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.
Thanks Robert. The example was for one of the Fan Laws in order to show the effects of changing RPM in relationship to CFM for a particular Fan irrespective of the design of the ductwork. Fan Law Example was for CFM (new) = CFM (old) x [RPM-new / RPM-old]. What you are stating is true for another of the fan laws which effects Static Pressure with a change in RPM as follows. SP (new) = SP (old) x [RPM-new / RPM-old]2. Great observation. Thanks.
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?
There are similarities, but air and water have their differences, here are some of them, such as Density and Specific Heat Capacity, flow rate equations, pressure drop, compressibility (Air is compressible) , heat transfer and capacity, friction factor and Reynolds number. Air is compressible with lower density and specific heat capacity, requiring different ductwork and fan power calculations. Water is incompressible with higher heat transfer efficiency, affecting pipe sizing, pump power, and pressure drop calculations.
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?
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
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.
The Industry Standards are a good place to start, which is ASHRAE if you're doing Mechanical Engineering, ASPE for Plumbing. Then study up on the local codes, especially if you're in California or a place where energy is a driving force for the code cycles. Good luck.
Break Horsepower (BHP) is a unit of measurement for the actual horsepower delivered by an engine to a pump, fan, or other machinery, after accounting for losses caused by friction and other factors within the engine itself. Unlike theoretical horsepower, BHP measures the effective power output available to do work.
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.
Thanks Robert. The example was for one of the Fan Laws in order to show the effects of changing RPM in relationship to CFM for a particular Fan irrespective of the design of the ductwork. Fan Law Example was for CFM (new) = CFM (old) x [RPM-new / RPM-old]. What you are stating is true for another of the fan laws which effects Static Pressure with a change in RPM as follows. SP (new) = SP (old) x [RPM-new / RPM-old]2. Great observation. Thanks.
Very useful....i got a very clear explanation about sp...thanks
Thank you for all your videos. I am learning so much.
You're Welcome
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?
There are similarities, but air and water have their differences, here are some of them, such as Density and Specific Heat Capacity, flow rate equations, pressure drop, compressibility (Air is compressible) , heat transfer and capacity, friction factor and Reynolds number. Air is compressible with lower density and specific heat capacity, requiring different ductwork and fan power calculations. Water is incompressible with higher heat transfer efficiency, affecting pipe sizing, pump power, and pressure drop calculations.
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?
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
Any increase in the resistance to airflow will cause a loss in CFM and performance.
Very good explanation!
Glad it was helpful! Thanks for watching.
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.
Thanks for your comment. I'll have the engineer review the calculation.
you really should get that fixed asap....@@MEPAcademy
I'm a MEP engineering intern. Any good resources I can learn from?
The Industry Standards are a good place to start, which is ASHRAE if you're doing Mechanical Engineering, ASPE for Plumbing. Then study up on the local codes, especially if you're in California or a place where energy is a driving force for the code cycles. Good luck.
How to calculate square root?
What is bhp correct definition please explain
Break Horsepower (BHP) is a unit of measurement for the actual horsepower delivered by an engine to a pump, fan, or other machinery, after accounting for losses caused by friction and other factors within the engine itself. Unlike theoretical horsepower, BHP measures the effective power output available to do work.
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Thanks for watching
CFM
CFM = Cubic feet per Minute