Add to the times when one will need a dryer, or a trip to the oven for the filament. I haven’t encountered such a situation yet.
Are you sure you are in a high desert? :). Kidding aside, that sucks. I am not in a high desert, but have not had to dry any PLA, PETG, TPU so far. Knowing that some have to spend hours drying their filaments before every print, I have always counted myself lucky, while admiring others’ dedication to 3D printing at the same time.
The main/only drying I’ve used up to now was in the AMS with fresh desiccant. I do tend to keep that active and it’s been sufficient until I got that roll of shiny black PLA from Bambu. People here indicated drying it could actually help and that’s when I got the dryer and then started seeing all the comments on how this particular filament dryer needs help. The filament I’ve been printing all the parts with has ironically only seen the drying that the AMS does.
But I have had issues commonly attributed to filament with too high water content. They’ve been relatively minor and things like the pebble surface textured PEI hide them pretty well. Yesterday when I was doing the different drying runs the ambient humidity was an almost constant 55% at about 24C with rainstorms moving through. It’s 44% right now on a mostly clear day.
I could probably get by without one but I’d like to be able to dry filaments before I print things that matter. Plus it would save on AMS desiccant.
Everyone whose anyone seems to agree that certain fancy pants filaments like nylon should be as dry as possible before printing and kept equally dry while printing. So, if you ever have ambition to use those kinds of filaments, then you need good enough gear to do a proper job of drying it. Once you’ve got the gear to do that, then 1. using it isn’t much effort, and 2. a sure path to being certain your filament is dry enough is to go ahead and dry it. Afterward, the dryness is guaranteed.
As for fire risk, I think this is probably the biggest reason that designs using suitably constrained PTC heaters are so popular: by making the right material selections, a fire becomes physically impossible because produced heat becomes self-limiting based on the particular heating element that’s chosen, which in turn guarantees temperatures that are lower than the ignitition temperatures of whatever other materials used in the construction. i.e. no matter what might fail, overheating beyond the defined limit and thermal runaway becomes physically impossible because resistance increases and caps the current. AFAIK, that’s the theory behind it.
So, for your own peace of mind, you might want to take the same approach so that you could run it worry-free without supervision. Or just buy something where the heating already works that way and then add on the desiccant dry air feed and/or the extra venting you want to do without needing to mod the heating at all. I think before long I’ll likely be trying this with my Print Dry filament dryer, but it would be more fun if there’s someone to compare notes with who is doing the same sort of thing.
Edit: If you were interesting in making your own PTC heater, I see on Aliexpress that there are a whole gamut of specialized ceramics, where you can pick among dozens of different fixed temperature specs and supposedly the temperature can’t ever exceed that spec. That’s also why PTC’s heat up quickly at first but then slower and slower as they approach their spec’d limit.
I hadn’t even considered a PTC heater. Do you know that’s what is in the S2? Ah - now I see these are the ceramic heaters? The ones in the S2 look like a thin film with kapton or something similar. The S2 fits the rolls pretty tight so might make that tough but also it means diving into the S2 electronics.
For me, though, I can be confident of my use not starting a fire anyway since most things I would heat in it are PLA rolls and desiccant to reactivate it. I just can’t control how others would use it and I know that some turn these on and let them run for long periods. I’m sure many would crank to 70C for filaments which is where I saw the softening. I’m trying to eliminate the highest heat air going into the base which is why the kicker duct to swirl the air around and the coolest goes down the duct to come back up through the fan.
I’m still building one of these for myself and I’d be happy to compare notes! As a matter of fact a new base just came off the printer that has thicker walls and floor with honeycomb infill to help insulate and cut heat loss through the base. I’m going to make a new kicker duct and fan mount for air out of the fan to help swirl it around the drying chamber but need to do it out of something different than PLA to better take the heat. I’d like to also be able to run at 70C if I need to. I know some want even higher temperatures so it would be good to be able to run at 70 since it seems there’s still situations where that’s not enough.
Maybe if it seems really safe with no danger in this new configuration I might release it, but seeing PLA get all limp and floppy reminded me of the potential issues. If anything happened even if it wasn’t directly caused by this mod, I could still end up on the hook.
I love the mods in terms of people getting creative, I hate them because they should not be necessary.
Here is my 5 cents worth of filament dryers:
I have a crappy and home made one sitting here that I use when I get some moist filament delivered.
And it is literally a food dehydrator as the base with a slightly modified lid on top - added a hydrometer and thermometer.
Means I have to set a temp manually and have to turn it off once done - but I can live with that…
I has slots in the lid you can open or close depending on the needs - I usually leave them closed and place a bag of silica gel in the thing while running.
If you pint a lot and are in a very humid climate - ever thought about getting a small humidor ? 
Not those expensive ones the rich people use of course…
More thinking in the direction of abusing an old bar fridge or such - offers a good seal for the door.
Place a silicone heating mat at the bottom, preferably on a small rack and with a nice fan.
And YES, if you already have a small filament dryer that has what is required but that is not to your liking: Salvage it for parts
Due to the size it would be best though to salvage a food dehydrator.
Of course it is no problem to do a full DIY job here.
Take an old fridge, drill some holes for the filament tubes and cables.
Seal them once the build is complete and confirmed working as planned.
