The economizer design of low temperature chiller plays an important role in optimizing the refrigeration efficiency and energy efficiency ratio. By introducing economizers, the energy efficiency of the refrigeration system can be significantly improved, energy consumption can be reduced, and the service life of the equipment can be prolonged at the same time.

1. The basic principles and functions of economizers

An economizer is a heat exchange device whose main function is to subcool another part of the refrigerant by recovering the heat released by the refrigerant in the evaporator. This subcooling process can enhance the heat absorption capacity of the refrigerant in the evaporator, thereby improving the refrigeration efficiency of the system. In addition, the economizer can also lower the exhaust temperature of the compressor, reducing the heat load and energy consumption of the compressor.

2. The improvement of refrigeration efficiency by economizers

The economizer enhances the heat absorption capacity of the refrigerant in the evaporator by increasing the subcooling degree of the refrigerant, thereby improving the refrigeration efficiency of the system. For instance, when the evaporation temperature is below -25℃, the economizer can significantly increase the cooling capacity and reduce the exhaust temperature of the compressor. Research shows that when the refrigerant is R22, the economizer can increase the cooling capacity by 19 to 44% and the unit power by 7 to 30%, with obvious energy-saving effects.

In a throttling system, the refrigerant liquid is divided into two paths. One path is throttled through the throttling valve and then enters the evaporator for cooling. The other path is depressified through the throttling valve and then enters the economizer to absorb heat, generating a flash gas that mixes with the gas in the evaporator for further compression. In the secondary throttling system, the refrigerant liquid enters the economizer through the throttling valve. The flash gas generated at the top continues to compress with the original gas, while the liquid at the bottom enters the evaporator for cooling after secondary throttling. Whether it is primary throttling or secondary throttling, the refrigerant entering the evaporator is subcooled, increasing the cooling capacity. At the same time, after gas replenishment, the mass of the gas in the unit volume increases, and the compression work increases, but the efficiency improvement is relatively slow. Therefore, the cooling coefficient of the chiller is improved, which has an energy-saving effect.

3. The improvement of energy efficiency ratio (COP) by economizers

The use of economizers can significantly improve the energy efficiency ratio (COP) of the chiller. For instance, under working conditions with a relatively low evaporation temperature, the adoption of an economizer for air replenishment cycle can enhance the efficiency of the single-stage screw compression refrigeration cycle, enabling the single-stage screw compressor to maintain efficient operation over a wider temperature range. Studies show that the use of economizers can increase the energy efficiency of screw chilled water by about 20%.

The economizer improves energy efficiency by dividing the liquid coming out of the condenser into two paths. One path is absorbed by the suction port of the compressor, and the other path is supplied to the evaporator, allowing the liquid supplied to the evaporator to be subcooled again. The discharge of medium-pressure refrigerant vapor in the flash generator reduces the enthalpy value of the refrigerant entering the evaporator and improves the efficiency of the refrigeration cycle. The cooling capacity of the unit has increased by more than 16%.

4. The influence of economizers on the performance of compressors

The use of economizers not only enhances the refrigeration efficiency but also has a positive impact on the performance of the compressor. For instance, through the gas replenishment process, the economizer can, on the one hand, enhance the gas delivery capacity of the compressor, and on the other hand, increase the degree of liquid subcooling. This enables the unit to transform from a single-stage compressor unit to a small two-stage compressor unit for heating in low-temperature environments, thereby improving the heating efficiency of the unit.

The use of economizers can reduce the heat load and energy consumption of compressors and extend their service life. For instance, the use of economizers can reduce the working time of compressors under high loads, thereby lowering the wear and failure rate of compressors.

5. The influence of economizers on the overall performance of the system

The use of economizers can significantly enhance the overall performance of the system, including cooling capacity, energy efficiency ratio and reliability. For instance, the use of economizers can enhance the energy efficiency of refrigeration systems, reduce operating costs, and simultaneously extend the service life of equipment. Economizers are particularly widely used in large cold storage facilities and industrial refrigeration systems.

The use of economizers can also reduce unnecessary energy loss and waste heat emissions, which is conducive to achieving the energy conservation and environmental protection goals of the refrigeration system. For instance, the economizer saves a significant amount of electricity and fuel consumption by lowering the condensing temperature and raising the evaporation temperature.

6. Design and selection of economizers

The design and selection of economizers are crucial for optimizing refrigeration efficiency and energy efficiency ratio. The size and shape of the economizer should be designed according to the flow rate of the refrigerant to ensure effective heat exchange. Furthermore, the higher the heat exchange efficiency of the economizer is, the better the energy efficiency of the system will be. Choosing an economizer with a higher heat transfer coefficient can improve the system performance.

The material selection of the economizer is also very important. Core components such as heat exchange tubes and shells usually adopt materials with good corrosion resistance and thermal conductivity, such as copper, stainless steel or aluminum alloy, to ensure long-term efficient and stable operation. 316L stainless steel, due to its excellent corrosion resistance, is particularly suitable for economizers that come into contact with corrosive refrigerants, effectively preventing corrosion and extending service life.

7. Installation and maintenance of economizers

The installation and maintenance of the economizer are crucial for ensuring its optimal performance. The installation of the economizer should avoid spraying liquid on the rotor and be equipped with a high-precision filter. The complete set of accessories for the economizer interface varies depending on the compressor model. The economizer circuit should remain disconnected until the working conditions stabilize.

The maintenance and upkeep of the economizer should include checks and maintenance operations such as lubricating oil, bearings, and rotor rotation direction. For instance, regarding the oil pump, each circuit of the 30GX/HX screw chiller uses an external lubricating oil pump as part of the start-up sequence. The oil pump starts first and reads the reading of the oil pressure sensor. After running for 20 seconds, the oil solenoid valve is activated and the oil inlet valve of the compressor is opened. If the oil pump establishes sufficient oil pressure, the compressor will start. Once the compressor starts, the oil pump shuts off within 10 seconds until the next start. If the oil pump fails to establish sufficient oil pressure, it will reactivate after 3 seconds and attempt to establish the oil pressure again. If it fails, the control device will issue an alarm.

8. The future development direction of economizers

With the continuous development of refrigeration technology, the design and application of economizers are also constantly innovating. In the future, the design of economizers will place greater emphasis on energy conservation and environmental protection to meet the demands of various application scenarios. For instance, through further research and improved design, the economizer can better adapt to the refrigeration demands under different working conditions and enhance the overall energy efficiency of the system.

Conclusion

The economizer design plays an important optimization role in the low temperature chiller. By increasing the subcooling degree of the refrigerant, the economizer can significantly enhance the refrigeration efficiency and energy efficiency ratio, reduce energy consumption, and extend the service life of the equipment. The design and selection of economizers should fully take into account factors such as the flow rate of the refrigerant, heat exchange efficiency, material choice, and installation and maintenance, to ensure their optimal performance. In the future, with the continuous development of refrigeration technology, the design and application of economizers will play an important role in more fields.