Doll mobile vented dryers extract humidity from the compartment air by constantly circulating compartment air through the device. In the process the humid air flows over the cold evaporator tubes, whereupon it is chilled below the dew point.

Thereby the humidity drops out and condenses on the tubes in form of waterdrops. This water can be drained off via a discharge nozzle.

The chilled air is now conducted through the hot condenser of the cooling-system, at which it is heated with the same energy (latent heat, latent energy), which it has been extracted from, during the cool down-period. Furthermore Doll devices are additionally using the waste heat from the compressor and ventilator motor for heating the compartment air. The into the room emited air now has a higher temperature, but a heavily reduced humidity, it can therefore absorb more humidity from the room air. By the use of this system the Doll DK devices achieve their well renown degree of efficiency. Conventional systems do have usually the problem of icing up tubes during longer operation - or operating in winter time - at construction sites. The degree of efficiency of conventional systems tends towards zero percent with  with increasing icing of the register. Doll devices are therefore serially equipped with a defrosting - automatic, which periodically uses hot gas to defrost the generated ice at the vaporiser. The high efficiency of Doll devices remains therefore, also at longer operational time or as well at low ambient temperatures, in full effect!