How Does a Refrigerant Dehumidifier Work?


Refrigerant dehumidifiers can solve the problem of humid air in the home.

But how exactly does a refrigerant dehumidifier work? A dehumidifier separates and pulls the water out out air by cooling it, then returns the remaining air by warming it back up again.

In more detail, a refrigerant dehumidifier works in the following 5 steps:

  1. First, it takes up moist air from the room with the use of powerful fans.
  2. Next, it passes this air over cold tubes that are infused with refrigerant.
  3. Water is then separated from this moist air and collected into a reservoir or moved through a drain tube.
  4. The remaining condensation is then moved over heated coils and returned back to the room as air again, with the air coming out of the dehumidifier being dryer than the air that came in.

This is the general working principle, but more specific detail is required to understand the functioning of refrigerant dehumidifiers fully.


What is Humidity?

When you think of it, the air isn’t just gas. The atmosphere outside and in our homes contains water, either as vapor or as a liquid when it’s raining. If you have central heating, it might feel like the atmosphere in the house is just dry air, but there’s moisture present.

If you do laundry or dry clothing in the house, or cook with little or no ventilation, then the moisture levels can be unbelievable significant. You can even deduce this by condensation on windows and even water dripping down walls.


Why Indoor Humidity Matters

Water is vital and necessary for life. Even our human bodies constitute 60% of water. That means high humidity in our homes would do us a lot of good, right?

Well, not really. High humidity can cause problems like the molding of clothes, rusting of metallic apparatus, short-circuit in electronic devices, blurring of screens and camera lenses – and it can cause problems in health too. High indoor humidity levels favor the growth of bacteria, mites, and fungi, and that means a greater risk of infection and disease.

And that’s where dehumidifiers come in, and here’s why you may in need of a dehumidifier:

  •         A persistent damp smell, especially in areas you often spend time in, in the home.
  •         There is apparent water leakage after rainfall
  •         The appearance of somewhat muddy air in the home. This actually means the water vapor has become visible and can be seen as a cloud.
  •         Allergy to dust mites.
  •         An increase in the appearance of unwanted household pests, like cockroaches, spiders, etc.
  •         Damp or moldy smell on your clothes, even when they were recently washed. Your clothes smell damp or moldy even when they have been freshly washed.


What Does a Dehumidifier Do?

Think of a dehumidifier as a vacuum cleaner: it sucks in air from the room at one end, removes moisture from the air, and then cycles it back into the room. The moisture from the air is collected in a collection tank that would need to be emptied from time to time that you have to empty, from time to time.

The way the moisture is removed from the air in a refrigerant dehumidifier is quite similar to the working principle of a refrigerator and an air-conditioning unit.


Working Principle of a Refrigerant Dehumidifier

Dehumidifiers work by two basic principles:

  •         Moisture extraction from the air: Moisture-rich air is sucked into a fan from the house and run over an evaporator, which is basically a cold coil. This evaporator condenses the moisture out of the air and collects it in a water tank via a drip tank. The result of this step is cold, dry air.
  •         Heating up the dry air: the resulting cold, dry air from the evaporator is passed over a hot coil. This brings the air temperature up to room temperature, which is then fed back into the room.


Most refrigerant dehumidifiers have some five basic components:

  •         Fan compressor — This component is responsible for compressing and expanding the refrigerant gas to cool the dehumidifier’s condenser coils.
  •         Reheater – It captures and recollects heat generated from the cooling process.
  •         Compressor cooling coils
  •         Reservoir / collecting tray


How a Refrigerant Dehumidifier Works, Step-by-Step

Refrigerant dehumidifiers work by condensing out moisture from the air, heating up the air to room temperature, and cycling the air back into the house. Here’s how it is achieved step by step:

  •         An electric fan draws in warm, moist air from the room through a grille on one side of the refrigerant dehumidifier.
  •         The warm, moist air passes over cold pipes. These pipes are kept freezing cold by coolants circulated continuously through them. As the air passes these cold pipes, the moisture in the air turns into liquid (condenses) and drips off.
  •         This liquefied moisture drips down into a collecting tray strategically placed at the bottom of the refrigerant dehumidifier.
  •         At this point, the air is a lot colder than it came in, but it is free of moisture (dry). This dry, cold air passes over a hot condenser/compressor unit, which warms up the air, bringing it to its original room temperature.
  •         The resulting warm, dry air passes out into the room through another grille.
  •         As the condensed moisture from the air collects into the collecting tray, a plastic float rises up to indicate the level to which the collecting tray fills up.
  •         When the collecting tray fills up, the float triggers an electric switch that turns off the fan and turns on the indicator light, signaling the need to empty the collecting tray.

In most cases, dehumidifiers are packed with a humidistat, which allows you to set the level of humidity you desire. This humidistat is made up of two parts: a sensor and a relay amplifier. The sensor is made up of two alternate metal conductors, in which the resistance between the two conductors changes with changes in the relative humidity. The relay amplifier measures the resistance between the conductors and triggers the dehumidifier on or off. All these components add up to make the dehumidifier functional and effective at what it does.


Thermodynamics Principles and Dehumidifiers

The functioning of the refrigerant dehumidifier rests entirely on the refrigerant. A refrigerant is a fluid used in devices involved in heat transfer, the commonest example being the refrigerator. Refrigerants facilitate heat transfer by undergoing phase changes from liquid to gas and gas to liquid.

Now, a dehumidifier makes use of cold coils (evaporators) to extract moisture from the air and hot coils (condensers) to raise cold, dry air from evaporators back to room temperature for re-circulation in the house. That means if you can re-create this path from the evaporator to the condenser, then you’ve indeed built yourself a dehumidifier. As such, an understanding of how refrigerants work is key to achieving this.

The refrigerant flows in a closed tube continuedly, where it encounters temperature changes. However, as its temperature changes, its volume doesn’t. For this, let’s look at the ideal gas equation:


By this equation, we see that temperature is directly proportional to pressure. What that means is, if the temperature changed, the pressure would follow suit, as all other things remain constant. This is referred to as a constant-volume (isochoric) process. Such a thermodynamic process is governed by the first Law of Thermodynamics.

To cut to the chase, the physics behind the functioning of refrigerant dehumidifiers can be quite complex but follows the general macroscopic principles of decreasing and increasing air temperature in a controlled environment.


Related Questions

How do you compare dehumidifiers?

How well dehumidifiers have perfected the general working principle would depict how good a particular brand is. Here are some measures to test this.


Amount of Water Removed Per Day

The amount of water a dehumidifier removed in liters is a great indicator of the quality of the dehumidifier. In this light, bigger machines would have the upper hand in achieving a greater amount of water removed per day.



The power efficiency of the dehumidifier can hint at its quality by calculating the energy factor of the machine. This can be calculated by the formula

It is measured in liters per kilowatt-hour (L/kWh). A higher figure is an indicator of a greater quality machine, and that means the machine would work harder in removing more water per hour.


How long does a dehumidifier take to work?

When used for the first time, a dehumidifier can take as much as 12 hours to get the required humidity level you desire.


How long should a dehumidifier run per day?

It might be commonplace to have your dehumidifier run for 24 hours a day, but that can be quite costly. If power bills aren’t an issue, then you can easily run your dehumidifier all day long, and it is especially essential to do so when you’re using your dehumidifier for large room sizes.