Help you calculate how much electricity can be saved by a permanent magnet variable frequency screw air compressor

Nowadays, the energy consumption of air compressors is huge. In general, up to 70% of the electricity bills of factories come from the consumption of air compressors, so energy saving is imperative, so which air compressors are more energy efficient?

  1 energy efficiency rating

   Assuming that it is calculated based on a model with a rated power of 37kW, the speed is the same as 3660rpm, the exhaust pressure is 0.8MPa, and the exhaust volume Qo=5.84m3/min

  A. The input power of the whole machine of the permanent magnet synchronous frequency conversion model is measured as Pi=40.36kW, then the input specific power of the whole machine is: qi=Pi/Qo=40.36/5.84=6.91

  B. The input power of the ordinary asynchronous industrial frequency model is measured as Pi=43.64kW, and the input specific power of the whole machine is: qi=Pi/Qo=43.64/5.84=7.47

According to the latest "GB15193-2009 Positive Displacement Air Compressor Energy Efficiency Limits and Energy Efficiency Grades" standard for screw air compressors, the first level of energy efficiency is input specific power qi<7.2, and the second level of energy efficiency is input specific power 7.2≤qi<8.1 Therefore, the permanent magnet synchronous model is energy efficiency level 1, while the normal asynchronous power frequency model can only achieve energy efficiency level 2.

  2 Analysis of several air volume adjustment methods of air compressor

In order to balance the exhaust volume of the air compressor with the air volume used by the user, the commonly used air volume adjustment methods for ordinary air compressors are air intake throttling adjustment, loading/unloading adjustment, etc. The vacuum is too large due to the intake throttling , And the pressure drop loss during loading and unloading, the energy saving effect of these methods is not ideal.

   Later, due to the development of motor frequency conversion control technology, there was an adjustment method by controlling the motor speed. This method can make the power consumption of the air compressor and the exhaust volume change close to linear proportions. It is gradually becoming popular. However, this control method has the following defects:

  2.1 When the speed and load of the ordinary asynchronous motor are less than the rated point of the design, the efficiency of the motor is significantly reduced, and the greater the difference, the more obvious the reduction in efficiency

  2.2 When the ordinary asynchronous motor is running at a lower frequency, the problem of insufficient output torque will occur, which makes the inverter "motor torque overload" and tripping fault

  2.3 When ordinary asynchronous motors run at lower frequencies, they will experience unstable speed, increased vibration and noise, and increased heat generation.

  2.4 Even if the current vector control method is adopted, these shortcomings cannot be completely eliminated.

2.5 The current new control method adopts a permanent magnet motor + a dedicated variable frequency drive control method, which has high efficiency and can always be maintained at a high level, constant torque operation at any speed, stable speed, and fast response to speed changes. (The acceleration time from 0 to rated speed is within 50ms, and there is no inrush current), low noise and other advantages.

  3 energy saving effect

Similarly, according to the previous two models with a rated power of 37kW, when the load rate is only 60%, the input power of the industrial frequency model with ordinary air intake throttle control is 38.2kW, and the shaft power of the permanent magnet inverter model is 23.6 kW, the power saving rate reaches 37.5%.

If calculated on the basis of 4,000 hours of work per year, the annual electricity cost of the ordinary asynchronous power frequency model is 107,200 yuan, and if the permanent magnet synchronous frequency conversion model is used, the annual electricity cost will be 65,800 yuan, which is an annual saving The electricity bill is 41,400 yuan.