Couverture de Desk Fans vs. Giant Chillers: Rethinking HVAC Through PECs - #OT49

Desk Fans vs. Giant Chillers: Rethinking HVAC Through PECs - #OT49

Desk Fans vs. Giant Chillers: Rethinking HVAC Through PECs - #OT49

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This week, we dive into a groundbreaking paper published in the Journal of Energy and Buildings titled A Methodology for Evaluating the Effects of Personalized Environmental Control Systems (PECs) on Building Whole Life Carbon CO2 Emissions, to explore a question that fundamentally challenges how we think about building design and decarbonisation: What if the single biggest opportunity to slash carbon emissions in buildings isn't just improving central HVAC systems—but radically downsizing them by giving occupants personalised control over their immediate thermal environment? For decades, we've conditioned entire office volumes to a uniform temperature, chasing an average comfort level that doesn't actually exist for individuals. Half the room wears sweaters while the other half sweats. It's energy intensive, carbon intensive, and ironically, nobody is truly comfortable. Personalized Environmental Control Systems (PEX)—think heated chairs, desk fans, local diffusers—flip this model. By controlling the microenvironment around each occupant, we can relax ambient set points, reduce operational energy, and potentially downsize massive central equipment. But here's the blind spot this paper addresses for the first time: what about whole life carbon? Key Topics Discussed: The Power Draw Problem: PEX devices with moderate corrective capacity (offsetting set points by 2 to 4 degrees) and low maximum power use (70 watts or less) achieve the best environmental balance. High capacity PEX drawing 80 to 100 watts start dumping heat back into the space, creating internal heat gain that puts load back onto the central cooling system, wiping out energy savings. If you oversize the personal devices, you lose. The Silent Killer: Standby Power: Most PEX studies completely ignore standby power. But in the real world, devices sit plugged in, drawing a trickle of power even when nobody is at the desk. The authors modelled a modest 5 watt standby draw per unit. For low capacity PEX like simple desk fans, that 5 watt standby completely wiped out operational energy savings. Why? Because the central system is already efficient enough to handle mild conditions, meaning the PEX spends massive hours on standby, leaking energy during idle time. Product developers must design ultra low power systems with zero standby draw. The Courage to Downsize: The massive carbon savings are locked in on day one when designers physically downsize the central HVAC infrastructure. Smaller air handling units, smaller chillers, smaller duct diameters, reduced suspended ceiling heights, lower floor to floor heights. These embodied carbon savings are permanent and non negotiable. Standby power cannot erase them. But if you install PEX and still install a massive full size central VAV system just in case, you're missing the point and leaving massive carbon savings on the table. A methodology for evaluating the effects of personalized environmental control systems (PECS) on building whole-life CO2 emissions https://doi.org/10.1016/j.enbuild.2026.117565 The Air Quality Matters Podcast in Partnership with Particles Plus https://particlesplus.com/ Eurovent (https://www.eurovent.eu/) - Aico (https://www.aico.co.uk/) - Lindab (https://www.lindab.ie/) - S&P UK (https://www.solerpalau.com/en-uk/) The One Take Podcast in Partnership with SafeTraces (https://www.safetraces.com/) - Inbiot (https://www.inbiot.es/?utm_campaign=simon&utm_source=airqualitymatters&utm_medium=podcast) - Farmwood (https://farmwood.co.uk/) - iE Electronics (https://www.eielectronics.ie/) iAir Group (https://iair-group.com/) and Zehnder Group https://www.zehndergroup.com/en 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 One Take Format and Personalized Environmental Control 00:01:11 The Dumb HVAC Problem: Why We Condition Entire Rooms for Nobody 00:01:39 The PEX Solution: Localized Control and Relaxed Ambient Temperatures 00:02:24 The Blind Spot: What About Whole Life Carbon? 00:03:08 The Methodology: Copenhagen Office Building Simulation and LCA 00:03:56 Retrofit Scenario Results: 50% Energy Reduction Without Physical Changes 00:04:39 Design Scenario Magic: Downsizing Central Systems for Massive Carbon Savings 00:05:53 The Catch: Maximum Power Draw and the Standby Power Silent Killer 00:07:45 The Embodied Carbon Lock-In: Why Design Scenarios Still Win 00:08:30 The So What: Whole Life Thinking and the Future of Human-Centric Buildings
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