8
Elaborate
Design Challenge
Duration
90 minutes
Type
Performance Task
Standards
MS-ETS1-2, MS-ETS1-3
Learning Objectives
Students will be able to:
- Apply engineering principles to optimize a CR box for a specific scenario
- Evaluate trade-offs between competing design criteria
- Justify design decisions with evidence and calculations
- Present optimized designs with supporting data
The Challenge
Your team has been hired as air quality consultants. A client needs a custom CR box solution for their specific space. Design and justify the optimal CR box configuration for your assigned scenario.
Scenario Options
A: School Nurse's Office
- Size: 12 ft × 15 ft × 9 ft
- Priority: Maximum protection (sick students visit)
- Budget: $150
- Constraint: Must be quiet (student rest area)
- Target ACH: 8-12
B: Art Classroom
- Size: 30 ft × 40 ft × 12 ft
- Priority: Handle dust and fumes from art supplies
- Budget: $300
- Constraint: Can't block workspaces
- Target ACH: 4-6
C: Community Wildfire Shelter
- Size: 50 ft × 80 ft × 15 ft (gymnasium)
- Priority: Handle extreme smoke (PM2.5 > 200)
- Budget: $500
- Constraint: Must be quickly deployable
- Target ACH: 6+ despite large space
D: Bedroom for Asthma Patient
- Size: 10 ft × 12 ft × 8 ft
- Priority: Allergen and particle removal
- Budget: $80
- Constraint: Must be very quiet (sleeping)
- Target ACH: 6-8
Design Process
Step 1: Analyze Your Scenario (15 min)
- Calculate room volume
- Determine required CADR for target ACH
- Identify priority constraints (budget, noise, space)
- Research any special considerations
Step 2: Design Your Solution (20 min)
- How many CR boxes needed?
- What filter configuration? (4-filter vs 5-filter cube)
- What MERV rating?
- What fan speed settings?
- Where should units be placed?
Step 3: Calculate & Justify (20 min)
- Calculate expected CADR (total)
- Calculate expected ACH
- Calculate total cost
- Explain trade-offs you considered
- Show how you meet constraints
Step 4: Prepare Presentation (20 min)
- Create visual diagram of solution
- Summarize key calculations
- Prepare cost-benefit comparison
- Practice explaining your reasoning
Key Formulas
Room Volume
V = L × W × H
Required CADR
CADR = (V × ACH) ÷ 60
CR Box CADR
CADR = Airflow × 0.85
(assuming MERV-13, ~85% efficiency)
Number of Units
N = Required CADR ÷ Single Unit CADR
Design Considerations
| If You Need... | Consider... |
|---|---|
| Maximum CADR | 5-filter design, high fan speed, multiple units |
| Quiet operation | Low fan speed (but more units), shroud/enclosure |
| Low budget | MERV-11 filters, single-filter design |
| Portability | Smaller fans (16"), lighter filters |
| Aesthetics | Decorative covers, fabric shrouds |
Example Calculation
Scenario: Art Classroom (30 × 40 × 12 ft), target 5 ACH
Room Volume = 30 × 40 × 12 = 14,400 cu ft
Required CADR = (14,400 × 5) ÷ 60 = 1,200 CFM
One CR box CADR (medium speed) ≈ 600 CFM
Number needed = 1,200 ÷ 600 = 2 CR boxes
Total cost ≈ 2 × $80 = $160 (within $300 budget)
Presentation Requirements
Your presentation should include:
- The Problem (30 sec): Your scenario and constraints
- Your Solution (1 min): Design choices and why
- The Evidence (1.5 min): Calculations showing it works
- Cost-Benefit Analysis (30 sec): How it compares to alternatives
- Recommendations (30 sec): What you'd advise for this scenario