If the ac unit is not vented outside or into another room the hot air will remain locked up inside the space.
Portable air conditioner venting into attic.
Put it in an attic full of blown insulation and you re forcing.
This will not only prevent the room from cooling but will actually make it hotter.
Note it must be a well ventilated attic in this case or you will have a buildup of heat which will lead to premature thermal breakthrough of your insulation.
The condenser in your air conditioner works hard to get rid of heat and pressurize refrigerant for the return trip through your house.
That unit has an auto evaporation function which is marketing speak for dumping the moisture that condenses on the evaporator into the vented air stream.
The purpose of a portable air conditioner is to cool down a room but in order to do that it must extract heat from the air.
The first option is to vent the portable air conditioner through an exterior wall.
According to the twh principle you can vent a portable air conditioner into any well ventilated space apart from the space being conditioned.
Hooking this up to your typical attic would be bad.
Fit the window kit to the length of your window and secure the kit in place.
Venting your portable air conditioner is easy.