Generally, drying is a process during which vapour is removed from air by means of using suitable methods and equipment. Most often it is achieved by lowering the air temperature or by vapour adsorption by special adsorbents in the form of water solutions or gels. The first method, called the condensation method, involves air cooling to the temperature at which water droplets precipitate and then reception and removal of this moisture. The advantage of such methods is effective drying of damp interiors, e.g. after a flooding, but it is worth noting that condensation drying is inexpensive and more cost-effective than heating and ventilation.

In the second method, called the adsorption method, the vapour is absorbed by hygroscopic material, such as bags filled with various adsorbents in the form of gel, crystals or balls. The advantage of this method is that it removed moisture at various air temperatures, even subfreezing and allows reaching a 2% humidity. The adsorption drying is a perfect solution e.g. in pharmaceutical or food processing industry in various types of cold stores and freezers.

In practice, in addition to two methods described above the drying by heating and ventilation is also used. The air temperature in the room is increased significantly and then the room is intensively ventilated. This is the least effective and the most expensive way to remove dampness from the room. Intensive heating means high energy costs, and the drying takes much longer, reducing effectiveness.

Depending on the method of operation and types of rooms from which the dampness is to be removed, there is a closed-circuit drying where the indoor air does not mix with the outdoor air, and an open-circuit drying with total or partial change of indoor and outdoor air by means of e.g. AC systems.