The average daily high temperature in Saskatoon, Saskatchewan, in December is 14 degrees F. It dips to a frigid 9 degrees F in January before climbing back to 16 degrees in February.
It's in that environment that Federated Co-operatives Ltd. operates a 300,178-square-foot grocery distribution center to serve retail outlets throughout the region. Federated provides distribution and other services to some 250 retail cooperatives across Western Canada.
During the winter, Federated's goal is to keep the temperature in the DC at about 20 degrees C (68 degrees F). That's proved high enough to keep everyone satisfied. "We had no comfort complaints," says Trevor Carlson, the cooperative's manager of environmental and technical services. Trouble was, maintaining that temperature required a lot of energy—as much as 250,000 cubic feet of natural gas each season.
For Federated's managers, that was cause for concern. The cooperative is committed to environmental sustainability,environmental sustainability, Carlson says. And the consumption of large amounts of fossil fuels seemed out of line with those goals. After they got a look at the fuel consumption figures, everyone agreed it was high time the cooperative started looking for ways to reduce the operation's reliance on carbon-based fuels.
A lot of hot air
Carlson suspected a lot of heat was being wasted because warmed air was rising to the ceiling. (While ceiling heights vary within the Saskatoon DC, they're about 28 feet high in most parts of the building.) That led him to explore the possibility of installing industrial fans to mix the air in the space—a process known as destratification.
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 F 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 direction and push air efficiently down to the floor," he says. The fan blades are airfoils, he adds, similar in profile 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 destratification raises the overall temperature 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 temperature settings on the building's thermostat, 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 the payback to be 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.