Why is air in air-conditioned room dry?

When we are in the room or car which is air conditioned, we feel air surrounding us is dry. How come?

Air contains several kinds of gases such as nitrogen, oxygen, carbon dioxide, etc. Besides that air also contains moisture. If moisture in the air is high, then it makes air becomes more humid. The amount of moister in the air is called humidity. Humidity can be quantified as relative humidity and humidity ratio.

 

Latent heat is heat which doesn’t change the temperature. This heat only change phase. Moister inside air causes latent heat becomes high. More moisture contained in the air will cause higher latent heat because heat removed from air is not only used to decrease temperature, but also condense moisture.

Air-conditioner cool the air and it causes air temperature decrease until dew point temperature, if the air is still cooled, temperature will decrease followed condensation of moisture. Dew point is the temperature when moisture is saturated.

Room air is sucked to the air conditioner and blown again to the room. Before it is blown again, air is cooled by air-conditioner. In other words air is circulated and cooled by air-conditioner. The component of air-conditioner which cool the air is evaporator, thus air which is close to evaporator is colder than other and achieve dew point temperature earlier, then start to produce condensate. That is why water is often (condensate) found at air conditioner.

Since moisture in the air condenses at evaporator, the amount moisture is being reduced and resulting dry air.