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5.7 Vacuum Drying
Vacuum drying should be performed to remove moisture
and non-condensable gases from the system. Removing
moisture prevents ice formation and oxidization of
copper piping or other internal components. The
presence of ice particles in the system will cause
abnormal operation, but particles of oxidized copper can
cause
compressor
damage.
non-condensable gases in the system will lead to
pressure
fluctuations
and
performance.
Vacuum drying also provides additional leak detection
(in addition to the gas tightness test).
CAUTION
Before performing vacuum drying, make sure
that all the outdoor unit stop valves are firmly
closed.
Once the vacuum drying is complete and the
vacuum pump is stopped, the low pressure in
the piping could suck vacuum pump lubricant
into the air conditioning system. The same
could happen if the vacuum pump stops
unexpectedly during the vacuum drying
procedure. Mixing pump lubricant with
compressor oil could cause the compressor
to malfunction. Therefore a check valve
should be used to prevent vacuum pump
lubricant from seeping into the piping system.
During vacuum drying, a vacuum pump is used to lower
the pressure in the piping to the extent that any moisture
present evaporates. At 5 mm Hg (755 mm Hg below
typical atmospheric pressure) the boiling point of water is
0°C. Therefore a vacuum pump capable of maintaining a
pressure of -756 mm Hg or lower should be used. Using
a vacuum pump with a discharge over 4 L/s and a
precision level of 0.02 mm Hg is recommended. The
vacuum drying procedure is as follows:
1. Connect the vacuum pump through a manifold with a
pressure gauge to the service port of all stop valves.
2. Start the vacuum pump and then open the manifold
valves to start vacuuming the system.
3. After 30 minutes, close the manifold valves.
4. After a further 5 to 10 minutes check the pressure
gauge. If the gauge has returned to zero, check for
leakages in the refrigerant piping.
5. Re-open the manifold valves and continue vacuum
drying for at least 2 hours and until a pressure difference
of 0.1 MPa or more has been achieved. Once the
pressure difference of at least 0.1 MPa has been
achieved, continue vacuum drying for 2 hours. Close the
manifold valves and then stop the vacuum pump. After 1
hour, check the pressure gauge. If the pressure in the
piping has not increased, the procedure is finished. If the
pressure has increased, check for leakages.
6. After vacuum drying, keep the manifold connected to
the master unit stop valves, in preparation for refrigerant
charging.
The
presence
of
poor
heat
exchange
36
Pressure gauge
Yellow hose
Master unit
Vacuum pump
Blue hose Red hose
5.8 Piping Insulation
After the leak test and the vacuum drying are
completed, the pipe must be insulated. Considerations:
Make sure the refrigerant piping and branch joints
are completely insulated.
Make sure the liquid and gas pipes (for all units) are
insulated.
Use heat-resistant polyethylene foam for the liquid
pipes (able to withstand temperature of 70°C), and
polyethylene foam for the gas pipes (able to
withstand temperatures of 120°C).
Reinforce the insulation layer of the refrigerant piping
based on the installation environment.
5.8.1 Selection of insulation material
thickness
Condensed water may form on the surface of the
insulation layer.
Table 5.3
Humidity<80%RH
Piping size
Thickness
Φ6.4~38.1 mm
≥ 15 mm
Φ41.3~54.0 mm
≥ 20 mm
5.8.2 Pipe wrapping
To avoid condensation and water leakage, the
connecting pipe must be wrapped with tape to ensure
isolation from the air.
Tape
Insulation material
Liquid pipe
Gas pipe
When wrapping insulation tape, each circle should press
half of the previous circle of tape. Do not wrap the tape
too tightly to avoid reducing the thermal insulation effect.
After completing the pipe insulation work, seal the holes
in the wall with sealing material.
Slave unit
Slave unit
Field piping
Gas pipe stop valve
Liquid pipe stop valve
Service port
Figure 5.30
Humidity≥80%RH
Thickness
≥ 20 mm
≥ 25 mm
Figure 5.31
V.1
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