Air Quality Matters

This week, we dive into a fascinating full scale experimental study published in the Journal of Indoor Environments titled Indoor Laundry Drying: Full Scale Determination of Water Emissions Rates and Impact on Thermal Comfort, to explore a question that fundamentally challenges how we think about energy efficiency advice: What if the single most common energy saving recommendation—drying clothes indoors instead of using a tumble dryer—is actually forcing us to turn up the heating and creating serious indoor air quality problems we've never properly quantified?

Across Europe, particularly during winter months, over 60% of laundries are dried indoors in countries like Poland, Hungary, Czech Republic, and Finland. In France alone, tumble dryers account for 20% of average annual household electricity consumption. The advice is clear: save energy, ditch the dryer, hang your clothes on a rack. But while we know this practice coincides with dust mite growth and high concentrations of airborne mould spores due to rising moisture, the actual kinetics—how much water is emitted, exactly when, and how it physically changes the room's environment—has never been properly quantified in a controlled, full scale way. Until now.

Key Topics Discussed:

The Cotton Culprit: A typical four kilogram load of dry cotton towels will hold about two litres of water after a standard 40 degree wash. Spinning faster than 1,000 RPM doesn't extract much more water. Cotton is the real moisture problem when it comes to indoor drying.

Three Phases of Drying: By constantly weighing the drying rack and monitoring room humidity in a controlled 40 cubic metre experimental chamber, researchers discovered water emission isn't a slow, steady trickle. It happens in three distinct phases: the initial burst (first two hours, exceeding 100 grams per hour, peaking at 360 grams per hour), the steady state (10 to 25 hours, stabilizing around 50 grams per hour as the room becomes humid), and the exhaustion phase (beyond 30 hours, gradually tailing off).

The Temperature Drop Problem: Evaporating water is endothermic—it literally sucks heat out of surrounding air. As laundry dried, room temperature dropped significantly, recording drops between half a degree and 3.8 degrees Celsius. If your room starts off quite dry, the initial humidity gradient is higher, water evaporates faster, and the temperature drop is even sharper.

The Thermal Comfort Failure: When researchers mapped these temperature and humidity changes onto standard thermal comfort charts like ASHRAE 55, the results were clear: passive indoor laundry drying actively drags room conditions right out of acceptable comfort zones. Even wearing thicker winter clothes only partially mitigates the discomfort.

The Heating Paradox: If we're told to avoid tumble dryers to save energy, but doing so drops the temperature of our living spaces by almost four degrees, what do we inevitably do? We turn up the central heating. The energy saving advice creates a new energy consumption problem.

Mitigation Strategies: We need to be strategic about where we dry clothes. Positioning drying racks in bathrooms close to air extraction points can avoid spreading moisture and physically cooling down living and sleeping spaces. The first hour or two of clothes drying is particularly critical for moisture emission.

Indoor laundry drying: Full-scale determination of water emission rate and impact on thermal comfort https://doi.org/10.1016/j.indenv.2025.100089

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/)

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) - Farmwood (https://farmwood.co.uk/)

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 the Mundane Routine of Laundry
00:00:58 The Energy Paradox: Why We're Told to Ditch the Tumble Dryer
00:02:21 The Cotton Culprit: How Much Water Are We Really Releasing?
00:03:03 The Three Phases of Drying: From Burst to Exhaustion
00:04:04 The Endothermic Effect: Why Drying Clothes Literally Cools Your Room
00:04:40 The Thermal Comfort Crisis: When Laundry Drags You Out of the Comfort Zone
00:05:04 The Heating Trap: Trading Tumble Dryer Energy for Central Heating
00:05:26 The Strategic Solution: Building Physics Meets Laundry Day
00:06:01 Closing Thoughts: Treating Mundane Tasks with Building Physics Respect

This week, we sit down with Rachel Hodgdon, President and CEO of the International WELL Building Institute (IWBI), to explore a question that fundamentally challenges how we think about healthy buildings: What if the single biggest barrier to transforming the built environment isn't our lack of knowledge about indoor environmental quality—but our inability to communicate complexity in ways that inspire action rather than paralysis?

Key Topics Discussed:

- Meeting People Where They Are: How do you communicate the holistic vision of indoor environmental quality without overwhelming stakeholders? Rachel explains why IWBI always starts with what matters most to the person across the table. If you're talking to a CEO, lead with recruitment, retention, and productivity. If you're talking to a facilities manager, talk about deferred maintenance and occupant satisfaction.
- Incremental Progress Over Perfection: Unlike many certifications that reward only finished projects, WELL is designed to celebrate incremental progress. WELL at Scale has proven that clients don't move in straight lines. They might start with one landmark building, then progress toward equity ratings across portfolios, or spend a year focusing on just a few features. One point earned toward any designation now counts toward full certification.
- Performance Testing Reveals the Invisible: WELL is proudly performance based. After a project is complete and occupied, third party testers measure air quality, water quality, thermal comfort, lighting, and sound. Buildings that fail must retest. Rachel shares stories of projects that discovered elevator shafts pumping unfiltered air into lobbies, printers off gassing VOCs, and contaminated soil beneath indoor plants. Without performance testing, these issues would never have been found.
- Residential and Affordable Housing: WELL for Residential launched as a pilot expecting 3,000 enrollments. It received 30,000 straight out of the gate, including 22,000 military homes. Rachel highlights a groundbreaking partnership with Enterprise Community Partners, embedding WELL into the Enterprise Green Communities standard for affordable housing. This means WELL is now legislated in over 50 percent of US states for affordable housing, ensuring the people most in need benefit first, not last.

GUEST:

Rachel Hodgdon

President and CEO, International WELL Building Institute

https://www.linkedin.com/in/rachelhodgdon/

IWBI https://www.wellcertified.com/

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/)

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) - Farmwood (https://farmwood.co.uk/)

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: Meeting Rachel Hodgdon and the IWBI Mission
00:02:50 The Complexity Challenge: Communicating Holistic Indoor Environmental Quality
00:03:53 One WELL: Simplifying Entry Points and Rewarding Incremental Progress
00:07:59 The Apple Approach: Building a Unified Ecosystem for Healthy Buildings
00:09:40 Evolution from Green Buildings: The Second Wave of Sustainability
00:12:29 Authority and Accessibility: Balancing Technical Rigor with Broad Appeal
00:21:37 Meeting People Where They Are: The Art of Advocacy and Communication
00:31:47 The Power of Experience: Case Studies and Exemplar Spaces
00:36:05 Beyond Headquarters: Reaching the Long Tail of the Built Environment
00:39:27 WELL at Scale and Existing Buildings: Flexibility for Portfolios
00:40:58 Military Housing and Affordable Housing: 30,000 Homes and Counting
00:55:56 The Australian Success Story: What's Happening Down Under
00:58:54 Navigating Headwinds: DEI, Sustainability, and the Great Rebrand
01:05:05 Performance Testing and Accountability: Making the Invisible Visible
01:23:23 The ROI of Healthy Buildings: Retention, Recruitment, and Productivity
01:20:48 Neurodiversity and Universal Design: Designing for the Extremes Benefits Everyone
01:42:45 The Medical Gap: Why Doctors Don't Ask About Your Home
01:47:15 The Future: Continuous Monitoring and the Next Ten Years
01:50:33 Closing Thoughts: Data is Knowledge, Knowledge is Power

This week, we dive into a fascinating paper from Douglas Booker published in the journal Athermira titled Unstable Air: How COVID-19 Remade Knowing Air Quality in School Classrooms, to explore a question that fundamentally challenges how we think about indoor air quality intervention: What if the single most important lesson from the pandemic isn't that we need to measure air quality—but that we need to fundamentally rethink who is responsible for fixing it, and whether our solutions are creating entirely new problems?

This paper offers a rare behind the scenes look at an applied indoor air quality research project that got completely hijacked and subsequently reshaped by the global pandemic. It examines how our understanding of what makes air good or bad is not just a scientific fact but something that shifts based on society, politics, and in this case, a novel virus.

Key Topics Discussed:

The Original Mission: Before COVID, researchers deployed sophisticated air quality monitors into 20 school classrooms across England and Wales to measure traditional pollutants—ultrafine particles, nitrogen dioxide, VOCs—things infiltrating from outside or off-gassing from furniture. The goal was straightforward: measure the bad stuff and see how effectively air cleaners could scrub it away.

The Pandemic Pivot: When COVID hit, the entire narrative flipped. Suddenly the greatest source of indoor air pollution wasn't traffic or cleaning products—it was human breathing. We became the source of contamination. The project had to adapt, but hit a microscopic hurdle: how do you actually measure a virus in the air when your monitors just count particles without telling you what they are?

The Carbon Dioxide Proxy: Unable to isolate viral particles, researchers pivoted to a reliable proxy: carbon dioxide. By watching CO2 levels rise and fall, they could measure how much air in the room had already been in someone else's lungs and calculate ventilation rates. Pre-COVID data showed classrooms regularly exceeded recommended limits. But graphs alone don't change behaviour.

