Indoor air pollution

BERG provides comments on proposed 2019 California Title 24 residential air filtration requirements

California’s Title 24 of the CA Code of Regulations — also known as the California Energy Code or part 6 of the CA Building Standards Code — is one of the most (if not the most) aggressive codes in the country in terms of advancing energy efficiency in buildings. It was created in 1978 by the CA Building Standards Commission in response to a legislative mandate to reduce CA’s energy consumption. It undergoes periodic revision and has continued to strength its efficiency standards over time, setting the pace for the rest of the country.

Most items in the code deal explicitly with energy efficiency, but in recent years more language has been adopted to promote better indoor environmental quality. We were recently asked to provide our opinion on some new proposed language regarding air filtration for the upcoming (2019) rulemaking process. Since this is an in which we are active, BERG PhD student Torkan Fazli and I decided to provide a brief opinion.

Among the changes proposed to Title 24 in 2019 is language to increase the level of air filtration required for new residential construction, from MERV 6 to MERV 13, with the stated goal of reducing indoor PM2.5 concentrations. This is quite a bold move in a relatively slow-to-change industry. To accommodate the higher efficiency filter requirements, the proposed changes would also require that return grilles be able to accommodate at least a 2-inch deep filter to ensure that MERV 13 filters can be installed with minimal impact on HVAC system performance. You can read more about the justification for the proposed changes at the Title 24 residential indoor air quality and ventilation stakeholders site.

This is an area that I’ve done a lot of work in, starting with my master’s thesis work under Dr. Jeff Siegel then at the University of Texas (here and here), and more recently at Illinois Tech working with several graduate students (e.g. here, here, and here). Even more recently, we’ve been conducting measurements of filter pressure drop, air handler flow rates (in a nominal 1000 CFM air handler with a PSC blower), and in-situ filtration efficiency for fine and ultrafine particles for a large number of commercially available filters with various manufacturer-reported ratings (e.g., MERV = minimum efficiency reporting value, FPR = filter performance rating, and MPR = micro-particle performance rating) and various depths (e.g., 1-inch, 2-inch, 4-inch, and 5-inch). You can read about some of this initial testing here. We’ve now tested about 50 filters, 36 of which have had a MERV rating reported by the manufacturer. We plan to publish this work in the near future, but until then, we provided some our data on pressure drop and MERV to help justify the proposed Title 24 changes. The figure below shows filter pressure drop measurements made with each of these 36 filters plotted against the manufacturer-reported MERV rating for each filter. Note that all pressure drops are measured with new (clean) filters.

Filter pressure drop versus MERV # for various depth new (clean) filters

From this work, our previous work, and the work of several others referenced throughout the publications linked above, I think we can generally conclude the following about higher efficiency residential filters:

  • PM2.5 is probably the most important indoor pollutant to control to mitigate long-term (chronic) adverse health outcomes associated with indoor pollutant exposure
  • Only MERV 13 filters and above are explicitly required to have a single pass removal efficiency of at least 50% for particles smaller than 1 µm (according to ASHRAE Standard 52.2)
  • Targeting removal of particles 0.3-1 µm generally increases PM2.5 removal efficiency, more so than targeting removal of 1-3 µm or 3-10 µm particles
  • Therefore, MERV 13 makes sense from a public health perspective
  • MERV 13 filters can have high pressure drops, particularly in the narrower 1-inch depth variety
  • The energy consequences of high filter pressure drops are probably smaller than most people think, but they can still cause increased fan energy consumption in residential systems with ECM fan motors that increase fan power to maintain the same airflow rate and can cause longer system runtimes (and thus higher energy consumption) in residential systems with PSC fan motors that respond to increased pressure drop by reducing air handler flow rates and thus capacity
  • Thicker depth filters — including at minimum 2-inch filters — tend to have lower pressure drops than 1-inch filters within a given MERV category
  • Therefore, if one is to move to MERV 13, one should strive to accommodate deeper bed filters that should have fewer pressure drop issues

For these reasons, we generally support the move to require MERV 13 and minimum 2-inch depth filters. You can read our full statement here, as recorded in the California Energy Commission docket log.

