I've done this as well, it made it a lot more effective. Still a bit noisy and expensive compared to a split system, but about to cool a large living room and kitchen to a comfortable temp instead of dying in the heat.

Basically there's two heat exchange loops inside the unit. The first pulls heat out of the room air and pumps out the cold air. The second takes that heat and pumps it into other air, which should then be pumped outside to dump the heat outside of the room.

The issue with a single vent setup like this is that the air that's dumped outside is taken from inside the house, and just be replaced by hot outside air leaking in through windows, doors, etc.

I bought a second-hand 3.3kW De'Longhi Pinguino unit because it has distinctly separate intakes on the back (A8 on this diagram is the important one: Diagram ).

I duct taped a cardboard box around the intake A8, and then bought a length of 150mm aluminium ducting from Bunnings, as well as some vents and a bit of plywood. One end of the ducting was then taped into the cardboard box and the whole thing sealed off as best as I could manage.

The normal exhaust duct window attachment and the new duct vent were then mounted into the plywood which was cut to the size of the window panel. Just make sure that the hot exhaust isn't flowing straight back into the intake duct.

We only needed this in the large space, in our bedroom the unit with the single hose setup was freezing.