Single duct several diffuser 1

[saeedplc]

Dear Experts,

Could you please let me know how the air is even distributed in pharmaceutical halls? I mean suppose that one of zones of an Air Handling Unit is
a big hall that contains several diffusers with on VAV at first of Duct(VAV is controlling the whole flow to the main duct). I know in this case the farthest
diffuser get lowest flow and the nearer diffuser get more flow because of the pressure difference but how can this problem be solved? or even this type of
air distribution is sensible and standard?

As far as know even air distribution for halls is possible by textile duct with laminar flow but don't know how it is possible with ceiling diffusers.

I would be appreciated to hear from you.

Thanks.

 

[EnergyProfessional]

Duct upstream of the VAV devices needs to be sized for the critical path (typically, but not always, the farthest away one). Same is true for the return or exhaust duct in relation to return or exhaust fan.

Downstream of each VAV, balancing dampers are used to distribute the flow to multiple diffusers. If a VAV only has one diffuser, no balancing damper needed.

 

[saeedplc]

Thank you for the reply,
I dont understand. You mean if a vav is installed in a duct and several diffusers are used after the vav all diffusers get same flow or farthest diffuser get lower flow?
Or is it only depend on designing and in the case mentioned above good designing can brings even flow distribution on all diffusers?

 

[EnergyProfessional]

How much airflow each diffuser gets depends on the design and layout, loads (by window etc.). that is determined by the designer and each diffuser in a VAV zone can have different design flows. the ducts have to be sized for that and dampers adjust the flow. Look at a few plans and you will see the flow number on the diffuser and also the balancing dampers.

 

[saeedplc]

Excuse me for the delay

Could you please show me a standard plan including vav and diffusers along with balancing dampers? I have not seen such a plan and new to this field.

Thanks a lot.

 

[willard3]

You should hire an HVAC guy to do this rather than screw it up.

 

[saeedplc]

Hvac guy for what?
I asked to know this over curiosity not doing anything on the system.
By the way i am asking to get a sample plan to work it out to increase my knowledge.

 

[willard3]

You are plainly looking fo0r free Engineering with this post.

 

[lilliput1]

You have to understand that for a ductwork system to be balanced to design flows the air pressure drop to each diffuser must match the pressure drop to the most remote diffuser. Note the fan discharge pressure must be dissipated to zero which is the pressure at each air outlet. So plan on providing manual volume dampers at each branch to dissipate excess available pressure and locate them them far from the diffuser so as not to be noisy. Each diffuser should also have volume damper at the diffuser neck. VAV box operating pressure drop should not exceed 2" wg. There are laminar flow diffusers available if required. Low returns would be required for true laminar flow rooms.