Not to prejudge the outcome, but closed loop does seem like it would be faster, since you could crank up the flow rate to be a lot higher, and you’re not fighting the dilution problem. Most of my measurements have been on filaments packaged on cardboard spools, but on the few measurements I’ve done for filaments packaged on plastic spools, I think I’ve only measured at most about 3g of moisture loss. Then again, I haven’t measured nylon or tpu, which are both sponges. For everyday filaments, though, suppose I’m 3x wrong and the worst case is 10g of moisture that needs to be dried out of a filament mounted on a plastic spool. It’s apparently enough to make a difference in print quality, but not really all that much in absolute terms, especially compared to your big jar of desiccant. And, as far as circulating heated air through the drierite, the manufacturer claims:
There is little change in efficiency at temperatures up to 100° C.
Drierite - Drierite Overview
The faster dry time might not only be more convenient, but it would also minimize the heating time of the filament (we’ve probably all read the same assorted vague warnings from different sources about dry heating filaments for “too long”).
For the more exotic filaments, though, your current strategy is probably the most bullet proof and least likely to fail, as it can surely cope with drying temperatures above 100C (well, not the sunlu, but the general approach). For worst case estimates, I look to Vision Miner, which typically cites higher drying temperatures than just about anybody else I’ve read:
It may not be my daily driver, but I could for sure see myself on occasion needing to dry PC and/or PACF, where Vision Miner recommends 120C as the drying temperature. Would drierite be only minimally degraded at 120C? Maybe. I doubt performance falls off a cliff at 120C, but without knowing, it’s a potential gotcha. If it were a gotcha, then your current approach would solve for it. But if we knew and didn’t have to guess, it might turn out to be overkill in comparison to closed loop. The answer is obviously discoverable, just not sure exactly what experiment would decide the matter definitively and settle the matter once and for all.