Fans in Parallel and Series Explorer¶
Run the Fans in Parallel and Series Explorer MicroSim Fullscreen
About This MicroSim¶
Two fans can serve one system side by side (in parallel) or one after the other (in series). This explorer combines Curve A, the illustrative fan curve from Chapter 10 (1,380 RPM, standard air), both ways and sets the result against two system curves from Chapter 25:
- Steep system: P = 4.0 × (Q ÷ 10,000)², the Chapter 10 design system.
- Flat system: P = 1.0 × (Q ÷ 10,000)².
The combined curves follow two rules:
- Parallel: airflows add at each pressure. Pressure at total airflow Q equals one fan's pressure at Q ÷ 2.
- Series: pressures add at each airflow. Pressure at Q equals 2 × one fan's pressure at Q.
Curve A is interpolated linearly between its table points and extended along its 14,000 to 16,000 CFM segment to zero pressure (16,500 CFM). Each operating point is the airflow, searched in 1 CFM steps, where the combined curve and the system curve are closest, using only the part of the curve where each fan's own airflow is at least 4,000 CFM (right of the peak pressure point). The part where each fan is below 4,000 CFM is drawn faded and marked "stall region". Results are rounded to 10 CFM and 0.01 in. wg:
| System | One fan | Two in parallel | Two in series |
|---|---|---|---|
| Steep | 10,000 CFM at 4.00 in. wg | 10,980 CFM at 4.83 in. wg | 12,300 CFM at 6.05 in. wg |
| Flat | 14,040 CFM at 1.97 in. wg | 20,000 CFM at 4.00 in. wg | 15,080 CFM at 2.27 in. wg |
The sim starts with three predictions, in this order, one attempt each, before the combined curves are drawn:
| # | Prediction | Answer |
|---|---|---|
| 1 | Steep system: parallel or series for more airflow? | Series (12,300 vs. 10,980 CFM) |
| 2 | Flat system: parallel or series for more airflow? | Parallel (20,000 vs. 15,080 CFM) |
| 3 | Steep system: a second fan in parallel adds about 10%, 50% or 100%? | About 10% (10,980 vs. 10,000 CFM) |
Mastery is 3 of 3. After the third prediction every combined curve, the operating points and a readout table appear, and Explore mode lets you switch the system and the configuration in any combination. Explore mode is never scored.
How to Use¶
- Read the question under the plot, which shows one fan on the steep system with its operating point at 10,000 CFM and 4.0 in. wg. Press Parallel or Series.
- A correct prediction reads "✓ Correct." with the operating points that prove it, in a solid green box. An incorrect one explains why in a dashed red box. "Predictions correct: n of 3" keeps the score. Press Next prediction; the plot switches to the flat system for prediction 2 and back to the steep system for prediction 3.
- After prediction 3, press Reveal the curves. The summary shows the first-attempt score and the mastery line.
- Explore: choose Steep or Flat and One fan, Parallel or Series. The chosen combined curve is drawn thicker, its operating point is the filled diamond, and the readout gives its airflow and pressure with the gain over one fan. Notice that the configuration that wins on one system loses on the other. Hover any curve or point for values. Start over clears the predictions.
Keyboard: keys 1, 2 and 3 choose a prediction; Enter goes to the next one. In Explore mode, S and F choose the system and O, P and R choose one fan, parallel or series. Tab reaches every button.
Data label: "Illustrative data · Curve A, Chapter 10 · standard air, 1,380 RPM per fan", below the plot.
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/ch25-parallel-series-explorer/main.html"
height="788px"
width="100%"
scrolling="no"></iframe>
Lesson Plan¶
Learning Objective¶
The learner will compare one fan, two fans in parallel and two fans in series on a steep and a flat system curve, correctly predicting which combination delivers more airflow on each system (Bloom: Analyze, verb: compare).
Audience¶
Adult professional development: new application engineers, sales staff, representatives and facilities staff.
Duration¶
10-15 minutes
Prerequisites¶
- Fan curve, system curve, operating point, peak pressure point and stall region (Chapter 10)
- Fans in parallel and fans in series (Chapter 25)
Activities¶
- Predict (3 min): Commit the three predictions. Write a one-line reason for each before pressing a button.
- Explore (5 min): On the steep system, step through one fan, parallel and series and record each airflow. Repeat on the flat system. Mark which configuration wins on each.
- Explain (3 min): Use the plot to explain why a second parallel fan on the steep system raises pressure from 4.0 to 4.8 in. wg instead of doubling the airflow.
Common Misconceptions Addressed¶
- Two fans in parallel deliver twice the airflow: prediction 3 and the steep-system readout show about 10% more.
- Series fans are only useful for pressure and never increase airflow: on the steep system the series pair moves the most air, 12,300 CFM.
- The better combination is a property of the fans: the same two fans win in series on the steep system and in parallel on the flat one.
Assessment¶
- "Predictions correct: n of 3" counts first-attempt predictions; mastery is 3 of 3. At the end the sim shows "First-attempt score: n of 3" and the mastery line.
- Switching configurations and hovering curves after the predictions is exploration, not evidence. Follow-up question: a VAV system holds a fixed duct static pressure. Is its system curve closer to the steep or the flat case here, and which pairing would you test first?
References¶
- Chapter 25: Fans in Parallel and in Series - the combining rules and the operating points this explorer draws.
- FanPedia: The Fan & Blower Encyclopedia - Twin City Fan's reference on fan curves, system curves and fan application.
- AMCA International - publisher of AMCA 201, Fans and Systems, which covers fan and system curve interaction, including multiple-fan systems.