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29-09-2011, 08:02 AM #1
Correct method for return air sizing???
Does anyone know how to calculate return air grille size properly not using a rule of thumb method?
I know how to size duct etc but not return air grille size.
Let's say I have 2 x 18kw fcu's from different manufacturers both with the same airflow but one has a much higher static pressure, disregarding return air noise how does the FCU with the higher static pressure provide me with more flexibility when sizing my return air grille?
Usually I base my return size on an airflow velocity of 1.5m/s, if I increase this velocity at which point will it actually reduce airflow?
If anyone can help explain this I would much appreciate it
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30-09-2011, 03:23 PM #2
Re: Correct method for return air sizing???
The pressure drop will depend on the grill type, design, etc. You will have to get that from the manufacturer as every one will be different.
If noise is a concern ... what are you looking to be flexible with?
Here is a selection chart for an extract typical grill
http://catalogue.systemair.com/file/...unIGoWvWD.aspx
If you have, say, 200l/s extract then for the 160 the pressure drop is 150pa or the 400 it's 10pa