# Limits on the volume of air recycled in a classified room

Dear friends,
I would like your help on, where i can find if there are limits on the volume of air recycled in a classified room.(the volume of air that returns)
I have calculate the volume of air delivered in the classified room and the air exchange rate.

Thank you

[quote=tedpliangos]Dear friends,
I would like your help on, where i can find if there are limits on the volume of air recycled in a classified room.(the volume of air that returns)
I have calculate the volume of air delivered in the classified room and the air exchange rate.

Thank you[/quote]

Dear tedpliangos,
What I am aware about in checking in a classified area is:

• air velocity
• air changes

What exactly do you mean by the volume of air that returns? Please be more specific.

By saying ‘the air that returns’ i mean the abducted air (i don’t know if i’m using the right word).
In HVAC system as we know we have continuous circulation of the air.
Air enters the cleanroom through filters ( I 've calculated the volume of air)
and air ‘returns’ or abducted from the cleanroom to the HVAC unit.
I want to know (for HVAC validation purposes) if i have to calculate the volume of air that is abducted
and for what reason do i have to do it. Are there any limits?

Thank you alot

I am not aware of any return air parameters. I would think air balancing would dictate the value, as well as air changes. As your are aware, a pressure differential is required between different grade rooms.

The normal setting for fresh air make up is in the region of 15% or 85% re-circulated air.
That is to make up for small loses(mainly due to leakages in the ducting, door seals etc) and for personnel comfort, but this figure does vary due to the way in which the system is set up to handle the differential pressures required.
I have yet to find any standard relating to a ‘set figure’ required for fresh air make-up or re-circulation of a cubicle/room.

If by ‘abducted air’ you mean the air that is being returned to the AHU, the main reason we measure the return air is to verify the losses of the system. The more fresh air, the greater the losses, the harder a system is required to work to maintain the correct critical parameter.eg %RH, Temperature, air change rates, filter life, air velocities increase to overcome the air quantity losses.

Hope that this is of some help. Anyone else?