To Lower Emissions, Add Air

Outdoor Kitchen at Hwange, Zimbabwe by Michael Sprague on Flickr

Our ongoing project goal at ARC is to create a cookstove that makes only 150 mg/mjd of PM 2.5 (Tier 3), so that when Air Changes per Hour (ACH) are tripled we are sure that PM 2.5 emissions are below 64 mg/mjd (Tier 4).

Under ISO/TR 19867-3 voluntary performance targets, a biomass cookstove emitting 150 mg/MJd of PM2.5 can reach Tier 4 compliance in real-world settings by leveraging high ACH. Doubling the ventilation rate (ACH) cuts pollutant concentrations and exposure metrics in half, allowing higher emission rates to satisfy health-based tier thresholds through atmospheric dilution. [1]

Principles of ACH Scaling in ISO 19867-3

• Inverse Proportionality: Indoor concentration scales directly as 1/ACH. Doubling air turnover halves the average PM2.5 concentration for an identical emission rate. [1]
• Baseline vs. Enhanced ACH: Standard laboratory metrics assume a baseline (often 15 ACH). Moving to high-ventilation conditions (such as ≥ 30—100 ACH via open architecture, outdoor verandas) shifts the allowable mass emission cap upward for a target health tier. [1, 3, 4]
• Dilution Threshold: At elevated ACH values, a stove emitting 150 mg/MJd effectively yields local operator exposure levels equivalent to stricter low-emission caps in tight, unventilated rooms. [2]

Implementation Strategies

• Architectural Adjustments: Cooking in semi-open spaces (e.g., roofed kitchens with half-walls or wide eaves) routinely achieves ~ 42 ACH or higher, multiplying dilution capacity. [1]
• Outdoor Integration: Transitioning to cooking fully outdoors moves ACH into the 84–100 ACH range, making a 150 mg/MJ PM2.5 profile comfortably meet Tier 4 health-exposure criteria. [2]

References

[1] Air Exchange Rates and the ISO Tiers of Performance -aprovecho.org

[2] Metered Methodology Health Methods – mecs.uk.org

[3] Using Air Changes to Meet ISO PM2.5 Performance Targets -aprovecho.org

[4] Video: Test Kitchen 2021 Natural Draft Hood -aprovecho.org

ISO/TR 19867-3:2018 Part 3: Voluntary performance targets for cookstoves based on laboratory testing -iso.org

This article was written by Gemini AI using the linked references, read and edited by Dean Still

Image licensed under CC BY-SA 2.0