The right installation and maintenance will secure energy savings
WAYS TO MAXIMIZE
Is your air conditioning bill running wild? Get your utility costs under control by adding an air-side econ- omizer. This device draws in outside air as a form of free cooling.
While the potential for savings is significant, facility
managers can lose all of an economizer’s benefits if they
fail to specify the right features and neglect maintenance.
Follow these tips to lock in your economizer’s potential.
1) Compatible Climate
Conditioning recirculated air can be a significant
expense, an average of 10% of a building’s energy load.
Depending on climate, square footage, and building type,
some properties may spend up to 20% on cooling, according to the latest data from the Commercial Building
Energy Consumption Survey (CBECS). An economizer
can reduce this load just by taking advantage of outside air
in lieu of mechanical cooling.
The most important consideration for an economizer
retrofit is your location. Climates that are humid and hot
aren’t typically a good fit as the outside air is rarely cool
or dry enough to bring inside, explains Dave Moser, senior
engineer with CLEAResult, an energy consulting firm.
If you’re not sure if your climate is compatible, take a
cue from requirements in the International Energy Conservation Code (IECC), recommends David Callan, vice
president of McGuire Engineers. For new construction
and major renovations, economizers are required in cooling systems with a capacity exceeding 33,000 BTU/h.
They are exempt, however, from Zones 1A and 1B,
which apply to the southern tip of Florida and islands like
Hawaii and Puerto Rico. In these hot and muggy environ-
ments, energy savings are minimal and won’t yield a solid
return on investment. Air that is too moist also increases
your risk for mold and mildew, adds Callan.
Keep in mind that humid air contains heat, what humans register as relative humidity. Excess heat not only
undermines your economizer cooling potential but it also
decreases your occupants’ thermal comfort, Callan cautions.
Even buildings in colder environments can add an economizer. The 2012 update of the IECC added Zone 7, which
covers northern parts of Maine, Michigan, Wisconsin, Minnesota, and North Dakota, as well as Alaska (Zone 8).
“In the winter, an economizer is a no-brainer because the
2) Proper Installation
air is generally cold and dry,” notes Callan. “A little bit of cold
air goes a long way so you’re not necessarily introducing a
ton of moisture into the ventilation even when it’s snowing.”
Apart from climate, economizers are suitable for facili-
ties of any size and type. Those with mission critical loads,
such as data centers, will experience significant benefits,
as well as those with year-round cooling needs. Buildings
with a high number of internal rooms are also good candi-
dates, says Mark Walsh-Cooke, principal and mechanical
engineer with Arup, a consulting firm. The only build-
ing environment that wouldn’t be ideal are those with
humidified spaces in a dry climate, such as hospitals or
museums, he adds.
Retrofitting an economizer doesn’t require major structural or mechanical changes. The units are a modest size
and should easily fit within your existing HVAC footprint,
says Walsh-Cooke. They are typically added along the
outside wall or roof so the air handling unit’s air intake
plenum is connected to the outside wall and motorized
dampers, adds Callan. Depending on your existing equipment, you can have the economizer custom-installed by a
contractor or packaged with a new air handling unit.
“Adding air-side economizers to packaged HVAC
equipment such as rooftop units is typically simpler than