What is it?
Mount for a standard 120x120mm computer case cooling fan. Slides into the top of a ~129x129mm cutout at the top middle of the rear acrylic sheet for the Prusa IKEA Lack Enclosure.
Why would you want a fan?
Particularly with PLA, a high ambient temperature screws with print quality. A little ventilation goes a long way to keeping the enclosure temperature low.
This is more effective than leaving the doors open. Also, keeping doors closed keeps cat hair out. :)
How do you control it?
Computer case fans take 12v. I'm controlling mine over Wifi using an ESP8266 and a MOSFET.
3D Solutech PLA