Air conditioning causes the air to dry primarily due to the cooling process and the removal of humidity from the indoor environment. Here's how it works:
Cooling process: Air conditioning systems work by circulating indoor air through a cooling unit. This cooling unit contains a refrigerant that absorbs heat from the air, causing the air temperature to drop. The cooled air is then blown back into the room, creating a comfortable indoor environment.
Condensation: As the air cools down, its capacity to hold moisture decreases. Cold air has a lower saturation point for humidity, which means it can hold less water vapor compared to warm air. When the cooled air reaches its saturation point (100% relative humidity) or comes in contact with a surface that is colder than the dew point temperature, the excess moisture in the air condenses into liquid water droplets. This is similar to the formation of dew on a cold surface in the early morning.
Water removal: The condensed water droplets are collected in a tray or a drainage system in the air conditioning unit. This moisture removal process not only helps to maintain a more comfortable indoor humidity level but also prevents excessive moisture from accumulating in the room, which could lead to mold growth and other issues.
As a result of this cooling and dehumidifying process, the relative humidity in the air-conditioned space decreases, making the air feel drier. The lower humidity level can sometimes lead to discomfort, such as dry skin, throat, or eyes, especially in prolonged exposure to air-conditioned environments.
To mitigate this dryness, some modern air conditioning systems include features like humidity control or "dehumidification mode" that can help maintain a more balanced and comfortable indoor environment by controlling both temperature and humidity levels. Additionally, using standalone humidifiers in air-conditioned spaces can help increase moisture levels, making the air more comfortable for occupants.