On the design of terminals/valves for radial systems

[Sparrowhawk]

I've got my first supply and extract terminals here (Zehnder Luma). Doing a radial system with semi-rigid ducting, my plan is to do the throttling for each run at the manifold and have the terminals wide open for less resistance and noise.

 

In this setup, does the solid central bit inside the terminal holding the flow adjuster do anything useful (like meaningfully shape the airflow) or would a radial system like this do just as well with a flat plate hiding the plenum, a place for a filter cone, and nothing more?

 

I'm thinking the design is a hangover from traditional branched systems where these are the flow restrictors, hence the name 'valves'.

 

Edited February 24 by Sparrowhawk

[Sparrowhawk]

Second question: I understand the base of extract valves is proud of the ceiling to prevent streaks forming as moist or dirty air is sucked towards it. But why is the base of a supply valve proud of the ceiling by 1cm? Is this required for better mixing/the coanda effect?

[G and J]

  On 24/02/2025 at 07:27, Sparrowhawk said:

Second question: I understand the base of extract valves is proud of the ceiling to prevent streaks forming as moist or dirty air is sucked towards it. But why is the base of a supply valve proud of the ceiling by 1cm? Is this required for better mixing/the coanda effect?

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Hmmmm, so do flush vents like ergovents get streaky marks round them then?

 

[Nickfromwales]

I don’t have this evidence around my Icon fan, which is routinely flowing air much faster, but it is proud of the surface.

 

To be honest, I doubt airflow is going fast enough for long enough to make this an issue, and I’d rather paint my ceiling every couple of years vs have the utilitarian looking vents on the ceiling. 
 

If you’re balancing at the manifold then just use a linear version which is bigger / longer than you need to distribute the airflow over a much bigger surface area.

 

Do you know what valves you’re using to control the flow of air, as poor ones will gain you the audibility that you are trying to rid the system of. 

[Mike]

  On 24/02/2025 at 07:27, Sparrowhawk said:

why is the base of a supply valve proud of the ceiling by 1cm? Is this required for better mixing/the coanda effect?

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Yes, to create the Coanda effect.

 

  On 23/02/2025 at 20:39, Sparrowhawk said:

my plan is... have the terminals wide open for less resistance and noise

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At the airflows involved, that shouldn't be an issue.

 

  On 23/02/2025 at 20:39, Sparrowhawk said:

I'm thinking the design is a hangover from traditional branched systems where these are the flow restrictors, hence the name 'valves'.

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It's because it's easy to adjust the flow at the valve during installation (25 different positions with that particular valve), avoiding the need to manually screw the valve in or out by X number of turns / avoiding the need to go backwards & forwards & cut sections out of a restrictor at the manifold.

 

[JohnMo]

  On 23/02/2025 at 20:39, Sparrowhawk said:

plan is to do the throttling for each run at the manifold

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Not really seeing any benefits. Works well at the terminals, zero noise, zero cost for more parts, measure, adjust done. Instead of measure, go to manifold pull off hose, pull out widget to change, re-assemble, check, repeat.

[Nickfromwales]

This is what I’ll be doing on the next job with plaster in terminals. 
 

One guy in the room and one at the plant room, with phones or radios. 

[Sparrowhawk]

  On 24/02/2025 at 09:29, Nickfromwales said:

I don’t have this evidence around my Icon fan, which is routinely flowing air much faster, but it is proud of the surface.

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Good to hear that these could be flush

  On 24/02/2025 at 09:29, Nickfromwales said:

If you’re balancing at the manifold then just use a linear version which is bigger / longer than you need to distribute the airflow over a much bigger surface area.

 

Do you know what valves you’re using to control the flow of air, as poor ones will gain you the audibility that you are trying to rid the system of.

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I don't yet (and in light of this thread now likely won't) but Ubbink's "pop out" rings were the kind of thing I was thinking of. Which valves are you using in your photo, they look well engineered?

[Sparrowhawk]

  On 24/02/2025 at 12:42, Mike said:

Yes, to create the Coanda effect.

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Yay, one of my guesses was right  

 

  On 24/02/2025 at 12:42, Mike said:

  On 23/02/2025 at 20:39, Sparrowhawk said:

my plan is... have the terminals wide open for less resistance and noise

Expand  

At the airflows involved, that shouldn't be an issue.

 

  On 23/02/2025 at 20:39, Sparrowhawk said:

I'm thinking the design is a hangover from traditional branched systems where these are the flow restrictors, hence the name 'valves'.

Expand  

It's because it's easy to adjust the flow at the valve during installation (25 different positions with that particular valve), avoiding the need to manually screw the valve in or out by X number of turns / avoiding the need to go backwards & forwards & cut sections out of a restrictor at the manifold.

Expand  

 

  On 24/02/2025 at 13:14, JohnMo said:

Not really seeing any benefits. Works well at the terminals, zero noise, zero cost for more parts, measure, adjust done. Instead of measure, go to manifold pull off hose, pull out widget to change, re-assemble, check, repeat.

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Thanks gents. I'd picked up - I think from this forum, but also from at least one supplier of radial systems - that it was easier to do it all back at the manifold. Good to have cleared this up before doing anything, and explains why the terminals are as they are and not £4.99 for a metal plate and 2 retaining clips.