In our dehumidifier buyer’s guide, we cover the different types of dehumidifiers on the market. Now, let’s take a closer look at desiccant based dehumidifiers. These units use a chemical (the desiccant) to remove moisture from the air. And, that means they are less complex and sometimes much quieter than a compressor based dehumidifier. This makes them an ideal choice for quieter areas of your home.
Within the desiccant based dehumidifier category there are multiple categories, which we will discuss below. We’ll also take a look at how these machines work. Which types you probably don’t need. And, which desiccant based dehumidifier types you should steer clear of.
Desiccant Dehumidifier Types
Desiccant based dehumidifiers fall into four main categories. Commercial grade, disposable, rechargeable, and full size. We’ll look at two of them in greater depth, but there are two types which we won’t be examining in much detail.
Commercial Grade Desiccant Dehumidifiers
These monsters produce incredible results, but are simply too big for the average home. As you can guess, they typically reside in large warehouse or factory settings. They systems cost thousands of dollars, process massive volumes of air, and need to be directly vented to the outdoors. You will rarely if ever, find a commercial grade unit drying the air in an average residence.
Disposable desiccant dehumidifiers
These appear to be worth a try (and in some circumstances they are) at only around $5 each. But using absorption (as opposed to adsorption – more later) to remove moisture from the air is an inefficient process. A cheap moisture absorber can remove somewhere in the region of 0.6 ounces of moisture from the air per day. Compare this to a full sized desiccant based dehumidifier, such as the EcoSeb DD122EA Classic which can remove 15 pints of water from the air.
Disposable dehumidifiers do have the advantage of being extremely cheap, and very small. They excel in a drawer or cupboard. In a very small spot that sometimes smells a little musty, these are adequate. However, serious dehumidification demands a full sized unit. Additionally, there is a risk that disposable moisture absorbers can spill their contents. And, that could damage anything in its path. Another problem disposable unit possess is that their cheaply-made enclosures house various chemicals. And, if you damage a unit the contents of moisture absorbers can be harmful to your health if ingested. Disposables need to reside out of the reach of young children and pets.
Full Size and Rechargeable
The final two types of desiccant dehumidifiers remove significant amounts of moisture. They are also better suited to a variety of in-home uses. They are the rechargeable desiccant dehumidifier and the full size desiccant dehumidifier.
Rechargeable Desiccant Dehumidifiers
Rechargeable desiccant dehumidifiers have a number of advantages, mainly that they are very affordable. But, their rate of moisture removal is still very low when compared to a full sized unit. These really are mini dehumidifiers for mini spaces. But, they are really solid performers when used correctly.
The manufacturers typically recommend these devices for spaces such as closets and kitchen cabinets – areas which may suffer from musty smells, but not major issues like condensation. We recommend the EvaDry E333 for use in areas of up to 333 cubic feet. With a ceiling height of just under 8 feet, this could be a closet or very small room measuring 6 x 7 feet. The Gurin DHMD-110 works up to 500 cubic feet. This works out to a space of around 10 x 5 feet.
Needing to be recharged every 20-30 days, these units can only remove about 4-8 ounces of water over that whole period, which is a very small amount compared to a full sized dehumidifier. They will however, give up to 10 years of service, making them very economical in the long run. For exactly how rechargeables work, see below.
How Do Rechargeable Desiccant Dehumidifiers Work?
Containing a silica gel, these units grab moisture from the air over a period of 20-30 days, in a process called adsorption. Adsorption is a chemical process where the atoms or molecules of one substance (in this case, water…two hydrogens and an oxygen) adhere to the surface of another substance (the silica gel inside the dehumidifier). The water forms a film all over the surface of the silica gel.
There are no fans in a rechargeable dehumidifier, to bring new air into the unit. Because water vapour can only adhere to the silica gel when it comes into contact with it, the unit can only process air that naturally drifts in. This means that the whole process is very slow, which is why there is a period of 20-30 days between needing to recharge. This is how long it takes for enough air to drift by and adhere to all of the gel inside.
