Get Technical data -> 6.1 Basics of air conditioning technology Guide for Volkswagen Touran 4 Door Second Generation (2015-2022)

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

Basic technical and physical proper‐

ties

⇒ “6.1 Basics of air conditioning technology”, page 16

⇒ “6.2 Physical properties”, page 19

⇒ “6.3 Product characteristics”, page 26

⇒ “6.4 Function and role of air conditioning system”, page 26

⇒ “6.5 Other reference material”, page 28

6.1

Basics of air conditioning technology

⇒ “6.1.1 Physical properties of air conditioning system”,

page 16

⇒ “6.1.2 Pressure and boiling point of refrigerant”, page 17

⇒ “6.1.3 Vapour pressure table for refrigerant”, page 17

⇒ “6.2 Physical properties”, page 19

6.1.1

Physical properties of air conditioning

system

The 4 familiar states of water apply to air conditioning refrigerants

as well.

1 - Gas (invisible)

2 - Vapour

3 - Liquid

4 - Solid

When water is heated in a vessel (heat absorption), water vapour

can be seen to rise. If the vapour is heated by further heat ab‐

sorption, the visible vapour becomes invisible gas. The process

is reversible. If heat is extracted from gaseous water -A-, it

changes first to vapour -B-, then to water and finally to ice.

A - Heat absorption

B - Heat dissipation

Heat always flows from a warmer to a colder substance

Every substance consists of a mass of moving molecules. The

fast moving molecules of a warmer substance give off some of

their energy to the cooler and thus slower molecules. As a result,

the molecular motion of the warmer substance slows down and

that of the colder substance is accelerated. This continues until

the molecules in both materials are moving at the same speed.

They are then at the same temperature and no further heat ex‐

change takes place.

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

6.1.2

Pressure and boiling point of refrigerant

The boiling point given in tables for a liquid is always referenced

to atmospheric pressure (1 bar absolute pressure). If the pressure

over a fluid changes, its boiling point changes as well.

Note

Pressure is indicated in various units: 1 MPa (Mega-Pascal) is

equal to 10 bar or 145 psi; 1 bar absolute pressure is equal to

0 bar, which is about the same as ambient pressure (atmospheric

pressure).

It is well known that e.g. the lower the pressure, the lower the

temperature at which water boils.

The vapour pressure curves for water and for R1234yf refrigerant

show that at constant pressure and falling temperature the vapour

becomes liquid (in the condenser), and that when pressure drops,

for example, the refrigerant changes from liquid into the vaporous

state (in the evaporator).

Vapour curve, water

A - Liquid

B - Gaseous

C - Vapour curve, water

1 - Pressure on the liquid in bar (absolute)

2 - Temperature in °C

Vapour pressure curve for refrigerant R1234yf

A - Liquid

B - Gaseous

D - Vapour pressure curve for refrigerant R1234yf

1 - Pressure on the liquid in bar (absolute)

2 - Temperature in °C

Note

The vapour pressure curves of both refrigerants, R1234yf and

R134a, are very similar across a broad temperature range. The

pressure difference between the two refrigerants in a temperature

range of 0 C to +50°C is only about 0.2 bar, for example, which

is why it is not possible to differentiate between the two refriger‐

ants ⇒ “6.1.3 Vapour pressure table for refrigerant”, page 17

and ⇒ Air conditioning system with R134a refrigerant; Rep. gr.

87 ; General information about the air conditioning system and

refrigerant circuit . It is only possible to determine a difference

using relevant sensors, which can analyse the chemical structure

of the refrigerant

⇒ “6.2.16 Analysis of refrigerant R1234yf”, page 24 .

6.1.3

Vapour pressure table for refrigerant

The vapour pressure table for every refrigerant is published in

literature for refrigeration system engineers. This table makes it

6. Basic technical and physical properties

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

possible to determine the vapour pressure acting on the column

of liquid in a vessel if the temperature of the vessel is known.

Since its own characteristic vapour pressure table is known for

each refrigerant, it is possible to establish the type of refrigerant

by measuring the pressure and temperature of refrigerants whose

vapour pressure changes over a certain temperature range (does

not apply when differentiating between R1234yf and R134a as

the vapour pressures are too close

⇒ “6.1.2 Pressure and boiling point of refrigerant”, page 17 ).

