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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Water, water everywhere. That's the normal condition of a refrigerated processing facility. If it's not in puddles or beaded on pipes, it's thick in the air.

At least, that often was the case before USDA started taking its own rules on condensation control seriously. "Until five years ago, the [focus and] emphasis for refrigeration engineers was only on temperature," notes Chuck Taylor, senior vice president of The Stellar Group (, Jacksonville, Fla. "That has changed. Today, USDA will shut down a plant for condensation problems."

For several years now, USDA has been enforcing long-standing but seldom observed rules on condensation control in refrigerated facilities.

Why the sudden change? In the past, enforcement had been impractical because moisture in many food plants, particularly refrigerated facilities, was extremely difficult to manage.

"We are literally trying to defy the laws of physics in processing plants by trying to maintain a cold room and, at the same time, control a big latent moisture load," explains Taylor.


Controlling Moisture in the Plant: Tornado Industries' floor scrubber
Sanitation often is a primary source of moisture problems. After two eight-hour processing shifts in a cold environment, hot water is bound to upset the moisture balance. Photo courtesy of Tornado Industries.

But food safety is a growing concern. Furthermore, moisture problems may be increasing in food plants. To reduce bacterial growth, processors are operating their facilities at lower temperatures, driving up energy costs and humidity challenges simultaneously.

"In all food plants, condensation off any part of the building or pipes is a no-no because of potential contamination from drippage onto product," says Roland "Lefty" Leavens, vice president of food processing systems for Food Facility Engineering (, Yakima, Wash.

Beads of moisture can become drips of contamination, with the condensation carrying dirt, microbes and other contaminants. At best, condensation poses a threat to product quality and, at worst, it could lead to consumer illness and a major recall. Moisture also can rot wood and cause other damage to the facility structure, inviting pests and other sources of contamination.

That standard industrial refrigeration equipment can control humidity is a mistaken notion, Taylor maintains. The problem stems from the very nature of the processing plant. Mix hot water, moist carcasses, warm-blooded operators and process heat into a 40°F processing environment, and moisture will accumulate. Guaranteed. The moisture the air cannot absorb results in condensation.

"A standard refrigeration unit simply can't control the water coming off the carcasses, equipment, etc.," Taylor goes on. "The air won't have the capacity to absorb more moisture until the air is warmed, and that is not likely to occur until the clean-up shift."

Condensation means more than slippery surfaces and wet pipes. It can mean big trouble on the food safety front.

The standard solution won't cut it

Condensation in a processing plant is a complex challenge with multiple components: temperature, moisture, pressure and filtration.

"We don't even call it condensation control anymore," says Taylor. "We call it psychrometrics." The term refers to a relatively obscure branch of science - the science of moist air - that is becoming better known to processors by the day.


Controlling Moisture in the Plant: Telatemp Micro Humidity Logging Thermometer
Telatemp Corp.'s Micro Humidity Logging Thermometer can record up to 10,922 date- and time-stamped temperature and/or humidity measurements and download those readings to a PC.

A greenfield plant today should include systems that deal directly with the conditions, equipment and materials creating or influencing moisture within the facility. To contend with moisture problems in an existing plant, begin with an air balance study.

A study typically starts with analysis of how air is moving in and out of the plant. This is followed by the introduction of a device to record the temperature, pressure and humidity within the plant over a 48-hour period.

"You need empirical data to have a complete idea of what is going on," says Taylor.

Sanitation often is the primary, even sole, source of the problem. After two eight-hour processing shifts in a cold environment, the introduction of hot water during the clean-up shift is bound to upset the moisture balance.

"All processing plants are trying to ‘sweat the equity,'" says Taylor. "They want to run the equipment as long and fast as they can for two shifts. They would stretch it to three shifts if they could, but they must clean the plant. When the cleaning shift hoses down with 140° water in a plant that has been operating at 40° temperatures, you have humidity everywhere. The solution may mean pulling in outside air, conditioning the air to 50° and re-heating the air to 80° and pushing it into the room. Then exhaust the air from the room. Hot air can absorb more moisture."

"Washdown is a challenge," echoes Leavens. "The walls are cold, but you are using hot water. You need air flow that avoids fog and heavy condensation."

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