Principles of Refrigeration
MAE 554 Professor H. Ezzat Khalifa Syracuse University
P-h Chart for R134a (SI Units)
1
Psychrome Psychrometric tric Chart Chart (ASHRAE) (ASHRAE)
Psychrome Psychrometric tric Processe Processes s
Air Conditioning Systems Cool & Dehumidify Air
Humidify
Cool
Heat
Cool & Dehumidify Dehumidify
2
Psychrome Psychrometric tric Chart Chart (ASHRAE) (ASHRAE)
Psychrome Psychrometric tric Processe Processes s
Air Conditioning Systems Cool & Dehumidify Air
Humidify
Cool
Heat
Cool & Dehumidify Dehumidify
2
A/C System Psychrome Psychrometric tric Processe Processes s
Coil temperature must be cooler than room dew point (DP) to dehumidify the air
Outdoor Air Room DP Coil Inlet Room Return Air
Coil Exit
Room Condition Line
Reversed Carnot Cycle T
TH
TC
s
3
Carnot Cycle Performance 30.0
Sat Cond T, °C 25.0
20.0 30.0 40.0
20.0
50.0 60.0
c
P O 15.0 C
70.0
10.0
5.0
0.0 -40.0
-35.0
-30.0
-25.0
-20.0
-15.0
-10.0
-5.0
0.0
5.0
10.0
Cold-Side Cold-Side Temperature - TC, C
Reversed Carnot Vapor Compression Cycle T
TH
TC
s
4
Reversed Rankine Vapor Compression Cycle T
Superheat Horn Increased Work
TH
TC
s
Ideal Practical Vapor Compression Cycle T
Superheat Horn Increased Work
TH Throttling Loss In Work
TC Throttling Loss in Refrigeration
s
5
Simple Vapor Compression Cycle
3
2
4
1
Single-Stage Vapor Compression Cycle P
TSC
PC
PE hWo TSH hE
hW
h
6
Ideal VCC Performance 10
25
R22 Ideal VCC 10 CFM Compressor
8
20
Cond. Sat. Temp., ºC 15 W k
6
, y t i c a p 10 a C
C
P O C 4
2
50.0 COP 35.0 Q 50.0 Q
5
0 -40.0
35.0 COP
0 -30.0
-20.0
-10.0
0.0
10.0
Evap. Sat. Temp., C
Comparison of Ideal VCC with Carnot Cycle 1.0
1.0
0.9
0.9
P O0.8 C e v i t a l e 0.7 R
0.8
35.0 50.0 0.7
0.6
0.6
0.5 -40.0
Cond. Sat. Temp., ºC
0.5 -30.0
-20.0
-10.0
0.0
10.0
Evap. Sat. Temp., C
7
P-h Diagram for Real Vapor Compression Cycle P 2d
PD PC
PE PS
3
2
1a 4
1
1b 1c
h
Effect of the Gas Specific Heat Ratio, γ
8
Two-Stage VCC with Flash Economizer
5
4
3 2
6
7
8
1
P-h Diagram for 2-Stage VCC with Flash Economizer P
TSC
PC PI PE
hW2
5
7
3
4
2
6
8
1
hW1
TSH hE
h
9
Two-Stage VCC with Subcooler Economizer
5
5
4
3 2
6
7
8
1
P-h Diagram for 2-Stage VCC with Subcooler P
PC
TSC
7
3
PI PE
hW2
5
4
2
6
8
1
hW1
TSH hE
h
10
Optimum Intermediate Temperature for 2-Stage VCC 2.4 2.2
COP C 2.0 1.8 r C
P O 1.6 C , C P 1.4 O C
COP Cr
1.2 1.0
Geometric-Mean Intermediate
0.8 0.6 -40
-30
-20
-10
0
10
20
30
40
50
Intermediate Sat. Temp., C
Comparison of Two-Stage and Single-Stage VCCs 10
R22 Ideal VCC
8
Cond. Sat. Temp., ºC 35/COP 1
6 C
50/COP 1
P O C
35/COP 2 4
50/COP 2
2
0 -40.0
-30.0
-20.0
-10.0
0.0
10.0
Evap. Sat. Temp., C
11
Performance of Multi-stage VCCs 1.8
1.6
R22 Ideal VCC
1.4
y t i a 1.2 p a C d n 1.0 a
Rel. COP Rel. Capacity
C
P O 0.8 C e v i t a 0.6 l e R 0.4
0.2
0.0 1
2
3
4
Number of Stages
Cascade System
High-Temperature Refrigerant
Low-Temperature Refrigerant
12
