Analysis of the Energy-saving Effect of Centrifugal Chiller Units in Air Conditioning Systems

2025-05-07

Traditionally, the industry standard is to regard the COP value under the operating conditions of the chiller unit as an important indicator for evaluating the performance of the air conditioning unit. However, in reality, the chiller unit only operates in a part-load state for a certain period of time. Therefore, evaluating it using this indicator has some one-sidedness. Evaluating it using the comprehensive efficiency of the air conditioner during operation can more truly reflect the energy-saving efficiency of the chiller unit. As a result, this indicator has been increasingly recognized within the industry. The magnetic levitation variable-frequency centrifugal chiller unit is also developed based on this concept, which will greatly reduce the energy consumption of the air conditioning system and reduce emission pollution.

Analysis of Working Principle and Energy-saving Effect
1.1 Working Principle of the Chiller Unit
The magnetic levitation variable-frequency chiller unit mainly relies on the magnetic levitation bearing to drive the magnetic levitation compressor to do work. A permanent magnet DC motor is installed axially on the centrifugal chiller unit. After the power is turned on, under the influence of the electromagnetic field, the bearing rotates at a high speed, and the displacement error between the bearing and the base is kept within no more than 0.007mm, reducing the possibility of friction between them.
It also saves the layout design of the lubrication and cooling system and improves space utilization.
1.2 Analysis of the Energy-saving Effect of the Chiller Unit under the Part-load State
By studying the operating conditions of the chiller unit in the central air conditioning system under the part-load state, adjusting the influencing factors of energy consumption, and formulating targeted technical transformation measures for regulation and control, the energy consumption of components can be reduced. Under the operating condition of setting the temperature of the chiller unit at 32°C, study the value range change of COP under different loads, and conduct a comparative study on three forms: the magnetic levitation centrifugal chiller unit, the variable-frequency centrifugal chiller unit, and the fixed-frequency centrifugal chiller unit.
The commonly used fixed-frequency centrifugal chiller unit usually controls the flow of the air conditioning compressor by adjusting the angle of the guide vanes. However, when operating under low-load conditions, the chiller unit is prone to surging, which affects the stable operation of the compressor. Moreover, the adjustable angle range of the guide vanes is limited. Therefore, experimental verification shows that when the opening degree of the guide vanes is less than 30%, there is an obvious throttling effect, but the energy consumption of the chiller unit also increases significantly.
In addition to controlling the opening and angle of the guide vanes, the variable-frequency centrifugal chiller unit coordinates and uses variable-frequency speed regulation means in combination, which expands the controllable range of the load and also increases the energy consumption adjustment range of the chiller unit. However, like the fixed-frequency equipment, it also has the surging phenomenon under low-load conditions. Moreover, with the occurrence of the variable-frequency effect, the guide vanes are frequently opened and closed for adjustment, resulting in greater energy loss and increasing the operating energy consumption.
As mentioned above, the magnetic levitation centrifugal chiller unit mainly uses a permanent magnet DC motor to drive the bearing to rotate, and at the same time combines variable-frequency technology to adjust the motor speed, refrigeration flow, etc. according to the work requirements at any time, ensuring the optimal compression state of the compressor under different load conditions. Therefore, although the COP curve shows a decreasing trend under different load operating conditions, within the 70% load range, the COP curve as a whole shows a horizontal state, and the energy-saving effect is significantly better than that of the other two forms of centrifugal chiller units.
1.3 Analysis of the Energy-saving Effect of the Chiller Unit with the Change of Cooling Water with Different Temperature Senses
Also conduct a comparative study on three forms: the magnetic levitation centrifugal chiller unit, the variable-frequency centrifugal chiller unit, and the fixed-frequency centrifugal chiller unit. Set the full-load condition, that is, at a 100% load rate, and study the change of COP of the chiller unit under the action of cooling water with different temperature senses. The temperature difference range of the inlet water is 10~36°C. Through comparative analysis, when the initial temperature is 10°C, the COP of the magnetic levitation centrifugal chiller unit reaches 22%. When the inlet water temperature rises to 16°C, the COP of the variable-frequency and fixed-frequency chiller units begins to appear, with an initial value of about 13%. And with the continuous increase of the inlet water temperature of the cooling water, the COP values of the three chiller units all show a decreasing trend. When the temperature reaches 32°C, the COP values of the three are equal at the intersection, and the COP reaches 6%.
In conclusion, under the same 100% load rate condition and the same inlet water temperature of the cooling water, the COP value of the magnetic levitation chiller unit is successively higher than that of the variable-frequency chiller unit and the fixed-frequency chiller unit, and it has a more obvious energy consumption reduction effect.
