Applied Example 3 – IAQP with a Simple Numerical Example (Solved Case)
This applied example demonstrates how the Indoor Air Quality Procedure (IAQP) can be used conceptually and numerically for a space with identifiable contaminant sources, using simple mass balance logic.
The purpose is not to perform a full regulatory IAQP submission, but to understand how numbers, assumptions, and logic interact to justify ventilation decisions.
Scenario Description (Printing Room)
Consider a printing and copying room in an office building.
Space characteristics:
- Floor area = 80 m²
- Ceiling height = 3 m
- Room volume = 240 m³
- Typical occupancy = 2 people (low and stable)
Primary IAQ concern:
- Volatile Organic Compounds (VOCs) emitted from printers and copiers
Operating conditions:
- Equipment operates continuously during working hours
- Space is mechanically ventilated and exhausted
Step 1: Define the Contaminant and Acceptable Limit
Under IAQP, we must define:
- The contaminant of concern
- An acceptable indoor concentration limit
Assume:
- Contaminant: Total VOCs (TVOC)
- Acceptable indoor concentration limit (design target):
Cₐ = 500 µg/m³
(This value is commonly referenced in guidelines and used here for learning purposes.)
Step 2: Estimate the Contaminant Generation Rate
Assume the printing equipment emits VOCs at a predictable rate.
Example assumption:
- VOC generation rate = 120,000 µg/hour
Convert to seconds for consistency:
- 120,000 µg/hour ÷ 3600 ≈ 33.3 µg/s
This represents the contaminant mass generated inside the space per second.
Step 3: Apply Steady-State Mass Balance Logic
At steady state:
- Contaminant generation rate = contaminant removal rate
For ventilation-based removal:
Removal rate = Outdoor air flow × Indoor concentration
Mass balance relationship (conceptual form):
Generation = Ventilation flow × Acceptable concentration
Step 4: Calculate Required Outdoor Air Flow
Required outdoor air flow (Q):
Q = Generation rate ÷ Acceptable concentration
Substitute values:
- Q = 33.3 µg/s ÷ 500 µg/m³
- Q = 0.0666 m³/s
Convert to L/s:
- 0.0666 m³/s × 1000 = 66.6 L/s
Convert to m³/h:
- 66.6 × 3.6 ≈ 240 m³/h
Result:
Minimum outdoor air required ≈ 67 L/s (240 m³/h)
Step 5: Compare with a VRP-Based Ventilation Rate
Now compare this IAQP-based result with a typical VRP calculation.
Assume representative VRP values:
- Rp = 10 L/s per person
- Ra = 0.3 L/s per m²
VRP calculation:
- People component = 10 × 2 = 20 L/s
- Area component = 0.3 × 80 = 24 L/s
Total VRP outdoor air:
- 20 + 24 = 44 L/s
Step 6: Interpret the Results
Comparison:
- VRP result = 44 L/s
- IAQP result = 67 L/s
Key observation:
- In this case, IAQP requires MORE outdoor air than VRP, not less.
This is a critical insight.
IAQP does not automatically reduce ventilation.
It aligns ventilation with actual contaminant behavior.
Step 7: How IAQP Enables Smarter Design Decisions
Now consider an improvement:
If local exhaust or improved filtration reduces VOC emissions by 40%, the new generation rate becomes:
- 33.3 µg/s × 0.6 ≈ 20 µg/s
Recalculate:
- Q = 20 ÷ 500 = 0.04 m³/s
- Q = 40 L/s (144 m³/h)
Now:
- IAQP with source control ≈ 40 L/s
- VRP ≈ 44 L/s
Result:
- Comparable ventilation
- Better IAQ control
- Lower energy penalty than simply increasing outdoor air
This illustrates the real strength of IAQP:
it rewards source control and targeted solutions.
Key Takeaway
IAQP uses mass balance to tie ventilation requirements directly to contaminant generation and acceptable concentration limits.
It does not guarantee lower airflow than VRP, but it allows ventilation decisions to reflect actual indoor air quality behavior.
When contaminant sources are identifiable and controllable, IAQP enables more rational and defensible design choices.
Reflection Question
In your projects, have you encountered spaces where ventilation was increased even though the dominant IAQ issue was related to a specific source rather than occupancy?
Pause here and reflect on how a simple mass balance calculation could have changed the design approach.