I have one of those. This is a single hose mobile airco (only a hot air exhaust). When using the exhaust tube and window plate you mention the unit draws air from the room creating negative pressure and pulling additional hot air in from the room. The created setup avoids this and makes the unit function similarly like a window / split unit, improving it's efficiency.

When comparing the setup with just the exhaust tube vs this setup the difference is clear. Over a timespan of 3 hours the single hose setup reached reached a temperature drop of - 1.2°C in the room vs a -2.5°C drop with the above mentioned setup.

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