After 2 weeks of comparing cooling solutions we finally decided to go for the downflow cooling (with the free air cooling option) from Uniflair.
The units are ordered and will be arriving within the next 2 weeks.
The build of the new walls for the data-room has been started. Also we are going to place a new wall against the existing brick wall. This is necessary because the brick wall is not completely dust free and not usable for a data-room.