Design Duct

Duct sizing at the preliminary stage is arithmetic between an airflow, a velocity, and a cross-section. The arithmetic is the same everywhere. The velocity you find acceptable, and the friction and loss values you design to, are choices and table rows, so they come from you.

Workflow

Step 1. Establish the basis

Ask, in one message:

1. Sizing to a velocity limit or a friction rate? State the value and where it came from: standard, office criteria, or a chart you read.
2. Unit system, as your documents use it.
3. Round, rectangular, or flat oval? For rectangular, the aspect ratio you will accept and any dimension caps from the ceiling space.
4. One segment, or a run you want tallied for pressure drop?

Step 2. Collect the segment

Airflow with its source. For a run: each segment's length and airflow, and each fitting named with the loss value you supply for it.

Anything unstated is missing. Never substitute a typical velocity or a familiar coefficient.

Step 3. Compute, showing every step

Segment <name>
  airflow                  <as given>  [source]
  limit                    <as given>  [cited]
  required area            A = Q / V   <arithmetic>
  trial size               <as given, or proposed within your caps>
  actual velocity          <arithmetic>  — vs limit: <pass/fail>
  equivalent diameter      <formula, then arithmetic>

For a pressure tally, per segment and fitting, each with its supplied loss value cited, then the running sum. Any segment missing a loss value shows unverified and the total names what it excludes.

Step 4. Report

Sizes and velocities per segment, the tally if run, the unverified list first, and the criteria you supplied printed at the top. Then:

Every limit, rate, and coefficient here came from you. I did the arithmetic and supplied no values. This is preliminary sizing; the mechanical Engineer of Record designs the system.

Step 5. Save, if asked

Ask whether to write the calculation to a file and where. Write it directly, including the arithmetic. There is no template and no script.

Rules

• Never supply a velocity limit, a friction rate, or a loss coefficient. There are none in this file.
• Proposed dimensions stay inside the caps you gave, and the aspect ratio is printed beside them.
• Show the arithmetic, including the equivalent-diameter steps; a converted size without its steps cannot be checked.
• A pressure tally names every value it is missing before it reports a total.
• Stop on a missing value rather than proceeding with a placeholder.
• Never convert unit systems on your own; mismatched inputs stop the segment.
• Say on every run that this is preliminary.

Anti-patterns

• Recalling a comfortable velocity for an office supply duct. The limit is a design choice the user owns.
• Reading a friction chart from memory because the flow is common.
• Filling a fitting coefficient because the fitting is ordinary.
• Balancing a branch by adjusting airflows nobody stated.
• Rounding a computed dimension to a neat size without saying the velocity moved.

Resources

None. This skill is one file. Output is written directly at the path you name.