EPISODE · May 4, 2026 · 1H 2M
The Physics of Fresh Air: Natural Ventilation Still Works in 2025 - Ben Jones #115
from Air Quality Matters · host simon jones
This week, we sit down with Ben Jones, Associate Professor at the University of Nottingham and one of the lead authors of AM10, CIBSE's guide to natural ventilation in non-domestic buildings, to explore a question that fundamentally challenges how we think about ventilation strategy: What if the oldest approach to ventilation—natural airflow—still has a critical role to play in some of the most advanced buildings we're designing today, and what if we've been making the same mistakes for decades because we never really understood the fundamentals? After a decade in development, AM10 has been completely rewritten for 2026—not just to update the maths, but to make natural ventilation accessible, understandable, and practical for everyone from salespeople to architects to engineers who need to know whether natural ventilation is even feasible for their project before they waste time and money chasing the wrong solution. Key Topics Discussed: Why AM10 Needed Rewriting: The 2005 version was intimidating, dense, and assumed too much prior knowledge. The 2026 version is structured in layers—chapter two is designed so that anyone, from a student to a salesperson, can understand the basic physics. If you want the deep maths, it's there. If you just need to know whether natural ventilation will work for your building, you can get that answer quickly. The Physics Made Simple: Warm air rises. Pressure differences drive flow. Wind complicates everything. But somewhere on every facade, there's a neutral pressure level where the sign flips—where air stops coming in and starts going out. Controlling that point is the essence of natural ventilation design. Get it wrong, and your building doesn't breathe. Effective Area vs Free Area: One of the biggest changes in AM10 is how openings are measured. Combining free area with discharge coefficients into a single effective area metric forces window manufacturers to actually test their products aerodynamically and gives engineers a real number they can design with. No more fudging the geometry. Single-Sided Ventilation Gets Smarter: The old equations were too simplistic. The new version accounts for recirculation zones in large openings—where air comes in at the bottom, goes out at the top, and mixes in the middle. It accounts for wind-driven turbulent mixing. The result: better-sized openings that won't leave buildings overheating in summer GUEST: Ben Jones Associate Professor, University of Nottingham | Lead Author, CIBSE AM10 https://www.linkedin.com/in/benjamin-jones-0686a214/ CIBSE AM10: Natural Ventilation in Non-Domestic Buildings https://www.cibse.org/knowledge-research/knowledge-portal/am10-natural-ventilation-in-non-domestic-buildings-2026-pdf/ The Air Quality Matters Podcast in Partnership with Particles Plus https://particlesplus.com/ Lindab (https://www.lindab.ie/) - Eurovent (https://www.eurovent.eu/) - Aico (https://www.aico.co.uk/) The One Take Podcast in Partnership with SafeTraces (https://www.safetraces.com/) and Inbiot (https://www.inbiot.es/?utm_campaign=simon&utm_source=airqualitymatters&utm_medium=podcast) Do check them out in the links and on the Air Quality Matters Website. (https://www.airqualitymatters.net/podcast) If you haven't checked out the YouTube channel its here (https://www.youtube.com/@airqualitymatters-SimonJones). Do subscribe if you can, lots more content is coming soon. Chapters 00:00:00 Introduction: The Return of Air Quality Matters 00:02:14 The Genesis of AM10: A 20-Year Evolution 00:06:03 From PhD to Practice: Ben's Natural Ventilation Journey 00:08:34 The Philosophy Behind AM10: Making Physics Accessible 00:10:14 Why Ventilate: Sizing for Summer, Surviving Winter 00:11:19 The Physics of Buoyancy: When Hot Air Actually Rises 00:13:09 When Design Meets Reality: The Complexity Challenge 00:14:41 The Feasibility Question: Is Natural Ventilation Right for Your Building? 00:15:48 The Neutral Pressure Level: Where Physics Flips Sign 00:16:50 Wind's Wild Card: Adding Complexity to Buoyancy 00:18:44 The Case for Natural Ventilation: Energy, Carbon, and Human Connection 00:19:17 The Adaptive Comfort Advantage: When Control Matters More Than Precision 00:23:19 Natural Ventilation Through the Ages: Ancient Wisdom Meets Modern Buildings 00:31:59 The Outdoor Air Reality: When Fresh Air Isn't Fresh 00:42:15 The Great Automation Failure: 3200 PPM in London's Smartest Building 00:35:04 What Changed in 2026: New Physics and Effective Area 00:39:25 From Spreadsheets to Software: How AM10 Gets Used 00:40:40 Designed for Everyone: Who Should Read AM10 00:42:40 The Sensor Revolution: Transparency in Natural Ventilation Performance 00:54:26 Hot Climate Solutions: Thermal Mass and Ancient Technologies 00:55:47 The Fundamental Design Principle: Natural Ventilation from Day One 00:56:43 Getting Your Hands on AM10: Access, Training, and the Future
What this episode covers
