Desiccant dehumidifiers are a favorite for controlling humidity among food processors, nutraceutical manufacturers and others for two specific reasons:  

• They operate well at sub-freezing temperatures. 
• Desiccant dehumidifiers maintain precise humidity levels. 

But, for processors needing to keep cold spaces cold, desiccants can present a challenge when it comes to how you handle regenerated air. The reason it’s an issue is that the air coming out of the desiccant dehumidifier is extremely hot and humid. That air not only will affect air temperature if it’s dumped back into the room; it also can condense as it cools. 

For many people, routing that hot, humid outside is an ineffective option. But before we address the solution, it’s worth understanding where to place the unit. 

Desiccant Dehumidifier placement 

Dan Dettmers, an applications engineer at Quest Dehumidifiers, said placement is more important than most people think.  

Try to keep the machine indoors to protect it from the elements. If that isn’t an option, make sure the machine is outdoor rated and shelter it from radiant sunlight or driving rain. It won’t take long for corrosion and other issues to set up shop inside the unit. 

But what about in the room you’re dehumidifying? That’s OK for high-temperature, low relative-humidity applications often found in the pharmaceutical industry, Dettmers said.  

“If it’s cold storage, we’d really, really like to see it outside the space,” Dettmers said. “Those cold, cold temperatures are going to cause condensation, and if that condensation occurs within the unit, it’s going to flow out and create puddles and issues inside your freezer.” 

For that reason, Dettmers always recommends placing it outside the space, often in an adjacent room. That way you can duct your process air from the room without issue. 

Handling regeneration air 

Many cold storage operators don’t know what to do with the hot, humid air that desiccants pull from their units because ducting it outside isn’t a viable option. Because it’s so hot (seriously, 180 degrees F or higher) and full of moisture, that air also can’t go back into the room. 

If you don’t have access to dumping that air outside, here’s how to handle it: 

• Using a special adapter, duct the desiccant unit (Quest 132D, for example) to a refrigerant dehumidifier like the Quest Hi-E Dry 195. 
• The adapter allows for cooler air to mix with the regenerated air prior to entering the refrigerant unit. 
• The refrigerant dehumidifier pulls the moisture out of the regenerated air. 
• The condensed water is then sent down a drain. 

• Voila. No complicated ductwork needed to push the air outside. 

“It’s such a simple solution,” Dettmers said. “But it’s one that works beautifully. This approach will allow you to reap the benefits of a desiccant in cold storage but without the headache of dealing with cumbersome, inefficient ductwork.”