adding them to interior air handlers, but there are still
aspects that need to be considered, such as controls and
relief air,” Moser notes. “A thermostat with two-stage cool-
ing capability may be required to fully take advantage of
the economizer cooling.”
If you’re adding an air-side economizer to an exist-
ing HVAC system, you need to plan carefully for a larger
outside air intake, a larger relief air opening, potentially
a relief air fan, proper damper sizes, and appropriate and
reliable controls, he adds.
You should also review your existing relief air and
ventilation components. Because economizers bring in
large amounts of outside air, you need a subsequent way
to relieve air in order to maintain acceptable building
pressure, says Moser. While an economizer adds fresh air
during its cycle, you will still need to ensure your HVAC
maintains appropriate ventilation in your building when
it’s not running.
3) Quality Parts
Because economizers have a number of continuously
moving parts that are exposed to weather conditions, it’s
critical to specify robust materials that can withstand the
climate and time.
“Good quality, low leakage dampers are very important. Even though a significant amount of surface area is
required to bring in air during the economizer cycle, you
don’t want it to leak when not in use,” Callan explains.
For dampers, aluminum is a good choice because it
won’t rust. Galvanized steel is another option, though
buildings in marine environments might need to upgrade
to stainless, notes Walsh-Cooke.
TYPICAL ECONOMIZER PACKAGE
An air-side economizer uses outdoor air
to provide free cooling. It offers the most
energy savings in dry climates, otherwise
it could let in too much moisture. Typically
packed with a rooftop air handling unit,
the device includes a series of dampers,
enthalpy sensors or dry bulb controls,
actuators, and linkages.
Compressor Fan motor
Heat section Supply air Return air
Economizer damper assembly