"220V Cooling Fan" speed is the number of revolutions per minute of the fan blades, the unit is rpm. Fan speed is determined by the motor inside the coil turns, voltage, number of fan blades, inclination, height, diameter and bearing systems. Fan speed and quality are not necessarily linked. Fan speed can be measured by the internal speed signal, can also be measured by an external? Because as the ambient temperature changes, sometimes different speed "220V Cooling Fan" to meet demand. Some manufacturers specially designed heat sink can adjust the fan speed, manual and automatic modes. Manual is designed to allow users to use a low speed in the winter low-noise, high speed to get good cooling effect during the summer. Automatic thermostat radiator general class with a thermostat sensor, according to the current working temperature control "220V Cooling Fan" of speed, then increase speed high temperature, low temperature, then reduce speed to achieve a dynamic equilibrium, so that the cooling effect of wind noise and maintain an optimal combination of points.