Reversing
First of: If it's on industrial laundry equipment, it makes sense.
Once you hit a certain load to drum volume ratio, reversing is a need with big items. Thus US dryers don't generally use it (keep in mind that most US washer to dryer ratios are about 3cuft to 7cuft) and EU dryers tend to use it.
For the commercial side, this video puts it well (past one minute):
How much you need and can do it depends on a lot of stuff.
Most commercial dryers have seperate motors for fan and drum.
On their first generation of heatpump dryers, Miele carried that design over, but ELux did so as well.
That way, you could tumble however you wanted and did not have to care about airflow.
A lot of older dryers did 50/50 reversing to, but more or less were designed to handle the heater output on both directions of turning.
With the desire to bring heatpump dryer cost down, BSH coupled the fan to the drum motor, increased airflow as needed for heatpump dryers but did that by optimising the fan in one direction only, makeing the other direction basicly useless.
Thus, they just cut reversing.
The T1 dryer range and ELux now both employ sensing of tangeling and both the upcomming Miele and current ELux ranges will feature cycles specificly designed for bedding and/or comforters.
Our current dryer in the flat up north is an Arcrelik and barely reverses (about one turn every 10min).
It's big bar type lifters and intense airflow paired with 100% constant tumbling speed due to the inverter motor keep tangeling from happening.
ELux does something simmilar by using 3 instead of 2 lifters.
What you don't often realize is how tangeling occurs: If an item drops onto itself, those overlapping areas get lifted up together and fall earlier then the rest of the load, falling back again onto themselfes, over and over.
If a motor is not speed controlled and loaded down, the load falls even earlier due to a verry minor and short but existent speed fluctuation caused by the bigger weight concentration of the particular area in the load.
If a motor is verry precisley speed controlled, these speed fluctuations won't happen thus makeing tangeling less likely.
It's funny that I basicly had this EXACT argument with combo52 about a dozen times, explained him a dozen times why reversing on more compact machines makes sense, and he never even acknowledged that or shows the slightes bit of a try to give any reason based argument against my points.
