Data center air handling unit including uninterruptable cooling fan with weighted rotor and method of using the same

A method of preventing damage to electrical equipment, the electrical equipment being cooled with cool air from an electrically powered air conditioning unit during normal operation using grid power, the method comprising the steps of:

• rotating a fan to a predetermined RPM using an electric motor powered with electricity from the grid power to cause at least a predetermined airflow, the fan including a weighted rotor assembly that includes a fan body and a plurality of fan blades, wherein the weighted rotor assembly weighs at least fifty pounds to create stored angular kinetic energy;
• directing the airflow to the electrical equipment;
• upon removal of the grid power to the fan, continuing to direct continued airflow to the electrical equipment for at least an interim period using the stored angular kinetic energy within the fan;
• and
• before expiration of the interim period, continuing to rotate the fan using the electric motor powered with electricity from a back-up generator to cause a predetermined further continued airflow to the electrical equipment;
• determining beginning and minimum ending angular speeds of the rotor assembly, as well as total energy lost by the rotor assembly during the interim period therebetween;
• calculating a minimum mass moment of inertia of the rotor assembly based on the beginning and minimum ending angular speeds of the rotor assembly, as well as the total energy lost,
• wherein said interim period is between 10 and 25 seconds, and the minimum mass moment of inertia of the rotor assembly is at least 6,000 lbs-in2.