How Does A Dehumidifier Work? (2-Step Dehumidifier Principle)

In simplest terms, a dehumidifier is an HVAC device that removes moisture from indoor air. To understand how does a dehumidifier work, however, we have to look into the device itself.

In technical terms, the dehumidifier uses a refrigeration-based and heater-based system to reduce relative air humidity from 50-100% to 30-50%.

As you can see from the photo above, the moisture removal process involves cooling (refrigerator-based system) and heating (heater-based system) of the indoor air.

Because of the way of how modern dehumidifiers work, they are more than capable to extract more than 100 pints of water from indoor per day.

Basic Dehumidifier Working Principle

Every dehumidifier follows the same 2-step principle:

    1. Extract moisture out of the air: Fan in the moist air in the house, run it over a cold coil (Evaporator) which condenses moisture out of that air and collect the water via a drip tray into a water tank. We end up with a cold but dry air.
    2. Heat the dry air back up: Run the cold but dry air over a hot coil (Condenser) to bring it up to room temperature. Fan the dry air back in the house.

The exploding-photo of a dehumidifier here depicts all the vital part of a dehumidifier:

how does the dehumidifier work
Key parts of the dehumidifier illustrate how this HVAC device combines the principles of a refrigerator and a heater.

The way that dehumidifier works is by being a refrigerator and a heater at the same time.

Step-By-Step Way Of How Does A Dehumidifier Work

Here are the 6 steps of the whole air dehumidification process:

  1. The compressor propels the fan and the flow of the refrigerant.
  2. The fan draws humid air into the dehumidifier via an air inlet.
  3. The humid air is met with a series of very cold coils (basically, a refrigerator). There the water from the air is condensed on the cold coils.
  4. The drip tray gathers the water in the water tank. The convenience of removing water from the dehumidifier’s water tank will be one of the key parts of the buying guide below.
  5.  The now dry cold air will run over hot coils to warm up (basically, a heater).
  6. The same fan that absorbs the humid air into the dehumidifier will now propel the dry air out.

The only difference between the best and the worst dehumidifiers is how well they have perfected this process. It’s difficult to see ‘under the hood’ of every dehumidifier; we have prepared a list of the best performing dehumidifiers for basement here if you are in need of a new one.

From capacity and energy-efficiency to the noise levels, all these specifications are simply based on the well-designed fridge-heater operation we see here. 

Thermodynamics Principles That Govern The Inner Workings Of Dehumidifiers

The key part of how every dehumidifier works is the refrigerant. Refrigerant is a fluid that is used in all kinds of devices where heat transfer is required – the refrigerator is the simplest example.

The way refrigerant facilitates heat transfer is by undergoing a phase transition from liquid to gas, and vice versa.

The dehumidifier uses the cold coils (evaporator) to remove moisture from the air. In turn, it uses hot coils (condenser) to reheat to room temperature.

If can create the airflow between these cold and hot coils, you have yourself a dehumidifier.

That’s why the key to how a dehumidifier works is understanding how refrigerant works. The refrigerant flows in a closed tube where it encounters temperature changes but not volume changes. From the equation for an ideal gas,

p*V=nRT

it is evident, that if the temperature will change, the pressure will also have to change (because everything else remains constant). Such a process is called an isochoric process, or constant-volume process, whereas refrigerant in gaseous stated is either compressed or expanded at contact volume.

Such a process – a thermodynamic process – is governed by the 1st Law of Thermodynamics.

In short, the physics behind how does a dehumidifier work is quite complex. Nevertheless, pretty much everybody can understand how a dehumidifier works on a macroscopic scale based on decreasing and increasing the temperature of the air that flows through the device.

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