Oh, wow! I'm psyched to read the replies for this post. I've been tinkering with fans (low tech airconditioning). What kind of fan are you using/do you plan to use?
So far, I've tested:
<ul>[*]
A case fan (from PC power supply (inside the housing)): You can easily power this type of fan with a 9 volt battery. It's capable of pushing air through the helmet, but unless it's actually embedded into the helmet it's not incredibly effective. OH - Let me also tell you about vibration...if you embed one of these fans into your helmet remember that they vibrate - that means sensation the entire time it on - as well as noise. My little case is quiet, but put anything next to your head and you hear it. If you embedded one of these onto the back panel of your chest piece it would keep you cooler, but not cold. Still it would look even cooler if you had an LED lit case fan. (Well, it wouldn't be "accurate" but it would still be neat!)[*]
A small children's foam blade fan: These can be powered by (depending which you get) 2 AAA or 2 AA batteries. I was drawn to these because they're self-contained - most importantly - the fan blades are foam (equals no hurt), but it fails miserably to push air unless it's 3 inches from your face. I haven't given up on them, though. I'm curious about the blades. Air gets pushed by the shape of the blade - regardless of how fast the blade spins, so I'm still tinkering with them. It figures the least complicated option would be the least effective...bummer.[/list]
There are a few things to consider when working with fans....(side note: All you physics folks out there need to chime in here):
<ul>[*]Weight: The more powerful fan usually means bigger battery, usually means bigger weight. Your armor will likely have some weight to it, so you should be mindful of all the batteries, as well as the weight the fan is going add. <Asrai envisions, "Yeah, nice suit, whew...I need to sit down...Wow! That's the best sitting Master Chief Evah! Woo!">
[*]Push: Even a small fan will push air, but open pockets in your armor don't really lend themselves the real estate to push air around your body. You'll need to route it somehow. You can route air, through the use of hoses, but it's a lot trickier than you'd think. The longer the hose to distribute air to certain parts of your body, the greater the fan must be capable to push air.[/list]
I have seen suggestions for water cooled vests
"Creating the PERFECT undersuit" (Read Post #13). Even if you don't get the water cooled vest...read this post, it's really excellent.
I've actually cut out a section of the back of my daughters pepakura chest piece (technically, it would be the back plate, but whatever) and before resin/glassing it, I added a small box. (I have pictures, but it's really a wreck right now because I am using it for a fiberglass mat alternative experiment right now). By adding the box, I've create a place that can house a fan. I'm not too hung up on accuracy. I'm a mom and I want to inspire and encourage my friends and family, so it's all about comfort, right? So that box on the back will lend itsself to housing a larger fan possibly, or whatever my daughter wants to put there (Barbie, crayons, whatever (eat your heart out, tough guys)), but I'm voting for a fan.
I live in FL (so I don't know if these are available to everyone), but the stores sell battery powered fans around hurricane season. There's a small (but larger than a case fan) box fan about 8" square that I plan on testing. I have yet to acquire one, but when I do, I'll share what I find.
I hope this helps and I truly can't wait to see what others will post. Thanks!