The Humidity Control Debate

Beyond traditional humidification, a new method improves coverage and responsiveness while reducing water use, over-wetness, maintenance, and installation costs.

Print facility managers know the problem. If they don’t control the facility’s relative humidity, paper and print quality, as well as production, suffer. The problem worsens when cold weather reduces the moisture in the air.

To assure consistent quality and production, print experts are turning from traditional humidification techniques to a new method that improves humidification coverage and responsiveness while reducing water use, over-wetness, maintenance and installation costs.

A Print Problem

Since paper products are porous, they can quickly gain or lose moisture from the surrounding air in the print or storage process. Low moisture is a particular danger in winter when relative humidity can go as low as 15 percent. When relative humidity falls below 50 percent, paper shrinks, curls and loses dimensional stability. This can cause paper to stick, mis-feed and mis-align colors. It can also cause tears in web-based newspaper printing, forcing costly downtime.

To prevent waste and downtime, print experts must keep the relative humidity of air around print production and storage between 50 and 60 percent. While achieving this once in a while may be easy, doing so thoroughly, consistently and efficiently can be difficult.

The challenge is that humidification coverage must be complete, uniform, and responsive to changing moisture levels in the air. It must keep all paper from getting too dry and too wet. Water vapor collecting in the wrong pattern, in fact, can “fall out” to create areas of wetness while other areas may remain too dry.

And in an age of tight budgets and rising commodity prices, thought also needs to be given to reducing water and energy use, and maintenance and installation cost.

Traditional Troubles

A number of traditional misting systems add moisture to the air in industrial applications. While these offer benefits, they’ve been limited by drawbacks.

Among high-pressure fog systems, which create and distribute tiny water droplets based on the humidity level needed in an area, static line systems and vertical fan systems have been common choices.

With static line systems, which mount and align tubes and nozzles to deliver mist, uneven humidification distribution can be a problem. Moisture may not completely or uniformly evaporate into the surrounding air, especially in facilities with low ceilings. Nozzles which spray a certain distance and direction can create areas of too much moisture or wetness under a nozzle. Other areas farther from mist-spraying nozzles may receive too little humidification.

With no airstream to spread humidification beyond the nozzle spray areas, it can be difficult to provide complete, uniform coverage and it can take longer to reach desired humidification levels. Water moisture “fall out” can damage paper products and increase water use—especially in areas with low ceilings—while labor-intensive tubing alignment and mounting can increase installation and maintenance costs.

A vertical fan humidification system adds an airstream to aid in the air moisture distribution, but a stationary airstream typically covers just a narrow band around 25-degrees wide. Like a flashlight’s beam, this leaves many areas outside its focus.

Thus humidification may be relatively slow to diffuse, with pockets of relative dryness remaining. Adding fan oscillation can distribute mist over a wider area, but still leave areas with less humidification while the airflow is pointed elsewhere. Turbulence is also created when airstreams cross, leading to increased fallout and water use with diminished humidification.

Air and water humidification systems, combining low-pressure water and high-pressure air to atomize water droplets, also have drawbacks for industrial use. These include high upfront costs for nozzles that combine air and water, expensive air compressors, and expensive separate lines for air and water. The cost of maintaining dual air-water systems typically runs high as well.