This paper derives the calculation formula of the change rate of energy efficiency level, and the calculation formula of the input specific power change of screw air compressor, when it is promoted to permanent magnet variable frequency screw air compres-sor from fixed frequency screw air compressor. The calculating results are listed based on the given values on standard condition. The results show that when the fixed frequency screw compressor is upgraded to the permanent magnet variable frequency screw compres-sor, the energy efficiency level has not been significantly improved, and even sometimes, the energy efficiency level has been re-duced. It is emphasized that the energy efficiency value of screw air compressor is conceptually different from the energy saving of screw compressor in using process. The high efficiency of the screw compressor products and the high efficiency energy saving in the using process should supplement each other in order to make better contribution to energy conservation.%推导螺杆空压机由工频提升为永磁变频时其能效水平的变化率和输入比功率变化值的计算公式,按标准工况取值列出计算结果.结果表明工频螺杆空压机提升为永磁变频螺杆空压机时,能效水平无明显提升,甚至有时是降低了能效水平.强调指出螺杆空压机产品的能效指标与螺杆空压机,在使用过程中的节能有概念上的差别.螺杆空压机产品的高能效和用户使用过程中的高效节能相辅相成,才能更好地为节能作贡献.
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