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  1. #1
    Join Date
    Apr 2008
    Location
    Princeton, NJ
    Posts
    581

    New ducts to lower static pressure

    Supply duct installation is almost complete. The system is a Trane XV95-100k btu/XL15i -4 ton system.
    The history can be found at an earlier thread called “Is 0.5 Max static Pressure a realistic target” by Key1cc. Here is the link.
    http://hvac-talk.com/vbb/showthread.php?t=175955
    In summary I had 3 trunk-ducts coming off the plenum one 12x9 out the top, one 8x9.5 out the back (that turned out to be ~ 8 x 7 because the installer used a flexible rectangular extender that folded into the air-stream), and one 12 x 8 trunk coming out the front (that I kept the damper closed because it led to the garage and laundry area where I do not require AC). My system had 16 total round runs off the 2 trunks that were open. All 16 lead to room registers. 13 were 5 inch and three were 6 inch. All static pressure (SP) was checked with factory filter after filter in blower bay and after blower before coil and with CFMs set to 350/ton. The SP with all dampers open (including the garage area front trunk) was 0.6 pos. and 0.32 neg which is a total of 0.92. This setup caused the upstairs to be 10-12 degrees hotter than the down stairs so the system was balanced with three 5 inch dampers closed and the front plenum damper to the garage closed. As a result the upstairs was now only 3-4 degrees different than down stairs but the static pressure jumped to 1.1 (0.8 pos and 0.3 negative).

    Now for the current situation.
    The 12x9 duct trunk coming out the top was not changed (at the plenum).
    The 8x 9.5 partially blocked trunk coming out the back of the plenum was converted to a 16x 8 for the 1st 5 feet then transitioned back into the 8 x 9.5 to continue supplying three 5” runs and one 6” run.
    The 12x8 that went to the garage was disconnected and the plenum opening was converted to a 14x14 four ft trunk off the plenum that made a 90 degree angle turn using 16x12 trunk for 5 ft then transitioned to a 16x 8 that took over supplying 7 of the 11 runs that were originally coming off the 12x9 trunk….thus leaving the 12x9 with only four 5 inch runs to supply.

    The supply work is not done but so far 6 of the 5” round runs have been converted into 6” runs in the basement only. Before going up the wall stacks the 6” runs are transitioned down to 5 inches with a reducer to that they can connect to the existing 5” pipe in the wall stack.

    I almost forgot…..Additionally, a new 8” hole was cut in the back side of the plenum for a new 8” round run that goes about 10 ft total with (three 90 degree elbows) before transitioning with a reducer into the 5” just before going up the wall stack. This run is for one of the registers in the master bedroom.

    My duct pro is at the house now so I will have new static numbers after lunch and possibly pictures.

    Anyone care to speculate what the static may be now?

    Changing the Return drop will start this week….going from a 24x10 to a 24x20.

    Key1

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    I thought you were going to increase all the supplies in the basement to 6"

    Just a guess.
    About .2" less after all work is completed.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Apr 2008
    Location
    Princeton, NJ
    Posts
    581
    After the work started we decided to increase 3 supplies to 7" and the rest to 6"....It just has not been done yet.

    I'm home for lunch now I'll write back shortly with new static info and pics.

    Key1

  4. #4
    Join Date
    Apr 2008
    Location
    Princeton, NJ
    Posts
    581
    Here are the pics, The duct pro has a run open so he can't give me static for another hour or so.
    Attached Images Attached Images      

  5. #5
    Join Date
    Apr 2008
    Location
    Princeton, NJ
    Posts
    581

    More pics

    More pics
    Attached Images Attached Images      

  6. #6
    Join Date
    Jan 2007
    Location
    N.E. Ok.
    Posts
    1,359
    To link your other thread

    find it and open it up, right click on the address bar and copy

    edit your original post, choose the little blue ball with paper clip (insert link) and paste the address.

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by key1cc View Post
    More pics

    I'd remove the supply plenum and return drop ,and start over with better fitting ,turning vanes ,etc..

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