The Engineering Design Process
Learning Objectives
- Apply the iterative engineering design process to IAQ challenges
- Define clear design criteria and quantifiable success metrics
- Identify constraints including cost, materials, time, and regulations
- Conduct stakeholder analysis and needs assessment
- Develop engineering specifications from design requirements
The Design Challenge
"Design an air quality improvement system for a specific indoor environment that maximizes pollutant removal while minimizing cost, energy use, and noise."
The Engineering Design Cycle
Problem
Constraints
Solutions
Build
Evaluate
Improve
Key insight: Engineering is iterative. Expect to cycle through design-build-test multiple times before reaching an optimized solution.
Defining the Problem
Problem Statement Framework
A well-defined problem statement includes:
- Target user: Who will use this solution?
- Need: What problem are they facing?
- Context: Where and when does this occur?
- Impact: Why does this matter?
Example: "Students in portable classrooms (target) experience elevated PM2.5 concentrations (need) during wildfire season (context), leading to reduced academic performance and health effects (impact)."
Criteria vs. Constraints
Design Criteria (Goals)
- CADR > 200 CFM
- Achieve 5+ eACH in target room
- Reduce PM2.5 by >50%
- Noise level < 50 dB
- Energy use < 100W
- Portable (< 20 lbs)
Design Constraints (Limits)
- Budget: < $150 materials
- Size: fit under desk
- Safety: no exposed hazards
- Code: UL/electrical compliance
- Time: 3 weeks to prototype
- Skills: no welding required
Quantifiable Specifications
Convert qualitative goals into measurable specifications:
| Goal | Specification | Test Method |
|---|---|---|
| "Good air cleaning" | CADR ≥ 200 CFM for particles | AHAM AC-1 protocol |
| "Quiet operation" | ≤ 45 dB at 1m on high speed | Sound level meter |
| "Energy efficient" | ≤ 0.5 W per CFM of CADR | Kill-A-Watt meter |
| "Affordable" | ≤ $0.50 per CFM of CADR | Bill of materials |
| "Durable" | ≥ 1 year operation, 6 mo filter life | Manufacturer specs |
Activity: Design Brief Development
Working in design teams, develop a comprehensive design brief for your chosen scenario:
Scenario Options
- Classroom air cleaner: Portable HEPA air cleaner for 900 sq ft classroom
- DIY Corsi-Rosenthal box: Optimize the box fan + filter design for performance and cost
- Smart ventilation controller: CO2-based demand ventilation system
- Personal air quality zone: Desk-level clean air delivery
Design Brief Components
- Problem statement (using the framework above)
- Target users and stakeholders
- Minimum 5 quantifiable design criteria
- Minimum 5 design constraints
- Preliminary research on existing solutions
- Initial concept sketches (3+ ideas)
Key Takeaway
Good engineering starts with clear problem definition. Before designing solutions, engineers must understand user needs, establish quantifiable success criteria, and identify constraints. The design brief serves as a contract that guides all subsequent work and provides objective standards for evaluating the final solution.