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Airflow Systems: How Dehumidification Works

Airflow Systems: Chapter 4


In this module we will explain what dehumidification is. We will explain why it is important and how it is implemented. Skip to quiz!

Need for Dehumidification

Humidity causes the growth of fungus and mold. Recall that in high humidity, our sweat cannot dry up as easily. This makes us feel warmer at room temperature.

Sweating normally cools us down because the water from our skin evaporates. This process removes heat from our body into the air. When the air is humid, there is already a lot of water in it.

This makes it hard for the sweat to evaporate and add more. This makes us unable to sweat as well, and thus feel hotter.

Some climates are more humid than others. Areas near large bodies of water are more humid because the water is added to the air. Warmer water evaporates more quickly, so warmer areas tend to be more humid.

Florida and Louisiana are good examples of humid places.They are surrounded by swamps and oceans so have a lot of water.They are also very warm climates, so this water evaporates quickly.

Air Conditioning

Let’s use the example of a cold glass of ice water in a room.The warm water in the air hits the cold glass and cools down. It cools so much that it changes from its gas state to a liquid one. This is called condensation and it is used in air conditioning to lower humidity.

Evaporators are devices in air conditioning that use condensation to remove humidity. Evaporators are very cold. when the fan blows air into them, it causes the water vapor to become liquid drops.Just like a glass of ice water! The droplets are then drained from the system and the air is less humid.

Evaporators consist of a cold coil, fan and drain pipe. The drain pipe is how the water is removed from the system.

Air conditioning is good for moderate humidity conditions. There is no need to install a dehumidifier. It is inexpensive and occupies less space. It also provides cool air by controlling humidity.

The amount of moisture removed by AC dehumidification is not very much. The cooler the air gets, the more water gets condensed. However, if we make the air too cold then it will not be within the range of human comfort.

Heat pipes are another way to dehumidify the air. A heat pipe is a simple device that can transfer heat from one point to another. Let’s take a look at how they work.

Heat pipes use a liquid called refrigerant to pre-cool the air coming into the AC. Because the air is cool, the evaporator can remove more moisture than normal.

Reheat Systems

Reheat systems provide an alternative to air conditioning systems. Let’s take a look at how they dehumidify the air.

When the air is dehumidified, the temperature of the air is reduced. Sometimes it becomes too low so we have to reheat the air. A reheat coil heats the air back up to a comfortable temperature.

When reheat coils are coupled with evaporators, the air is comfortable and dehumidified. The evaporators remove the moisture and the reheat coils fix the temperature.

Reheat systems can cool and heat the air, while AC can only cool. They can also work on very hot and humid days, while AC works in mild climates. However, reheat systems cost more and take up much more space than AC units.


Dehumidifiers are another way to remove moisture from the air. These devices are very efficient and won’t cool the air around you. Let’s take a look at how.

Dehumidifiers bring in moist air and cool it down. This causes the water to condense and collect in a tray inside. This water collection system can then be emptied manually.

Compared to reheat systems and air conditioning, dehumidifiers are the most effective. The primary purpose is to dehumidify the air. However, they are the most expensive systems.

The three dehumidifying systems we explored today are air conditioning, reheat and dehumidifiers. Each system works to make indoor spaces more comfortable.


Types of Dehumidifiers

In this module we will learn about different types of dehumidifiers. Each dehumidifier has a different purpose. We want to understand the suitable environments for each. Skip to quiz!


One humidifier can adjust the conditions in a single room. But what if we want to dehumidify a whole home or building? One big humidifier can substitute 10 small humidifiers for an entire building.

Dehumidifiers work in two ways. The first is when they remove moisture using condensation. The second is when they use water absorbing material. Just like a sponge can absorb liquid water, these materials absorb water vapor.

The capacity of a dehumidifier is the amount of moisture it can remove over 24 hours. Capacity of dehumidifiers is measured in pints. Let’s take a look at how to pick dehumidifiers based on capacity.

As you can see from the video, different dehumidifiers serve different purposes. The three main types of dehumidifiers are:

  • Console,

  • Whole house, and

  • Desiccant.

Console Dehumidifier

Console dehumidifiers are good for removing moisture in one room. Console dehumidifiers use a compact refrigeration system. Let’s see how they work.

Moist air is sucked on one side by a fan and passes over cold evaporator coils. The evaporator coil collects the moisture the passes over the hot condenser coil. Now the warm dry air blows back into the room.

Console dehumidifiers are portable and easy to install. These devices are very easy to control and operate. They work best when we need to dehumidify a single room.

Console dehumidifiers are noisy and not very energy efficient. Additionally, you have to manually remove the collected water from them. They have a much shorter life span than Whole House Dehumidifiers.

Whole House Dehumidifier

These dehumidifiers can support more than one room. They rely on ductwork and a strong fan to do so.

The dehumidifying process of whole house and console dehumidifiers is the same. However, whole house dehumidifiers have ducts at both ends. This allows them to use a strong fan to push the dry air to different rooms.

