Michael S. Waring

Particle loading rates for HVAC filters, heat exchangers, and ducts

UNLABELLEDnThe rate at which airborne particulate matter deposits onto heating, ventilation, and air-conditioning (HVAC) components is important from both indoor air quality (IAQ) and energy perspectives. This modeling study predicts size-resolved particle mass loading rates for residential and commercial filters, heat exchangers (i.e. coils), and supply and return ducts. A parametric analysis evaluated the impact of different outdoor particle distributions, indoor emission sources, HVAC airflows, filtration efficiencies, coils, and duct system complexities. The median predicted residential and commercial loading rates were 2.97 and 130 g/m(2) month for the filter loading rates, 0.756 and 4.35 g/m(2) month for the coil loading rates, 0.0051 and 1.00 g/month for the supply duct loading rates, and 0.262 g/month for the commercial return duct loading rates. Loading rates are more dependent on outdoor particle distributions, indoor sources, HVAC operation strategy, and filtration than other considered parameters. The results presented herein, once validated, can be used to estimate filter changing and coil cleaning schedules, energy implications of filter and coil loading, and IAQ impacts associated with deposited particles.nnnPRACTICAL IMPLICATIONSnThe results in this paper suggest important factors that lead to particle deposition on HVAC components in residential and commercial buildings. This knowledge informs the development and comparison of control strategies to limit particle deposition. The predicted mass loading rates allow for the assessment of pressure drop and indoor air quality consequences that result from particle mass loading onto HVAC system components.

An evaluation of the indoor air quality in bars before and after a smoking ban in Austin, Texas.

This study assessed differences in the indoor air quality and occupancy levels in seventeen bars due to a city-wide smoking ban that took effect on September 1, 2005 in Austin, Texas, USA. We measured the following in each venue before and after the smoking ban: mean number of occupants, mean number of lit cigarettes, temperature, relative humidity, room volume, and PM2.5, CO, and CO2 concentrations. Additionally, VOC measurements were conducted at three of the venues. There was not a statistically significant change in occupancy, but the best estimate PM2.5 concentrations in the venues decreased 71–99%, a significant reduction in all venues, relative to the pre-ban levels; CO concentrations decreased significantly in all but one venue; and concentrations of VOCs known to be emitted from cigarettes decreased to below the detection limit for all but two common compounds. These results suggest that the smoking ban has effectively improved indoor air quality in Austin bars without an associated decrease in occupancy.

Indoor Secondary Organic Aerosol Formation Initiated from Reactions between Ozone and Surface-Sorbed D‑Limonene

Reactions between ozone and terpenoids produce numerous products, some of which may form secondary organic aerosol (SOA). This work investigated the contribution to gas-phase SOA formation of ozone reactions with surface-sorbed D-limonene, which is common indoors. A model framework was developed to predict SOA mass formation because of ozone/terpenoid surface reactions, and it was used with steady state experiments in a 283 L chamber to determine the aerosol mass fraction of SOA resulting from surface reactions, ξs (the ratio of mass of SOA formed and mass of ozone consumed by ozone/terpenoid surface reactions), for ozone/D-limonene reactions on stainless steel. The ξs = 0.70-0.91, with lower relative humidity leading to both higher mass and number formation. Also, surface reactions promoted nucleation more than gas-phase reactions, and number formation due to surface reactions and gas-phase reactions were 126-339 and 51.1-60.2 no./cm(3) per μg/m(3) of formed SOA, respectively. We also used the model framework to predict that indoor spaces in which ozone/D-limonene surface reactions would likely lead to meaningful gas-phase SOA formation are those with surfaces that have low original reactivity with ozone, such as glass, sealed materials, or smooth metals.

From commensalism to mutualism: integrating the microbial ecology, building science, and indoor air communities to advance research on the indoor microbiome

People throughout the world spend most of their time indoors, cohabitating with diverse microbial communities both on material surfaces and suspended in the indoor air. Advances in DNA sequencing techniques that allow rapid, high-throughput characterization of taxonomic marker genes (e.g., bacterial 16S rRNA and fungal ITS) and metagenomic DNA from environmental samples have enabled a sharp increase in the number of studies exploring various aspects of microbial diversity and abundance in indoor environments (Kelley and Gilbert, 2013; Konya and Scott, 2014; Peccia et al., 2011; Ramos and Stephens, 2014). Compared to culturing or chemical-marker based techniques, the new DNA-based methods provide a deeper insight into the structure (i.e., relative proportions of rare and abundant organisms) and composition (i.e., the phylogenetic structure of taxa) of microbial communities in environmental samples. Recent investigations in indoor environments—many of which have been initiated with research funding from the Alfred P. Sloan Foundation’s program on the Microbiology of the Built Environment (MoBE)—have characterized microbial communities on surfaces and in air within the spaces in which we live and work, emphasizing buildings without obvious mold or moisture problems. Environments investigated include offices and other commercial buildings, university classrooms, healthcare facilities, homes, public restrooms and transportation settings. Several key findings have resulted from this group of studies: