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The first mini-split system was sold in 1961 by Toshiba in Japan, and the first wall-mounted mini-split air conditioner was sold in 1968 in Japan by Mitsubishi Electric, where small home sizes motivated their development. The Mitsubishi model was the first air conditioner with a cross-flow fan.
These motors are sometimes called DC motors, sometimes EC motors and occasionally DC/EC motors. DC stands for direct current and EC stands for electronically commutated.. DC motors allow the speed of the fans within a fan coil unit to be controlled by means of a 0-10 Volt input control signal to the motor/s, the transformers and speed switches associated with AC fan coils are not required.
Traditional AC systems with ducts have maximum SEER ratings slightly below these levels. Also, practically, central systems will have an achieved energy efficiency ratio 10–20% lower than the nameplate rating due to the duct-related losses. Additionally, there are ground-source residential AC units with SEER ratings up to 75. [15]