Once the silica gel can’t hold any more moisture, a color change indicator on the front will warn you that it is time to recharge the system. To recharge you just plug the unit into an electrical socket, the silica gel is then warmed gently, and the moisture is released.
Pros and Cons of Rechargeable Desiccant Dehumidifiers
- Very portable and compact
- Cheap to buy – usually $10-30
- 10 year Service Life
- No spills, unlike disposables
- During recharging, the collected moisture is released back into the air, so you need to recharge in a well ventilated area a good distance away from the area you want to dry out
- Very low capacity – only around 8 ounces overall (depending on model)
- Very slow rate of moisture removal – less than half an ounce per day
Full sized desiccant based dehumidifiers
A full sized desiccant based dehumidifier is the only type comparable to a compressor based dehumidifier. They are about the same size, and both types are great for household use, but a desiccant based machine has the advantage of being very quiet.
They’re relatively affordable, most will set you back one to three hundred bucks. But, they’re worth every penny. Desiccant dehumidifiers will remove up to 20 pints of water in a 24 hour period. Once plugged in, they require very little attention, other than to empty the water tank occasionally. Some have laundry settings which will allow you to dry a rack of laundry indoors in just a few hours.
How do Desiccant Based Dehumidifiers Work?
There are a few stages to the dehumidification process inside a desiccant based dehumidifier. The machine relies on a chemical ‘desiccant’ to capture water vapor from the air. The desiccant material is packed into a wheel, which turns continuously, allowing one portion to be dried while another attracts moisture, in a chemical process called adsorption.
During the first stage, air is drawn in through the front of the machine, and the first thing it does is pass over the outside surface of the condenser unit (remember that for later). This air is then directed through the ‘processing’ part of the wheel of desiccant material. Here, adsorption causes the water from the air to adhere to the surface of the desiccant, and most of the dry air coming out the back of the wheel exits the machine.
Some of the dry air is heated and forced back through the saturated portion of the desiccant wheel. This hot air dries the desiccant, allowing it to carry on capturing water from the air on its next rotation.
The hot air now carries water vapour from the desiccant. And, that water needs to be removed. This is achieved by channeling this air through a condenser. Because the outside of the condenser is surrounded by cooler air coming in from the atmosphere, the resulting temperature difference causes the water vapour to condense inside the condenser pipes and drip down into the waiting tank.
Desiccant vs. Compressor
Unlike desiccant based dehumidifiers, compressor based machines become less efficient as the air temperature drops. Manufacturers often test dehumidifiers in temperatures of 80°F and with a relative humidity (RH) of 60 percent. These are basically tropical conditions, and the majority of homes are much cooler than this, so direct comparisons between compressor and desiccant based dehumidifiers can be misleading.
Desiccant based dehumidifiers excel in much lower temperatures, and pull more moisture from the air than a similar capacity compressor based dehumidifier working in the lower range of its ability. They can also achieve a RH of 35% which is much drier than a compressor based dehumidifier can manage.
A compressor based dehumidifier uses refrigerated coils to cause the temperature difference needed for condensation. This means that as the temperature of the surrounding air decreases, the difference between its temperature and that of the coils also decreases, causing the condensing process to become less efficient. This is why compressor based models don’t work well in lower temperatures.
In desiccant dehumidifiers, the chemical adsorption will occur in most temperatures, so there is no loss of efficiency in that part of the moisture removal process. The condensing of the water for draining does rely on a temperature difference, but because this is the difference between the surrounding air’s temperature and the heated air, the process can continue right down as low as 34°F.
Pros and Cons of Desiccant Based Dehumidifiers
- Operate in temperatures ranging from 34°F to approximately 104°F
- Efficient in a range of temperatures – no loss of efficiency as temperature falls
- Can achieve RH as low as 35%
- Relatively compact and lightweight
- Very quiet to operate – sounds no louder than a desk fan. A compressor based dehumidifier is loud in comparison
- Relatively small capacity – compared to compressor based models, which can remove twice as much moisture in some conditions
- Expensive – a similar priced compressor based model will remove more moisture