Note

♦ The means of differentiation are only given for pure refriger‐

ants whose vapour pressures differ sufficiently. If different

refrigerants are mixed for form a new refrigerant (e.g. 3 differ‐

ent refrigerants to form R407C refrigerant), a vapour pressure

will be created in accordance with the vapour pressures of the

individual refrigerants and their percentage in the mixture.

♦ Absolute pressure means that “0 bar” corresponds to an ab‐

solute vacuum. The normal ambient pressure corresponds to

“1 bar” absolute pressure. On most pressure gauges, a read‐

ing of “0 bar” corresponds to an absolute pressure of one bar

(which is confirmed by the existence of a “-1 bar” marking be‐

neath the “0” scale marking).

♦ Pressure is indicated in various units: 1 MPa (Mega-Pascal)

is equal to 10 bar or 145 psi; 1 bar absolute pressure is equal

to 0 bar, which is about the same as ambient pressure (at‐

mospheric pressure).

♦ The vapour pressures of the two refrigerants, R1234yf and

R134a, are very similar across a broad temperature range,

which is why no difference can be established between them

⇒ Air conditioning system with R134a refrigerant, General in‐

formation about the air conditioning system . It is only possible

to determine a difference using relevant sensors, which can

analyse the chemical structure of the refrigerant

⇒ “6.2.16 Analysis of refrigerant R1234yf”, page 24 .

Temperature in °C

Pressure in bar (positive pres‐

sure) R1234yf

-40

-30

-25

-20

-15

-10

-5

-0.40

-0.01

0.12

0.50

0.83

1.21

1.65

2.15

2.72

3.36

4.09

4.90

5.81

6.82

7.93

9.17

10.52

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

Temperature in °C

Pressure in bar (positive pres‐

sure) R1234yf

12.01

13.64

15.41

17.35

19.46

21.75

24.24

26.94

29.09

6.2

Physical properties

⇒ “6.2.1 R1234yf refrigerant”, page 19

⇒ “6.2.2 Potential risks with R1234yf refrigerant”, page 20

⇒ “6.2.3 Physical and chemical properties of R1234yf refrigerant”,

page 20

⇒ “6.2.4 Critical point”, page 20

⇒ “6.2.5 Environmental aspects of refrigerant R1234yf”,

page 21

⇒ “6.2.6 Trade names and designations of R1234yf refrigerant”,

page 21

⇒ “6.2.7 Colour and odour of R1234yf refrigerant”, page 22

⇒ “6.2.8 Vapour pressure of R1234yf refrigerant”, page 22

⇒ “6.2.9 Physical properties of R1234yf refrigerant”, page 22

⇒ “6.2.10 How R1234yf refrigerant reacts to metals and plastics”,

page 22

⇒ “6.2.11 Critical temperature / critical pressure of R1234yf re‐

frigerant”, page 23

⇒ “6.2.12 Water content of R1234yf refrigerant”, page 23

⇒ “6.2.13 Flammability / decomposition of R1234yf refrigerant”,

page 23

⇒ “6.2.14 Charge factor of refrigerant R1234yf”, page 23

⇒ “6.2.15 Evidence of leaks in a refrigerant circuit with R1234yf

refrigerant”, page 24

⇒ “6.2.16 Analysis of refrigerant R1234yf”, page 24

⇒ “6.2.17 Returning contaminated R1234yf refrigerant for analy‐

sis, processing or disposal”, page 25

6.2.1

R1234yf refrigerant

♦ Air conditioners in vehicles employ the evaporation and con‐

densation process. A substance (the refrigerant) is moved

about a circuit within an enclosed system.

♦ The substance is one that has a low boiling point, in this in‐

stance R1234yf refrigerant.

♦ The R1234yf refrigerant is marketed under various names

(e.g. HFO 1234yf, Opteon 1234yf etc.).

6. Basic technical and physical properties

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Technical data -> 6.1 Basics of air conditioning technology for Your Volkswagen Touran 4 Door Second Generation (2015-2022)

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