You could find 120v fans, and run a plug into your wall!
Or you could find 12v fans, use an old cell phone charger or something that uses 12v. Then use the plug end to plug into your wall, and pigtail the other side.
This is very easy to do. Since it is three sided I would put 1 fan blowing in, and 1 blowing out. That way your circulating the air. Stick them on opposite sides so they are at a steady flow. This will allow the air to be 'sucked' out while cooler air is being blown in. Very handy.
-- Edit --
When I say fans I mean like computer fans (12v) and they make them bigger and support higher voltage (120 I believe for your wall socket).
55gal Beginner FOWLR - 40lb Live Rock, 1 True Percula, 1 Sand Sifting CUC, 1 Scooter Blenny, 1 Sally LF Crab, 2 Turbo Snails, Frag Brain Coral, Tree Coral Frag, Zoanthid Colony