Coarse mode respiratory aerosols can carry viral loads over long distances and have very different dynamics than submicron particles, but experimental studies under realistic conditions remain limited. To study the differential impacts on exposure under different mixing conditions, we co-released 7-10 & micro;m particles and carbon dioxide (CO2)-which served as an indicator of gas and submicron particle dynamics-in a 158 m3 room at LBNL's FLEXLAB facility with an overhead heating, ventilation, and air conditioning (HVAC) system. The room was arranged as a distanced meeting then a classroom with eight heated manikins and a researcher. Spatial variability was measured using 16 particle counters and 22-26 CO2 sensors throughout the space. Conditions included: HVAC off or supply air at 1000-1060 m3 h-1 at neutral, cooling, or heating temperatures; with and without 20% outdoor air; and added HVAC filtration, portable air cleaners (PACs), or a physical barrier between the speaker and occupants. We found that good mixing via neutral or cooling supply air or use of PACs under heating lowered coarse particle exposure at some locations, but increased exposure for one-quarter to two-thirds of manikins compared to poor mixing under heating. A physical barrier reduced direct transfer of coarse particles during heating, but less during cooling. High spatial variability shows that a single measurement cannot represent occupant exposure. Instantaneous air mixing assumptions overstate the effectiveness of ventilation, HVAC filtration, and upper-room germicidal ultraviolet disinfection for coarse particles, as relatively few particles reach the return grille or upper room under most conditions.

Air mixing and movement are often driven by the design and operating conditions of the heating, ventilation, and air conditioning (HVAC) system, and are influenced by occupants and thermal gradients at windows and walls. Air mixing affects the indoor-generated pollutants dispersion and thus influences the effectiveness of ventilation and within-room air cleaning systems, including upper-room germicidal ultraviolet disinfection (GUV). In rooms with a ceiling exhaust and/or upper-room GUV, upward airflow from occupants can enable faster pollutant removal compared to well-mixed conditions. We used pulsed ethanol as a tracer and measured concentration at 2 s time resolution using fast-response metal oxide sensors at three levels: near the floor at 0.1-0.4 m, mid-height at 1.1-1.4 m, and at 2.4 m, 0.3 m from the 2.74 m ceiling. Forty experiments were conducted under the following conditions: HVAC off; supply air at ~380 (low) or ~1200 m3 h−1 (high) at neutral, cooling, or heating temperatures with 20% or 100% outdoor air; and added mixing fans. Air mixing times were determined from the start of ethanol release until the relative standard deviation of the concentrations fell below 20%, indicating an approximately well-mixed condition. We found that the air mixing time was longest with the HVAC off (15.1-15.4 min), followed by conditions with a low total supply airflow rate at all temperatures (6.6-11.4 min under heating; 5.6-10.1 min under neutral/cooling), and was fastest under high airflow at neutral/cooling temperatures (2.9-5.6 min) or when mixing fans were added (1.9-1.8 min). The outdoor airflow rate (20% or 100%) did not significantly affect spatial heterogeneity or air mixing time. Long air mixing times resulted in high spatial variability of absolute integrated concentrations and relative exposures. Under slow mixing conditions (HVAC off or low airflow rate) and with releases associated with heaters simulating occupants, several upper or mid-level sensors peaked after the release, and mixing into the upper room and occupied space was slow. Under fast mixing conditions (high airflow rate with neutral/cooling settings or added fan), air reached and mixed in the upper room more quickly and spread faster in the occupied zone.

