APPLICATION GUIDE
Overview
Fans and air compressors are the two most common types of loads in industrial energy-saving transformation.
Most centrifugal fans have square torque loads, while reciprocating or screw air compressors mostly have constant torque loads. The ideas for frequency conversion transformation between the two are different - the core is "selecting the right control mode and degree of protection" rather than simply "installing a variable-frequency drive".
Retrofit Considerations
Judgment of load type: Centrifugal fans and centrifugal air compressors are square torque loads and are suitable for selection according to the energy-saving curve (torque reduction mode); reciprocating/screw air compressors are mostly constant-torque loads and need to be selected according to the constant torque curve, and the energy-saving mode of the fan cannot be directly applied.
Protection level: There is a lot of dust at the fan site. It is recommended that the drive be IP54 or install a protective cabinet. The temperature of the air compressor room is high, so it is necessary to calculate the heat dissipation of the drive and the temperature rise in the cabinet.
Harmonics and electromagnetic compatibility: Harmonics and electromagnetic compatibility should be evaluated based on the variable-frequency drive capacity, short-circuit capacity of the power supply system, sensitive loads on the same bus and local power quality requirements; whether to configure input reactors, filters or other harmonic control measures should be determined based on system calculations and manufacturer recommendations.
Whether a bypass cabinet is needed: Key fans (such as fire supplementary air and smoke exhaust fans) usually require automatic switching to power frequency for direct operation when the frequency conversion fails. It is necessary to design a frequency conversion-power frequency switching bypass cabinet, which is subject to local fire protection regulations.
The air compressor frequency conversion transformation also needs to pay attention to the pressure closed-loop control logic. Usually, pressure sensor feedback is used for PID adjustment instead of simple manual speed adjustment.
Comparison of key points of frequency conversion modification of fans vs. air compressors
| Comparison point | fan | Air compressor (reciprocating/screw type) |
|---|---|---|
| load characteristics | variable-torque loads | constant-torque loads |
| control curve | energy-saving variable-torque mode | constant-torque mode |
| Common degree of protections | There is a lot of dust on site, so IP54 or a protective cabinet is recommended. | The temperature in the computer room is high and heat dissipation needs to be calculated. |
| whether a bypass is required | Special fans such as fire protection usually require | Depends on specific process requirements |
Common Pitfalls
Applying the fan's energy-saving torque reduction curve directly to the air compressor results in insufficient torque and failure to load normally.
Ignore the bypass direct operation requirements of special fans such as fire protection, and the fire protection acceptance will not be met after modification.
Only the cost of the drive body is calculated, and supporting investments such as reactors and bypass cabinets are not reserved.
Frequently Asked Questions
Are all fans suitable for frequency conversion energy-saving transformation?
The energy-saving effect of fans running at variable load for a long time is the most obvious; the investment payback period for frequency conversion transformation of fans running at full load for a long time will be lengthened. It is recommended to calculate the actual load curve before making a decision.
Will the noise of the air compressor change after frequency conversion modification?
The noise will usually decrease as the speed decreases, but attention should be paid to whether the heat dissipation and bearing lubrication during low-frequency operation meet the requirements.
Can fire fans be retrofitted with frequency conversion to save energy?
Dual logic can be adopted: daily energy-saving operation uses variable frequency, and in case of fire alarm, it automatically switches to bypass and starts at full voltage. The specific design must be implemented in accordance with local fire protection regulations.
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