How can I vent a portable air conditioner when there's no window?
Do you have a budget in mind for adding the ac? You can use a water-cooled unit, but plan to spend $1500 and up. These units can be hooked up to a water supply (sink, garden hose, etc.) and drained back to a sink, outside, or wherever is available.

The heat from the air is transferred to the water - much like a geothermal ac or heat pump works. We use these a lot in restaurant food storage rooms and for portable ac's at public events.

The so-called vent-less ac units work by dripping cool water over a screen in front of a fan. The humidity becomes unbearable and people will feel very uncomfortable quickly. Avoid these systems entirely.