CO2 Article (Danfoss Industrial Refrigeration)

CO2

Refrigerant for Industrial Refrigeration

Article

Refrigeration and Air Conditioning Controls

R E F R I G E R A T I O N A N D A I R C O N D I T I O N I N G

2 RZ0ZR102 � Danfoss A/S (RC-CM / MWA), 12- 2002

Article CO2 - Refrigerant for Industrial Refrigeration

Contents Page

Introduction .................................................................................................................................. 3

CO2 as a refrigerant ..................................................................................................................... 4

CO2 as a refrigerant in industrial systems ................................................................................... 6

Design pressure .......................................................................................................................... 7

Efficiency ..................................................................................................................................... 8

Oil in CO2 systems ....................................................................................................................... 8

Component size .......................................................................................................................... 8

Refrigerant charge in CO2-NH3 cascade systems ...................................................................... 9

Material compatibility ................................................................................................................. 10

Water in CO2 systems ................................................................................................................ 10

Leaks in CO2-NH3 cascade systems ......................................................................................... 12

Safety valves in CO2 systems .................................................................................................... 12

Safety ......................................................................................................................................... 13

Conclusion ................................................................................................................................ 13

Danfoss valves and controls for CO2 ......................................................................................... 14

� Danfoss A/S (RC-CM / MWA), 12 - 2002 RZ0ZR102 3


The application of carbon dioxide (CO2)refrigeration systems is not new. Carbondioxide was first proposed as a refrigerant byAlexander Twining [1], who mentioned it in hisBritish patent in 1850. Thaddeus S.C. Loweexperimented with CO2 military balloons, buthe also designed an ice machine with CO2 in1867. Lowe also developed a machineonboard a ship for transportation of frozenmeat.

From reading the literature it can be seen thatCO2 refrigerant systems were developedduring the following years and they were attheir peak in the 1920's and early 1930's. CO2

was generally the preferred choice for use onboard ships whilst ammonia (NH3 or R717)was more common in land applications [2].With the advent of the "Freon" refrigerantsinitially R12, the application of CO2 lessened.The main reason for its decline was certainlythe rapid loss of capacity and pressureincrease at high temperatures.

Ammonia has continued to be the dominantrefrigerant for industrial refrigerationapplications over the years.

Introduction

In the 1990's there was renewed focus of theadvantages offered by using CO2, due toODP (Ozone Depletion Potential) and GWP(Global Warming Potential), which hasrestricted the use of CFC's and HFC's andrestrictions on the refrigerant charge in largeammonia systems.

CO2 belongs to the so-called "Natural"refrigerants, together with e.g. ammonia,hydrocarbons such as propane and butane,and water. All of these refrigerants have theirrespective disadvantages: Ammonia is toxic,hydrocarbons are flammable, and water haslimited application possibilities. Incomparison, CO2 is non-toxic and non-flammable, but has a double role in theenvironment. CO2 is necessary for all life onearth, but is also a green house gas, whichcan change the environment if itsconcentration in the atmosphere changes.

[1] Bondinus, William S ASHRAE Journal April 1999[2] Lorentzen, Gustav Reprint from IIR Conference 1994 Proceedings "New Applications of Natural

Working Fluids in Refrigeration and Air Conditioning"



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10

100

1000

-80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Temperature (°C)

Pre

ss

ure

(b

ar)

Liquid

Solid

Vapour

Supercritical

CO2 Phases

Triple point

CO2

1

10

100

-200 -100 0 100 200 300 400 500

Enthalpy(J)

Pre

ss

ure

(b

ar)

Solid - Vapour

Liquid - Vapour

Liquid

Solid

Solid - Liquid

73.6

-5.2

- 78.4°C

+31°C

1

10

100

-200 -100 0 100 200 300

Solid - Vapour

Liquid -

Liquid

Solid

Solid -

-

Vapour

56.6°C

Supercritical

Pressure Temperature Pressure Temperature

Triple point 5.18 bar –56.6°C 0.06 bar –77.7°C

Critical

pressure73.6 bar (31°C) 113 bar (132°C)

CO2 NH3



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–20°C (1.9 bar)

+30°C

–20°C

–15°C

–40°C

Pre

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Enthalpy

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–40°C (10 bar)

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Enthalpy

CO2

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Enthalpy

CO2

R717

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CO2 compressor

CO2-receiver

CO2-R717 Heat exchanger

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–40°C (10 bar)

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–20°C

-40°C

–40°C

Pre

ss

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Pre

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Enthalpy

CO2

R717

+8°C

+8°C (43 bar)

–15°C

CO2-

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CO2 defrostcompressor

CO2-receiver

CO2 evaporator

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–40°C (10 bar)

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–45°C

–40°C

–40°C

Pre

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Pre

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Enthalpy

CO2

R717

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CO2-

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CO2 evaporator

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Practical limit: PS Psaturated +15%

Design pressure

Pressure peaks 5%

Saturated pressure10%Safety valve

≥

CO2

20

25

30

35

40

45

50

55

60

-30 -20 -10 0 10 20

Design temperature (°C)

Pre

ss

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(b

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Design pressure (bar-g): PS + 15 %

"Saturated"pressure (bar-a)

PS + 10% (bar-g)

