Draw and size a duct network

A duct network carries one air system's air of one kind: supply, return, exhaust or outdoor air. Kelvin sizes each segment against the sizing criteria you choose, works out its friction and fitting losses, and marks the index run, the path whose pressure the fan is sized on.

1. 1

   Under Network, give it a Network name and choose its Role and Air system. Under Sized by, choose the Method, Sizing criteria, Duct material and the size list for each shape you'll use.

2. 2

   In the Duct plan, choose SA duct for supply (RA duct, EA duct or OA duct for the others). Start on the unit, click each corner, and end on a register.

3. 3

   Select each run to give its bends and branches a loss coefficient, then check Sizing results and choose Save network.

A new network follows the ducts drawn on the plan and is sized again as the drawing and its register airflows change. Each segment's size and velocity are drawn on the plan; the full results are below it.

• –Each kind of air is its own network, drawn with its own tool and pen. A supply duct starts on the system's unit or on another supply duct it branches off.
• –Branch off a run by starting the new run on it. A run can tee only off a duct of the same air and the same system.
• –End a run on a register of the same air, or double-click or press Enter to cap it. A capped run is sized to its last branch; the stub past it carries no air and isn't sized. Finish and Cancel do the same as Enter and Escape, and Backspace takes off the last corner.
• –With 90° on, each corner is square to the last. Hold Shift to draw at any angle.
• –One run leaves the unit; tee the others off it. Risers between levels aren't drawn yet.

Select a run to set its Shape (Round or Rectangular, with an Aspect ratio) and, if you want it held, a Fixed diameter (optional). Left blank, it is sized by the network's criteria. Its length is the drawn centre-line.

• –Turn on Flexi-duct to draw flexible runs, or set Duct to Flexi-duct on a selected run. They are drawn corrugated.
• –Flexi-duct is sized on its own roughness row: choose it under Its roughness, or under New flexi-duct roughness before drawing. Kelvin doesn't default it.
• –Compressed is how much shorter the installed run is than the duct fully extended, in per cent. Kelvin multiplies its friction by the compression correction in ASHRAE Fundamentals Ch.21. Left blank, the run is sized fully extended and the result says so.
• –Connect registers with flexi-duct runs flexi-duct from the nearest rigid duct of the same air to every register not yet connected, and lists any it skipped with the reason.

• –Equal friction takes the smallest standard size whose friction gradient and velocity are both inside the criteria. Velocity takes the smallest whose velocity is. A criteria row with only a velocity limit can't size by equal friction.
• –Friction is Darcy–Weisbach with the Colebrook–White friction factor, on the duct material's roughness and the air state under Air in the ducts. Take the air system's supply air there with the link beside it.
• –A rectangular duct's friction is read at its equivalent round diameter, and its velocity is the flow over its actual area.
• –Each fitting's loss is its coefficient times the velocity pressure at the velocity the coefficient is referenced to. A register's datasheet drop is added to the run it ends.
• –The index run is the path from the fan to a register with the greatest total drop. Fans take their duct pressure from it.

Choose Type the segments instead to enter the network as a Segment table: Start with the segment at the fan, then add each segment with its parent, length, shape, flow, fittings and any terminal drop. Follow the drawing goes back to the plan's segments.