The screw refrigeration compressors are all carried out by oil injection lubrication. According to the different ways of connecting the compressor and the motor, they are divided into three types: open type, semi-closed type and fully closed type.
Open type unit: The compressor is connected to the motor through a coupling, and a reliable shaft seal is required to be installed on the extension shaft of the compressor to prevent the leakage of refrigerant and lubricating oil.
Semi-hermetic unit: The motor and the compressor are integrated, and the flange is connected in the middle, which can effectively prevent the leakage of refrigerant and lubricating oil, and the use of refrigerant to cool the motor eliminates the noise of the motor cooling fan in the open unit.
Fully enclosed unit: The motor and compressor are enclosed in a container, which completely eliminates the leakage of refrigerant and lubricating oil, and the noise is the lowest. At present, the refrigeration compressor has a cooling capacity range of more than 3500KW under standard conditions (evaporating temperature: -15°C, condensing temperature: 30°C).
The fully enclosed screw compressor unit is mainly suitable for independent air conditioning or central air conditioning systems in office buildings, transportation vehicles, libraries, commercial buildings, hospitals, civil residences, hotels and other places that are particularly sensitive to noise. Open and semi-closed units are widely used in industrial and mining enterprises and civil air defense projects.
Comparison of two types of compressor units
1. The advantages of the open unit:
(1) The compressor is relatively separated from the motor, and there are no special requirements for the motor, so the compressor has a wide range of applications.
(2) The same compressor can be adapted to different refrigerants. In addition to using halogenated hydrocarbon refrigerants, ammonia can also be used as refrigerant by changing the material of some parts.
(3) Motors with different capacities can be used according to different refrigerants and working conditions.
(4) The cooling capacity of a single-head unit can reach more than 2 million kcal.
(5) The cost is lower and the price is cheaper.
(1) Shaft seals are required to seal the passage of refrigerant and lubricating oil leakage, which is also the focus of frequent maintenance by users. JB/T6906-93 The standard of screw single-stage refrigeration compressor stipulates the amount of oil leakage: the amount of oil leakage at the shaft seal when the open-type unit is running should not exceed 3ml/h. Since Freon and refrigeration oil are mutually soluble, the simultaneous leakage of Freon and refrigeration oil cannot be avoided during use, especially after 1000 hours of operation, due to the wear of the shaft seal, the leakage of Freon and refrigeration oil will be aggravated, and maintenance will be increased. and operating costs, affecting normal use.
(2) The supporting motor rotates at a high speed, the airflow noise formed by the cooling fan is large, and the noise of the compressor itself is relatively large. The general noise of the open-type unit is above 90dB(A), which causes noise pollution to the environment.
(3) It is necessary to configure complex oil system components such as separate oil separators and oil coolers, resulting in large unit volume, inconvenient use and maintenance, and large weight and floor space.
(4) Low efficiency, due to the need to use an external motor to drive the oil pump and use an ordinary low-efficiency motor, the energy efficiency ratio under nominal operating conditions generally does not exceed 4.0.
2. Semi-hermetic unit Advantages:
(1) Due to the semi-closed method, the motor and the compressor are integrated, so the noise is low, the vibration is small, and there is no leakage of freon and lubricating oil of the open type unit, which reduces the maintenance and management costs of users. It will affect the normal use of users due to leakage.
(2) Due to the semi-closed method, the motor and the compressor are integrated, and the built-in oil separator muffler greatly reduces the operating noise. The noise difference between the open type and the semi-closed type with the same cooling capacity is about 15 dB (A ).
(3) Since the built-in oil separator adopts the oil supply method of internal pressure difference, there is no need to configure an external motor to drive the oil pump, which improves the energy efficiency ratio of operation. The energy efficiency ratio under nominal working conditions is generally greater than 4.5.
(4) For occasions with higher requirements, double-head or triple-head type can be adopted. Each refrigeration system is relatively independent. Once a system fails, other systems can work normally without causing too much impact on production and the environment.
(1) At present, most of the semi-hermetic screw compressors used in China are imported from abroad, and the price is relatively high.
(2) Due to the use of Freon-resistant, lubricating oil-resistant and high-temperature-resistant special motors, the material cost of the compressor is increased, so the price of the semi-hermetic compressor of the same grade is higher than that of the open compressor.
(3) The capacity of a single machine is small, and the capacity of a single machine head generally does not exceed 1.5 million kcal.