Anyone who’s ever gotten stuck outside on a muggy day where even the air feels heavy knows the value of dehumidified air. Humidity, or the moisture in the air, can come with a range of negative effects, from encouraging mold and bacteria growth to potential equipment damage from rust and short circuits.
When paired with high heat, humidity also comes with a range of health effects you might not expect, like dehydration, fatigue and even a bad mood. Humidity is one of the reasons we get “feels like” temperatures that are much higher than the actual temperature.
To fight excess humidity, many business owners turn to dehumidifiers. This equipment can come in a variety of styles, with two popular methods of drying air being refrigerated or desiccant dryers. But what is the dehumidification process, and how do dehumidifiers work?
Airflow in the Dehumidification Process
To explain how dehumidifiers work, we need to start by looking at airflow. All types of dehumidifiers rely on the movement of air to remove its moisture. Generally speaking, fans pull air into the dehumidifier and move it over the drying mechanism, whether that is a desiccant material or cooling coils. As the air moves over that mechanism, the moisture is removed. It then moves along to the output duct and is released back into the space.
Depending on the type of dehumidifier, there may be multiple streams of air involved. A desiccant wheel, for instance, needs a second stream of air that replenishes the system’s ability to dry the air. In dehumidifiers that rely on condensation to remove moisture, there is just one airstream.
What Are the Typical Air Conditions Before the Dehumidification Process?
To compare and measure dehumidification processes, we need a benchmark. In most cases, we talk about incoming air as air that has a dry bulb temperature of around 80 degrees Fahrenheit and relative humidity of 60%.
Dry bulb temperature refers to the temperature on a thermometer that’s not affected by moisture in the air, making it a key marker when measuring dehumidification capabilities. We can also use dew point temperatures, which refer to the temperature to which the air needs to be cooled to achieve a relative humidity of 100%.
The relationship between dew point and dry bulb temperatures can be misleading because of the way the percentages work. The National Weather Service provides the example that a temperature of 30 and a dew point of 30 create a relative humidity of 100%, while a temperature of 80 with a dew point of 60 generates relative humidity of 50%. Still, that 80-degree day with a higher dew point is going to feel much more humid than the 30-degree day, even though the relative humidity is considerably lower.
Regardless of what temperature it happens at, when the dew point is reached, moisture starts to leave the air. It might condense onto a nearby surface or be absorbed by desiccant materials. Dehumidifiers rely on that dew point to operate. In refrigerated dehumidifiers, they get to it by bringing down the temperature. Desiccant dehumidifiers, however, absorb moisture until the desiccant is saturated and reactivation air helps dry out the desiccant.
Another useful metric is grains of moisture per pound. Incoming air at 60% relative humidity corresponds to 92 grains of moisture per pound. These values apply to both the process air and the reactivation air.
How Does Air Flow Through a Desiccant Wheel?
One of the most popular types of dehumidifiers is a desiccant dehumidifier, which uses a desiccant wheel and doesn’t call for energy-intensive refrigeration. This wheel is filled with silica, the same moisture-absorbing material you often find in white packets with sensitive products like medication and electronics.
Process air, or the air being pulled into the dehumidifier, is pulled through the wheel via a fan system. Moisture from the process air gets absorbed — i.e., sticks to another molecule — into the silica, sending dry air back out into the space through an output vent.
But process air only moves across about three-quarters of the wheel. The other quarter is devoted to reactivation air. This type of air is used to “refresh” the silica so it’s able to absorb more incoming process air. Reactivation air enters the dehumidifier and moves across the wheel on a separate airstream. Before it reaches the wheel, reactivation air is heated to a high temperature to prime it for the next step.
When the heated reactivation air moves through the wheel, the silica releases its moisture back into it. The air remains humid, but it serves the important job of returning the silica to a moisture-absorbing state that can again dehumidify the incoming process air. Desiccant dehumidifiers can, of course, feature a few different designs, but for the most part, reactivation air moves opposite to the process air stream.
Heating the Reactivation Air
Reactivation air is generally heated with an electric heating device. It serves the role of bringing ambient-temperature reactivation air up to a temperature as high as 284 degrees Fahrenheit. The heating process makes the reactivation air readily receive moisture from the silica. It pulls this moisture off the desiccant and takes it away, leaving dried silica on the wheel, where it rotates around to dry out the process air and keep the cycle moving.
What Are the Air Conditions Following the Dehumidification Process?
Dehumidifiers can vary in their capabilities, but you can generally expect the air to increase in temperature and decrease in relative humidity in the dehumidification process.
Take, for example, our 400-millimeter wheel on a system that accommodates 6,000 cubic feet per minute of airflow — one of the most common models we offer. On average, air will exit the dehumidifier at about 123 degrees Fahrenheit, with less than 10% relative humidity and 54 grains of moisture per pound. That comes out to a temperature increase of 43 degrees Fahrenheit, a relative humidity decrease of 50% and 38 fewer grains of moisture per pound. (Data derived assuming 80F DB / 60% RH entering air).
These numbers illustrate how effective dehumidifiers are. Whether you need to avoid the moisture in a humid climate for a building full of shoppers or need to achieve exceptionally low moisture content for industrial or food-grade applications, a dehumidifier can get it done.
Reach out to Smart Family to Learn More
Dehumidifiers are a key part of many commercial operations. If you’re in need of one, the experts at the Smart Family of Cooling Products can help with rental-ready desiccant dehumidifiers for sale. We’re also well-versed in the ins and outs of dehumidifiers and can conduct service on Smart Family Cooling equipment and dehumidifiers from other providers.