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
Pure
Mixtures
Natural
CFC
HCFC
HFC
Zeotropes
Azeotropes
Ammonia
R12
R22
R134a
R407C
R502
Propane
R114
R123
R32
R290-R600a
R507
Iso-Butane
R11
R125
Propane/Iso-Butane
R410A*
CO2
R143a
R404A* *Near-Azeotropes
Used in or considered for Refrigeration
13
Mixture Phase Diagrams P2
e r u t a r e p m e T . t a S
P1 Tsat
Liquid Mole-Fraction 0.0
0.1
0.2
Vapor Mole-Fraction 0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Mole Fraction, x
Mixture Phase Diagrams P2
e r u t a r e p m e T . t a S
P1 Tsat
Liquid Mole-Fraction 0.0
0.1
0.2
Azeotrope 0.3
0.4
0.5
Vapor Mole-Fraction 0.6
0.7
0.8
0.9
1.0
Mole Fraction, x
14
NIST Refrigerant Properties
ASHRAE Refrigerant Safety Classification
No Flammability
Low Flammability
High Flammability
Low/No Toxicity
High Toxicity
A1
B1
R11, R12, R22, R125, R134a, R407C, R507, R404A, R410A, R744
R123, R764, R21
A2
B2
R32, R142b, R143a, R152a
NH3
A3
B3
R170, R290, R600a, R1150
R1140
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.
15
Refrigerants: Methane Group
Refrigerants: Ethane Group
16
ODP and GWP for Various Refrigerants Refrigerant
ODP
GWP
Refrigerant
ODP
GWP
CFC-11 CFC-12 CFC-13 HCFC-22 HFC-23 HFC-32 CFC-113 CFC-114 HCFC-123 HCFC-123a HCFC-124
1.0 1.0 N/A 0.051 0.0 0.0 0.87 0.74 0.016 0.016 0.018
1.0 3.05 N/A 0.370 N/A 0.130 1.300 4.150 0.019 0.019 0.095
HFC-125 HFC-134 HFC-134a HFC-143a HFC-152a R500 R502 R503 R410A R507
0.0 0.0 0.0 0.0 0.0 0.78 0.245 N/A 0.0 0.0
0.84 0.25 0.25 1.2 0.029 2.39 5.10 N/A 0.49 0.96
ODP (Ozone Depletion Potential), and GWP (Greenhouse Warming Potential) are calculated relative to CFC R11.
Refrigerant Comparison
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
(1.0)
7100
1500
1300
3750
1730
3
0
GWP (100yr)
(1.0) means reference value
17
Refrigerant Pressure-Capacity Relationship 1.0
m f c / n o T [ I R A @ y t i c a p a C c i r t e m u l o V
R22 & its near neighbors
0.8
Best Fit R123 R11 R245fa R114 R600a R12 R134a R290 R22 R407C R717 R507 R410A
R410A
NH3
0.6
R22 R404A/R507
Propane
R407C
0.4 R134a
0.2
0.0 0
100
200
300
400
500
Pressure Difference @ ARI [psi]
Comparison of Simple Cycle EER 1.10
EER Relative to R22
1.05
1.00 ARI 0.95 CHEER 0.90
0.85
0.80 R22
R134a
R290
R407C
R507
R410A
18
Relative ARI Capacity [Same Displacement] 2.0
Capacity relative to R22
1.5
1.0
0.5
0.0
Relative Compressor Displacement [Same Capacity] 3.0
Displacement relative to R22
2.5
2.0
1.5
1.0
0.5
0.0
19
Low Temperature Capacity Comparison 1.0 I R A o t e v i t a l e R y t i c a p a C
R22 R507 R134a R410A
0.1 -50 -40 -30 -20 -10
0
10
20
30
40
50
Saturated Evaporator Tem perature [F] SCT=130F; SH=20F; SC=15F; No LSHX; No Quench
Low Temperature EER Comparison 1.0 I R A @ 2 2 R o t e v i t a l e R R E E
R22 R507 R134a R410A
0.1 -50 -40 -30 -20 -10
0
10
20
30
40
50
Saturated Evaporator Tem perature [F] SCT=130F; SH=20F; SC=15F; No LSHX; No Quench
