Daikin VRV II Series Design, Installation & Testing Instructions page 37

Si39-303
3.2.6 Vacuum Drying
What is vacuum
Vacuum drying is:
"The use of a vacuum pump to vaporize (gasify) the moisture (liquid) inside the pipes and expel it leaving
drying?
the pipes completely dry inside."
At 1 atm (760 mmHg) the boiling point (evaporating temperature) of water is 100°C but if a vacuum is
created inside the pipes using a vacuum pump then the boiling point is rapidly reduced as the degree of the
vacuum is increased. If the boiling point is reduced to a level below that of the ambient temperature then
the moisture in the pipes will evaporate.
<Example>
When outside temperature is 72°C
As shown in the table on the right, the degree
of vacuum must be lowered below –75.2mmHg.
The evacuation of air conditioner piping provides the following effects.
1. Vacuum drying
2. Removes air and nitrogen (used in air-tightness test) from the inside of pipes.
Therefore, it is necessary to ensure that the both purposes have been achieved in the vacuum drying
operation.
General Information
Key points
Lower the degree of vacuum to below –755mmHg
Boiling point
of water (°C) ∗ mmHg
40 –705
30 –724
26.7 –735
24.4 –738
22.2 –740
20.6 –742
17.8 –745
15.0 –747
11.7 –750
→
7.2 –752
0 –755
Above figures (mmHg) are gauge pressure readings.
(V1216)
Installation
Pressure
Pa Torr
7333 55
4800 36
3333 25
3066 22
2666 20
2400 18
2000 15
1733 13
1333 10
1066 8
667 5
31