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.

Some thoughts on conducting energy and environmental research during the first 2 months of the Trump administration

I don’t think of Twitter threads as a particularly helpful means of communication, but it’s a good way to rant about my experience conducting energy and environmental research during the first 2 months of the Trump administration:

Thanks to Chuck Haas at Drexel University as well for making a Storify of this thread.

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:


Comments on new working paper ‘Do Energy Efficiency Investments Deliver? Evidence from the Weatherization Assistance Program’

Economists Meredith Fowlie and Catherine Wolfram at the University of California, Berkeley and Michael Greenstone at the Energy Policy Institute at the University of Chicago (EPIC) have published a new working paper on the economics of residential energy efficiency retrofits, in which they present some discouraging results:

I first read the short research summary from EPIC, “Costs of Residential Energy Efficiency Investments are Twice their Benefits: Implications for Policy,” and found some surprising conclusions that led me to dig deeper into the actual working paper, “Do Energy Efficiency Investments Deliver? Evidence from the Weatherization Assistance Program.”

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