How Does a Dehumidifier Work

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Dehumidifiers aren’t as well-known, popular or common as humidifiers, but they can have a huge impact on the air quality and environmental conditions in a building. However, even if you know they exist, you’ve likely never considered how they actually work – especially on an industrial scale. We at Best of Machinery have put together this quick explanation of what they do, how they work and why they’re so important.

The Basics

Humidifiers add moisture to the air, and dehumidifiers are meant to do the exact opposite – they extract moisture from the air and dispose of it somewhere else, creating a net loss of moisture that affects the feel and atmosphere of the room. This can help protect furniture from moisture damage, get rid of mold and prevent skin damage from too much exposure to humidity, and can also affect the average temperature of the room or building. In industrial settings, there can be even more benefits to keeping an area dry, but we’ll get into that later.

Commercial dehumidifiers come in a few different varieties, but they all serve the same purpose. Below are some of the most popular types, but keep in mind that this isn’t all of them, especially not when you count DIY designs.

Refrigerant Dehumidifiers

These work through condensation and are some of the most common due to the fact that they’re often built to work automatically without needing any manual checks or input. Most designs use a cold evaporator coil to cool air that passes into it, condensing the water vapor into droplets without freezing the air as well – this quite literally removes the water from the air entirely, drying it out and sending it back into the room.

The water droplets are then collected in a pan, hose or other disposal method and moved away from the room – since they’re often completely clean, certain systems put this water back into a reserve tank for later use, but others will just discard it completely through a drain or pipe instead. Since they work based on cooling the water, they can struggle in colder conditions.

Desiccant Dehumidifiers

These types work by using a moisture-absorbent material to collect water from air that passes through it, which is then heated in a separate section to re-evaporate the water into moisture that’s piped out of the building. This can technically work as both a dehumidifier and a regular humidifier since it simply transfers the water vapor from one room to another, but it’s often used as a one-way system instead.

Desiccant dehumidifiers can work at very low temperatures, but need to be powered constantly and won’t usually work unless they have electricity running them. They’re the most common type to see in industrial buildings since the power requirement is less of a problem if the building is already full of machines.

Whole House Dehumidifiers

Whole house setups are the exact opposite of building-wide humidifier systems, forcing fresh air into the building to push the moisture-filled air out. These are often mounted in attics, ceilings and other high-up areas to that they can work downwards, meaning that they’ll refresh the air in the highest-up rooms first.

You’ll usually see these in office buildings and other tall structures since they work best when they’re collecting air from up high.

Ionic Membrane Dehumidifiers

One of the most complex types, ionic membrane dehumidifiers use an electrolyte membrane to remove water molecules through electrolysis. This doesn’t take much electricity, but also can’t remove much moisture at once, making it similar to a desiccant dehumidifier on a much smaller scale. However, they don’t need much maintenance, so they can generally be set up in a room and left there without needing to be repaired or replaced.

Industrial Models

Industrial dehumidifiers are often used to get rid of humidity that could break important equipment or make stock useless and are generally just bigger versions of standard dehumidifiers with a greater reach.  They’re sometimes also used alongside humidifiers so create a constant supply of ‘fresh’ humid water, or to keep the humidity at a very specific level without removing it entirely.

They’ll also turn up in construction jobs sometimes, especially open areas that don’t have any protection from bad weather or mold. These will sometimes be temporary ones that are set up during the construction process and removed once the building is finished.


Once water droplets and/or moisture are collected, there are multiple ways it can be disposed of. A lot of portable dehumidifiers contain sensors that will automatically shut them off if they’re almost full, signalling the owner than the water needs to be dumped somewhere before it can keep operating – however, some will be able to connect to pipes so that they can continually pump the water away from the building rather than slowly filling up.

Dehumidifiers that are mounted to a building will either be self-contained or connected to the building’s water system, depending on whether or not it’s clean enough to re-use. If it’s too dirty, then it’ll usually just be piped out into a drain or sewage pipe instead, and very rarely stored for further use.

Whole house dehumidifier systems usually work in a similar way, taking water from every room and discarding it through a pipe system – since this is a larger volume of water, these pipes might link into other sewage pipes, such as those used in bathrooms.

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