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4.If the leakage is detected, refer to following part "Leak
detection". Once the leak has been found and fixed, the
gas tightness test should be repeated.
5.If not continuing straight to vacuum drying once the
gas tightness test is complete, reduce the system
pressure to 0.5-0.8MPa and leave the system
pressurized until ready to carry out the vacuum drying
procedure.
Outdoor unit
Liquid side of
stop valve
Gas side of
stop valve
Nitrogen
Gas pipe
Liquid pipe
Leak detection
The general methods for identifying the source of a leak
are as follows:
1. Audio detection: relatively large leaks are audible.
2. Touch detection: place your hand at joints to feel for
escaping gas.
3. Soapy water detection: small leaks can be detected by
the formation of bubbles when soapy water is applied to
a joint.
5.7 Vacuum Drying
Vacuum drying should be performed in order to remove
moisture and non-condensable gases from the system.
Removing
moisture
prevents
oxidization
of
copper
piping
components. The presence of ice particles in the system
would cause abnormal operation, whilst particles of
oxidized copper can cause compressor damage. The
presence of non-condensable gases in the system would
lead to pressure fluctuations and poor heat exchange
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 of pump lubricant with
compressor oil could cause compressor
malfunction. Therefore a check valve should
be used to prevent vacuum pump lubricant
seeping into the piping system.
Indoor unit
Fig.5.40
ice
formation
and
or
other
internal
32
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 in excess of 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 stop valves, in preparation for refrigerant charging.
Pressure gauge
Yellow hose
ODU unit
Vacuum pump
Blue hose Red hose
Fig.5.41
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 temperature 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 5.6
Humidity<80%RH
Piping size
Thickness
Φ6.35~38.1 mm
≥ 15 mm
Φ41.3~54.0 mm
≥ 20 mm
Field piping
Gas pipe stop valve
Liquid pipe stop valve
Service port
Humidity≥80%RH
Thickness
≥ 20 mm
≥ 25 mm
V.1
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