PolyDryer Air Exchanger

Most 3d printing filament dryers have a fundamental flaw:
they heat the filament and pass air over it, but they are a closed system with no venting, so moisture escapes only by accident.

With single piece dryers, fixing this is intrusive - you have to modify the dryer itself: Sunlu S1 Filadryer Turbo Mod.
The PolyDryer being modular, allows for a non-intrusive approach.

The result of allowing a measured amount of air exchange between the dryer and the ambient, is that it reduces the humidity of the air in the dryer more rapidly, greatly reduces condensation build up within the case, and improving drying speed.

I provide two versions of this print, a 5% and a 10% air exchange.
The 10% versions seems close to optimum for the stock PolyDryer.

Best printed out of ABS or PETG for temperature resistance, with supports.

I also modified my PolyDryer by replacing the plastic vent covers that restricted airflow with stainless steel mesh that allows more airflow while still preventing stray filament from making contact with the heating element. Because of the higher airflow, I use the 5% air exchange. In my testing, this arrangement improved drying speed by about 25%, and reduced humidity within the case from an initial 85% to 33% after one hour on medium, where the stock dryer only reduces humidity to 65%.

The introduction of air exchange did not appear to affect the temperature achieved within the case to any noticeable degree.

Note that a filament dryer that relies on heating ambient air to work, is able to achieve a final humidity in the filament that is determined by 1) the humidity of the ambient air and 2) the temperature difference between the heated air and the ambient air. As long as the heated air temperature isn't changed by it, using additional air exchange doesn't change this limit - it just speeds the process up. If the humidity of the ambient air and/or its temperature is such that you can't get the filament as dry as you want, then you need to switch to loading the dryer with a dry descant such as  silica gel, and making the air circulation as closed as possible.