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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
lk
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
17
GETth
English 
