I don't know what landlords are like in European countries, but some landlords in America forbid people from connecting any kind of AC exhaust port to a window.
Generally anything you do indoor that falls under normal usage(painting walls, hanging furniture with big screws,etc.) is ok without approval, at least in my country/city(austria) and the land lord can't deny any of this and is not even required to be notified.
As you would have an open window and a not so noise machine running this would be ok, but energy efficiency is quite bad and you lose the benefits of the thermal insulation of your building.