Do Air Conditioners Make the Air Too Dry and Cause Sick?


hygrometer and air conditioner

The air conditioner blows out chilling air. I wonder does an air conditioner make air dry? Thus, I went on to find out.

It turns out air conditioner does make air dry. An air conditioner reduces air moisture to a relative humidity of 40% to 60%. Air condenses and forms water droplets when in contact with the evaporator of the air conditioner. Water is extracted from the air during this process. Thus, drying the air.

Many people don’t realize that the air conditioner is drying the air to make us feel more comfortable. Knowing why the air conditioner does so will help us understand the importance of dehumidification in air conditioning.

Why Does Air Conditioner Dry Air?

The air conditioner is designed to reduce the humidity of air in order to provide better comfort. Condensation happens at the evaporator of the air conditioner and water droplets are formed and discharged through a drain pipe. But, why it does that?

Humans Feel Comfortable at a Certain Humidity Level

Humans generally feel comfortable at a relative humidity (RH) of 40% to 60%. Above 60% RH, we feel sticky and wet. Below 40% RH, we feel too dry and we can suffer from dry lips and sore throat when exposed to such a dry environment for a long period of time.

Our world is quite humid. We can live in a humid environment but, it’s just not so comfortable. In Malaysia, the average relative humidity ranged between 74% and 86%. It inevitably makes the air conditioner the top electrical appliance in Malaysia.

Personally, I do enjoy the sun if the air is dryer. I’ve experienced it when I travel to Korea during the summer. In the afternoon, I walked on the street without wearing any hat or using an umbrella. The sun was shining, I felt the heat but I was comfortable. It was hot but the air was dry enough for me to feel comfortable walking around the streets. If I were to do the same in Malaysia, I’ll be sweating like crazy and very quickly run to an air-conditioned shopping mall. It is just too uncomfortable with high relative humidity.

Comfort Environment Boost Humans’ Productivity

I doubt anyone disagrees that when we feel comfortable, we are more productive. Offices are always air-conditioned for people to stay for long hours without feeling uncomfortable. Working at non-air-conditioned places such as construction sites and farms is generally more tiring and getting less work done. The air conditioner reduces the humidity of the air to help us stay comfortable and reach a higher productivity level.

How Does an Air Conditioner Dry Air?

The air conditioner draws in air and allows the air to pass through a finned tube heat exchanger. The heat exchanger is icy cold due to the refrigerant flowing via the copper pipes. When the air contacts with the chilling surface of the heat exchanger, the air condenses, and water droplets are formed.

condensation at heat exchanger

Through this process, the air loses its water or humidity every time a water droplet is formed. Thus, the air becomes dryer than before.

The dew point of water during the operation of the air conditioner is about 15°C to 20°C, assuming the air temperature is 26°C and 50% to 60% RH. In order for the water vapor in the air to become water droplets, the temperature of the surface of the heat exchanger must drop beyond the dew point of water.

Will an Air Conditioner Make Air Too Dry?

If we define “too dry” as relative humidity of the air below 40%, cooling only air conditioner almost impossible to achieve that. The colder the air, the more moisture it can extracts but there is a limit. So, if you worry about your air conditioner dries up your room to like 20% RH, you can stop the worry.

On the other hand, if the air conditioner has both heating and cooling functions, an oversized air conditioner can reduce the relative humidity to below 40% which affects our health over time.

In addition, some commercial air conditioners use a heat pipe or pre-heat the air to achieve extremely low RH as required.

What If My Air Conditioner Is Not Drying the Air?

If you are cold and still feeling sticky while using an air conditioner, you probably have an oversized air conditioner.

An air conditioner reduces the temperature of the room while removing the air moisture. The air conditioner needs time to circulate air and extract sufficient water in order for you to start feeling the reduced air moisture.

If you have an oversized air conditioner, your room temperature will drop to the setpoint very quickly and the air conditioner will stop the cooling, leaving no time for dehumidification. If this is what happens, you can try the “dry mode” where the air conditioner will focus on dehumidification.

What to Do If Your Air-Conditioned Room is Too Dry?

You can try a humidifier and putting a few bowls of water but it hardly helps because the dehumidification power of an air conditioner is simply too strong and it’ll just quickly condense all the water vapor produced by the humidifier and the few bowls of water.

Perhaps, you can use an air cooler instead if your area has naturally dry air. Otherwise, use a dehumidifier close up.

Related Questions

Does dry mode cool the air? Dry mode is not intended to cool the air. The function of dry mode is to remove the moisture and reduce the relative humidity of the air.

How to know the humidity in my room? You can use a hygrometer to measure the humidity of the air. It usually comes with temperature measurement as well.

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Yu was working in the air conditioning industry for the past 7 years, covering from design to installation and maintenance. Yu wish to share all the things he learned with the people around the world.

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