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Written by Pierre Husson   
Monday, 31 December 2007 19:00

High-pressure humidification systems can improve quality and reduce energy costs.

Static electricity and the potential for defects due to ESD is one of the biggest manufacturing headaches a board manufacturer can face,” says Itron’s Paul Anderson. In snowy Minnesota winters, the potential for ESD problems soars as icy outside air is heated to normal plant operating temperatures of around 70°F. Without proper humidity control, relative humidity in Anderson’s plant could plunge, creating ideal conditions for ESD problems.

Anderson is facilities operations manager for Itron Inc.’s 540-employee, 110,000 sq. ft. manufacturing plant in Waseca, MN, which produces RF devices and automated meter reading equipment used by utilities and large water and power users. Anderson has managed the facility’s operations since 1999 and has 25 years of facilities management experience.

Every year Anderson and Itron’s plant engineers huddle to make sure everything is working right. A constant discussion item has been process improvements aimed at continuing to reduce ESD damage to components.

The physics is simple: Static builds as RH levels drop – the colder the air, the greater the potential for dry air and static buildup. As cold winter air is heated, it dries and loses its capacity for carrying moisture. For instance, when outside air with a temperature of 10°F and RH of 50% is heated to an internal temperature of 70°F, RH will drop to about 10%.

Industry standards recommend minimum RH levels of at least 30% to avoid ESD problems, with levels of 40-50% RH considered desirable. Keeping RH at an acceptable level requires most plants add large amounts of water to the air through humidification systems.

In warmer, drier climes like California, ESD problems are often a year-round issue, and maintaining consistently appropriate RH levels may require adding water to plant air all year.

“Keeping ESD problems at bay was a topic that occupied our attention every year,” Anderson explains. “For years we operated a compressed air humidification system throughout the plant. It did a good job, but as humidification technology has moved forward, so has the capability to control RH levels tighter and more consistently, meaning ever tighter control of ESD.”

The compressed air humidification system lacked the precise control Anderson and Itron personnel sought. It also came with other annoying, costly baggage:

  • Inefficiency. “The moisture it produced didn’t cover the area as uniformly as we wanted. That’s a tough problem here, because we have ceiling heights as low as 11' and 12' in some parts of our manufacturing area.”

  • Expense. “Compressed air is a very expensive commodity, and operating the humidification system had just about eaten up our compressor capacity, so manufacturing couldn’t use it. Adding compressor capacity wasn’t an option. Moreover, the cost of electricity to drive the compressor was very expensive.”

  • Noise. The system annoyed workers with a high-pitched whine and spawned constant complaints.

Anderson looked at other humidification technologies, including ultrasonic and electric steam systems, but was unhappy with his options. He estimated that an electric steam system would have energy costs of about $25,000 annually, and would require large amounts of time-consuming, costly maintenance and nozzles and steam cores replacement.

Energy costs for an ultrasonic system would have been less expensive than electric steam, but more expensive than a high-pressure system. An ultrasonic system’s open water bath would require constant maintenance to prevent bacteria and possible air quality problems. Anderson was also concerned about the ultrasonic system’s high installation costs.

Furthermore, steam and ultrasonic systems were plumbed with stainless steel pipes, making them more expensive to install and virtually impossible to reconfigure, as Itron’s plant layout changed several times a year.

On a suggestion from his energy company, Anderson investigated high-pressure humidification systems as a way to cut his energy costs. He decided on a system from ML System (ml-system.dk) for a number of reasons:

  • The high-capacity humidifiers have the capacity (10 gph) and versatility the job required, and could work individually or be aggregated in groups.

  • The system produces a fine, cool mist that is quickly absorbed into the air.

  • Integral distribution fans make possible faster, more complete absorption of moisture, even in areas with low ceilings.

  • The system would provide more precise and consistent humidification.

  • Estimated energy costs would be $300 a year, less than 10% the cost of the compressor-driven system and 1-2% the cost of an electric steam system.

  • The system is plumbed with a high-pressure hydraulic hose instead of steel pipe. Anderson determined that would save money on the system’s installation and make future plant layout revisions faster, easier and far less costly.

  • A payback analysis conducted by his energy company predicted the system would pay for itself with energy savings and improved defect rates in fewer than two years.

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The new system included eight units configured in two zones: one for warehouse areas, the other for production. The system includes reverse osmosis (RO) water to eliminate minerals in the water by 97%, and a UV filter to kill bacteria.

Humidity sensors in each zone monitor RH levels and report to a remote PLC that controls the system. If RH in a zone drops below Itron’s 40% set point, the PLC activates the units in that zone until RH returns to the desired level.

The effects were immediate and dramatic. Anderson says, “We could feel the difference in the RH level almost immediately, and the system kept it at a uniform level. Our ESD numbers improved quickly.”

Anderson says Itron has had very few mechanical problems with the system. When the plant was expanded in 2004, six more units were added, almost doubling the number of units, without having to increase pump capacity. “Now it’s virtually automatic; we rarely think about dry air and static electricity,” he says. “They really aren’t issues anymore.”

Pierre Husson is president of Husson Inc.(hussoninc.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Last Updated on Wednesday, 02 January 2008 18:58
 

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