20
Discharge Superheat Comparison 300 250 ] F [ r a 200 e h r e o u S 150 e g r a h 100 c s i D 50
R22 R507 R134a R410A
0 -50 -40 -30 -20 -10
0
10
20
30
40
50
Saturated Evaporator Temperature [F] SCT=130F; SH=20F; SC=15F; No LSHX; No Quench
Total Equivalent Warming Impact (TEWI)
Medium Temperature Refrigeration From DoE's ORNL Report, 1997
21
Fluid Comparison - R134a vs. R744 (CO 2) R134a
R744 (CO2)
Region of Operational Interest
Region of Operationa l Interest
Critical Point Low Pressure High Pressure
R134a 214 F 10-50 psi 100-250 psi
R744 88 F 110 - 500 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
22
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
23
Positive Displacement Vapor Compressors
Compressor Application Range Centrifugal [HVAC]
Screw [HVAC]
SH Recip [HVAC]
H Recip [HVAC]
Scroll [HVAC]
Rotary [HVAC]
0.1
1.0
10.0
100.0
1000.0
10000.0
ARI Capacity, Tons
24
Positive Displacement Compressors
Piston (Reciprocating)
25
Comparison of P-V Diagrams Clearance Volume
e r u s s e r P
Up to 60% More Capacity Recip. Refrig. Recip. AC Scroll/Screw (AC & Refrig.)
Volume Displacement
Piston Compressor Volumetric Efficiency 1.0
n = 1.15
y c 0.8 n e i c i f f E c i r 0.6 e t e m u l o V 0.4 l a c i t e r o e h 0.2 T
C 0.000 0.010 0.015 0.020 0.030 0.050 0.070 0.100
0.0 0
10
20
30
40
50
60
Pressure Ratio
26
Rolling Piston (Rotary) Compressor Pump
Typical Rolling Piston Compressor
ASHRAE Handbook of Systems and Equipment, 2004
27
Hermetic Scroll Compressor
Scroll Compressor
28
Scroll Compressor Operation
Scroll Operation (DTU)
Typical Scroll Compressor Performance
ASHRAE Handbook of Systems and Equipment, 2004
29
Twin Screw (Lysholm) Compressor
Single Screw Compressor
ASHRAE Handbook of Systems and Equipment, 2004
30
Typical Screw Compressor Performance
ASHRAE Handbook of Systems and Equipment, 2004
Over/Under-compression Loss 100%
s s o L n o i s s e r p m o c r e d n U / r e v O e g a t n e c r e P
80%
VR Under-compression
60%
3.0 3.5 4.0 5.0 6.0
40%
20%
0% 0.0
1.0
2.0
3.0
4.0
5.0
Relative Di scharge Pressure (P d/Pd*)
31
Screw Compressors Efficiency Improvement 2.0
1.0
1.8
Close Close leakage leakage gaps gaps & & reduce reduce oil oil injection injection
0.9
1.6
0.8
1.4
0.7 n
s s o 1.2 L e v 1.0 i t a l 0.8 e R
Pump Efficiency
y c
e i
c 0.6 i f f
0.5 E 0.4 Leakage Losses
0.6
Flow & Viscous Losses
0.3
0.4
0.2
0.2
0.1
0.0
0.0 0
10
20
30
40
50
60
70
80
c i p o r t n e s I
90
Male Rotor Tip Spe ed [m/s]
Sliding Vane Compressor
32
Centrifugal Compressors
Centrifugal Compressor
33
Typical Centrifugal Compressor Impeller
ASHRAE Handbook of Systems and Equipment, 2004
Ns-Ds Diagram for Single-Stage Compressors From O. E. Balje: Turbomachines - A Guide to Design Selection and Theory, Wiley, NY, '81
34
2-Stage Centrifugal Compressor
ASHRAE Handbook of Systems and Equipment, 2004
Polytropic Efficiency 0.850 0.848
p
