The Energy Efficiency Ratio (EER) is the rate of efficiency of the mechanical chilling systems and indicates the ratio of cooling capacity (measured in kW) to the power input (measured in kW). The higher the EER the more efficient the air conditioner. The Energy Efficiency Ratio cannot always be used to make a comparison between air conditioner manufacturers as some use ‘total’ cooling capacity as their reference point and others ‘sensible’ cooling capacity.