You can temperature control your fans by using a variable temp. line voltage thermostat contained within the cabinet. Most quickly obtainable at many hardware stores, these are designed for household electric heating and will switch a lot of current (not that you would need that capability). If you have the electrical expertise, you can order more specialized thermostat controls from an HVAC supplier or an electronics parts house and adapt to your specific application; even use a pilot relay.
One method I have used for keeping fans quiet is to run 240 volt muffin fan(s) at half rated supply (typical household 120V) line. They turn quite slowly and of course are very quiet. Fabricate a mounting to fit your rack and fans dimensions of course. You can also slow down a standard voltage 120V or even a 240V fan (again I used muffin fans, although squirrel cage or centrifical designs would work too). You use a variac and just dial them down to about 60 to 75 volts or so to keep them quiet while still moving a reasonable airflow volume. Muffin fans and other types too are available from hobbiest computer shops, and of course from the electronics shops (Radio Shack) & suppliers. Be creative and you'll accomplish your goal.
Or you could just have Unsound to blow air on them for you, seeing as he's so windy (sorry couldn't resist - do enjoy the sense of humor however). Too Cute.
