Classification of Screw Chiller Compressors

2022/09/05 ClassificationIndustry News 396

Classification of Screw Chiller Compressors

Screw chillers are all lubricated by oil injection, and are divided into three types: open type, semi-closed type and fully closed type according to the connection method between the compressor and the motor.

Open type: The compressor is connected to the motor through a coupling, and a reliable shaft seal is required to be added to the protruding shaft of the chiller to prevent the leakage of refrigerant and lubricating oil.

Semi-hermetic unit: The motor and the compressor are integrated, and the intermediate flange is used to connect, which can effectively prevent the leakage of refrigerant and lubricating oil, and use the refrigerant to cool the motor to eliminate the noise of the motor cooling fan in the open unit.

Closed unit: The motor and the compressor are sealed in a container, completely eliminating the leakage of refrigerant and lubricating oil, with minimal noise. Under standard operating conditions (evaporating temperature: -15°C, condensing temperature: 30°C), this unit can produce a cooling capacity of more than 3500KW.

The fully enclosed screw compressor unit is mainly used in independent air conditioning or central air conditioning systems that are particularly sensitive to noise, such as offices, transportation, libraries, commerce, hospitals, residential buildings, hotels and other places. Open machine and semi-closed machine are widely used in civil air defense engineering of industrial and mining enterprises. The following is a comparative analysis of these two forms of compressor units:

1. Open unit.

Advantages: Since the compressor is relatively separated from the motor, there is no special requirement for the motor, so it has a wide range of applications. Motors with different capacities can be configured for different refrigerants and usage conditions. The same compressor can adapt to different refrigerants. In addition to using halogenated hydrocarbon refrigerants, ammonia can also be used as refrigerant by changing the materials of some components. The cooling capacity of a single-head unit can also reach more than 2 million kcal, and the cost is relatively low.

Defect: Refrigerant and lubricating oil passages need shaft seals, which is also a focus of frequent maintenance by users. In the standard of JB/T6906-93 screw-type single-stage refrigeration compressor, there are regulations on the amount of oil leakage: the amount of oil leakage at the shaft seal of the open unit shall not exceed 3ml/h. Because Freon and refrigeration oil are mutually soluble, the simultaneous occurrence of Freon and refrigeration oil leakage cannot be avoided during use, especially after 1000 hours of operation, due to shaft seal wear, it will aggravate the leakage of Freon and refrigeration oil, increase maintenance and Operating costs, affecting normal use.

Complex oil system components, such as independent oil separators and oil coolers, will cause the unit to be bulky, inconvenient to use and maintain, heavy and occupy a large area. The motor is matched to rotate at a high speed, the airflow noise formed by the cooling fan is large, and the compressor itself is also noisy. The switching noise is generally above 90dB (A), resulting in noise pollution. Due to the need for an external motor to drive the oil pump and an ordinary low-efficiency motor, the energy efficiency ratio of the air conditioner under nominal operating conditions is generally not more than 4.0, so the efficiency is low.

2. Semi-closed unit.

Advantages: In the semi-closed mode, the motor and the compressor are combined into one, and equipped with a built-in hydraulic muffler, which greatly reduces the running noise. The same cooling capacity, the noise difference between the open type and the semi-closed mode is about 15dB (A). The integrated design of the motor and the compressor has low noise, low vibration, no problems such as poor switching and oil leakage, which reduces the maintenance and management costs of users, and will not affect the normal use of users due to water leakage. For occasions with high demand, two-head or three-head forms can be used. 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. The internal pressure differential oil supply method does not require an external motor-driven oil pump, which improves the energy efficiency ratio of operation. The energy efficiency ratio under the actual working conditions of the air conditioner is generally above 4.5.

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