The main difference between the two series is the area of floor space that they serve.
The AR-100 series is the ‘work-horse’ and serves up to 45 sq. metres of floor space (suitable for large living rooms and offices), and the AR-200 series up to 25 sq. metres (suitable for most bedrooms, and smaller offices).
The AR-200 series is a little quieter than the AR-100 series and includes more functions (i.e. a timer, a tilt and oscillation mode, as well as a remote control) and is therefore priced higher than the AR-100.
Both series are modular, meaning that larger floor areas can be served by additional units.