In addition, the air conditioning compressor of the magnetic levitation centrifugal chiller unit only needs a current of 2A to start a single unit, and it can be started and operated under a low-current condition, which greatly reduces the risk of the high-current starter breaking down the power grid and reduces the starting energy consumption of the compressor. Combining the multiple advantages of the magnetic levitation centrifugal chiller unit, such as variable frequency, zero friction, no need for lubricating oil, and a relatively high COP under low-load conditions, as well as good adaptability to the water temperature of the cooling water, it has a relatively high overall energy-saving effect.
Analysis of the Economic and Practical Performance of the Chiller Unit
2.1 Refrigeration and Cooling Supply in the Energy Center
As a supporting facility of the airport terminal, the energy center needs to have sufficient cooling capacity to ensure a suitable temperature in the airport environment. Generally, the indoor venues set up include facilities such as the waiting hall, the command center, and the public service area, with a usable area of approximately 720,000 m², and the budgeted cooling load during the summer peak period is approximately 97,500 kW.
2.2 Influence of Energy Policies
In order to effectively control the actual power consumption of the upper-level power supply, combined with the requirements of electricity consumption policies, make the most of the electricity price difference between the peak and off-peak periods, reasonably regulate the usage duration of large power-consuming facilities at the airport in different time periods, rationally distribute the electricity load of different equipment, formulate the best load distribution plan, and achieve optimized electricity consumption.
2.
3 Air Conditioning Cooling Supply Scheme
Combined with the energy and electricity consumption policies of the local government and the power department, comprehensively analyze the electricity consumption requirements of different areas and facilities at the airport, and mainly adopt the cooling supply scheme of water thermal storage. It is planned to build 12 chiller units with a capacity of 2000 RT to form a water-cooling system thermal storage facility, and build 3 water-cooling tanks with a capacity of approximately 18,000 m³, with a thermal storage capacity reaching 117,400 IHH. Use the water thermal storage method for cooling supply during the low electricity price period at night, and ensure to meet the load requirements of the air conditioner at night. Release the cooling capacity of the water-cooling tanks during the high electricity price period during the day for centralized cooling supply. The main equipment involved includes centrifugal chiller units, chilled water multi-stage pumps, water-cooling tanks, and electrical control equipment, etc.
2.4 Comparison of Economic Effects
Calculated according to the standard summer air conditioning usage time of 170 days, conduct a comparative analysis between the fixed-frequency centrifugal chiller unit and the magnetic levitation centrifugal chiller unit. The basic equipment is equipped with cooling towers, cooling water pumps, chilled water multi-stage pumps, water-cooling tanks, thermal storage ponds, auxiliary power supply systems, and pipeline facilities, etc., and the parameters such as the model, power, and number of installed units of various equipment are basically the same. However, for the complete construction of the entire system, the initial investment of the supporting facilities of the fixed-frequency centrifugal water-cooling unit is 132.65 million yuan, while the initial investment of the supporting facilities of the magnetic levitation centrifugal water-cooling unit is 139.35 million yuan, which is 6.7 million yuan more than that of the fixed-frequency unit, and the economic cost is relatively high.
Conduct a comprehensive analysis of the power consumption of each model of equipment under different operating load conditions. Preset the proportion of the equipment operating load to the total full-load as 25%, 50%, 75%, 100%, etc., and conduct a vertical comparison of the power consumption during different electricity consumption periods, such as the peak period, high period, flat period, and off-peak period, under the same load conditions of the chiller unit and the supporting equipment and facilities. Through practical verification, the power consumption of the fixed-frequency centrifugal chiller unit and its supporting facilities reaches 32.3052 million kW·h/year, while the power consumption of the magnetic levitation centrifugal chiller unit and its supporting facilities is 22.0891 million kW·h/year. The cooling supply system of the magnetic levitation centrifugal chiller unit saves 10.2161 million kW·h of electricity per year compared with that of the fixed-frequency centrifugal chiller unit, saving 4.801 million yuan in electricity costs, and the operating cost is greatly reduced.
Although the initial investment of the magnetic levitation centrifugal chiller unit is relatively high, through low-cost maintenance during the normal operation period in the later stage, the initial investment cost can be recovered within a cycle of 1.4 years, with quick results and high returns. Moreover, under the condition of the same equipment depreciation and annual loss, the operation and maintenance cost of the overall supporting facilities of the magnetic levitation centrifugal chiller unit is greatly reduced, which is helpful for the long-term stable operation of the unit, has good economic savings value, and also has a better advantage in power saving and energy consumption reduction compared with the fixed-frequency unit. Therefore, the overall performance of the magnetic levitation chiller unit is more superior.