reference value

Refrigerant CO2 R12 R22 R134a R404A R410A C3H8 NH3

Natural? Yes No No No No No Yes Yes

Flammable? No No No No No No Yes Yes

Toxic? No No No No No No No Yes

Relative Cost 0.1 - (1.0) 4.0 5.0 5.0 0.3 0.2

Volum. Capacity 4.8 0.6 (1.0) 0.7 1.2 1.5 0.9 1.0

Critical Temp.(F) 88 234 205 214 163 158 206 270

P @ 70F (psia) 852 85 136 86 165 216 125 129

ODP 0 1.0 0.05 0 0 0 0 0

GWP (100yr) (1.0) 7100 1500 1300 3750 1730 3 0

18

Refrigerant Pressure-Capacity Relationship

0.0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400 500Pressure Difference @ ARI [psi]

Volu

met

ric C

apac

ity @

AR

I [To

n/cf

m]

Best FitR123R11R245faR114R600aR12R134aR290R22R407CR717R507R410A

R22

NH3

R404A/R507Propane

R407C

R410A

R134a

R22 & its near neighbors

Comparison of Simple Cycle EER

R22 R134a R290 R407C R507 R410A0.80

0.85

0.90

0.95

1.00

1.05

1.10EER Relative to R22

ARICHEER

19

Relative ARI Capacity [Same Displacement]

0.0

0.5

1.0

1.5

2.0Capacity relative to R22

Relative Compressor Displacement [Same Capacity]

0.0

0.5

1.0

1.5

2.0

2.5

3.0Displacement relative to R22

20

Low Temperature Capacity Comparison

SCT=130F; SH=20F; SC=15F; No LSHX; No Quench

0.1

1.0

-50 -40 -30 -20 -10 0 10 20 30 40 50

Saturated Evaporator Temperature [F]

Cap

acity

Rel

ativ

e to

AR

I

R22R507R134aR410A

Low Temperature EER Comparison

0.1

1.0

-50 -40 -30 -20 -10 0 10 20 30 40 50

Saturated Evaporator Temperature [F]

EER

Rel

ativ

e to

R22

@ A

RI

R22R507R134aR410A

SCT=130F; SH=20F; SC=15F; No LSHX; No Quench

21

Discharge Superheat Comparison

0

50

100

150

200

250

300

-50 -40 -30 -20 -10 0 10 20 30 40 50

Saturated Evaporator Temperature [F]

Dis

char

ge S

uoer

hear

[F]

R22R507R134aR410A

SCT=130F; SH=20F; SC=15F; No LSHX; No Quench

Total Equivalent Warming Impact (TEWI)

Medium Temperature RefrigerationFrom DoE's ORNL Report, 1997

22

Fluid Comparison - R134a vs. R744 (CO2)

Region of Operational Interest

Region of Operational Interest

R744 (CO2)R134a

R134a R744Critical Point 214 F 88 FLow Pressure 10-50 psi 110 - 500 psiHigh Pressure 100-250 psi 750-2000 psi

Other CO2 Properties:High throttling losses Solid CO2 (Dry Ice) at -80F (70 psi)Transcritical Cycle (typical)Much Higher heat transfer potential (2-3x)Temperature ‘glide’ on heat rejection HX

Refrigerant-Lubricant Viscosity

23

Vapor Compressors

Classification of Vapor Compressors

Positive Displacement Machines [PD]: • Reciprocating Piston, Rolling Piston, Scroll, Screw,

Sliding Vane …

Rotodynamic (Turbo) Machines [RD]:• Radial, Mixed-flow Centrifugal; Single and Multi-stage

24

Positive Displacement Vapor Compressors

Compressor Application Range

0.1 1.0 10.0 100.0 1000.0 10000.0

Rotary [HVAC]

Scroll [HVAC]

H Recip [HVAC]

SH Recip [HVAC]

Screw [HVAC]

Centrifugal [HVAC]

ARI Capacity, Tons

25

Positive Displacement Compressors

Piston (Reciprocating)

26

Comparison of P-V Diagrams

Pre

ssur

e

Scroll/Screw (AC & Refrig.)

Volume Displacement

Clearance Volume

Recip. AC

Recip. Refrig.

Up to 60% Up to 60% More CapacityMore Capacity

Piston Compressor Volumetric Efficiency

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 50 60

Pressure Ratio

Theo

retic

al V

olum

eter

ic E

ffici

ency

0.0000.0100.0150.0200.0300.0500.0700.100

C

n = 1.15

27

Rolling Piston (Rotary) Compressor Pump

Typical Rolling Piston Compressor

ASHRAE Handbook of Systems and Equipment, 2004

28

Hermetic Scroll Compressor

Scroll Compressor

29

Scroll Compressor Operation

Scroll Operation (DTU)

Typical Scroll Compressor Performance

ASHRAE Handbook of Systems and Equipment, 2004

30

Twin Screw (Lysholm) Compressor

Single Screw Compressor

ASHRAE Handbook of Systems and Equipment, 2004

31

Typical Screw Compressor Performance

ASHRAE Handbook of Systems and Equipment, 2004

Over/Under-compression Loss

0%

20%

40%

60%

80%

100%

0.0 1.0 2.0 3.0 4.0 5.0

Relative Discharge Pressure (Pd/Pd*)

