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07-21-2008, 11:11 AM #1
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.
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.