if u take windowed version and u wanna mount fan the only way is to make custom acrylic. 
windowed side panel version is mainly for people who like to admire their hardware inside especially those who opt for liquid cooling setup. and without the fan mounting at the side it also mean smoother air flow inside of the casing. it also means lesser dust.
(as in the air comes in from the front and flow directly to the back and top)
honestly if u opt for the windowed panel version why bother about mounting fan on it. because after u mount the fans it would just block the view of ur hardware which makes it.... pointless... u should had went with the mesh panel instead. cheaper too.

I don't got 2 version ma. I buy at Viewnet @ lowyat only sell windowed panel version. Is best buy price about RM365. Is recommended by the sale person. Anyone now this casing worth how much?

u can install 2 fan on the mesh version actually
and depending on ur setup especially those with powerful graphic card that cooler doesn't push the hot air directly our of the back of the casing ones quite need the side fan either as intake to push the air up to the top of the casing faster or direct exhaust from the side depending on ur GPU cooler.
remember 922 doesn't have bottom intake fans.

psu fan mostly is intake as well

you already got enough air flow la bro. Later your casing become vacuum cleaner

@ZeneticX
i have the tendency to give out everything i know.. it's just me....

PSU fan either bottom or the back all serve as intake so no worries about bottom intake fan will take in hot air from the PSU. and u have marble or hard wood floor then it would be even better as they are cooler.

922 install fan at the drive bay not bad wud since got filter at the mesh. easy to clean. buy 1 can of compress air and shot till clean. more cool air for ur CPU. if u are the kind like me of occupy all 5 drive bay at the bottom. the front intake fan that blows at the hdd cage and the air would warm up slightly by ur hdd.
i install my stock 14cm fan at the drive bay now as intake in my 932 without filter mainly to push the air back in coz i got 5 12 cm intake fan from the side and bottom. without the 14cm fan the air will flow out from the front =/

saw b4 din use b4 ...lol

pci cooler not use to blow hot air inside out from ur casing...?
u using it to blow ur gc?

if can plug out some pci slot bracket...
so some hot air will flow out...

lol good way to use it also xD

10 bucks~