Portable air conditioning units are significantly less efficient than both wall units and central systems. In addition, they are generally not as portable as they appear in pictures.
Portable air conditioning units must vent heat outdoors to work, and the hoses they use draw a significant amount of power. As a result, they use more energy than units that are able to vent hot air through freon or another refrigerant.
Portable air conditioning units can also create a slight vacuum in rooms that are sealed well. Because of this, using a portable air conditioner to heat a single room can be counterproductive.