Why does static pressure decrease as CFM increases on blower fan charts?

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Static pressure decreases as CFM increases on blower fan charts due to the inherent characteristics of fans, which differ from ductwork. As airflow rises, the pressure required to push air through a system increases, but fans experience reduced airflow with greater resistance. Fan charts illustrate the performance range of a fan, indicating how much CFM it can deliver against specific resistance levels. To determine actual fan performance, one must match the fan curve with the system's resistance. Understanding this relationship is crucial for effective airflow management in duct systems.
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Hi, Looking at blower fan charts, why does the static pressure drop with increased CFM, what makes sense to me should be a pressure difference rise with increasing CFM.
 
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The pressure required to blow air through a ductwork system rises with increasing airflow. But fans aren't ductwork. For a fan, the greater the resistance, the lower their airflow.
 
Thanks!
Does that mean that fan charts tell what CFM flow will the fan be able to give at a given resistance to its inflow?
The resistance coming from a pipe wall for example, a fan at the outlet will be able to suck the air out at a given CFM overcoming the wall resistance given in terms of Pa/inches of water ?
 
hali24953 said:
Does that mean that fan charts tell what CFM flow will the fan be able to give at a given resistance to its inflow?
The resistance coming from a pipe wall for example, a fan at the outlet will be able to suck the air out at a given CFM overcoming the wall resistance given in terms of Pa/inches of water ?
Yes, the fan curve alone won't tell you the performance of the fan, just the performance range. To find the actual performance you need to match the fan curve to the system resistance.
 
oooooooooo thanks!
 

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