7
the inlet of expansion valve or capillary full of liquid state refrigerant.
On the contrary, the insufficient sub cooling will cause flash gas occurring at the inlet of expansion valve,
which will result in capacity reduction and increasing vibration, noise.
2.1.3 Superheating Degree
In order to prevent compressor from flooded back operation, a minimum suction superheating degree of 5K
[10F], and a minimum sump superheating degree of 12K [21F] must be maintained.
It is necessary to keep the proper superheating degree since too big superheating will cause the high
discharge temperature and the decrease of refrigerant mass flow rate.
2.1.4 Discharge Gas Temperature
The recommended discharge temperature is not higher than 95
℃
[200F] under the standard conditions.
2.1.5 Suction Accumulator
For air-conditioning system in which capillary is used or heat pump system, suction accumulator is necessary
to prevent the uncontrolled liquid flooding back.
The proper size suction accumulator can:
1)
Prevent liquid refrigerant migrating to compressor
2)
Prevent liquid refrigerant being sucked into compressor.
The suction accumulator used in the system should at least meet the requirements as follow:
1)
The size of the accumulator must be greater than 60% total refrigerant volume.
2)
To ensure well oil return, a
φ
1.5 mm orifice is necessary in the suction accumulator.
3)
Filter mesh must be used to prevent orifice being blocked when orifice is smaller than
φ
2.0 mm
2.1.6 System Charge Limit
The proper system charge can keep the system parameters in the normal level, such as cooling and heating
capacity, sub cooling degree, suction and discharge temperature, compressor’s sump temperature, etc.
The refrigerant charge and refrigerant oil in the system should keep the ratio as follow:
Oil (kg)/ Refrigerant (kg)
≥
0.35
Note: Specific gravity of the Oil using in R22 series compressors is 0.92
Specific gravity of the Oil using in R407C/R410A/R134a series compressors is 0.94
If oil/refrigerant ratio is lower than 0.35, it will cause dilution of oil and lack of lubrication inside of compressor.
So please inform us before the system being tested under 0.35>oil(kg)/refrigerant (kg)
≥
0.3 condition,
some detailed advices will be given about oil level in compressor .
As a general requirement, oil (kg)/refrigerant (kg) >0.3 shall be kept.
