What is coanda effect and why it is important to HVAC supply air diffusers selection?

What is coanda effect?



How does coanda effect relate to HVAC supply diffusers?

How to relate this to practical installation situations?

When diffusers are installed flushed with ceiling, one will need to relate the supply air throw and drop performance characteristic against the design volume flow rates.

Essentially, we want to avoid air from supply diffusers dumping cold air onto the occupied zone. Air diffusers need to be selected to ensure the air velocity say 1.8m at about head height defined for the top of occupied zone; should not exceed air terminal velocity of 0.25m/s, this will ensure a gentle air velocity within the occupied zone.

In the absence of a ceiling (hence absence of coanda effect), if the diffusers are not selected appropriately, you will be dumping air into the occupied zone if the air diffusers discharge velocity is too high.

Check out the video below that aptly put these concepts into play.

To maintain acceptable comfort and air quality within the occupied zone, ASHRAE Standard 62.1 define the methodology for air distribution effectiveness (Ez).

So the next time you have a complain … better still, select your diffusers appropriately to mitigate the problems before its a problem.

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