I stay in Houston Texas as well as summer season temps tend to be in the 90's for several months or more of the year. The home of mine is relatively new and has a good quality core HVAC system. In spite of very much of my air conditioner is done by the more mature technology of a room or maybe "chillwell portable ac for car (www.techtimes.com noted)" window unit.
The bedroom product of mine is a 12,500 BTU Energy Star design that cost you about $260. It's not rated being as efficient as the central unit of mine but uses a reduced amount of power every BTU in the opinion of mine. This's as it does not run a significant fan to blow air with the complete home. We run the window unit from about 8PM to 8PM on days that are hot. When we are not home the central unit is shut off and the window product will keep the home about 15 degrees cooler than the exterior for our 1,900 sq foot home. Additionally, it keeps the moisture low. We supplement the window product when we're home with the central AC. Cooling the home this way decreases the energy costs of ours. We now run the central unit aproximatelly 50 % less, therefore it should have a long life. On the very hot days, when operating the window product and the central device, we get extra cooling power.
In Texas it's a major deal when your central AC fails during the summer. We run a second 12,000 BTU unit once the main AC is broken. Which makes the house livable during the repair time.
Another benefit of having window AC units occurs when there is a power failure. Windstorms as well as hurricanes are routine in the Houston region. We like getting a generator and window AC devices as insurance for power failures. Throughout IKE we ran 2 window units by generator for a week, along with the fridge, microwave, and some lights.