The Wells Riley Translation: To translate numbers into risk, researchers used the Wells Riley equation to calculate airborne infection probability. The results were powerful: in one scenario, low ventilation created an 80% probability of infection. Simply increasing airflow to 100 cubic metres per hour dropped that to 40%. Small ventilation improvements created massive risk reductions.

The Milk Out of Your Tea Problem: In the rush to dilute the virus by opening windows, we might be trading one severe health risk for another. If your school sits on a busy urban road, opening windows drops CO2 and virus risk but floods classrooms with toxic traffic fumes. Running a portable air cleaner with windows wide open to a polluted street is like trying to take milk out of your tea.

The Inequality of Personal Responsibility: By handing out CO2 monitors and telling teachers to manage windows, the government effectively individualised air quality. The message: here's a blinking light, fixing it is your responsibility.

Unstable air: How COVID-19 remade knowing air quality in school classrooms https://www.researchgate.net/publication/378714580_Unstable_air_How_COVID-19_remade_knowing_air_quality_in_school_classrooms

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/)

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) - Farmwood (https://farmwood.co.uk/)

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 Unstable Air
00:01:27 The Outdoor Air Quality Paradox: Why We Ignored Indoor Spaces
00:02:30 The Original Mission: Measuring Classroom Pollutants in 2020
00:03:18 The Pandemic Pivot: When Humans Became the Pollution Source
00:03:58 The Measurement Problem: You Can't See a Virus in Particle Counts
00:04:33 The CO2 Proxy Solution: 150 Years of Measuring Bad Air
00:05:57 The Wells-Riley Equation: Translating Numbers Into Infection Risk
00:07:18 From Concern to Care: The Ethical Intervention That Worked
00:08:25 The Window Paradox: Trading Viral Risk for Toxic Fumes
00:09:35 The Inequality Problem: When Air Quality Becomes Personal Responsibility
00:10:23 The Critical Future: Building Better Pandemic Infrastructure

This week, we sit down with Christopher Mueller, Global Director of the High Purity Segment at AAF International (American Air Filters), to explore a question that fundamentally challenges how we think about indoor air quality: What if the single biggest gap in our approach to healthy buildings isn't particulate filtration—but our complete failure to address the invisible chemical soup we're breathing every single day?

Chris brings over 40 years of deep expertise in environmental air quality and gas phase air filtration. With more than 200 peer reviewed papers, hundreds of seminars, and co authorship of major industry handbooks including the NAFSA Air Filtration Handbook and ASHRAE standards, Chris has testified at OSHA on indoor air quality standards and consulted with governments worldwide. He is the former chair of ASHRAE 145, which developed the first standard for assessing gas phase air filtration media performance, and remains a member of key technical committees shaping the future of air cleaning globally.

Key Topics Discussed:

The Fundamental Difference: Particulate filtration is catching. Gas phase filtration is reacting. Gases move by diffusion, from high to low concentration, and removing them requires adsorption—getting molecules out of the air and onto the surface of materials like activated carbon, alumina, or zeolites. Unlike particle filters, gas phase filters don't fill up. They run out. They lose effectiveness over time, and there's no pressure gauge to tell you when.

Surface Area Is Everything: Most activated carbons have around 1100 square meters per gram of surface area. That's not the exterior of the pellet. That's the interior pore structure. Volatile organic compounds get inside, condense back into liquid form, and stay there. The physics of adsorption depend on molecular weight, concentration, residence time, and contact efficiency. You need the air to touch the adsorbent before it exits the filter.

One Filter Won't Do It All: You can't use one type of gas phase media to remove everything. Basic activated carbon handles many organic compounds. Acid gases like sulfur dioxide require chemically treated carbon. Ammonia requires another type entirely. Think of it like particulate filtration: pre filter, intermediate filter, final filter. Same logic applies to chemicals.

The Four Global Markets: Corrosion control accounts for 60 to 65 percent of the global gas phase filtration market, driven by electronics manufacturing, data centers, and industrial facilities where chemical contamination voids equipment warranties. Wastewater odor control is second. Indoor air quality in commercial buildings is third. Airborne molecular contamination in semiconductor manufacturing is fourth. The total global market is approximately $2 billion and growing at 5.5 percent annually.

