Fan Curves

Fan curves, from first spin to first savings

Four live demos for a one-hour session. One fan runs through all of them: a backward-inclined centrifugal, rated 1,750 RPM, designed for 10,000 CFM at 3.5 in. w.g. on a 10 hp motor. Every number on every page comes from the same model and the same three fan laws.

TimeSectionWhat happens
0:00–0:05 Hook & agenda Why fans: airside fans are typically the largest single electrical end-use we design. One question frames the hour: “who decides the CFM?”
0:05–0:14 1 · Moving air Animated fan + duct. Spin it, throttle it — a fan is a pressure machine, and airflow is a negotiation with the system. Ends with the reveal: sweeping the damper traces a line, and that line is the fan curve (it’s also the AMCA 210 lab test).
0:14–0:36 2 · The fan curve The centerpiece. Build the chart layer by layer: fan curve, system curve, operating point, speed family, surge zone, efficiency rails, and the BHP curve on its right-hand axis — the way every manufacturer prints it. Run the scenarios (dirty filter, VFD hold, VFD turndown) and do live fan selections from the schedule.
0:36–0:45 3 · The fan laws Why the picture works: Q ∝ N, P ∝ N², W ∝ N³ — with the intuition for each exponent, and the proof that the laws generate the entire curve family from one test.
0:45–0:55 4 · The payoff Part-load power four ways: dampers vs. VFD vs. VFD + static reset vs. the ideal cube. Annual dollars from a real load profile, the 90.1 hooks, and the 60-second pump translation.
0:55–1:00 Recap & questions Three sentences: the fan offers a curve, the system picks the point, speed is how you move it cheaply. Then Q&A.

Presenting tips

  • Zoom the browser to ~125–150% (Ctrl + +) before sharing; every layout is fluid.
  • Charts are keyboard-friendly: click a chart (or Tab to it), then / walks the crosshair — steadier than a mouse on a screen share. Shift jumps 10×.
  • Demo 2 starts intentionally sparse. Reveal layers top-to-bottom as you talk; the story is in the reveal order.
  • Prose hides behind ▸ arrows — page intros and explainer cards are collapsed so each tab reads as a demo at first glance. Expand them live as you teach (they double as leave-behind notes for engineers exploring later).
  • Every chart has a “View as table” under it — great for the “what’s the actual number” person.

The running example

  • Fan: backward-inclined SWSI centrifugal, rated 1,750 RPM
  • Design duty: 10,000 CFM @ 3.5 in. w.g. static
  • At design: ≈ 8.3 BHP, static efficiency ≈ 67%, 10 hp motor
  • Shutoff: 4.0″ · peak: 4.5″ @ ~4,300 CFM · free delivery: 16,000 CFM
  • Off-speed behavior is pure fan law — the demos never cheat.