I believe the middle underscore _ means the wall/separator whereby the miner will go through it, just like the average set-up most of us use to isolate the miner's intake from the heat.
... but he will need very good separation of hot from cold.
He sure does, with only 5 meters in width there isn't enough room for the heat to sit in before crossing back to the cold section, and thus the exhaust will need a lot of work, I would use only shutters and fans and no walls.
The hot air wall would look something like
shutters - fan - shutters - fan - shutters - fan - shutters - fan
fan - shutters - fan - shutters - fan - shutters - fan -shutters
This will result in a very good air extraction and if you haven't build the wall yet, it might even cost you less, all you need is galvanized steel pole tied vertically and horizontally creating squares/rectangles to hold the fans and the vents/shutters.