Purdue Nanotechnology Labs Employ Advanced Grounding Device to Ensure a Constant Flow of Clean Air

The Birck Nanotechnology Center at Purdue University, West Lafayette, Indiana, houses over 20,000 square feet of climate-controlled cleanroom laboratoriesfor cutting-edge nanotechnology research.

A SINGLE SPECK OF DUST could spoil a whole experiment at Purdue University’s new Birck Nan-otechnology Center. To minimize the likelihood of such a scenario, the building’s HVAC system has to be fast, forceful, and flawless. Such high performance is attained by carefully selected air-handling equipment thatincludes a new grounding device to extend motor life.

Adjacent to the Purdue campus in West Lafayette, Indiana, the 3-story Birck Center has many state-of-the-art laboratories for advanced nanotechnology research. The 71,000 square foot building is part of Purdue’s Discovery Park, a 50 acre cluster of buildings devoted to interdisciplinary technological researchin collaboration with corporations and government agencies.

The Birck Center’s HVAC system maintains the labs at 30-50% relative humidity at all times and replaces the air at least 15 times per hour. Temperature is allowed to vary by no more than 1°C; a rise of just one degree causes microscopesand other equipment to expand by an amount equivalent to thousands of atoms.

Many of the labs (more than 20,000 square feet) are maintained as cleanrooms. The building’s clean-rooms, equipped with vibration-isolation equipment and special filtration systems to keep the air nearly free of dust particles, are so tightly controlled that some have as many as 120 air changes per houryet are not allowed temperature changes of more than 0.1°C.

Key to maintaining such conditions are high-volume fans, each equipped with a variable frequency drive (VFD) that enables the fans to automatically adapt to the weather outdoors, laboratory occupancy levels, and other factors by quickly changing speed. During construction of the Birck Center in the spring of 2005, the contract to supply eight of these HVAC fans went to Colby Equipment Co. Inc., headquartered in Indianapolis. Colby turned to Wisconsin-based Green-heck Fan Corp. for four 25 HP fans, each capable of moving more than 20,000 cfm of air; and four 5 HP fans, capable of moving morethan 5,000 cfm each.

Colby specialist Tom Hall, a Purdue alumnus with a degree in mechanical engineering/technology, knew that without grounding devices, currents induced by the VFDs on the shafts of the fans’ AC motors would discharge through the bearings, causing fusion craters on the bearing race walls. This phenomenon, if allowed to continue, would result in the race becoming severely pitted, leading to bearing (and motor) failure. Prior to failure, the pitting may cause noise and vibration that is magnified and transmitted by HVAC ducts. Because many of today’s motors have sealed bearings to keep out dirt and other contaminants, electrical damage has become the most common cause of bearing failure in AC motors with VFDs. Depending on the business, the downtime and lost production resulting from such failures can cost many thousands of dollars in addition to the costof replacing or repairing the motors.

In his search for grounding devices that would optimize the performance and durability of the variable-speed fans, Hall concluded that conventional metal grounding brushes would be difficult to attach, since the fans had already been installed. An Internet search turned up Elec-tro Static Technology, a division of Illinois Tool Works and a Maine-based manufacturer of the AEGISSGR™ Conductive MicroFiber Brush.