= 0.85;
= 1.1
0.846
y 0.844 c n e 0.842 i c i f f E 0.840 c i p o r 0.838 t n e s 0.836 I 0.834 0.832 0.830 1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
Pressure Ratio
35
Typical Centrifugal Compressor Performance
Variable-Speed Control
IGV Control – Fixed Speed
ASHRAE Handbook of Systems and Equipment, 2004
Centrifugal Chiller Part-Load Performance
ASHRAE Handbook of Systems and Equipment, 2004
36
Comparison of Chiller Compressors
ASHRAE Handbook of Systems and Equipment, 2004
Expansion Devices
37
Short Restrictor Expansion Device
ASHRAE Handbook of Refrigeration, 2004
Thermostatic Expansion Valve
ASHRAE Handbook of Refrigeration, 2004
38
Constant-Pressure Expansion Valve
ASHRAE Handbook of Refrigeration, 2004
Float-controlled Expansion Valve
ASHRAE Handbook of Refrigeration, 2004
39
Thermally Activated Heat Pump Concept
ASHRAE Handbook of Refrigeration, 2004
Single-Effect LiBr-H2O Absorption Cycle Condenser
Generator 4"
6
3
4'
Solution HX
Pump 7
2
5
1
Evaporator
Absorber
40
Practical Configuration of LiBr-H 2O System
ASHRAE Handbook of Refrigeration, 2004
Mixture Phase Diagrams P2
e r u t a r e p m e T . t a S
P1 Tsat
Liquid Mole-Fraction 0.0
0.1
0.2
Vapor Mole-Fraction 0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Mole Fraction, x
41
Single-Effect LiBr-H2O Cycle Duhring Diagram P 6
PC
Pure H2O; x=0
3
x=xw
4', 4"
x=xs
Crystallization PE
1, 7
2
TE
TC~TA
5
TG
T
Double-Effect LiBr-H 2O Absorption Cycle [1] Condenser
4"
Generator 2 8
9
Generator 1 6
4'
7"
7'
3'
6
3
Solution HX
Solution HX
Pump 5
10
Pump
2
8
4
1
Evaporator
Absorber 3'
42
Double-Effect LiBr-H2O Absorption Cycle [2] Condenser
Generator 1
Generator 2 8'
8
4"
10
3'
3
4'
9"
4 5
9'
Solution HX 6
Pump 12
2
6'
1
Evaporator
Absorber
Single-Effect LiBr-H2O Cycle Duhring Diagram P 7
PC
Pure H2O; x=0
3
x=xw
4, 6
x=xs
Crystallization PE
1, 8
2
TE
TC~TA
5
TG
T
43
Pumpless Aqua-Ammonia System
Bubble Pump
ASHRAE Handbook of Refrigeration, 2004
Simple and Regenerative Reversed Brayton Cycle T 2
2
3
3
1
4 6, 1 5 S
44
Regenerative Air Cycle Ambient air Recuperator
Gas Cooler
Power
Exp.
Comp.
Conditioned Space
Simple Air Cycle Performance 0.6
Load Temp. ºC
0.5
22.0 12.0 0.4
2.0 -8.0
P O0.3 C
-18.0 -38.0 -58.0 -78.0
0.2
-98.0 -118.0 0.1
0.0 1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
Expander Pressure Ratio
Ta = 35 ºC; ε R = 0.9; η′ E = 0.88; η′ C = 0.87; δ P/P = 0.05; ΔT A = 10 ºC
45
Regenerative Air Cycle Performance 0.6
Load Temp. ºC
0.5
22.0 12.0 0.4
2.0 -8.0
P O0.3 C
-18.0 -38.0 -58.0 -78.0
0.2
-98.0 -118.0 0.1
0.0 1.0
2.0
3.0
4.0
5.0
6.0
Expander Pressure Ratio
Ta = 35 ºC; ε R = 0.9; η′ E = 0.88; η′ C = 0.87; δ P/P = 0.05; ΔT A = 10 ºC
Comparison of Air Liquefaction Cycles 12000
10000
r 8000 i A d i u q 6000 i L g k / J k 4000
2000
0 Revrsible (Ideal)
Linde
Linde + VC Precooler (-45 C)
DualPressure Linde
DualPressure Linde + VC Precooler
Claude
46
