Deciding how to condition the air in your home usually comes down to two choices—a centralized system or a single-room unit such as a window air conditioner. Both have their pros and cons when it comes to energy efficiency and decisions often boil down to preference and whether or not a centralized system is more practical than room-by-room conditioning.
Central air conditioning systems are rated higher when it comes to seasonal energy efficiency ratio, but only because it is impossible to fit in a much advanced hardware into a small window box. For instance, while modern air conditioners have the capacity to work at a certain range of speeds, the condensers in window units often only have two. This causes significant differences in energy use because air conditioners don’t only work to lower air temperature but also to remove moisture.
The amount of moisture removed depends on the amount of air that passes through the device. This means that machines that only work at full speed can drop a room’s temperature much quicker by cooling a small volume of air to a cold state. Greater dehumidification, on the other hand, is possible through an air conditioner with variable speed settings as it can process a larger volume of air and cool it by a smaller amount. This means that central air conditioners can be set to a higher temperature and still achieve the same level of comfort because air is less humid at that point.
Window units, on the other hand, don’t suffer from duct losses, which centralized systems are prone to. Because cooled air requires passing through a system of ducts on its way to each room, the air warms up and would usually leak through the fittings. Losses can decrease a centralized air conditioner’s efficiency by as much as 30 percent, where as no such loss occurs with a window unit.