If Flex Duct is used refer to the Equivilent Flex column to select the correct duct size. Under the supply truck section, select the associated supply runs for this supply trunk section and the CFM will automatically calculate. If more than four 4 supply trunk sections are required select the Duct Sizing 2 Tab. Equivilent Rect. Duct Height Width. Open navigation menu. Close suggestions Search Search.
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Report this Document. Flag for inappropriate content. Download now. Original Title: Manual-D. Related titles. Carousel Previous Carousel Next. Jump to Page. Search inside document. Documents Similar To Manual-D. Julian Arlisdianto. There are three basic steps: determining the total effective length of the duct system, determining the design friction rate, and finally sizing the duct.
Effective Length Manual D looks for the worst case duct run and bases the design friction rate on that longest run. The idea is that if the blower can move the air through the longest run, it can easily push the air through the other ducts. The assumption is made that each run will have a balancing damper, and that the balancing dampers will be used to balance the system airflow once the system is installed.
The speed sheet gives you four columns to use for determining the longest effective length. Note that you are NOT entering data for every run, just looking for the longest run. There are three rows labeled Trunk. They are there for systems which have multiple branching trunks. Most systems will only use one.
Enter the length of the trunk duct from the plenum to the branch takeoff in one of the Trunk rows. Then enter the length of the branch run beside Runout Length.
The second set of rows on this tab are for entering the equivalent length of all the fittings. They are arranged in groups of fittings with similar functions.
Click on a group to go to the tab showing the different fittings. Choose a fitting that best matches the fittings you will use. You will need to remember it, or jot it down.
Click return to return to the Effective Length tab. You will probably NOT have a fitting for every group. Just leave spaces blank which do not apply to your system.
Repeat the process for the return. Note that the group numbers change bit because the equivalent length of return air fittings varies from supply air fittings. Friction Rate The second tab is for determining the design friction rate.
You need to know the specific unit for this part because you will be entering the unit airflow and external static pressure. The idea is pretty simple.
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