Arcticpro 7000 BTU Portable Electric Air Conditioner $200 at eBay

just so you know these things suck down the electricity more then a HVAC system.

^ have any numbers to quantify that?

Personally, I've often wondered why in this day and age we don't have systems where at least some of the heat from the condenser coil is moved into our hot water heaters to heat the water instead of additional heat being created by the water heater with a high % of that heat eventually needing to be removed by the A/C.

Keep in mind that regardless of the EER that these portable units are rated at, most of them exhaust inside, cooled air into the great outdoors... and pull hot outside air in to operate. For this reason, they are power hogs.

On the positive side, they typically work when they are used to cool a warm room in an air conditioned space. Just keep in mind that the primary HVAC system will need to work harder too.

You're always best to use a window air conditioner when possible for every application a portable would be used for. They are cheaper, quieter and more efficient.

^ your post is confusing. They can't exhaust inside, it would not lower the temperature it would raise it.

The inefficiency in a portable is that the condenser coil heat has to be piped out a window/etc so there is a lower flow rate and/or higher fan power needed to move the heated air out of the room. Because we don't live in a vacuum, to exhaust that air there has to be air sucked into the room passively from whatever environment is around the cracks, crevices, vents, etc in that room.

It is true a wall/window, let alone central A/C is more efficient though the point of a portable unit is that it is portable... they don't quite replace each other due to different virtues.