Desiccant Dehumidifiers

How a desiccant dehumidifier works

A desiccant dehumidifier does not use a cold coil. It uses a slowly rotating wheel coated in a material, usually silica gel, that pulls moisture directly out of the air passing through it. Roughly three quarters of the wheel is drying the process air. The remaining quarter is being regenerated: a separate, heated airstream passes through it in the opposite direction, drives the collected moisture back out of the desiccant, and exhausts it outside as warm wet air.

The wheel turns continuously, so every section is dried, regenerated and back in service in a few minutes. The result is a machine that removes moisture without ever condensing it, and that is what gives it two capabilities a refrigerant unit does not have.

Where desiccant beats refrigerant

For most UAE spaces, which are warm, a refrigerant dehumidifier is the more efficient machine and the one we would normally recommend. Desiccant becomes the right answer in two specific situations, and in both of them it is the only answer that works.

Cold spaces. A refrigerant unit works by cooling air below its dew point. As the air gets colder there is less moisture to condense, the coil frosts, and below around 10 degrees the unit spends more time defrosting than dehumidifying. A desiccant wheel is not affected by temperature in the same way and keeps removing moisture in a cold store, a chilled production area or a blast freezer anteroom where a refrigerant unit has effectively stopped.

Very low humidity targets. A refrigerant unit can practically hold a space at around 40 to 45 percent relative humidity. Below that, it is fighting physics. A desiccant unit can take a space to 20 percent, 10 percent, or lower where the process needs it, because it does not depend on the air holding enough moisture to condense.

Applications

Cold storage and food processing. The most common industrial use. Cold store doors open, warm humid air enters, and it freezes on the evaporator, the floor, the ceiling and the product. Ice on the floor is a safety problem, ice on the evaporator is a defrost cycle and energy problem, and frost on packaging is a quality problem. A desiccant unit drying the anteroom or the air entering the store stops it at source.

Pharmaceutical production and storage. Where humidity is a validated parameter, where tablets and powders are hygroscopic, and where the specification is often well below what refrigerant can hold.

Confectionery and food production. Chocolate, sugar coating, powder handling and dry mixing all need low humidity to prevent sticking, caking and blooming.

Electronics, batteries and clean assembly. Lithium battery production in particular needs extremely dry rooms, and semiconductor and precision assembly need static control that depends on holding humidity in a narrow band.

Archives, museums and document storage. Where the target is stable low humidity over years rather than comfort.

Coatings, blasting and painting. Surface preparation and coating application in shipyards, tank work and structural steel need the surface held above dew point so coatings cure correctly. Desiccant drying is the standard method.

Water damage recovery and construction drying in cool conditions. Where the space is air conditioned to a low temperature and refrigerant units lose effectiveness.

Regeneration: what it needs from the building

The regeneration airstream has to be heated, and the wet exhaust has to go outside. Both are installation requirements that do not exist with a refrigerant unit.

Heating is usually electric on smaller units, which is simple but is the main running cost. Larger units can regenerate with steam or hot water where a supply exists, or with gas, and on plant with waste heat available that is worth designing in. The regeneration exhaust needs a duct to outside, and it needs to be routed so that warm wet air does not find its way back into the space or onto a cold surface where it will condense.

The process air also comes out warmer than it went in, because the desiccant releases heat as it absorbs moisture. In a space that is being held cold, that heat has to be removed by the cooling system, and it should be included in the cooling load calculation at the design stage.

Sizing

Desiccant units are sized on the moisture they remove at the process conditions, expressed as kilograms of water per hour, against the moisture load entering the space. That is why the RY series table above quotes capacity at 20 degrees and 60 percent humidity rather than the warm, wet conditions refrigerant units are rated at: it is the condition a cold store or a pharmaceutical area actually runs at. The load comes from air infiltration, door openings, ventilation air, people, product and process. In a cold store the dominant item is almost always the doors, and how often they open matters more than the store volume.

Reducing the load pays for itself faster than adding capacity. Strip curtains, fast acting doors, an anteroom, and sealing the envelope all reduce the amount of humid air the unit has to deal with, and they do so permanently and without a running cost.

Installation and servicing

A desiccant installation needs the process air intake and discharge positioned to circulate through the whole space, the regeneration exhaust ducted to outside, a power supply sized for the regeneration heater, and access to the filters and the wheel. Filters matter more on desiccant units than refrigerant ones, because dust reaching the wheel reduces its capacity permanently rather than temporarily.

Servicing covers filters, the wheel and its drive, the regeneration heater and controls, and the seals between the process and regeneration sides. A unit with worn seals leaks wet regeneration air into the dry process stream and quietly loses capacity. Climatech installs and services desiccant dehumidifiers as well as supplying them.

Frequently asked questions

Is a desiccant dehumidifier more expensive to run?
Per litre of water removed in a warm space, yes, because of the regeneration heat. That is why refrigerant is the right choice for most UAE applications. In a cold space or at a low humidity target, the comparison does not apply because the refrigerant unit is not removing the water at all.

Can I use one in a swimming pool room?
Normally no. Pool halls are warm and the target humidity is moderate, which is refrigerant territory. Pool duty refrigerant units also recover the heat from the moisture they condense and put it back into the pool water or the air, which a desiccant unit cannot do.

How low can the humidity go?
Well below 10 percent relative humidity where the process needs it, with the right unit and regeneration temperature. Most industrial applications need somewhere between 20 and 40 percent.

Do you supply portable desiccant units?
Yes, for cold construction drying, coating work and temporary industrial use. Ask us about the portable RY units.

Talk to us

Call +971 54 574 2443 or email info@climatech.ae with the type of space, its temperature and target humidity, its dimensions, and how often doors open if it is a cold store. That is enough for us to size the unit and tell you whether desiccant is the right technology for it.

For warm spaces and normal humidity targets, see industrial and commercial dehumidifiers and the full dehumidifier range.