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Technical Concepts of Ventilation
A fan is
avaluated with regard to output and pressure .
| OUTPUT - | Is defined by the quantity by the unit of time. This quantity can be air, water, cars etc. |
For the purpose of
ventilation, we normally use
| l/s | - | Liters per second |
| l/min | - | Liters per minutes |
| m3/h | - | Cubic meters per hour |
| m3/s | - | Cubic meters per seconds |
| cfm | - | Cubic feet per minute |
CONVERSION TABLE
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= cfm | ||
|
= cfm | ||
| m3/min * 16.67 | = l/s |
Please remember that 1
1/s is aproximately half cfm.
| 10 l/s | = | 20 cfm |
| 50 l/s | = | 100 cfm |
| PRESSURE - | Power acting on the area |
Pressure is indicated by
| mmca | - | millimeters water columm |
| mmHg | - | millimeters mercury |
| 1 mmca | = | 9,8 Pa |
| 1 mmHg | = | 133,3 Pa |
There are two kinds of pressure - STATIC and DYNAMIC pressure
| ESTATIC - | The mass of air is stagnant and equal in all directions. Example: balloon |
| DYNAMIC - | The mass of air is moving . Example: wind blowing against a wall |
For
Fans, we generally disregard the dynamic pressure. We would measure the dynamic
pressure only if there existed some kind of shield. In our example it was the wall.
Example to demonstrade the definition of the fan's pressure
Graphic representation of a fan
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