Fans Lower Rising Hot Air in Fleet Facility
Dan Carey has a big job. As Director of Building Operations for the City of Chicago, he’s the man in charge of all five hundred of the citys buildings. Fleet Managements Throop Building is one of the five hundred, and houses one of eight vehicle maintenance shops located across the City. The Throop pronounced troop is the largest fleet maintenance building in Chicago. The 200+ employees who work there maintain and repair the Citys fire department, park district, and housing authority fleets. That means the Throop sees all of the citys big rigs fire trucks, fire engines, ambulances, garbage trucks, and dump trucks, to name a few.
At approximately 400,000 square feet, with anywhere from 45 55 ceilings, the Throop Street facility is large enough that employees use golf carts to get around. Its also large enough to have its own climate or three separate climates, as Carey is quick to point out. Along the perimeter of the building where we have ten heating units, the ambient temperature is comfortable, but that wasnt the case as you got into the center of the building. There, says Carey, temperatures could be as low as 55 degrees on any given winter day. The heating units did a great job of warming a twenty-foot radius, but after that, the heat soon rose to the ceiling, where temperatures reached 95 degrees. From there, rooftop exhaust fans vented the heat to the outside. Energy efficiency was a problem, and so was employee comfort. We knew we needed to fix the problem.
Commonwealth Edison Solves the Problem
As a Professional Engineer (PE) for Commonwealth Edison, its Chris Philbricks job to assist customers in finding energy saving opportunities. They do that by improving the effectiveness of lighting, heating, air conditioning, and air movement. The Com Ed engineers evaluate a companys out-dated lighting for example, suggest alternatives, and show how the costs will save the company money over the long term.
Cost was a consideration for both Carey and Philbrick as they began looking for solutions. The building was built in the 1920s , says Philbrick. The cost of insulating it and adding more heating units would have been too high. We didnt want to spend that much money to retrofit an old building.
We had a problem, says Carey, and spending millions of dollars wasnt going to save us. We knew we had enough heat, we just needed to bring it down where it would benefit employees.
Keeping Heating Costs Down, Saving Money
Like typical industrial heating systems, the Throop buildings was notoriously inefficient. Over the years, the City expended thousands of dollars sending heat to an area where it had no employees working or equipment namely the ceiling.
Stratification the natural occurrence of hot air rising to upper levels increases the heating requirements of a facility. Energy experts figure a one-degree floor-to-ceiling temperature differential per vertical foot. For example, there is a 30-degree temperature difference between a 30-foot high ceiling and the floor. The heating system, which is usually installed near the ceiling, continually chugs away hour after hour, grinding out heat to reach a set-point temperature at floor level.
One solution Carey and Philbrick considered was installation of traditional propeller fans used on cooling towers, but, as Philbrick says, the 20 horsepower fans weigh 2,000 pounds each. We would have needed thirty-six of them, which would have added to the roof load and to the facilitys energy consumption. Besides that, turbulent, high-velocity airstreams dissipate very quickly, which gives them less impact than youd expect for the cost and energy usage.
It was soon after their search began that Philbrick spotted an article on high-volume/low-speed fans. He was intrigued by the concept large, relatively light fans moving at slow speeds to destratify cold and hot layers of air inherent in high-ceilinged buildings.
Destratification & Overheating
Destratification pulls warmer air down from the ceiling and, consequently, raises the temperature of colder air at working level. The simple process of destratification reduces temperatures at upper levels, while decreasing the loss of heat through the roof and upper walls.
Most facility managers intuitively understand that their buildings must be overheated to maintain a comfortable temperature for their employees. That means setting thermostats at a temperature to superheat the upper levels, high enough so the heat will reach employees on the floor. According to Michigan Consolidated Gas Company, stratification is the single biggest waste of energy in buildings today.
By destratifying the air that is, thoroughly mixing the overheated ceiling air with the cooler floor level air the thermostat settings can be lowered without loss of employee comfort while saving 25% or more on heating costs.
And this is exactly what the City of Chicago found. The facilitys thermostats are at floor level, says Philbrick. As the fans push down warm air to mix with the cold air, temperatures at the floor rise. That wasnt happening before the fans were installed. The gas fired heating unit was running constantly.
Carey agrees. Theres now only a ten degree difference between ceiling and floor temperatures, he says.
Optimized to Destratify
The fans come in diameters 6 feet to 24 feet and in three designs Standard, Wickerbill, and the new Powerfoil. The latter one is especially superior for destratification since it was developed and optimized for even greater energy-efficiency for the winter months.
In wintertime, the fans are set to spin slowly to push large volumes of superheated air at the ceiling to floor level to warm employees.
At one-twentieth of the horsepower of traditional propeller fans, and weighing one-tenth of what those same fans weigh, both Philbrick and Carey were convinced that buying the Big Ass Fans would be the way to go. The facility now sports nineteen twenty-foot diameter fans. City electricians installed them, says Philbrick, whenever they had a spare moment. As Philbrick points out, mounting the fans was not difficult. They require little or no added structural support, he says, and the effects were noticed immediately.
Two Bonuses: Summer Cooling and Air Exchange
Another surprise for Philbrick was how well the fans work for employees in Chicagos sweltering summers. Its a bonus, he says. The Throop Building isnt air conditioned, but you can speed up the fans on hot days and they create a nice breeze.
For Carey, the fans offered another critical benefit. We had a diesel problem, he says. Carbon monoxide and diesel fumes were hovering in a layer about 30 above the floor, trapped there by hot air at the upper levels. We now get eight air exchanges an hour. Before we bought the fans the building had no air exchanges. Our flue gas analyzers tell us the diesel fumes and carbon monoxide problem has been resolved by the fans.
Making Employees Happy
The fans are doing what we asked them to do, says Philbrick. Weve seen temperature fluctuations reduced. We wanted to even-out temperatures and the fans are doing that beautifully.
I couldnt be happier with the fans, says Carey. Now you can feel the heat all over the building. I look at it as a great way to save the City money and to keep our employees happy. Id recommend them to anyone.
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