Prototyping and Testing
Learning Objectives
- Build functional air cleaner prototypes using available materials
- Develop testing protocols for CADR, noise, and power consumption
- Collect and analyze quantitative performance data
- Apply iterative design based on test results
- Document design decisions and testing methodology
Prototyping Approaches
Low-Fidelity
Cardboard mockups, sketches, concept models. Test form factor and basic feasibility.
Medium-Fidelity
Functional but rough prototypes. Test airflow and filtration with real components.
High-Fidelity
Near-final design. Refined construction, full performance testing.
Corsi-Rosenthal Box Build Guide
Materials
- 1x 20" box fan (higher CFM = better)
- 4-5x 20x20x2" MERV-13 filters
- Duct tape or foil tape
- Cardboard for base/top panels
- Optional: shroud to direct airflow
Assembly Steps
- Arrange 4 filters in a square with filter arrows pointing inward
- Tape edges securely - no air leaks at seams
- Cut cardboard panel for bottom, tape in place
- Place box fan on top, blowing upward (exhausting filtered air)
- Seal fan to filter box with tape
- Optional: Add 5th filter on bottom instead of cardboard
Safety note: Do not obstruct fan motor. Ensure adequate ventilation around motor housing.
Testing Protocol: CADR Estimation
Without a certified test chamber, estimate CADR using decay rate method:
Procedure
- Select a test room (ideally 150-300 sq ft, sealed from outside)
- Measure room volume precisely
- Generate test particles (incense smoke works for PM2.5)
- Wait for concentration to reach steady state (~50-100 ug/m3)
- Turn on air cleaner and record PM2.5 every minute
- Continue until concentration reaches background
Analysis
Fit exponential decay: C(t) = C0 x exp(-k x t)
CADR = (kwith device - knatural) x Volume
Natural decay: Run control test without device to measure background particle loss rate.
Additional Testing Protocols
Airflow Measurement
- Use anemometer at exhaust
- Measure velocity at multiple points
- Calculate CFM = Area x Velocity
- Compare loaded vs clean filter
Noise Measurement
- Sound level meter at 1m distance
- Measure at all speed settings
- Record in dBA
- Compare to background
Power Measurement
- Kill-A-Watt or similar meter
- Record watts at each speed
- Calculate efficiency: CADR/Watt
- Estimate annual energy cost
Pressure Drop
- Manometer across filter
- Measure at various airflows
- Track increase as filter loads
- Determine replacement threshold
Iterative Design Process
Optimization Variables
| Variable | Test Range | Expected Effect |
|---|---|---|
| Fan speed settings | Low/Med/High | CADR increases, noise increases |
| Filter MERV rating | 11, 13, 16 | Higher MERV = better filtration, more pressure drop |
| Number of filters | 4 vs 5 | More area = more airflow at same pressure |
| Seal quality | Tape types | Better seal = less bypass |
| Shroud design | With/without | May improve directional airflow |
Design of experiments: Change one variable at a time to isolate effects.
Activity: Build and Test
Week 1: Initial Build
- Construct first prototype per design specifications
- Document build with photos and notes
- Conduct initial qualitative testing (does air flow?)
Week 2: Quantitative Testing
- Measure CADR using decay method (3 replicates)
- Record noise at each speed setting
- Measure power consumption
- Calculate performance metrics
Week 3: Optimization
- Identify weakest performance area
- Design and implement modification
- Re-test to verify improvement
- Document design evolution
Key Takeaway
Prototyping transforms design ideas into testable reality. Quantitative testing provides objective data for design decisions. The iterative cycle of build-test-improve is the heart of engineering practice. Documenting the process - including failures and lessons learned - is as important as the final result.