Highly efficient fan shroud with heat-sink. It seems to work better then the original UM+ 50mm fan shroud with a small 30mm fan obtainable from E3D. I use 24V fan version, but adjust power with Cura or Ulticontroller (19V fan provided with Ultimaker has a range from 0-250 speed, and 24V fan from E3D has a range from 0-25 which is a maximum velocity). 
There is absolutely no back-draft (all blown air is blown on the model) due to thermal expansion and the air is kept cool as it propagates the copperfill shroud (EDIT The blown air cools the heater block significantly when near the build plate, so some kind of thermal resistance on it is advisable). The geometry focuses air inwards from all sides, therefore cooling symmetrically. There are heat-sink fins which serve to reduce the heat of the shroud and disable heat distortion. 
The model is asymmetrical, and wires from heater cartridge should be on the opposite side from the fan for the hotend to fit in the middle.
 Clip I haven't tested (use the rai head mount where I can screw the shroud in) but should work fine.
Print slowly at 0.1mm layer height and clean up the finished model

Um+ Pla settings:
Blue painters tape, 50C bed if needed
Fan full at height: 2mm
Fan min: 15 (out of 250 for 24V fan, or 8%)
Fan max: 25 (10%)
Min layer time: 5