# Axial fan for HVAC with HEPA filters

I have a background in mechanical engineering but HVAC is not my specialization. I am trying to properly size an axial fan to get a determined airflow from a duct. Both inlet and outlet are at atmospheric pressure. You can see in the diagram that it is a very simple system with 1 inlet and 1 outlet. I have a main filter at the inlet with the given pressure drop at the CFM i am trying to achieve. I also have a secondary filter with much lower pressure drop. Assuming a laminar flow condition and negligible pressure losses in the duct (I can check these assumptions on my own), what would be the way to determine the required pressure from the fan to achieve the desired CFM output?

Thank you

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• So laminar really? And all you need to do is calculate the pressure drop caused by each element.: filter 1, pipe & filter 2 plus fan efficiency. – Solar Mike Aug 11 at 9:30
• We need dimensions of the duct (or flow velocity). An axial fan probably won't work very well in this application. We use some form of radial fan in HVAC for a reason. The factor of interest is how the velocity pressure (1/2 p V^2) relates the the pressure gain (300 Pa). That establishes the mechanical geometry of the device for best efficiency. – Phil Sweet Aug 11 at 9:42
• You also have to consider the noise spectrum. You can push the primary frequency above 22,000 hz with a convention blower with a lot of little blades. – Phil Sweet Aug 11 at 9:45
• The dimensions are tentatively: 0.4m wide, 0.6m tall, 2m long. Thank you for your help – JC ME Aug 11 at 14:27
• After cursory googling a agree with @PhilSweet - unlikely you'll find an axial blower. If noone here is willing & able to answer I'd try a a sales person for blowers, just give them numbers and ask for an idea how to integrate it. – mart Aug 13 at 15:01