Fan Laws How to Calculate CFM BHP SP RPM

How to calculate the CFM, BHP (Brake Horsepower), SP (Static Pressure ) and RPM. Learn how changing anyone of these factors changes the other.

If you increase the Static Pressure, what happens to the CFM? Learn how to read a fan chart.

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[robertallen]

Starting at ~5:13 into your video: if you increase the RPM, the flow rate will increase along with a corresponding increase in the resistance to flow, i.e., ~static pressure. The static pressure can not stay at 0.4" w.c (in your example) UNLESS you have physically changed the ventilation system to make it have less resistance, e.g., few elbows, better transitions, etc.

[jwisquitethefellow]

Thank you for all your videos. I am learning so much.

[munthasirmi]

Very useful....i got a very clear explanation about sp...thanks

[samuelgenovese]

I am confused - according to the curve CFM and SP are inversely proportional but according to the calc they are directly proportionate. What do I have confused?

[aznmadhatter]

Good morning! Thank you for the video.

Studying for HVACR PE Exam and looking at the video it seems these equations are specific to pumps from PE handbook section 3.7.6. Unlike the fan equations shown from PE handbook section 9.3.8.3. Would you know why it’s different? I assumed it would be treated the same just different fluid. Thoughts?

[JohnnyJr]

Dose this apply to prop fans?
Looking for why prop fans increase current when static increases .. on blowers it makes sense that air is the load and if there is less air then the current drops

[andrew]

Your equation to calculate CFM based on SP does not appear to be correct. It should be CFM1 / SqRt (SP2/SP1). An increase in SP at the same RPM would decrease the CFM.

[deloran]

I'm a MEP engineering intern. Any good resources I can learn from?

[maggurichiranjeevi]

What is bhp correct definition please explain