From Thermal Comfort to Heat Stress: Buildings That Don't Overheat with Paul O'Sullivan - #102

In this essential episode, we sit down with Paul O'Sullivan, lecturer in Sustainable Energy Engineering at MTU and co-lead of the MESO Research Group, to explore one of the most pressing—yet often overlooked—challenges in our built environment: how do we design buildings that don't overheat? Paul brings deep expertise in low-energy demand-side technologies, building retrofit strategies, indoor thermal environments, and ventilative cooling. His work sits at the fascinating intersection of thermal comfort, air quality, decarbonization, and the future resilience of our homes, schools, and workplaces. The Central Question We've spent decades designing buildings to be thermally comfortable in winter—airtight, well-insulated, energy-efficient. But in doing so, have we created a new problem? As our climate warms and our buildings become better at keeping heat in, how do we ensure they can also let heat out when they need to—without resorting to energy-intensive air conditioning? Key Topics Discussed: Thermal Comfort vs. Overheating: What's the difference between discomfort and a genuine health risk? Why overheating is not just about temperature, but about duration, vulnerability, and the capacity of a building to respond. The Unintended Consequences of Energy Efficiency: How our drive to decarbonize heating has created buildings that struggle to cool—and why Ireland's cooling season now starts in March. The Cooling Ladder: A design philosophy for tackling overheating—starting with prevention (solar shading, orientation), then modulation (thermal mass, phase-change materials), then dissipation (ventilative cooling), and only finally, supplementary mechanical cooling. Ventilative Cooling and the New CEN Technical Specification: How natural and mechanical ventilation can provide free, sustainable cooling—and why the European standard Paul helped develop is a game-changer for designers. The Performance Gap: Why buildings that look great on paper often overheat in reality—and why simulation tools are struggling to keep pace with the rate of climate change and building innovation. Agency and Adaptation: The power of openable windows, external shutters, and giving occupants control. Why buildings that allow people to adapt perform better—and why we've lost some of that agency in modern construction. This is a conversation about trade-offs, resilience, and the path forward. It's about recognizing that comfort isn't a luxury—it's a fundamental aspect of health, well-being, and productivity. And it's about designing buildings that work with their climate, not against it. DESCRIPTION: HOST: Simon Jones: https://www.linkedin.com/in/simon-air-quality-matters/ GUEST: Paul O’Sullivan - https://www.linkedin.com/in/paul-d-o-sullivan-441b9023/ The Air Quality Matters Podcast in Partnership with Zehnder Group - Farmwood - Eurovent- Aico - Aereco - Ultra Protect - The One Take Podcast in Partnership with SafeTraces and Inbiot Do check them out in the links and on the Air Quality Matters Website. If you haven't checked out the YouTube channel its here. Do subscribe if you can, lots more content is coming soon. Chapters 00:00:00 Introduction: Paul O'Sullivan and the Science of Thermal Comfort 00:02:18 Thermal Comfort vs Air Quality: Different Lenses on Indoor Environment 00:04:07 Maslow's Hierarchy: Is Comfort a Luxury or a Necessity? 00:05:34 The Decarbonization Dilemma: Energy Efficiency vs Thermal Comfort 00:09:31 Expectation and Adaptation: The Psychology of Thermal Experience 00:14:29 The Cooling Ladder: A Design Philosophy for Passive Solutions 00:15:44 Where Are We With the Science? Progress and Gaps in Thermal Comfort 00:24:07 Defining Overheating: From Discomfort to Health Risk 00:24:15 The Measurement Challenge: 20 Different Ways to Assess Overheating 00:27:52 Conditioned vs Free-Floating: Two Different Overheating Problems 00:37:09 Ireland's Paradox: Overheating in a Cool Climate 00:37:16 The Building as Battery: Thermal Mass and Night Cooling Strategies 00:52:55 The Performance Gap: Why Simulations Don't Match Reality 01:00:40 The Data Desert: Why We Don't Know How Our Buildings Perform 01:20:50 Behavior and Technology: The Human Element in Building Performance 00:49:07 Ventilation's Role: Free Cooling Potential and Air Quality Trade-offs 00:56:08 Heat Recovery Dilemma: Winter Efficiency vs Summer Cooling Needs 01:10:20 Hybrid Solutions: The Future of Resilient Cooling 01:40:55 Climate Shelters: Schools as Community Heat Wave Refuges 01:43:36 Double Jeopardy: When Heat Waves Meet Power Outages and Poor Air Quality 01:26:51 The MESO Research Group: From Ventilative Cooling to Citizen Science 01:29:44 Window Aerodynamics: The Forgotten Performance Metric 01:34:55 European Standards: Translating Research into Design Tools 01:48:26 Citizen Science: Engaging Occupants in Building Performance Research 01:51:30 The Path Forward: Data, Standards, and Human-Centered Design