- #1
StudYMA
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I have a question regarding the relationship between airflow restriction and fan power. If the pressure drop across an airflow restrictor (filter bank, heat exchanger coils, etc.) is known by measuring with a magnehelic differential pressure gage and that dP changes (filter replacement/removal, etc), how will that affect fan speed/fan power?
I am talking about a variable speed fan which aims to maintain a constant duct static pressure downstream of said obstructions, so I believe that the fan speed would decrease, but how do I calculate how much?
To find power reduction I initially used an extended bernoulli equation ignoring kinetic and potential energy factors which reduced to [(pressure reduction)*(mass flowrate)]/(air density), or (pressure reduction)*(CFM) but this is coming out lower than I expected.
I'm also aware than fan power varies with the cube of fan speed, so maybe I'm skipping an intermediate step?
Thanks in advance to anybody who can assist me!
-Brian
I am talking about a variable speed fan which aims to maintain a constant duct static pressure downstream of said obstructions, so I believe that the fan speed would decrease, but how do I calculate how much?
To find power reduction I initially used an extended bernoulli equation ignoring kinetic and potential energy factors which reduced to [(pressure reduction)*(mass flowrate)]/(air density), or (pressure reduction)*(CFM) but this is coming out lower than I expected.
I'm also aware than fan power varies with the cube of fan speed, so maybe I'm skipping an intermediate step?
Thanks in advance to anybody who can assist me!
-Brian