Hi.

These single-hose 'portable' airconditioners... how can they cool any room at all ?

The hot exhaust expels the heat from its condenser cooled by the room air cooled by the evaporator + the heat extracted from the room air by the evaporator + the building heat entering the room under the door and leaks + the compressor heat. 

Can someone explain ?

Lowers the pressure in the room(assuming room is reasonably sealed). Loading up with heat the air that is leaving.

They are less efficient like you say. Better not to cause a leak in the first place than to have to pump fast enough to stay ahead of it. Dual hose or a proper Window unit are better options.

Edited July 28, 20196 yr by Endy0816

4 hours ago, Externet said:

Hi.

These single-hose 'portable' airconditioners... how can they cool any room at all ?

Not very efficient, but the exhaust gas has a higher temperature than the replacement air getting back in the room. If the difference is enough to also make up for the energy input to the unit you get a cooler room.

Otherwise you certainly can get negative efficiency and heat the room further.