Anyone that has printed PLA for any length of time has experienced nozzle jams due to heat creep.  Essentially the heat from the hot end slowly warms the material to the point where the gear teeth chew instead of feeding the filament.  This shroud will help direct air flow above the hot end to keep the filament cool during PLA print operation.  I have tested the design and it works well in my setup - dual Taz head.  Holes align with 60mm fan.  The flat on the top works with 3M Command Strips attached to the shroud and base of the head mount.  Important - Be sure to remove the fan during z-home and bed-leveling (If you leave it on it will hit the bad when touching off on Z (which goes below the bed height).  Also, it will hit the tip wiper during the clean cycle.  Simply attach it to the bottom of the head just prior to the print starting while the heads heat up.  Space is at a minimum on the dual head!!  See attached pictures.  Happy printing!!