For the heating literally anything can be used, heating mats, and old hot plate, a PTC heater with an open heatsink to mount a fan, an old fan heater…
All you have to add is some small Arduino or dedicated temp controller.
A $10 digital fridge controller works sine here if you want to avoid programming things.
Similar price for a simple hygrostat.
Temp reaches set point and the heater goes off, humidity goes below set value and the heater goes off.
Sure, you won’t get any presets this cheap and simple way but you do get a filament dryer that has no issues holding 10 more rolls for under 50 bucks…
Just saying…
Sounds like it’s most likely a PI Heater: What is PI heating film? I’m guessing it relies on a temperature sensor, MCU, and probably PWM or similar to regulate the temperature, with maybe a thermal fuse or similar as a failsafe if one or more components fail. It’s not inherently self-limiting like a PTC.
By the way, why is the Creality filament dryer called the Space PI? I’m guessing it’s because that’s the kind of heater it’s using, which is kinda ironic since it’s a meaning that’s probably completely unknown to most people.
In contrast, PTC is supposed to self limit, so that it never exceeds its rating: Self-regulating heater - Wikipedia
I’ve seen a number of DIY PTC filament dryers on youtube that 1. use a PTC rated for a much higher temperature than their target because they want it to heat up quickly, and 2. use temperature controls like a PI would use to keep that temperature in check. Well, I suppose with enough different types of redundant failsafes maybe that’s OK, but even then without somebody like UL to check their work and prove it can’t fail, would you really want to trust it? In contrast to that, relying on a PTC’s inherent temperature limit seems like a much simpler problem to analyze by narrowing the scope without having to think through all possible combinations of what might go wrong, and in what temporal order, and with all possible unexpected consequences from who knows what, like power surges, static electricity, cosmic rays, lightning strikes, corrosion, faulty capacitors that someday go bad and short out, and whatever else might eventually go wrong but give no advance hints, so you never see it coming.
Edit: I only mention all that because drying cycles are usually long enough that you aren’t going to supervise it. You might be sleeping when it’s running. You might not even be home when it’s running. My view is that if you can’t tolerate a failure, then it should be failure proof. It’s not impossible.
I think once you get your design right, switch from PLA to PETG to test for a little while.
Once your happy with everything, print it in ASA (or ABS)…JMO
It seems to be a simple heater on/off with a temperature sensor. When you turn on the LED ring (maybe when it’s off, too) when the heater turns on there is a special display. The LEDs cycle during the heater on time. It’s got the touch screen display with adjustable setpoints so definitely some kind of MCU.
For my purposes I’m not worried. I do keep an eye on those kinds of things and don’t leave appliances like that running unattended. I won’t be using it outside its limits and think it should be fine especially with the new mods to it.
It turns out this guess was 100% wrong. According to Creality, the Space Pi uses PTC heating, and they even proclaim PTC to be superior to PI heating:
So why on earth would they name it the Space PI? Go figure.
On an entirely different topic, I had ruled out the AMS Lite because of its open-to-atmosphere filament storage. Well, along came someone who re-imagined the entire thing, merged it into a Sunlu S4 so that it doubles as a filament dryer and (?) keeps the filament dry afterward too? Now, with that as an option, and given the asking price, I’m starting to think the A1 + AMS Lite may be pretty good value for money as an extra printer to complement my X1C. Pretty cool:
I run an S2 through my AMS Lite, but then again, I don’t use my dryers for storage. I thought about the S4, but I just don’t have enough room behind the printer.
What does that look like?
I’m printing right now, but I’ll take a pic later.
Basically I have the dryer behind the AMS Lite. I pull off the roller for the hub I’m going to use. I have the filament running out of the dryer, around the roller stem for tension & into the hub.
If the filament is run to Slot 1 or 4, I usually run it out of the bottom, sometimes from the top.
If I’m using Slot 2 or 3 I run filament from the top only.
I will run TPU & ASA from the dryer 100% of the time, PLA & PETG depends if the print is more than 4-5 hours.
If I’m doing a multi-color print, I usually don’t use the dryer unless I’m worried about a roll. I have 4 dryers, so I have time to pre-dry. Plus I keep all my filaments in dry bags.
Check out this design. I’ve been using it for a few months now and it works great for printing from the dryer!
I’ll admit though, when I’m just drying something and not actively running it to the printer, I just prop the lid with the stern end on a Benchy LOL I flip the Benchy upside down and that little post/hole thingy on the stern of the Benchy holds the lip. I know there’s lots of prop models out there, but I’ve got enough Benchy models laying around that it’s just easier…and so far, it’s worked pretty well.
That is a nice one! Only thing is my original fan was just the perfect pitch to really annoy and and open lid will let that all hang out. The Noctua fan is much quieter. But looks great for printing!
The parts I developed here work great though. I thickened up the base walls and used honeycomb infill to seal lots of little voids off in the walls - basically printed insulation. I did a slight change to the fan mount to separate the hood and print it out of something higher temp and will be putting it back together today. The design so far seems to work fine. And should be totally fine at PLA temperature which is almost all that I print.
I haven’t cracked the too low draw through desiccant yet but worst case is I add a battery powered booster fan inline to overcome the resistance. It sounds a bit shade tree but I’ve got battery holders, rechargeable AA batteries, pushbutton switches, 5V fans, and can print housings. 
