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If, Yes, then how the Static pressure of the fan is maintained constant in the Variable Air Volume system(VAV)?
Pease refer to law of affinity
Law 1. With impeller diameter (D) held constant:
Law 1a. Flow is proportional to shaft speed:[1]
Law 1b. Pressure or Head is proportional to the square of shaft speed:
Law 1c. Power is proportional to the cube of shaft speed:
Law 2. With shaft speed (N) held constant: [1]
Law 2a. Flow is proportional to the impeller diameter:
Law 2b. Pressure or Head is proportional to the square of the impeller diameter:
Law 2c. Power is proportional to the cube of impeller diameter (assuming constant shaft speed):
where
So according to the the two laws depending on if you keep diameter size constant then the ESP will change .
yes the friction losses increase the static pressure
ESp for a fan will remain same with same rpm and flow rate.
In constant air flow systems the ESP has been calculated for specific flow rate and duct routing what ever it is. During the installation and balancing the system shall be balanced for a specific flow and ESP than for that specific fan the system shall remain under same conditions for ever untill unless the system parameters are same the flow rpm and ESP shall be same.
yes static pressure can be high or low debending on rpm
yes, if fan impeller shaft rpm increase => shaft power increase the air flow increase, the friction losses increase then ESP increase
compared to the incompressible fluid such as water, the friction loss due to the air movement is negligible in straight ducts.
Static pressure again depends on the size of duct, fittings, rpm and flow rate.
the question is not sufficient to justify the "Yes"
No.not affect the only thing affect the type of duct.