They have the ability to automatically control humidity throughout the building.They are located out of sight and have a lower sound level. They are much more energy efficient than consoles.

Whole house humidifiers are more expensive on initial purchase. It can be a more complicated setup and install.They are larger and heavier than a console dehumidifier as well.

Desiccant Wheel Dehumidifier

Recall that some dehumidifiers use water absorbing materials. Silica gel is a similar material used in desiccant wheel dehumidifiers. Silica gel is the same thing that comes in new shoes to keep them dry. This gel is implemented in desiccant wheel dehumidifiers.

Desiccant wheel dehumidifiers use silica gel to attract moisture. They contain a honeycomb design of this gel to capture the water vapor passing through.

These dehumidifiers pull air through them with a fan. The air passes through a rotating wheel with silica gel on its edges. The silica gel absorbs the water vapor as the air passes through it.

Desiccant dehumidifiers are best suited for hot and humid climates. They are the best dehumidifier at removing moisture. Also, they can remove moisture very quickly.

Desiccant wheel dehumidifiers cost more to both purchase and install. They consume more energy and are also unable to cool the air.

Each humidifier is good for a different purpose. Console dehumidifiers are cheap, portable and work well for one room. Whole house dehumidifiers can cool a larger space but cost more. Desiccant wheels are the most expensive but the best sat removing moisture.


Question #1: Why doesn’t sweat evaporate in high humidity?

  1. The temperature is not high enough

  2. There is already too much water in the air

  3. Your body doesn’t generate it

Scroll down for the answer...

Answer: There is already too much water in the air

It is difficult for sweat to evaporate when there is a lot of water in the air. This is why we feel hotter.

Question #2: Which of these places would have the highest humidity?

  1. Kansas

  2. Florida

  3. Arizona

  4. Idaho

Scroll down for the answer...

Answer: Florida

Florida is warm and near a large body of water. This will result in high humidity.

Question #3: Which component of an AC system removes moisture from the air?

  1. Exhaust

  2. Ductwork

  3. Evaporator

  4. Supply Fan

Scroll down for the answer...

Answer: Evaporator

The evaporator condenses the water vapor to remove it from the air.

Question #4: What is the cooling liquid in heat pipes?

  1. Cold water

  2. Mercury

  3. Liquid Nitrogen

  4. Refrigerant

Scroll down for the answer...

Answer: Refrigerant

Refrigerant is the fluid used in heat pipes to cool down the air.

Question #5: What is the advantage of reheat systems over air conditioning?

  1. Only reheat systems dehumidify the air.

  2. Reheat systems keep air at a comfortable temperature.

  3. Air conditioning systems cannot dehumidify a whole room.

Scroll down for the answer...

Answer: Reheat systems keep air at a comfortable temperature.

Both systems dehumidify the air in an entire room or building. Air conditioning systems can over cool the air.

Question #6: Which system is the most efficient for dehumidification?

  1. Air Conditioning

  2. Reheat System

  3. Dehumidifier

Scroll down for the answer...

Answer: Dehumidifier

Although dehumidifiers are more expensive, they are better suited to remove moisture.

Question #7: Which of the following is not a method of dehumidifying air?

  1. Water Vapor Condensation

  2. Water Evaporation

  3. Water Vapor Absorption

Scroll down for the answer...

Answer: Water Evaporation

Evaporation is the process of turning water from a liquid to a gas. This would add more moisture to the air.

Question #8: Where would you use a Console dehumidifier?

  1. A single room

  2. An entire building

  3. An outside space

Scroll down for the answer...

Answer: A single room

Console dehumidifiers work best in small enclosed areas.

Question #9: How do whole house dehumidifiers supply an entire home?

  1. Plumbing systems

  2. Powerful intake fans

  3. Ductwork

  4. Moving through it

Scroll down for the answer...

Answer: Ductwork

Ductwork allows whole house dehumidifiers to efficiently remove moisture. The ductwork pulls air from different rooms than where the dehumidifier is located.

Question #10: What is one benefit of a console dehumidifier over a whole house one?

  1. Larger area

  2. Easier to install

  3. Less Noisy

  4. More energy efficient

Scroll down for the answer...

Answer: Easier to install

The other three choices are true of a whole house dehumidifier over a console one.

Question #11: Which dehumidifier uses silica gel to change the room conditions?

  1. Console

  2. Whole House

  3. Desiccant Wheel

Scroll down for the answer...

Answer: Desiccant Wheel

The console uses condensation. The whole house uses condensation or water absorbing material other than silica gel.

Question #12: Which humidifier would you choose for a building with a moderate budget?

  1. Console

  2. Whole House

  3. Desiccant Wheel

Scroll down for the answer...

Answer: Whole House

Console dehumidifiers can only dehumidify one room at a time. Desiccant wheel dehumidifiers are very expensive.


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