24
WARNING: To ensure proper operation of 30RY units there
must be at least 12 K of subcooling as the liquid refrigerant
enters the expansion valve.
The 30RY units use refrigerant. For your information, we are
reproducing here some extracts from the official publication
dealing with the design, installation, operation and
maintenance of air conditioning and refrigeration systems
and the training of people involved in these activities, agreed
by the air conditioning and refrigeration industry.
12.3 - Apparent and actual subcooling
Pressure
Enthalpy
3
4
5
1
6
2
L
L + V
V
12 - MAINTENANCE
Any technician attending the machine for any purpose must be
fully qualified to work on refrigerant and electrical circuits.
All refrigerant charging, removal and draining operations
must be carried out by a qualified technician and with the
correct material for the unit. Any inappropriate handling can
lead to uncontrolled fluid or pressure leaks.
WARNING: Before doing any work on the machine ensure
that the power is switched off. If a refrigerant circuit is opened,
it must be evacuated, recharged and tested for leaks. Before
any operation on a refrigerant circuit, it is necessary to
remove the complete refrigerant charge from the unit with a
refrigerant charge recovery group.
12.1 - General maintenance of the refrigerant circuit
•
Keep the unit itself and the space around it clean and free
of obstructions. Remove all rubbish such as packing
materials, as soon as the installation is completed.
•
Regularly clean the exposed pipework to remove all dust
and dirt. This makes detection of water leaks easier, and
they can be repaired before more serious faults develop.
•
Confirm that all screwed and bolted connections and
joints are secure. Secure connections prevent leaks and
vibration from developing.
•
Check that all insulation joints are securely closed and
that all insulation is firmly in place. Check all heat
exchangers and all pipework.
If water jets are used inside the units (e.g. to clean the coils), the
lower holes (for possible condensate removal) must be blocked.
12.2 - Verification of the refrigerant charge
CAUTION: The 30RY units are supplied with a precise
refrigerant charge (see Physical Data table).
To verify the correct system charge prodeed as follows:
Ensure that no bubbles appear in the sight-glass, when operat-
ing the unit at full load for a while, at a saturated condensing
temperature of between 55 and 57°C. If necessary cover a
section of the coil surface to obtain this condensing tempera-
ture. Under these conditions the apparent subcooling which is
equal to the saturated condensing temperature (1 - on the
saturated dew point curve) minus the liquid refrigerant tem-
perature (3) ahead of the expansion device must be between 12
and 14°C. This corresponds to an actual subcooling temperature
of between 5 and 7 K at the condenser outlet, depending on the
unit type. Actual subcooling is equal the saturated liquid tem-
perature (2 - on the saturated bubble point curve) minus the
liquid refrigerant temperature (3) ahead of the expansion device.
Use the pressure tap supplied on the liquid piping to charge
refrigerant and to find out the pressure of the liquid refrigerant.
If the subcooling value is not correct, i.e. lower than the speci-
fied values, a leak detection test must be carried out on the unit,
as it no longer contains its original charge.
In order to measure the liquid refrigerant pressure and tem-
perature ahead of the expansion device, an access port must be
opened on the expansion device which causes a slight air
bypass on the condenser. Wait until unit operation has stabil-
ized before carrying out pressure and temperature measurements.
Legend
1
Saturated condensing temperature at the dew point
2
Saturated liquid temperature at the bubble point
3
Liquid refrigerant temperature
4
Saturation curve at the dew point
5
Saturation curbe at the bubble point
6
Isotherms
7
Apparent subcooling (1 - 3)
8
Real subcooling (2 - 3)
L
Liquid
L + V vapour
V
Vapour