Perc

enta

ge O

ver/

Und

er-c

ompr

essi

on L

oss

3.03.54.05.06.0

VR

Under-compression

32

Screw CompressorsEfficiency Improvement

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 10 20 30 40 50 60 70 80 90Male Rotor Tip Speed [m/s]

Rel

ativ

e Lo

ss

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Isen

trop

ic E

ffici

ency

Leakage Losses Flow & Viscous Losses

Pump Efficiency

Close leakage gaps & reduce oil injectionClose leakage gaps & reduce oil injection

Sliding Vane Compressor

33

Centrifugal Compressors

Centrifugal Compressor

34

Typical Centrifugal Compressor Impeller

ASHRAE Handbook of Systems and Equipment, 2004

Ns-Ds Diagram for Single-Stage CompressorsFrom O. E. Balje: Turbomachines - A Guide to Design Selection and Theory, Wiley, NY, '81

35

2-Stage Centrifugal Compressor

ASHRAE Handbook of Systems and Equipment, 2004

Polytropic Efficiency

0.830

0.832

0.834

0.836

0.838

0.840

0.842

0.844

0.846

0.848

0.850

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Pressure Ratio

Isen

trop

ic E

ffici

ency

ηp = 0.85; γ = 1.1

36

Typical Centrifugal Compressor Performance

ASHRAE Handbook of Systems and Equipment, 2004

IGV Control – Fixed SpeedVariable-Speed Control

Centrifugal Chiller Part-Load Performance

ASHRAE Handbook of Systems and Equipment, 2004

37

Comparison of Chiller Compressors

ASHRAE Handbook of Systems and Equipment, 2004

Expansion Devices

38

Short Restrictor Expansion Device

ASHRAE Handbook of Refrigeration, 2004

Thermostatic Expansion Valve

ASHRAE Handbook of Refrigeration, 2004

39

Constant-Pressure Expansion Valve

ASHRAE Handbook of Refrigeration, 2004

Float-controlled Expansion Valve

ASHRAE Handbook of Refrigeration, 2004

40

Thermally Activated Heat Pump Concept

ASHRAE Handbook of Refrigeration, 2004

Single-Effect LiBr-H2O Absorption Cycle

1

6

4"

7

3

2

4'

5

Solution HX

Condenser

Evaporator Absorber

Generator

Pump

41

Practical Configuration of LiBr-H2O System

ASHRAE Handbook of Refrigeration, 2004

Mixture Phase Diagrams

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Mole Fraction, x

Sat.

Tem

pera

ture

Tsat

Liquid Mole-Fraction Vapor Mole-Fraction

P1

P2

42

Single-Effect LiBr-H2O Cycle Duhring Diagram

T

P

CrystallizationPE

PC

Pure H2O; x=0 x=xsx=xw

TGTC~TATE

1, 7

6 3

2 5

4', 4"

Double-Effect LiBr-H2O Absorption Cycle [1]

3'

1

9

6

10

7'

5

6

2

Condenser

Evaporator Absorber

Generator 1

Pump

7"

Solution HX

3'

8

Pump

Solution HX

Generator 2

4'

4

3

8

4"

43

Double-Effect LiBr-H2O Absorption Cycle [2]

1

10

9"

12

3

2

4'

6'

Condenser

Evaporator Absorber

Generator 1

Pump

4"

3'

54

9'

8' 8

6

Solution HX

Generator 2

Single-Effect LiBr-H2O Cycle Duhring Diagram

T

P

CrystallizationPE

PC

Pure H2O; x=0 x=xsx=xw

TGTC~TATE

1, 8

7 3

2 5

4, 6

44

Pumpless Aqua-Ammonia System

ASHRAE Handbook of Refrigeration, 2004

Bubble Pump

Simple and Regenerative Reversed Brayton Cycle

S

T

2′

3′

6, 1′5

4

3

2

1

45

Regenerative Air Cycle

ConditionedSpace

Exp. Comp.

Recuperator

Gas Cooler

Ambient air

Power

Simple Air Cycle Performance

Ta = 35 ºC; εR = 0.9; η′E = 0.88; η′C = 0.87; δP/P = 0.05; ΔTA = 10 ºC

0.0

0.1

0.2

0.3

0.4

0.5

0.6

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Expander Pressure Ratio

CO

P

22.0

12.0

2.0

-8.0

-18.0

-38.0

-58.0

-78.0

-98.0

-118.0

Load Temp.ºC

46

Regenerative Air Cycle Performance

0.0

0.1

0.2

0.3

0.4

0.5

0.6

1.0 2.0 3.0 4.0 5.0 6.0

Expander Pressure Ratio

CO

P

22.0

12.0

2.0

-8.0

-18.0

-38.0

-58.0

-78.0

-98.0

-118.0

Load Temp.ºC

Ta = 35 ºC; εR = 0.9; η′E = 0.88; η′C = 0.87; δP/P = 0.05; ΔTA = 10 ºC

Comparison of Air Liquefaction Cycles

0

2000

4000

6000

8000

10000

12000

Revrsible(Ideal)

Linde Linde + VC Precooler

(-45 C)

Dual-Pressure

Linde

Dual-Pressure

Linde + VCPrecooler

Claude

kJ/k

g Li

quid

Air

47

Rotary Magnetic Refrigerator