Relative Humidity

Relative humidity (RH)

Relative humidity conditions can vary widely within manufacturing plants depending on season of the year, indoor and outdoor temperatures, time of day and operational characteristics. RH levels often vary from plant area to area, and from building to building in a multi-facility complex. Low RH problems result in process inefficiencies and material waste. Specific low RH characteristics:

Low humidity problems
Static Electricity	Viscosity changes
Cracking	Increased dust
Warping	Unpredictable drying or curing
Wrinkling or curling	Dry eyes, nose, lips
Shrinking	Increased allergies and colds

Accurate humidity control is key to maintaining and improving operations productivity, product quality as well as reducing waste. Even small changes in RH levels can have major effectives on productivity, quality and profit. Proper RH levels have also proven to be a major component in improved indoor air quality and better working conditions. Optimum humidity levels will improve employee comfort and reduce the incidences of allergies, colds and sick days.

In most industries, RH levels from 40% to 50% are typically best for maximum production efficiency, quality and reduced product waste.

Humidity and Manufacturing

All organic raw and finished materials (and some inorganic materials) contain water as described as moisture content. Examples include paper, boxboard, and wood:

• Paper and boxboard normally come from the mill at 6.5%-9.0% moisture
• Kiln-dried lumber used in woodworking at 6.0% to 11.0% moisture

These materials can quickly dry out or add moisture when exposed to dry or extremely humid air. Materials outside of optimum moisture content ranges result in a variety of manufacturing problems. These problems are most common in low humidity environments.

Seasonal Humidity Problems

In most of North America, dry air problems are seasonal in nature, typically encountered during the winter heating season. Dry air is less of a problem in warmer months when indoor air is less frequently heated, although air conditioning can have a major affect on controlled RH levels.

Dry, desert regions can experience adverse low humidity conditions year round.

In winter heating season, cold supply air is heated to normal indoor temperatures. This process can reduce indoor RH levels to extremely low levels (in some cases less than 10% RH). Warming supply air just a few degrees requires adding moisture in a controlled manner to maintain optimum RH levels.

Winter with humidification




Winter without humidification

Humidification & Energy

Organic and some inorganic materials require consistent RH levels for consistent use and efficiency in a variety of manufacturing settings. Most indoor air needs the addition of humidity during winter heating season.

Many methods exist to increase RH levels. Current humidification products used in business and industry usually rely on the introduction of very fine droplets of water into surrounding air, where they can be absorbed. Consistent production and distribution of these droplets throughout the manufacturing area are critical. RH levels are measured with remote sensors connected to electronic controls.

Many humidification technologies will introduce moisture into the air with the intent of raising RH and reducing dry air problems. As in most cases, not all are created equal in their effectiveness, versatility or cost. For most end-users, energy and maintenance cost will be key factors in the selection of a humidification system.