PS 50

PS 40

PS 25

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Wet suction line

0

20

40

60

80

100

R717 CO2

DN

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15

20

25

R717 CO2

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Relative permeation

coefficient

Relative diffusion

coefficient

Relative solubility

coefficient

Q D S

N2 - Nitrogen 1 1 1 1

CO2 – Carbon Dioxide 24 1 24 24

CH4 - Methane 3.4 0.7 4.9 7

He - Helium 15 60 0.25 0.004

O2 - oxygen 3.8 1.7 2.2 1.29

S/D

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0

200

400

600

800

1000

1200

1400

1600

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Temperature [°C]

mg

of

wa

ter/

kg

of

refr

ige

ran

t [p

pm

]

CO2

NH3R134a

R22

R404A

0

10

20

30

40

50

60

70

80

90

100

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

Temperature [°C]

mg

of

wa

ter/k

g o

f re

frig

era

nt

[pp

m]

CO2 + H2O gasPhase

CO2 +

ICE

CO2 +

WaterCO2

Water Solubility in Refrigerants.

Liquid Phase(Y-Axis Linear)

0

500

1000

1500

2000

2500

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Temperature [ oC]

mg

of

wate

r/kg

refr

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nt

[pp

m]

Water Solubility in Refrigerants.

Gas Phase(Y-Axis Linear)

0

200

400

600

800

1000

1200

1400

1600

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Temperature [oC]

mg

of

wate

r/kg

of

refr

igera

nt

[pp

m]

CO2

CO2

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r/kg

refr

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The availability of components for CO2

industrial refrigeration systems havingreduced pressure to approx. 30 bar is good.Several manufacturers of equipment for thetraditional refrigerants can also supply somecomponents for CO2 systems, but theavailability of higher-pressure components forCO2 industrial refrigeration systems is limited.An important factor in the speed of

introducing CO2 systems, is very muchdependent on the availability of criticalcomponents for high pressure CO2.Within the area of industrial refrigeration, CO2

will not replace ammonia. The industrial CO2

systems are all hybrid systems, which alsorequire ammonia on the high temperatureside of the system, but only with a smallammonia charge.

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CO2

1

10

100

-200 -100 0 100 200 300 400 500

Enthalpy (J)

Pre

ss

ure

(b

ar)

Solid - Vapour

Liquid - Vapour

Liquid

Solid

Solid - Liquid

73.6

-5.2

- 78.4°C

+31°C

1

10

100

Solid - Vapour

Liquid -

Liquid

Solid

Solid -

-

56.6°C

Supercritical 50 bar

at the

Safety valve 35 bar

Safety valve

Safety valve 35 bar

0% solid CO

triple point

Vapour

2

at the

Safety valve 50 bar

5% solid CO

triple point2



Danfoss industrial refrigeration valves havebeen used for CO2 systems for more than 15years. The CO2 systems have beenrefrigeration, process and fire fightingsystems where the pressure has been limitedto 25 bar. During the last few years, Danfosshas supplied an increasing number of valvesfor several CO2 systems at different pressurestages up to 50 bar.

Danfoss valves andcontrols for CO2

Today, Danfoss is offering a broadprogramme of industrial products applicablefor CO2, however this is dependent ondemands regarding the design pressure. Thetable below includes the componentsavailable for the different pressure stages.

��

All marked components areapplicable for CO2 in thestandard execution.These components areapplicable for CO2 40 bar or50 bar.

High pressure components

DN PS

25

bar

PS

40

bar

PS

50

bar

Modulating liquid level regulators PMFL PMFH all 25-65

Main Valves, Solenoid Valves PM1 PM3 PML PMLX all 25-125

Pilot Valves for PM Main Valves EVM

Other pilots

Motor Regulating Valves MRV all 25-65

Motor Expansion Valves MEV all 25-65

Float Valves HFI 100, 150 100 - 150

SV 1-3 & 4,5,6

Stop Valves SVA 15-200 15-200

SVA 250, 300 250-300

Regulating Valves REG all 15 - 40

Stop Check Valves SCA all 20-125

Gas Powered Stop Valve GPLX 80, 100, 125 80-125

SFV 15, 20, 25 15 - 25

BSV 8 8

DSV 32 32 **) 1

POV 40, 50, 80 40-80

Filters FIA all 32-200

NRVA all 15 - 65

NRVS 20, 25, 32 20-32

CHV all 20 - 40

Solenoid Valves EVRA all 15-40 **) 1

EVRS all 15-25 **) 1 **) 1

Liquid Injection AKVA all 15-40 **) 1

Level Indicator AKS 45 all

The product can

be used in

standard version.

All products are

CE approved

The product must

be manufactured

in a special

version (design

modif ication,

higher test

pressure, marking

All products are

CE approved

and documentation).

Safety Valves and Change Over Valves

Check Valves

The product must

be manufactured

in a special

version (higher

test pressure,

marking and

documentation).

All products are

CE approved

Danfoss industrial refrigeration

In connection with the CE approval of thesevalves, Danfoss has implemented productmodifications and approved them for themaximum pressure. The products aresubject to specific testing and marking,but all of them are CE approved.

CO2

20

25

30

35

40

45

50

55

60

-30 -20 -10 0 10 20

Design temperature (°C)

Pre

ss

ure

(b

ar)

Design pressure (bar-g): PS + 15 %

"Saturated"pressure (bar-a)

PS + 10% (bar-g)

PS 50

PS 40

PS 25

CO2 Article (Danfoss Industrial Refrigeration)

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