Twin screw compressor parallel technology

With the increasing energy shortage, people's awareness of energy conservation is also increasing, and the energy-saving requirements for air-conditioning units are also increasing. For conventional air conditioning units, more than 90% of the time is running under load. The overall performance of the air-conditioning unit throughout the season is more objective than the performance under full-load nominal conditions. In recent years, environmental protection agencies have actively advocated the setting of high indoor temperature in summer and low indoor temperature in winter. The government departments have also issued policies requiring that the air conditioning set temperature of public buildings in summer should not be lower than 26 ° C, and winter should not be higher than 20 ° C. This allows the air conditioning unit to run more time in a partial load state. Increasing the partial load performance of the unit has great significance for building energy conservation.

Due to the constraints of materials, processing level, cost and other factors, it is more difficult to improve the full load performance of air conditioning units, and the partial load performance of the unit can often be improved by system optimization, and the implementation is less difficult and economical. Parallel compressors are an effective means of improving the performance of the unit. For large refrigeration units, a single large capacity compressor or two smaller compressors can be used, and the two compressors can be divided into two independent systems or two compressors in parallel. When a single large-volume compressor unit is used, the efficiency of the motor will decrease significantly. When a unit with a dual-compressor independent system is unloaded, nearly half of the heat exchange area of ​​the evaporator and the condenser cannot be exchanged. heat. The unit with parallel connection of dual compressors will not reduce the efficiency of the compressor when the unit is unloaded, and the heat exchange area of ​​the heat exchanger will not decrease. Therefore, the partial load performance of the refrigeration unit with parallel compressor is relatively high.

The parallel technology of scroll compressor and piston compressor has been widely used in air conditioning units. However, since the screw compressor oil tank is on the high pressure side of the compressor, the oil balance of the compressor is difficult after parallel connection, so the screw Compressor parallel technology has not been well promoted and applied in the air conditioning industry. At present, screw compressor is the most widely used compressor in large public building refrigeration units. Improving the partial load performance of the screw type refrigeration unit is of great significance for reducing the energy consumption of public buildings.

The semi-closed screw compressors commonly used in air-conditioning units mainly include three parts: motor, compression section and oil separator. The mixture of refrigerant and refrigeration oil passes through the oil separator and separates most of the frozen oil. Store it in the oil sump at the bottom of the oil separator. A small amount of chilled oil enters the system and circulates with the refrigerant, and finally returns to the compressor through the suction. For parallel compressor system oil, there is bound to be a problem of refrigerating oil migration between the two compressors. Therefore, oil balance control must be performed after the compressors are connected in parallel.

A large amount of manpower and financial resources have been invested in improving the overall performance of the screw air conditioner unit, and various air conditioning systems such as a cross drain type parallel system, a centralized oil supply parallel system, and an oil and gas balanced parallel system have been developed. There are two intersecting drain pipes between the compressors of the cross drain type parallel system. The drain pipes are led out from the oil storage tank of one compressor and connected to the suction side of the other compressor. When one of the compressors has a good oil return effect, too much refrigeration oil will return to the other compressor through the drain pipe. The cross drain type parallel system can reliably ensure the oil balance of the compressor, but control Improper impact on the performance of the unit. The two compressors of the external oil separator centralized oil supply parallel system are connected in parallel, and the exhaust gas of the compressor is connected to an external oil separator. The refrigeration oil separated from the compressor internal oil separator is also sent to the outside. In the oil separator, the oil and oil circuits of the two compressors are uniformly taken out from the external oil separator. The exhaust gas of two parallel screw compression sections of the oil-gas balanced parallel system maintains the same pressure of the refrigerant in the oil separator through a gas balance pipe before the oil and gas separation, and sets an oil balance in the oil tank. Tube, when there is a difference in the refrigerating oil separated by the two parallel compressor oil separators, the refrigerating oil in the high oil level compressor is transferred to the low oil level compressor through the oil balance pipe to make the oil of the two compressors The position is balanced.