Yes, a window AC unit needs a window for installation and operation. These units are specifically designed to be mounted in a window frame, allowing them to effectively expel hot air outside while cooling the room. The installation design requires that part of the unit extends outside the window to create a barrier between the warm outdoor air and the cool indoor environment. If a window is not available, alternative options such as portable air conditioners can be considered, which do not need a window directly but require some type of venting, or ductless mini-split systems, which consist of indoor and outdoor units and do not rely on windows for operation. In conclusion, the proper functionality of a window AC unit is contingent upon its installation in a window.

Window AC units generally consume less electricity than split AC units in small spaces, but it depends on various factors, including the specific models and their efficiency ratings. 
Split systems are designed for larger areas and use advanced technology, such as inverter compressors, which improve energy efficiency by adjusting the cooling capacity based on the room's requirements. Therefore, while split systems may have a higher electricity consumption overall, they often provide better efficiency when cooling larger spaces or multiple rooms, resulting in potentially lower energy costs in the long run. In summary, for small rooms, window ACs might use less electricity, but in larger settings, split ACs may prove to be more efficient over time.

The primary differences between a window AC unit and other types of air conditioners, such as wall-mounted or split systems, lie in their design, installation, cooling capacity, and efficiency. 
Window AC units are designed to be mounted in a window frame, consisting of a single unit that houses all components, making installation straightforward and suitable for small spaces. In contrast, wall AC systems, often referred to split air conditioners, have two separate units: an indoor unit that cools the space and an outdoor unit containing the condenser. 
Additionally, window ACs generally have a cooling capacity that ranges from 18k to 24k, making them suitable for smaller rooms. In contrast, wall ACs can vary significantly in size and are designed to cool larger areas, often providing more powerful cooling options. While window ACs are typically more cost-effective upfront, wall AC systems can offer better energy efficiency and noise reduction since their compressors are located outside. Therefore, the choice between a window AC and other air conditioning systems largely depends on the size of the area to be cooled, desired energy efficiency, and installation preferences.