2. Guideline for each installation process
29
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Heat pump 50Hz/R410A
Part 3 Design and installation
2.7. Vacuum drying work
2.7.1 What is Vacuum drying?
Vacuum drying is : The use of a vacuum pump to vaporize(gasify) the moisture (liquid) inside the pipe and expel it leaving
the pipes completely dry inside.
At 1 atm(760mmHg) 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 11.7°C as shown in the table on the right
, the degree of vacuum must be lowered below -750mmHg
The evacuation of air conditioner piping provides the following effects.
- Vaccum drying
- Removes air and nitrogen(used in air-tightness test) from the inside
of pipes.
Therefore , it is necessary to ensure that both purposes have been
achieved in the vacuum drying operation.
Boilng point of
water(°C)
40
-705
7,333
55
30
-724
4,800
36
26.7
-735
3,333
25
24.4
-738
3,066
22
22.2
-740
2,666
20
20.6
-742
2,400
18
17.8
-745
2,000
15
15.0
-747
1,733
13
11.7
-750
1,333
10
7.2
-752
1,066
8
0
-755
667
5
The degree
of a vacuum
Pressure
mmHg
Pa
Torr
Absolute pressure (mmHg)
Temperature
-20
760
755
740
720
710
700
690
680
670
660
560
460
360
260
160
60
0
-10
0
10
20
30
40
50
60
70
0 mmHg
mmHg
5
10
20
30
40
50
60
70
90
100
200
300
400
500
600
700
760mmHg
x
Required degree
of vaccum
3.8MPa
Outside
temperature
range
Evaporation
point
(C)
The degree of a vacuum (mmHg)
730
730
730
Key point: Maintain a vacuum level of -755mmHg
NOTE