New 3D printer test: Up Box+ Printer with HEPA filter

We recently tested emissions of ultrafine particles (UFPs) and spectated volatile organic compounds (VOCs) from an Up Box+ desktop 3D printer using ABS filament, which is a relatively unique product on the market because it includes a 100% recirculating HEPA filter inside a full enclosure in order to reduce particle emissions. It’s one of the first, if not the first, printer that we’ve seen specifically address UFP emissions. (However, we should also note that it does not have any intentional gas phase filtration to reduce VOC emissions). Results of our tests are provided in detail in the full report, but briefly:

  • The total number of UFPs emitted throughout the test print job was reduced by about 74% simply by printing with the enclosure completely closed (but no filter operating) compared to operating the printer with an open enclosure
  • The total number of UFPs emitted throughout the test print job was reduced by about 91% by printing with the enclosure closed and HEPA filtration system switched on compared to operating the printer with an open enclosure
  • VOC emissions were relatively low compared to other printers and filaments we’ve tested, although surprisingly, operating the printer with the enclosure closed (but without the filter operating) actually increased VOC emission rates by about 50%, while operating the printer with the enclosure closed and with the HEPA filtration system switched on decreased VOC emission rates by about 20%. However, both of these values are near the estimated uncertainty in our measurement and we didn’t get a chance to perform replicate testing, so it’s not clear how meaningful the VOC results really are

New batch of 3D printer filament emissions tests available

We have released 7 new reports on ultrafine particle (UFP) and volatile organic compound (VOC) emissions tests conducted in our lab in 2016 using a Lulzbot Mini 3D printer and 7 different commercially available filaments. Scroll down to the bottom of our 3d printer emissions testing page to see the reports, or download them below:


20 papers every BERG student should read

My colleague Michael Waring, who directs the Indoor Environment Research Group at Drexel University, recently shared a thought with me. He was thinking about compiling a list of about 20 papers that every graduate student in his group should read and be very familiar with. It’s a great idea, so here I am doing the same.

Below is a list of 20 papers I think every Built Environment Research Group student (BERGer) should read. Narrowing to only 20 papers is tough. In fact, this may forever be considered a rough draft of a list, and it will most certainly change or expand over time. But I have chosen these articles to span a wide range of topics related to energy and air quality in the built environment, including the physics or chemistry of indoor air pollutants, human exposure to indoor pollutants and health effects, and energy efficiency in buildings. There may be other even better articles on each topic, but these were chosen for their combination of impact on research and thought in their areas of inquiry, the usefulness of their methods, their clarity in presentation, and for the references included within them as well as their links to other papers that have referenced them upon publication.

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Air quality monitoring on Metra trains in Chicago, IL


We recently partnered with investigative reporter, Dave Savini, from CBS 2 Chicago to make air quality measurements in and around Metra trains and train stations in downtown Chicago. The Chicago Tribune had previously reported high concentrations of soot (black carbon particles) onboard trains over 3 years ago, which were thought to be caused by re-entrainment of diesel engine exhaust. We know that diesel exhaust emits a number of pollutants that are problematic for respiratory and cardiovascular health, including ultrafine particlesblack carbon particles, metals, and VOCs and SVOCs. This report prompted Metra to take action, primarily by installing particle filters on the cabin ventilation systems (MERV 13 instead of MERV 8) and by installing (or planning to install) devices that shut-off the diesel engines as they enter stations. The filters were shown in 2011 to measurably reduce black carbon particle concentrations in the rail cars, which was good to see. I’ve also found links to documents showing that Metra was upgrading ventilation systems to include vent hoods on intakes and exhausts, manual closing of outdoor air dampers, and exhaust deflectors on the locomotives themselves. I’m not sure of the status of these repairs or the extent to which MERV 13 filters have been installed across the fleet.

UPDATE: Watch a video of the CBS 2 story

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“Great moments in building science”

I haven’t posted in a while, but I just came across Joe Lstiburek’s article in the March 2014 ASHRAE Journal, “Great moments in building science,” and thought I’d share. It’s a great look at a few seemingly minor mistakes made throughout the legendary building scientist’s career — all of which he learned valuable lessons from.

