A condensation dryer draws in humid air, cools it below dew point and collects the condensate. That only works in a closed space: with a window open you are drying the outside air.
The stated capacity in litres per 24 hours applies at 30 °C and 80 % relative humidity. At lower temperatures the yield drops, which is why some extra heat helps.
Position a fan so the air sweeps along walls and floors. Moisture inside the material is only released once air moves over it.
Track progress with a moisture meter rather than by eye: timber and screed look dry on the surface while the core is still wet.