Controlling Fan Speed on Guardian 921

I just built a new pc using the NZXT Guardian 921 as my case.

Are the fans just set to a standard speed and that's what they always run at or will they increase with in speed if the temperature in the case turns on? I ask because, when I turn the computer on the fans speed up briefly to a much higher speed than they usually run at.

If they don't respond to the temperatures of the case (and I don't know how they would, besides maybe through the built in temperature monitors), is there any way to increase the speed of the fans. I'm guessing not since they're attached directly to the PSU and not to the mobo, but I figured I'd ask.

Right now my system runs at about 40C, even after playing WoW for a few hours, so I don't really think temperature is that much of an issue but information is never a bad thing