VAV-107 - page 4

Fan Selection Guidelines
Design47 fanswere testedand ratedon
thebasisof handlingair at standardden-
sity of .075 lb./ft.
In order to select a fan for operation at
any other temperature or altitude, it is
necessary to correct the pressure from
operatingdensity tostandarddensity, se-
lect the fan, then correct the required
horsepower from standard to operating
The correction factor chart below gives
the ratio of actual to standard densities
at various temperatures and altitudes.
Apply the factors as follows:
Ps Standard = Ps Actual ÷ Factor;
BHPActual =BHPStandard xFactor
For Example
RequiredDuty: 30,000CFMat 1.58"Ps
at 120°Fat 4000' elevation
Fromchart below: Factor is .790
1.58Actual ÷ .790=2.0"PsStandard
Select fanmodel fromselectionchart:
4450 - B12 - 1160
BHPat Standard=14.6
Changes in volume, pressure, and horsepower occur in ac-
cordancewith the fan lawswhen fanspeedand/or gasden-
sitychangeswhile the fan isappliedtoa fixedsystem.When
operatingdensity isother thanstandard (.75#/ft.3),pressure
must be corrected to standard conditions for fan selection
andhorsepowermust becorrected fromstandard tooperat-
ingconditionsas intheexampleabove.Performancemaybe
adjustedaccording to the fan lawsbychanging fanspeed.
Basic Fan Laws
1,2,3 5,6,7,8,9,10,11,12,13,14,...16
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