Plant Moisture Control

Once-ignored USDA requirements for condensation control are compelling processors to take a closer look at humidity problems. Also: tips on choosing between desiccant and mechanical dehumidifiers.

By Mike Pehanich, Plant Operations Editor

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"We created a two-foot stratum of dry air," says Taylor. "As the humidity rose, you could see it evaporate. The condensation problem completely went away."

Desiccant or mechanical?

By no means are desiccant systems always the better solution.

An engineering team faced with condensation and temperature problems in a slaughterhouse, for example, concluded that a mechanical dehumidifier would be most cost-effective. They added refrigeration equipment with reheat coils to solve the problems.

Desiccant systems cost more than mechanical dehumidification systems, but they also absorb more moisture. So which system is more cost-effective? It depends on the conditions of the plant.

Count on one constant: every situation is different.

Ironically, the psychrometric principles that are solving condensation problems in refrigerated facilities today have been long employed by HVAC engineers. Why there hasn't been more rapid carryover into cold processing engineering is puzzling to many, but, as they say, better late than never.

Today's engineer must understand the tools available to apply the appropriate solution to a moisture or condensation problem.

Whether you are building a new facility or attempting to solve a moisture problem in an existing plant, understanding the dynamics of airflow, heat and humidity of your process and plant will be critical to containing condensation and moisture problems.


Note to management, engineering and quality assurance

USDA is tightening the safety belt with its policing of facility condensation. The cost and challenge of modifying existing plants to meet long-standing but seldom enforced requirements can be considerable. But the impact on new plant designs is likely to be quick, effective and not nearly so painful.

Building condensation into a plant from the blueprint stage should be relatively simple, given what we have learned in recent years. The important thing to impress upon your project team is that facility engineers, whether on payroll or for hire, are aware of rules governing condensation control and put the necessary elements for control into the design.

Keep in mind that the long-term result of effective moisture control is a safer plant, safer product and a more responsible and respected industry.



Water pooling on the plant floor is not just a food safety concern. It also creates slippery floors and stairwells, causes plant traffic to spread moisture and creates pedestrian hazards in other sections of the plant.

"Floors should have a quarter-inch per foot of slope," says Roland "Lefty" Leavens, vice president of food processing systems for Food Facility Engineering (, Yakima, Wash. "That used to be a USDA requirement. Today it has been changed to a Good Manufacturing Practice and the requirement is simply that the floor ‘must drain.' If the slope is 3/16-inch instead of ¼-inch, it is still OK. The important thing is that the floor drains."

The products run in the plant should largely determine floor material. What kind of cleaning materials will be used? Does the floor need to be chemical-resistant? Will the floor material be subjected to sugars or acids?

One response to slippery grates, steps, floor plates, catwalks, metal ladders and stairwells is SlipNot Metal Safety Flooring ( products. The Detroit-based firm applies its patented super-hard molten metal alloy plasma stream deposition at over 400 psi to the surface of aluminum, stainless steel, galvanized steel and other steel materials subjected to plant foot traffic. The "random hatch matrix surface" results in a hardness of better than 55 on the Rockwell "C" scale, providing slip-resistance and durability. The material - available in fine, medium and coarse grades - exceeds OSHA and NFPA safety requirements. USDA and FDA have approved the material for incidental food contact.

"A lot of food plants are using SlipNot now," says sales rep Jeff Baker, who includes Campbell Soup among its oldest and most satisfied customers. Its customer base includes frozen food manufacturers, cheese makers, poultry operations, slaughterhouses and a wide range of processed food segments.

SlipNot materials provide sure footing even under wet or oily conditions. "The material is like walking on sandpaper," says the plant manager of a dairy product plant in Wisconsin, who asked that his plant not be identified. "Yet it is not so rough that it poses a tripping hazard. We have had no accidents - no slips or falls - since it was installed."

He also notes that the material cleans easily with a high-pressure hose and, with good ventilation, dries quickly.

The product line includes plates, grates, stair tread and landing flats. But the company also customizes materials for plant space and specific application.

Designing your plant for condensation control

If you are planning a new processing facility, eliminate condensation problems from the get-go by adhering to these principles:

  • Keep critical areas clean.

  • Control the flow of contaminants.

  • Pressure packed near packaging.

  • The plant needs air.
Have a constant supply of air in the plant. Measure exhaust from the room and add sufficient outside air to maintain desirable air pressure in the plant. The highest pressure in your plant should be at the juncture of the processing line and the packaging area. If you have negative air pressure in your packaging area, contaminated air may migrate from a raw product area to the packaging area. Make your plant a "positive pressure" plant so that air flow dynamics do not bring air with potential contaminants into the processing area.
    Identify areas that need to be the cleanest, such as the ready-to-eat area.

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