We have a portable A/C unit from when we didn’t have central A/C, and it seems to use almost as much energy as the central air unit. Unless we’re doing something wrong, I just don’t think they’re worth the extra expense *if* you already have central A/C.
OTOH, if you didn’t have central air, I’d recommend the portable as they make a HUGE difference in rooms that just don’t cool down naturally (facing wrong way, no air flow, etc.).