GUEST:

Christopher Mueller

Global Director, High Purity Segment, AAF International

https://www.linkedin.com/in/chrismullerconsulting/

AAF International https://www.aafintl.com/

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/)

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) - Farmwood (https://farmwood.co.uk/)

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: Meeting the Gas Phase Air Cleaning Guru
00:02:51 The Fundamental Difference: Particulate vs Gas Phase Filtration
00:09:29 The Science of Adsorption: How Gas Phase Filters Actually Work
00:17:10 The Swiss Cheese Approach: Multi-Stage Gas Phase Filtration
00:23:20 Form Factors and Physical Products: From Pleats to Packed Beds
00:28:00 Precision and Specificity: Can You Target Individual Chemicals?
00:34:20 The Four Markets: Where Gas Phase Filtration Is Applied Today
00:38:24 Corrosion Control: The Hidden Giant of Gas Phase Filtration
00:44:00 Indoor Air Quality and the IAQP Opportunity
00:48:38 The Commercial Reality: Why Gas Phase Is Still a Hard Sell
01:13:49 Materials and Sustainability: What Is Activated Carbon Made From?
01:24:13 The Path Forward: Education, Standards, and Market Evolution
01:36:35 Closing Thoughts: Making the Invisible Visible

This week, we dive into a groundbreaking computational fluid dynamics study from KTH Royal Institute of Technology in Sweden that fundamentally challenges how we think about portable air cleaners in care homes: What if the single most important decision about air cleaning isn't which device you buy—but where you put it in the room?

During the height of the COVID-19 pandemic, care homes experienced devastating mortality rates among elderly residents. These environments are uniquely challenging—combining elements of healthcare facilities with residential living spaces, housing vulnerable populations who spend prolonged periods indoors with limited mobility and compromised immune systems. Portable air cleaners emerged as a promising, accessible solution. But does it actually matter where you place them? Can you just plug them in wherever the cable reaches and assume the job is done? And critically, will the airflow create cold drafts that make elderly residents so uncomfortable they simply switch the device off?

Key Topics Discussed:

The Care Home Challenge: Why care homes represent such a unique built environment challenge. Vulnerable populations with reduced mobility, chronic illnesses, compromised thermoregulation making them sensitive to drafts, and prolonged indoor exposure without control over their immediate environment. Any intervention has to work within these constraints.

The 74% Variation Problem: Using computational fluid dynamics simulations, researchers tested the same portable air cleaner in nine different locations within a typical care home room. The result: placement alone created a 74% variation in infection risk. Same machine, same room, same people—completely different outcomes based purely on where the device sat.

The Worst Case Scenario: In one placement configuration, positioning the air cleaner near the infected healthcare worker created a powerful airflow jet that actively transported exhaled virus particles directly into the breathing zone of the elderly patient. The infection risk skyrocketed to 85.9%. The air cleaner didn't just fail—it made things dramatically worse.

The Best Case Scenario: Placing the air cleaner in the centre of the room created the lowest infection risk—75 to 86% reduction compared to no air cleaner—by forming an invisible air barrier between occupants. But it's completely impractical due to tripping hazards in environments with wheelchairs, walking frames, and elderly residents with limited mobility.

The Thermal Comfort Win: Across all tested scenarios, draft rates remained below the 10% discomfort threshold. This is critical. There's no point achieving perfect air quality if the occupant is freezing cold and turns the device off. The study proves portable air cleaners can reduce infection risk without compromising thermal comfort—if used correctly.

The Training Gap: The on demand, plug and play nature of portable air cleaners means frontline workers—nurses, cleaners, facility managers—play a critical role in their effectiveness. Without proper training and clear visual guidance showing safe placement zones, we risk unintended consequences. Procurement isn't enough. Education is essential.

CFD study on performance of portable air cleaner on infection risk and draught rate in care homes https://doi.org/10.1016/j.indenv.2026.100151

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/)

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) - Farmwood (https://farmwood.co.uk/)

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 This Week's CFD Study
00:01:03 The Care Home Crisis: Why COVID-19 Hit the Elderly So Hard
00:01:37 The Vulnerable Population: Mobility, Immunity, and Thermal Sensitivity
00:02:09 The Portable Air Cleaner Promise: Easy Solution or Placement Problem?
00:02:50 The CFD Simulation: Mapping Invisible Airflow and Virus Particles
00:03:43 The Good News: 75-86% Risk Reduction Without Creating Drafts
00:04:26 The Shocking Discovery: 74% Variation Based on Placement Alone
00:04:58 The Worst Case Scenario: When Air Cleaners Blow Virus Directly at Patients
00:05:45 The Best Placement Dilemma: Center of Room vs Practical Safety
00:06:47 The Real World Lesson: Education, Training, and Strategic Deployment