install airflow monitoring stations, a device that is placed
in the air stream to measure how much air is flowing
through an opening.
“If your economizer is cycling back and forth, it’s easy to
disrupt the pressure balance in the building,” says Callan.
“You can have tremendous pressure inside the building if
the economizer is full running and your exhaust or return
system isn’t keeping up or isn’t properly designed. The air-
flow sensors allow you to track and calculate more directly
You may also want to bypass the economizer on days
when pollen counts or smog levels are excessive.
“If you have excellent outdoor air quality, an economizer will improve indoor air quality as it provides more
oxygen to occupants. But if it’s poor air quality, you could
be introducing pollutants and allergens at a higher volume
than you would without an economizer,” Callan stresses.
“In those cases, you need to increase filtration, which can
be difficult in a one-pass system.”
5) Preventive Maintenance
If you’re in the bad habit of deferring maintenance,
don’t bother with an economizer. While by no means a
delicate piece of equipment, any number of issues can
trigger a chain reaction that ultimately causes the unit
to waste energy. The longer you ignore inspections and
cleaning, the more likely you are to run
“Many air-side economizers aren’t
working properly due to lack of mainte-
nance. BOMA’s Preventive Maintenance
Guidebook: Best Practices to Maintain
Efficient and Sustainable Buildings lays
out a plan for upkeep,” Moser says. “The
mixed air plenum of an air handler or
rooftop unit may be a dark and windy
place, but it’s important to regularly test
the operation of air-side economizers to
ensure their long-term performance.”
“If you have a qualified engineering
staff, they should evaluate the economiz-
er and its dampers during their routine
daily checks,” adds Callan. “You should
also do a full inspection before and after
economizer season, he adds, or every six
months if you have year-round cooling.”
Pay special attention to all moving
parts, including the actuator and link-
ages, as well as seals, recommends
Walsh-Cooke. Properly calibrated sen-
sors are another area to keep an eye on.
This should be done at least once a year.
“You already have a number of sensors around your
building that need to be maintained and inspected – an
economizer is only adding a few more to the good maintenance practices you should already be doing,” Walsh-Cooke notes. “If you’re not calibrating your other building
sensors and keeping up on equipment care, you’re already
losing energy elsewhere.” B
Jennie Morton firstname.lastname@example.org is senior
editor of BUILDINGS.
Another overlooked component is the enthalpy sensor, which measures the combination of temperature and
humidity. This is done so the economizer can compensate
for the differential between the total heat content of the
outside air and inside air.
“If the enthalpy sensors aren’t calibrated properly,
it doesn’t take much on either side to turn your benefit
upside down and increase the load of your air conditioning
equipment rather than decreasing it,” warns Callan.
You might also consider a fixed or differential dry bulb
rather than enthalpy sensors: “Dry bulb-based economizer
controls are more reliable due to the error potential of enthalpy sensors. Recent research shows that dry bulb-based
controls are more suitable than enthalpy-based controls,
even in humid climates,” says Moser.
4) Smart Control Sequences
Because an economizer’s performance is dependent on
so many variables, you truly need dedicated BAS monitoring. This will allow you to keep tabs on performance and
alert you to any mechanical problems. It also provides a
degree of customization, which can be beneficial during
the shoulder months or a specific weather event.
One critical element is having a high-limit cutoff, a
setpoint that disables the economizer if the temperature is
too hot or humid.
“You need to have high-limit cutoffs in place and working properly, particularly in the swing seasons. They’re the
difference between wasting energy and saving it,” Callan
If you oversee a portfolio, keep in mind that the cutoff
limit for one location may be unfavorable for a property in
a different climate zone.
“For example, a building in a humid climate may have a
lower economizer changeover temperature setpoint than
one in a dry climate,” Moser explains.
If you want more control than your BAS, you can also
THIS ECONOMIZER DAMPER has been poorly maintained and is showing signs of
corrosion. Buildup and debris on economizer parts can cause it to malfunction
and any energy savings can be lost. Stay on top of daily checks and preventive
cleaning to avoid issues.