How to Calculate Fan Power
- 1). Measure the total air pressure of the fan in inches of water gauge, the unit of measure used for fan calculations. To do this, place one end of a manometer at the fan inlet and the other end at the fan outlet; measure the difference between the height of the liquid on the two sides of the manometer to determine the total pressure.
- 2). Measure the air speed at the fan outlet in feet per second. Use a vane anemometer to take several velocity readings at different points on the face of the fan, then average the readings. The University of Connecticut recommends a minimum of nine velocity measurements to calculate an accurate air speed.
- 3). Measure the diameter of the fan in feet. Divide this number by two, square the result, and multiply it by pi, or 3.14, to find the area of the fan.
- 4). Multiply the area of the fan by its air speed to find the air flow in cubic feet per minute.
- 5). Multiply the total pressure by the air flow, then divide this number by 6,356 to find the horsepower.
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