ASHRAE Journal Supplement - AMCA InMotion - November 2021 - 20

modulating actuator, along with the correct blade rotation
(parallel or opposed), is vital to optimal system operation.
Design Considerations
Volume-control dampers are used when it is necessary
to control fl ow, pressure, humidity, or temperature in
an air system. Specifying and selecting the appropriate
damper for a ventilation strategy requires consideration
of various performance factors, such as static-pressure
loss, leakage, and thermal effi ciency.
Static-pressure loss. Per ASHRAE, static-pressure
Control dampers ready for installation at a data
center. Photograph courtesy of Ruskin
can modulate open or closed to
achieve a desi red posit ion or
fl ow via a signal from a building
management system. Employing
modulating actuated dampers with
specifi c control strategies allows
the owner to take advantage of
free cooling-that is, the use of
outdoor air at ambient temperature,
rather than the refrigeration
process, to reject heat-and air-side
economization-defi ned in ANSI/
ASHRAE/IES 90.1-2019, Energy
Standard for Buildings Except
Low-Rise Residential Buildings,
as the use of outdoor air, through
a duct-damper arrangement and
automatic control system, to reduce
the need for mechanical cooling-
when the outdoor temperature and
humidity are mild. Selecting the
most appropriate damper for a system design is critical in
ensuring system performance and optimizing data-centerequipment
functionality.
There are several styles and methods of construction
of volume-control dampers and numerous options that
can provide additional value to a ventilation strategy.
Understanding the differences enables designers to properly
specify, design, and maximize the benefi ts of systems
utilizing control dampers. Selection of the appropriate
20
2021 AMCA inmot ion
loss is the difference in pressure between two points in
a fl ow system, usually resulting from frictional resistance
to fl uid fl ow. Blade design and construction greatly
affect static-pressure-loss performance.
Increased static-pressure
loss translates to greater energy and
load required to operate a system.
Standard volume-control dampers
used to regulate fl ow in a system
commonly are constructed with
one of three types of blades: triple V,
formed airfoil, or extruded airfoil.
Because of its aerodynamic
Thermally insulated control dampers
mounted on the outside wall of a data
center. Photograph courtesy of T. A. Morrison &
Company Inc.
shape, a formed airfoil blade typically
will have considerably less
static-pressure loss in the fully open
position than a triple-V blade. This
has been shown in air-performance
testing performed in accordance
with ANSI/AMCA Standard 500-D.
Because of the smoother shapes
that can be achieved via the
extruding process, an extrudedaluminum
" true " airfoil blade will
have a lower static-pressure drop than a formed-steel
airfoil blade. Additionally, it will have a longer service
life because of less corrosion. Although an extrudedaluminum
damper can be costlier, in a system with
velocities greater than 2,000 fpm (10 m/s), it should be the
fi rst choice to minimize static-pressure loss and possibly
reduce the fan energy required to operate the system.
Leakage. Where a damper is required for air shutoff,
the amount of air leakage through the damper should be
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ASHRAE Journal Supplement - AMCA InMotion - November 2021

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