specialreport SUSTAINABILITY
Normally, the warm air coming
out of a forced air heater (which is
lighter than the surrounding air)
goes right to the ceiling, with the
result that the ceiling can be 10 to 30
degrees warmer than the ground
level. Fans can reduce heat buildup
at the ceiling by forcing the warm
air back to the ground. The aim is to
mix the air thoroughly enough to
achieve even temperatures throughout the facility.
Christian Taber, an applications
engineer for Big Ass Fans, a supplier
of industrial fans, says destratifying
a facility’s air can reduce the temperature variation between ceiling
and ground level to a degree or two.
But there’s more to a successful
destratification than just plugging
in a few fans, he cautions. For one
thing, you have to put the fans in
the right places—positioning them
over racks, for example, could
impede air flowing to the floor.
More importantly, you have to
choose the right equipment—in
this case, large fans that are capable
of operating at low speeds.
Low speeds are necessary because
they eliminate the drafts associated
with air circulation, Taber explains.
“Essentially, we’re trying to spin the
fans at low speed in a forward direc-
tion and push air efficiently down
to the floor,” he says. The fan blades
are airfoils, he adds, similar in pro-
file to airplane wings. “The curved
aerodynamic profile allows us to
move air at slow speeds.”
As for how all this translates into
energy savings, Taber says destratifi-
cation raises the overall tempera-
ture in a facility, which means less
fuel is needed to heat the space.
Further savings can be achieved by
using variable-speed fans, he adds.
Taber explains that the relationship
between fan speed is cubic, so that a
fan running at one-third of full
speed uses about 1/27th of the electrical
power it would use at full speed.
Giving fans a whirl
Although he was intrigued by the idea,
Carlson says he was initially skeptical of the
gains promised by Big Ass Fans. Eventually,
curiosity won out, however, and he decided
to conduct a pilot test.
The pilot took place in the winter of
2008–2009 in the Saskatoon DC. Based on
recommendations from Big Ass Fans,
Federated installed five 24-foot fans, placing them near the loading docks and the
facility’s battery charging room. “We
believed that would destratify the whole
warehouse,” Carlson says.
The results came close to expectations.
“Our numbers were good—not as good as
promised but pretty close,” Carlson reports.
“The amount of air the large-diameter fans
move is surprising. The amount of heat
they pull off the ceiling is phenomenal.”
In fact, the DC became too warm. After
receiving requests from workers to turn
down the heat, Federated lowered the tem-
perature setting on the building’s thermo-
stat, thereby generating further savings.
What kind of savings are we talking
about? Quantifying the cost benefits of a
project like this can be tricky, largely
because of complications like temperature
variations from one heating season to the
next. However, Federated had good data on
its natural gas consumption by degree day,
and Carlson was able to use those numbers
to calculate payback. (His calculations also
included the cost of electricity for operating the fans, but Carlson says that was not a
significant factor.) The result? Carlson says
he expects to see payback within five years,
perhaps less.
As for the cooperative’s goal of cutting
energy use, Big Ass Fans says the project
succeeded on that count as well. According
to its figures, natural gas consumption at
the facility dropped by about 10 percent,
resulting in estimated savings the first winter of about $18,500.
The results of the test were good enough
to convince Federated to take the next step.
It plans to install fans in all of its other DCs
except for an agricultural products facility
that Carlson says is too small to benefit
from the installation. ;
