VAV-107 - page 10

To properly compare variousmethods of
volume control, you need to look further
than just brakehorsepower savings.Own-
ersdonot pay for brakehorsepower, they
pay for electricityconsumed (input power).
Inefficiencies in powered equipment
should be included in any comparison of
the power consumption of various types
of volume control apparatus applied to a
fan operating on a normal system curve
where the requiredpressurevariesas the
squareof thevolumeof air).Theblue line
depicts the systembrake horsepower re-
quirements as a percentage of the full
load requirement. The other lines depict
the input power requirements for the var-
ious typesof volumecontrolwhenapplied
to this system in conjunction with a 90%
The green line indicates the input
power required for a controllablepitch
VAVVane axial fan. Note at full load,
since we are using a 90% efficient
motor, the input power requirement is
greater than100%.
The orange line indicates the input
power requiredwhen applying an ad-
justable frequency speedcontroller to
the same fan (published data from
manufacturer of adjustable frequency
speedcontroller).Noteat full load, the
input power requirement is greater
due to inefficiencies inbothmotor and
speed controller.
The red linedepicts the input power re-
quired for the same fan utilizing an
inlet vane control damper.
Note that until you exceed 50% turn-
down, theControllablePitch fan requires
lesspower than theadjustable frequency
speed controller. This is due to the
inefficiencies in the frequency control
At 80%of full load flow, the controllable
pitch fanconsumes15%lesspower than
the adjustable frequency and 39% less
thana variable inlet vane control.
At 70%of full load, the controllable pitch
fan consumes 10% less power than the
Compare the
Efficiency of a
Pitch Fan
Blade angle canbe
adjustedwhile fan is
operating... provides
power savings
1,2,3,4,5,6,7,8,9 11,12,13,14,15,16
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