CR magazine just gave bad reviews to portable A/Cs...
Think of a portable A/C as the air conditioner of last resort, if you can't mount a window or wall model. They're better than a fan, but not much. Even the largest we tested struggled to cool a 250-square-foot space down to the 78 F the government considers minimal for comfort, despite claims of up to 550 square feet right on the box.
The best window A/Cs chill an area quickly and efficiently by cooling and recirculating inside air air and releasing mainly heat to the outdoors. By contrast, portable units must continuously draw in unconditioned air from surrounding areas as they exhaust hot air through a long, ungainly hose that vents through a window. The result is a vacuum effect that keeps room temperatures relatively torrid by constantly pulling warmer air into the room. Indeed, about 20 to 40 percent of portable A/Cs are returned by unhappy customers..