Energy and environmental literature round-up, November 2013

I haven’t posted one of these literature round-ups since June. The last one was right before I post in which I said “I’m going to start blogging more!” That turned out to be completely false, but now that our semester is wrapping up, I thought I’d try to jump back in! So here are a few recent papers related to building science, energy, environment, and health that have sparked my interest:

  • Improving airflow measurement accuracy in VAV terminal units using flow conditioners – A good friend and colleague of mine Michael Waring at Drexel recently published an article with coauthors on using a simple flow conditioner to make airflow measurements in HVAC systems more accurate, reducing errors from 10-45% (depending on nearby elbows and kinks) to about 5%.
  • Human exposure to airborne particulate matter leads to oxidative DNA damage
  • Both soil and paint contributes to lead levels in Australian homes
  • Particle size distributions form e-cigarettes – Always controversial, this team measured particle concentrations and particle size distributions in mainstream smoke from electronic cigarettes under a range of liquid flavors, liquid nicotine contents, and “puffing times.” Particle size distributions peaked around 120-165 nm, similar to conventional cigarettes. Resulting particle concentrations were actually higher than a conventional cigarette. Flavor didn’t matter.
  • Meta-analysis of high penetration renewable scenarios – A meta-analysis of several studies evaluating the possibility, operability, and implications of high levels of renewable sources of electricity in grid scale power systems shows that in most regions, renewable sources can provide the majority of a country’s or region’s electricity demand, at least on an hourly scale.
  • Systemic and vascular effects of circulating diesel exhaust particulate matter – Diesel exhaust particles (DEPs) were shown to increase inflammatory responses when they enter the bloodstream. Also, DEPs were shown to be quickly sequestered in the spleen and liver in mice.
  • Fine particulate matter from urban areas was shown to generate a higher reactive oxygen species (ROS) response than rural and/or coarse PM – responses were independent on PM chemical composition.
  • Fine and ultra fine particle decay rates in homes – Using time-resolved data over the course of 1 week in 74 homes in Edmonton, CA, Wallace et al. used concentration peaks and subsequent decay periods of both PM2.5 and submicron particles (representative mostly of ultra fine particles), to estimate decay rates. Median and interquartile decay rates were 1.08 per hour (IQR: 0.62-1.75 per hour) for PM2.5 and 1.26 per hour (IQR: 0.82-1.83 per hour) for submicron particles. Air exchange contributed about 25% of these values, on average. Window opening, home age, use of central furnace fans and kitchen/bathroom exhaust fans, use of air-conditioners, use of air cleaners, and indoor-outdoor temperature differences all influence these values.
  • Diversity and distribution of fungi on residential surfaces – Rachel Adams and coauthors sampled fungi from 3 surfaces in homes: drains in kitchens and bathrooms, sills beneath condensation prone windows, and the skin of human occupants. Weedy genera and a large set of fungi likely of outdoor origin were found on the window sills; human foreheads contained a surprising amount of plant pathogens. Indoor fungal richness was generally high, but the authors conclude that most fungi were unlikely to be growing on the surfaces but are more likely to have been deposited/settled from other sources.
  • Asthma and the diversity of fungal spores in air – many studies in the past have found correlations between asthma symptoms and exposure to fungi indoors; this short article highlights some of that past work and suggests that by doing more species identification we will be able to learn more about which fungi species contribute to asthma and inflammation
  • Low fungal diversity in house dust is associated with childhood asthma development – Somewhat contrary to the previous paper, a new study of low-income children whereby house dust was collected at age 1 and asthma status determined 6 years later. Although the study had a small sample size of 13 cases and 28 controls, decreasing fungal diversity within the genus Cryptococcus was significantly associated with increased asthma risk. No fungal taxon (species, genus, class) was positively associated with asthma development. Hmm…
  • PVC flooring at home and development of asthma in young children – Last article on asthma this time… in a 10-year follow up study of children in Sweden revealed that children who had PVC floorings in their bedroom at baseline (when hey were 1 to 5 years old) were more likely to develop asthma during the following 10 year period than compared to children without PVC flooring. Exposure to PVC flooring – and the phthalate plasticizers emitted – during pregnancy may be critical to development of asthma in children later on.

Dr. Stephens gives EWB-IIT lecture on indoor air pollution in developing countries

It’s a little late for this as a news item, but I wanted to post slides here. I gave a lecture to the IIT chapter of Engineers Without Borders USA (EWB-USA) today at their general body meeting. I covered some of the basics of the huge global health burden attributed to indoor and household air pollution primarily in developing regions of the world. Some EWB members had recently been in Nicaragua on a separate bridge-building project and happened to notice women in the community cooking on inefficient cook stoves. They also noticed their interior walls were covered with soot — a pretty solid lead-in to this presentation. Hopefully they will be able to work on some cleaner stove intervention projects in the future!

My slides are available here.