Centrifugal fan performance curves and practical operation issues
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I’ve been in the VOCs waste gas treatment industry for not long, and I’m a bit confused about centrifugal fans. If one examines different points on the performance curve of a centrifugal fan, there are cases where the frequency and static pressure vary while the air volume remains the same, as well as cases where the frequency and air volume vary while the static pressure stays the same. But if its frequency is changed during actual fan operation, both the air volume and static pressure will change, right? When the PLC changes the fan frequency, how exactly do the actual air volume and static pressure change? Is it possible to maintain the air volume while only changing the static pressure, or to maintain the static pressure while only changing the air volume? How should this be done? Please, experts, help me figure this out!
This setting cannot be considered solely in terms of \"static pressure\"; the equipment is configured according to its own characteristic curves at the time of manufacture, and such settings are not allowed to be changed arbitrarily as per the regulations. To be honest, if you are not a technical expert in this field but just a user, it is best to start by learning the principles, for reference.
Common fans exhibit a monotonic variation, with only slight upward and downward curves. Only fans with rising and falling curves can exhibit different airflow rates while maintaining the same static pressure; this occurs because the airflow rate and total pressure (static pressure + dynamic pressure) automatically adjust when the frequency of the fan does not change. If you change the frequency to 0.5, the rated speed will be 0.5 of the original value, the air volume will also be 0.5 of the original value, and the total pressure will be 0.25 of the original value. Even the fan manufacturers need to conduct tests to find out, and fans of the same specification produced by different manufacturers can also vary in quality【although their fan sample parameters appear identical】
Thank you, sir. I feel that my understanding has improved from being confused to having a rough idea of it; after all, I’m not a technician from a specialized fan manufacturer. I welcome those who know much about fans to continue the discussion
Someone who knows about fans is here. Your question is too simple – it’s possible to achieve this. It can’t be done solely through frequency conversion; centrifugal fans require a constant flow rate or constant pressure. When using frequency conversion, it’s also necessary to adjust the system’s resistance curve, which is achieved by using valves
The answer above is correct; it is recommended that the original poster read the sections on regulation in books related to pumps and fans. Your understanding is correct; changing the frequency actually means changing the speed of the fan, which in turn alters its performance curve. Without any change in the resistance curve of the piping system, it becomes impossible to maintain constant pressure and flow rates. The operating point of the fan is the intersection of the performance curve and the pipeline network resistance curve; understanding this point resolves the issue easily.
First, understand what dynamic pressure is and what static pressure is. There’s too much typing to do. The dynamic pressure work, static pressure work, and fan drive work together constitute the total power output of the fan. The rotational speed is essentially proportional to the frequency.