This week, we sit down with Ben Jones, Associate Professor at the University of Nottingham and one of the lead authors of AM10, CIBSE's guide to natural ventilation in non-domestic buildings, to explore a question that fundamentally challenges how we think about ventilation strategy: What if the oldest approach to ventilation—natural airflow—still has a critical role to play in some of the most advanced buildings we're designing today, and what if we've been making the same mistakes for decades because we never really understood the fundamentals? After a decade in development, AM10 has been completely rewritten for 2026—not just to update the maths, but to make natural ventilation accessible, understandable, and practical for everyone from salespeople to architects to engineers who need to know whether natural ventilation is even feasible for their project before they waste time and money chasing the wrong solution. Key Topics Discussed: Why AM10 Needed Rewriting: The 2005 version was intimidating, dense, and assumed too much prior knowledge. The 2026 version is structured in layers—chapter two is designed so that anyone, from a student to a salesperson, can understand the basic physics. If you want the deep maths, it's there. If you just need to know whether natural ventilation will work for your building, you can get that answer quickly. The Physics Made Simple: Warm air rises. Pressure differences drive flow. Wind complicates everything. But somewhere on every facade, there's a neutral pressure level where the sign flips—where air stops coming in and starts going out. Controlling that point is the essence of natural ventilation design. Get it wrong, and your building doesn't breathe. Effective Area vs Free Area: One of the biggest changes in AM10 is how openings are measured. Combining free area with discharge coefficients into a single effective area metric forces window manufacturers to actually test their products aerodynamically and gives engineers a real number they can design with. No more fudging the geometry. Single-Sided Ventilation Gets Smarter: The old equations were too simplistic. The new version accounts for recirculation zones in large openings—where air comes in at the bottom, goes out at the top, and mixes in the middle. It accounts for wind-driven turbulent mixing. The result: better-sized openings that won't leave buildings overheating in summer GUEST: Ben Jones Associate Professor, University of Nottingham | Lead Author, CIBSE AM10 https://www.linkedin.com/in/benjamin-jones-0686a214/ CIBSE AM10: Natural Ventilation in Non-Domestic Buildings https://www.cibse.org/knowledge-research/knowledge-portal/am10-natural-ventilation-in-non-domestic-buildings-2026-pdf/ The Air Quality Matters Podcast in Partnership with Particles Plus https://particlesplus.com/ Lindab (https://www.lindab.ie/) - Eurovent (https://www.eurovent.eu/) - Aico (https://www.aico.co.uk/) The One Take Podcast in Partnership with SafeTraces (https://www.safetraces.com/) and Inbiot (https://www.inbiot.es/?utm_campaign=simon&utm_source=airqualitymatters&utm_medium=podcast) Do check them out in the links and on the Air Quality Matters Website. (https://www.airqualitymatters.net/podcast) If you haven't checked out the YouTube channel its here (https://www.youtube.com/@airqualitymatters-SimonJones). Do subscribe if you can, lots more content is coming soon. Chapters 00:00:00 Introduction: The Return of Air Quality Matters 00:02:14 The Genesis of AM10: A 20-Year Evolution 00:06:03 From PhD to Practice: Ben's Natural Ventilation Journey 00:08:34 The Philosophy Behind AM10: Making Physics Accessible 00:10:14 Why Ventilate: Sizing for Summer, Surviving Winter 00:11:19 The Physics of Buoyancy: When Hot Air Actually Rises 00:13:09 When Design Meets Reality: The Complexity Challenge 00:14:41 The Feasibility Question: Is Natural Ventilation Right for Your Building? 00:15:48 The Neutral Pressure Level: Where Physics Flips Sign 00:16:50 Wind's Wild Card: Adding Complexity to Buoyancy 00:18:44 The Case for Natural Ventilation: Energy, Carbon, and Human Connection 00:19:17 The Adaptive Comfort Advantage: When Control Matters More Than Precision 00:23:19 Natural Ventilation Through the Ages: Ancient Wisdom Meets Modern Buildings 00:31:59 The Outdoor Air Reality: When Fresh Air Isn't Fresh 00:42:15 The Great Automation Failure: 3200 PPM in London's Smartest Building 00:35:04 What Changed in 2026: New Physics and Effective Area 00:39:25 From Spreadsheets to Software: How AM10 Gets Used 00:40:40 Designed for Everyone: Who Should Read AM10 00:42:40 The Sensor Revolution: Transparency in Natural Ventilation Performance 00:54:26 Hot Climate Solutions: Thermal Mass and Ancient Technologies 00:55:47 The Fundamental Design Principle: Natural Ventilation from Day One 00:56:43 Getting Your Hands on AM10: Access, Training, and the Future
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The Physics of Fresh Air: Natural Ventilation Still Works in 2025 - Ben Jones #115
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