Cooling Fans

• When would I use a cooling fan?
• If the fan does not have an earth terminal, how can I ground it?
• I would like to change the wiring of the blower so that the suction port and discharge port are reversed. Is this possible?
• When using multiple fans with the same noise level, is there a way to calculate the total noise level?
• Is there a way to tell when the fan motor has stopped?