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CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 1
Semi-Hermetic Compressorsfor CO2 Cascade Systems
Hermann RenzBitzer Kuehlmaschinenbau GmbH Germany
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 2
Semi-Hermetic Compressorsfor CO2 Cascade Systems
Contents
Introduction
Example of CO2 cascade system
Properties of CO2 vs. R22
Requirements on compressor design
Development Stages / Design Features
Summary
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 3
Introduction
Due to its environmentally benign characteristics and specific properties CO2 has good potential for:
The extended use in subcritical cascade systems like for example: Supermarket applications Industrial refrigeration systems
Specific features Very high volumetric cooling capacity Favourable TEWI, energy demand & installed cost Reasonable safety requirements
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 4
Example of Supermarket Application – MT with HFC / LT with CO2 Cascade
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 5
Comparison of Properties –Low Temp CO2 Cascade vs. R22
0
100
200
300
400
500
600
700
800
900
1000
R22 Reference
CoolingCapacity
COP SuctionPressure
DischargePressure
VapourDensity
(LP)
Co
mp
aris
on
CO
2 vs
. R2
2 [%
]
R22 / to -35°C, tc -10°C
CO2 / to -35°C, tc -10°CCompressor displacement counter-proportional to relative cooling capacities
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 6
Pressure Ranges –CO2 Cascade vs. R22 and R410A
Comparison of pressure levels CO2 & R410A vs. R22
5
10
15
20
25
30
35
40
0 5 10 15 20
Suction pressure [bar]
Dis
ch
arg
e p
res
su
re [
ba
r]
'
R410ACO2
Cascade
R22
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 7
Requirements on Compressor Design
Consideration of CO2 properties High Pressure levels
Strength of housing and crank gear High volumetric cooling capacity
Adaptation of displacement relative to motor power High vapour density / absolute mass flow
Adaptation of working valves & cross sections High gas solubility in oil
General requirements High isentropic efficiency Compact & solid design, use of “standard” parts
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 8
Design Features Pressure Levels
High pressure levels of CO2
Compressor housing with high strength pressure
Safety factor “3“ acc. (pr)EN12693
Required pressures (approx.)
HP 40 bar
LP 25 bar (standstill pressure)
Realised compressor construction
Compact design
Closed housing w/o bottom plate
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 9
Adaptation of displacement Optimum match to
“standard” motor sizes Potential for the use of
“standard” parts cost issue
Smaller displacement allowing for generously sized crank gear
Design FeaturesDisplacement / Crank Gear (1)
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 10
Design FeaturesDisplacement / Crank Gear (2)
Adaptation of displacement by modified piston stroke Allowing for larger piston diameter
Potential for generously sized piston pin and for special piston pin bearing
Connecting rods with closed big end (large diameter) Potential for large cross sections of working valves
Adaptation to high vapour density Improvement of compression process
Reduced piston velocity Improved running smoothness
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 11
Lubricant Issues with CO2 Compressors
Relevant to compressor Heavy mechanical load on crank gear High gas solubility in oil Strong oil foaming tendency with pressure fluctuations
High danger of boundary friction
Relevant to (commercial) refrigerating systems Oil return from system / avoiding strong oil migration
and fouling effects in heat exchangers require: Good flow characteristics, low viscosity on suction side Sufficient miscibility with CO2
Suitable Solution especially formulated POE lubricant
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 12
Oil / Refrigerant (CO2) Properties
-40 -20 0 20 40 60 80 100Temperatur [ oC]
5
10
20
50
100
Dam
pfdr
uck
[ba
r]
9595
9090
8585
8080
5
10
20
50
100
5001000
10000
kin.
Vis
kosi
tät
[ m
m2 /s
]
100 M-% Öl100 M-% Öl
9595
9090
8585
BSE60K
0 20 40 60 80 100Konzentration [M-% Öl in CO2 ]
-50
-40
-30
-20
-10
0
10
20
30
Tem
pera
tur [
o C]
PhasentrennungPhasentrennung
NominalConditions
Miscibility Limits
Pull down
Pressure / Temperature / Viscosity
BSE60K
Vap
our
Pre
ssur
e [b
ar]
kin.
vis
cosi
ty [
mm
2 /s]
Temperature [°C] Concentration [M-% Oil in CO2]
Phase separation
Tem
pera
ture
[°C
]
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 13
Compressor Lubrication
Enhanced centrifugal lubrication Quick oil supply after start Enlarged oil pocket at
the shaft end Separation of oil foam
by gravity principle Reduced oil carry over
minimum oil side flow Potential for oil monitoring
system in oil pocket
CENTRO STUDI GALILEO
INDUSTRIA & FORMAZIONE
CENTRO RICERCA AMBIENTE ED IMPRESAUNIVERSITA’ DEGLI STUDI DI MILANO
European seminar: carbon dioxide as a refrigerantMilan, 27th November 2004
CO2 CascadeComp_Studi Galileo 14
Summary
Convincing arguments for the application of CO2 in low temperature cascade systems
Very high volumetric cooling capacity – allowing for: Small compressor displacement Small pipe sizes, favourable installed cost
High specific load on compressor housing and crank gear to be considered High pressure levels & vapour density
Need for Adapting compressor design and Lubrication system