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Principles of air distribution

Room cooling air distribution

UPDATED :  

Room air distribution is probably the most important part of comfort in the occupied space. Proper air distribution can compensate for minor design deficiency

Discomfort may rise from various conditions such as:

  • Excessive room temperature variations;

  • Excessive air motion (drafts);

  • Failure to deliver adequate air to cold or hot spots;

  • Too rapid a fluctuation of room temperature; and

  • Too rapid a fluctuation of air motion (gusts).

Always bear in mind that when cooling, the supply air is denser than the room air and tends to drop down while in heating the opposite occurs. The air distribution must accommodate all the above with an acceptable sound level.

Throw

Throw is the distance that an airstream travels on leaving an outlet. At the end of the Throw the air stream has reached the desired terminal velocity which depends on application. There are various terminal velocities for different applications.

  • 0 to 0,08 m/s – complaints about stagnant air

  • 0,125m/s – favourable for all commercial applications

  • 0,125-0,25 m/s – favourable but 0,25 m/s is maximum tolerable for seated persons

  • 0,325m/s – unfavourable as light papers are blown off the desk

  • 0,375m/s – for people moving about slowly like retail stores

  • 0,375-1,5 m/s – factory air conditioning for spot cooling

The most desirable air direction for a seated person is from the top or from the front. Air blowing from behind or directed at angles should be avoided.

Drop or rise

Drop or rise is the vertical distance the air moves between the time it leaves the outlet and the time it reaches the end of its throw.