Much of today’s advancements have come in fans and fan motors, the engines that move exhaust air out of the kitchen.

“Fan technology is a fairly high state of art,” says Bob Luddy, president of Captive-Aire Systems. Constantly looking for improvements, fan manufacturers in recent years have been adapting products used in other industrial applications. Better materials, better designs, and hybrid combinations of techniques have been paying off.

Fans typically used in kitchen exhaust systems include centrifugal upblast fans, rooftop-mounted utility sets, and less common in-line axial fans.

Upblast fans (most commonly, the aluminum mushroom-shaped fans sprouting from restaurant roofs everywhere) exhaust kitchen effluent up into the air away from the roof. More manufacturers such as Acme Engineering & Manufacturing, Loren Cook and Exhausto are introducing direct-drive versions of these fans and more powerful fans that can handle additional static pressure (resistance caused by pulling air through grease filters and long or narrow ducts).

Direct-drive fans have been around a long time, but only recently have they been used in foodservice. The most obvious benefit of direct-drive fans is that there is no drive belt to wear out or break. An even bigger benefit is that direct-drive fans can run at varying speeds. In a traditional exhaust system, a fan sits on top of a duct over the kitchen, and the fan runs all day, and sometimes all night.

“A variable-speed fan allows you to adjust the exhaust volume based on what you’re cooking,” says Steen Hagensen, president of Exhausto Inc. “That saves energy to run the fan and reduces the amount of make-up air needed, which is usually tempered. When you look at the bottom line, payback on most of these fans is two years at most.”

Utility sets are usually constructed of steel, not aluminum, so they can handle higher temperatures than aluminum, often UL-listed up to 500&Mac251;F. They’re also designed to handle higher static pressure (up to 5”) and can move a greater volume of air. Originally intended for other applications, utility sets have been adapted for foodservice, and manufacturers are making improvements.

“We use utility set fans, not upblast, because of their cleanability,” says Mark Fink, engineer, worldwide strategic operations R&D, for Burger King Corp.

Proper cleaning is important, Fink says. If it isn’t done correctly, residual grease can unbalance the fan wheel and causes vibration that can tear up the motor, or worse. “We’ve had fan fires on the roof caused by friction from an unbalanced wheel setting grease on fire.”

Loren Cook now builds a utility set with a special nonstick coating that doesn’t allow grease to accumulate on the fan wheel. Most fan manufacturers also now offer utility sets for foodservice with direct drive.

In-line fans are rarely used in kitchen exhaust systems because of the amount of grease in the effluent. The only in-line fans approved for foodservice, in fact, are axial fans, that use a propeller-like blade. Loren Cook, however, recently introduced an in-line mixed-flow fan, the first tubular in-line fan that is a combination centrifugal and axial fan.