Re: What is the scientific principle that a dehumidifier is based on?

Air can only hold so much moisture for a given air temperature.  This 
measure is the relative humidity.  If the air is saturated with moisture, 
we say it is at 100% relative humidity.  That is like when you are in a 
steamy shower with clouds of moisture in the air. If the temperature in 
the room is lower, it will steam up even more since the air can't hold as 
much moisture before it condenses (changes from vapor to liquid) on a 
surface.  The air in a room will will lose moisture to a dehumidifier 
because it is cooled below the existing temperature and cannot hold as 
much moisture as it did at the warmer temperature. The cold surface will 
cool the air, and the moisture in the air will condense from vapor to 
liquid onto the cold surface. To condense a vapor to liquid, it must give 
up a certain amount of energy.  This is absorbed by the chilled plate in 
the de-humidifier. (An example is the mirror in a steamy bathroom with the 
shower running.)

The best explanation of humidity and its control is at the How Stuff Works 
Web site. 
 http://home.howstuffworks.com/

Look at the explanation for How does a Humidifier work and then the 
explanation for how a de-humidifier works.  The explanation of the 
humidifier explains the moisture and the concept of relative humidity.