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Anatomy of a Fan Duty Statement

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About This MicroSim

A duty statement is the line on a schedule or specification that tells you what a fan must do. This infographic shows the one built from Chapter 1's worked examples:

12,000 CFM at 3.0 in. wg static pressure, 1,173 RPM, 7.9 BHP, at 0.075 lb/ft³ (70°F, sea level), clean air.

Its six parts are marked as clickable segments, each with its quantity name underneath:

# Segment Quantity name What it tells you
1 12,000 CFM Airflow volume Cubic feet of air per minute, measured at the fan inlet conditions.
2 3.0 in. wg static pressure Static pressure The system's resistance at this airflow, which the fan must overcome.
3 1,173 RPM Fan speed Impeller revolutions per minute; here set by a 6 in motor sheave and a 9 in fan sheave on a 1,760 RPM motor.
4 7.9 BHP Brake horsepower Power required at the fan shaft; a 10 hp motor would run at 79 percent load. It is not the motor size.
5 0.075 lb/ft³ (70°F, sea level) Air density The density the rating assumes; here standard air. Hot air or a high site changes pressure and power.
6 clean air Airstream condition What the air carries; contaminated airstreams change the impeller, arrangement and construction.

In Explore mode, clicking a segment opens its callout. A ✓ badge marks each part you have opened ("Visited n of 6").

In Quiz mode the names are hidden. The sim highlights one segment at a time, in an order shuffled once per session, and you choose its name from the six quantity names. Each segment has one scored attempt. A correct choice shows "✓ Correct: ." with the callout text. A wrong one shows "✗ Not quite. That segment is the ." with the callout text, and the answer is marked on the line. The running score reads "Correct on first attempt: n of 6". Mastery is 5 of 6 correct on the first attempt. After the sixth segment a summary lists any missed parts, with Start over and Back to explore.

The duty statement is illustrative, not a catalog selection, and the infographic says so.

How to Use

  1. In Explore mode, click each part of the rating line (or Tab to it and press Enter) and read its callout.
  2. When you know all six, press Quiz.
  3. For each highlighted part, choose its name (or press 1 to 6). Read the feedback, then press Next prompt.
  4. Read the summary. Press Back to explore to review the parts, or Start over for a new quiz.

Keyboard: Tab moves between the parts and the buttons; Enter or Space opens a part; in the quiz, keys 1 to 6 pick a name, and Enter on Next prompt goes on.

Data label: "Illustrative duty statement, not a catalog selection · Values from the Chapter 1 worked examples", shown under the rating line.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

<iframe src="https://moroshek.github.io/FanTASTIC-textbook/sims/ch01-fan-duty-statement/main.html"
        height="722px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Learning Objective

The learner will identify each of the six parts of a fan duty statement by its quantity and unit, with at least 5 of 6 correct on the first attempt (Bloom: Remember, verb: identify).

Audience

Adult professional development: new application engineers, sales staff, representatives and facilities staff.

Duration

5-10 minutes

Prerequisites

  • Airflow volume and cubic feet per minute
  • Static pressure and inches of water gauge
  • Fan speed and RPM
  • Brake horsepower
  • Air density and standard air
  • Airstream

All are defined earlier in Chapter 1.

Activities

  1. Explore (3 min): Open all six callouts. For each, say which unit tells you what the quantity is.
  2. Quiz (3 min): Name the six highlighted parts without the labels.
  3. Discussion (2 min): A customer's schedule gives only "12,000 CFM at 3.0 in. wg". What two parts are missing, and why can the line not be checked against a catalog without them?

Common Misconceptions Addressed

  • BHP is the motor nameplate size: the brake horsepower callout says it is the power at the fan shaft, with a 10 hp motor running at 79 percent load.
  • Static pressure is a property of the fan alone: its callout calls it the system's resistance at this airflow.
  • The density can be left off because every catalog uses standard air: its callout says hot air or a high site changes pressure and power.

Assessment

  • First-attempt score shown as "Correct on first attempt: n of 6"; mastery is 5 of 6 on the first attempt. The summary shows "Mastery reached (5 of 6 needed)." or what is still needed.
  • Explore mode is not evidence of mastery. Follow up: rewrite the line for 250°F air. Which parts change, and which stay the same?

References

  1. Chapter 1: Air, Pressure and the Fan - "Putting It Together: What a Fan Delivers" and the worked examples "From Duty Point to Motor" and "Setting a Belt-Driven Fan's Speed".
  2. FanPedia online, Twin City Fan - The fan and blower encyclopedia this textbook is built from.
  3. Chapter 26: Reading Catalogs and Performance Tables - Where to find this line in a performance table.