Volume Control Damper and Ceiling Register

[nayusa]

When making HVAC duct layout, do I need to specify volume control damper in branch duct if ceiling supply diffuser has the opposed blade damper?

Otherwise, having VCD in branch duct, shall I specify ceiling supply diffuser without OBD?

Please advise.

thank you.

 

[GMcD]

If you want to reduce noise in the space, delete the diffuser/air terminal damper, and use only the branch duct balancing damper, which should be located at least 2 meters (7 feet) back from the air outlet. The neck dampers and opposed blade dampers at the air supply terminal are just noise-makers.

Washrooms and un-occupied type spaces (storage rooms) would be fine with a terminal damper.

 

[imok2]

There is no way you can properly balance a duct system unless you install volume dampers on the branch ducts in a constant volume system. Trying to balance with just ceiling diffusers is asking for trouble as noise would be a critical factor

 

[nayusa]

Hi GMcD and imok2, Thank you very much for your reply.

 

[williamsGA]

Just as a note. For a VAV system you do not need balancing (volume) dampers upstream of the VAV boxes. Also I would still require the OBD at the diffusers. This allows you to fine tune the system.

 

[walkes]

Further note to WilliamsGA response, if you have a crappy VVT system you would still require a balancing/volume damper upstream of the box.

I agree with the opposed blade dampers at the diffuser for fine tuning only.

 

[HVACHawaii]

why is it required for VVT?

 

[walkes]

Some of the VVT dampers/boxes that I have come across are pretty flimsy (not all though) and these systems do not always control properly without the balancing damper. It could be the one bad installation from my experience, but I have since put balancing dampers ahead of the VVT units.

 

[SPHenryEnergy]

Having done TAB, I've found diffuser mounted OBDs to be consistantly problematic ( noise, impropoer diffuser neck velocity, and flow turbulance). A quality volume damper (with a low leak dial regulator, spring lock bearing, end bearing)located properly in the branch duct serving the diffuser should be more than adequate for air balancing purposes.