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Thread: HVAC ducting question

  1. #1
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    HVAC ducting question

    Hi,

    I'm an engineering trainee working on rehabilitation of a unfinished construction of a villa, the villa contains 16 VRV systems, and the HVAC systems were designed by a major company.

    looking at the blueprint attached below, I'm not sure if i should suggest adding a duct damper in this system as the air flow in each branch might not be consistent, can anyone explain what is the correct choice in this case?

    Thanks

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  2. #2
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    I would agree that there is likely to be an imbalance of flow between the branch ducts, and it appears there is no room to add a diverter or splitter. (path of least resistance) (the duct on the left is nearly a straight shot) However, it does appear that they serve a common area, and depending, any imbalance might be managed with diverters at the grill face, or a specific grill face designed to allow orientation changes for throw.

    Adding a balancing damper in each of the branch ducts is cheap insurance though, and that's what I would require.

  3. Likes Alwreikat1996 liked this post.
  4. #3
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    I'm not really understanding the print.

    Are those five red 'bars' off of each branch six inch round ducts? And each branch is 30" x 30"? If so, I'm guessing that is your limiting (also known as self balancing) factor.
    I do a triple evac with nitro to remove non condensables.

  5. #4
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    Looks like it would work pretty good to me just like it is. I’m guessing metric numbers. So what if a little more air comes out of one part.

  6. #5
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    Looks like someones homework guys..

  7. #6
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    Could be, I've never seen prints that look like that. Besides, it looks like two rooms are infected with The Rona.


    Quote Originally Posted by mofotech View Post
    Looks like someones homework guys..
    I do a triple evac with nitro to remove non condensables.

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  9. #7
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    Quote Originally Posted by Scoobie View Post
    Looks like it would work pretty good to me just like it is. I’m guessing metric numbers. So what if a little more air comes out of one part.

    The "so what" could easily be a comfort, or other unacceptable issue.

    For example...... and simplified........

    Cold air sinks in a mass of warmer air. This is why we need to take supply air volumes, velocities, and the throw of supply grills into consideration when we design a comfort cooling system.
    Hot air rises in a cooler mass of air..........

    We don't know the use, or layout of the area that his supply grills are intended to condition. Could be, the supply duct with the lower volume might cause a cold draft right where the bosses chair is.

    Or, the supply duct with the higher volume of air is washing the rear wall of the conditioned space as designed, but the velocity is so high that it blows the paperwork off the desk at the rear of the room.

    To do it correctly, there's a little more to it than simply dumping cold or hot air into a room.


    By the way... "the HVAC systems were designed by a major company." Means nothing.

  10. #8
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    Too much of the drawing is unreadable for me to tell what they are trying to do. It looks like a large supply grid at the bottom. They really don't show any diffusers. Looks like a trick question to me.
    No man can be both ignorant and free.
    Thomas Jefferson

  11. #9
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    Thread Starter
    The red bars are 6 inch round flexible ducts, and it is 30cm x 30cm

  12. #10
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    Thanks everyone, I will suggest adding a balancing damper to the duct on the left or a splitter in between the two ducts if possible, as this VRV has 2 Fans.

    Btw, this blueprint was drawn by Daikin, thats why i was confused on whether they missed something or i was just wrong.

  13. #11
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    That's like what? 12" x 12" ?

    Won't need any balancing dampers for that. Because there won't be any air to balance.


    Quote Originally Posted by Alwreikat1996 View Post
    The red bars are 6 inch round flexible ducts, and it is 30cm x 30cm
    I do a triple evac with nitro to remove non condensables.

  14. #12
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    Quote Originally Posted by Alwreikat1996 View Post
    Thanks everyone, I will suggest adding a balancing damper to the duct on the left or a splitter in between the two ducts if possible, as this VRV has 2 Fans.

    Btw, this blueprint was drawn by Daikin, thats why i was confused on whether they missed something or i was just wrong.
    So this is a slim duct unit?

    Edit: looks like it is. This is a medium static unit. Not sure of the ESP on this bit it might be .8.

    https://www.daikin.co.uk/en_gb/products/fxsq-a.html

    I would put dampers also on the trunkline.. im not sure if those are round pipe? But it would be a good idea ans plus dampers on each duct run. So air can be balanced afterwards. I hope you guys oversized the return. Those slim ducts love alot of return air. Sometimes double the size is good to do on the return size. Try also to use 2 inch filters or 4".

  15. #13
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    Quote Originally Posted by Artrose View Post
    The "so what" could easily be a comfort, or other unacceptable issue.

    For example...... and simplified........

    Cold air sinks in a mass of warmer air. This is why we need to take supply air volumes, velocities, and the throw of supply grills into consideration when we design a comfort cooling system.
    Hot air rises in a cooler mass of air..........

    We don't know the use, or layout of the area that his supply grills are intended to condition. Could be, the supply duct with the lower volume might cause a cold draft right where the bosses chair is.

    Or, the supply duct with the higher volume of air is washing the rear wall of the conditioned space as designed, but the velocity is so high that it blows the paperwork off the desk at the rear of the room.

    To do it correctly, there's a little more to it than simply dumping cold or hot air into a room.


    By the way... "the HVAC systems were designed by a major company." Means nothing.
    Whoever drew that out did a good job. The duct is symmetrical and will self balance. I don't see any reason to add dampers if its actually built as drawn.

    Heck crank it up and read the flow. Let us know if it works okay.

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