FANS do not actually reduce the temperature of the room in which they run. In fact if a fan were left running continuously in a room that was perfectly insulated, the temperature of the room would rise because of the heat generated by the running fan.
Fans produce a cooling effect by moving the air surrounding you and taking away the heat produced by your body. Human beings generate a lot of heat. This heat surrounds our bodies and moves away very slowly. Fans remove this heat quickly and make us feel cooler. In addition to removing the heat the moving air helps to evaporate the sweat on the body, cooling the body in the process.
A fan that rotates faster will provide a greater cooling effect as it will move a greater amount of air. A fan with longer blades will also cool more efficiently than one with shorter blades.
However having four blades instead of three does not mean that the fan will produce more movement of air. For the same motor size, having an extra blade means that there is a greater drag on the motor and therefore a reduction in speed. Many of the old propeller aircraft had just two blades and worked just fine.
You must have noticed that the blades of the fan are not straight but are slightly inclined. A fan whose blades are inclined more will be better than another whose blades are not inclined as much.
To run a fan, all that is needed is a motor to make the blades of the fan rotate quickly. However, the electricity that is supplied to homes is a single-phase supply. A motor that works on a single-phase supply cannot start by itself. Additional circuitry namely a starting coil or winding and a capacitor is required to make the motor behave like a two-phase motor. The motor then starts and runs by itself. A fan whose starting winding, or capacitor is faulty will not start by itself, but may sometimes run if given a firm push to start it.
Fans also require regulators to control the speed at which they operate and thus the cooling effect they produce. The older regulators used a series of resistors to divert some of the power away from the fan motor. This resulted in a large amount of heat being produced in the regulator, as well as a loss of electric power.
Modern electronic regulators control the amount of power given to the fan motor, and using them can help reduce electricity costs. However the initial cost of these regulators can be quite high compared to the older type.