This study examines whole-house mechanical ventilation (WHMV) and indoor air quality (IAQ) in 51 single-family homes constructed since 2013 in the humid southeastern U.S. Homes were monitored for one or two weeks, operating with or without WHMV, or under both conditions (two-week homes, n = 11). Measurements included envelope and duct airtightness; mechanical ventilation airflows; time-resolved CO₂, PM2.5, formaldehyde, and radon; and time-integrated gravimetric PM2.5, NO₂, NOₓ, and formaldehyde. Participants reported on ventilation use, IAQ-related activities and perceptions. Major deficiencies were observed in WHMV installation, operation, and occupant awareness. Thirty-seven homes had controlled WHMV equipment. Twenty-one could meet the ASHRAE 62.2–2010 airflow requirement with continuous or controlled runtime, but only 11 systems were operating at the field team’s arrival (as-found condition). Performance and homeowner awareness varied by system type. Most energy recovery ventilators and ventilating dehumidifiers were functional and operating as found, with owners aware of their purpose. Fifteen homes had exhaust fans with compliant airflow and sound ratings but no labeling, and owners did consider them WHMV. Central Fan integrated supply (CFIS) systems were rarely functional. Six homes had no kitchen exhaust ventilation, and only 35 had airflow above the 50 L/s requirement of 62.2–2010 at any setting. PM2.5 concentrations were low in most homes. WHMV operation did not discernibly lower PM2.5 or formaldehyde but did significantly reduce CO2 and radon in both two-week homes and all homes with/out WHMV. Occupants of homes with WHMV operating as found felt they had better control of temperature and relative humidity.

This paper reports on equipment and procedures that enable the application of the pulsed tracer method to study air movement, contaminant transport, and mixing in rooms. We use ethanol as a non-toxic tracer and a network of low-cost, fast response (2 s) metal oxide sensors to measure airborne concentrations at high frequency. The method was demonstrated in a 158 m3 room of the FLEXLAB facility at Lawrence Berkeley National Laboratory, with an overhead HVAC system with controllable supply airflow and temperature. The room was configured as a meeting space with 8 simulated occupants. The sensors were mounted in a 3 × 4 grid in the upper room (0.3 m from the 2.74 m ceiling), in the middle height of the room at 1.1–1.4 m, and at several locations 0.1–0.4 m from the floor. Vaporized ethanol was released in pulses of 20 s. Sensors were cross-calibrated in-situ to provide quantitative information about relative concentrations and exposures. Results show that the method provides quantitative information about air movement patterns and mixing. For example, mixing throughout the room took 3–4 min with high supply airflow at neutral temperature and 7.5–9 min with heated supply air provided at a lower rate. The test can be used to evaluate whether air movement from the occupied zone to the upper room is fast enough to achieve the extremely high air cleaning rates that are possible with upper room germicidal ultraviolet disinfection (GUV) systems under ideal mixing conditions.

This study compares air pollutant concentrations resulting from cooking with gas or induction cooktops, with or without either of two recirculating range hoods with filters. A meal of pasta, plant-based “meat” sauce and stir-fried broccoli was cooked three times for each cooktop and hood combination in a 158 m3 room. Time-resolved measurements were made of nitrogen oxides, carbon dioxide, size-resolved particles, and speciated volatile organic compounds (VOCs) during cooking and 30minutes after cooking. Cooking with induction used half as much energy and produced no discernible NOX and significantly reduced ultrafine particles (UFP, diameter < 100nm) and CO2 compared to gas cooktops. Induction produced statistically higher PM2.5 when calculated using size-resolved particle measurements from one pair of instruments, but the difference was not discernible when calculating from another pair. With gas cooktops, roughly half of the PM2.5 was in particles smaller than 0.3 μm and thus below the lower quantitation threshold for many optical particle instruments; optical devices may thus substantially under-report PM2.5 from gas cooking. VOCs did not significantly differ between gas and induction. Both recirculating range hoods substantially reduced all particle sizes when cooking with either fuel, and the reductions were larger for gas cooking. One of the range hoods also substantially lowered some of the VOCs.

Data were collected to characterize whole-house mechanical ventilation (WHMV) and indoor air quality (IAQ) in 55 homes in the Marine climate of Oregon and the Cold-Dry climate of Colorado in the U.S. Sixteen homes were monitored for two weeks, with and without WHMV operating. Ventilation airflows; airtightness; time-resolved CO2, PM2.5 and radon; and time-integrated NO2, NOX and formaldehyde were measured. Participants provided information about IAQ-impacting activities, perceptions and ventilation use. All homes had operational cooktop ventilation and bathroom exhaust. Thirty homes had equipment that could meet the ASHRAE 62.2-2010 standard with continuous or controlled runtime and 34 had some WHMV operating as found. Thirty-five of 46 participants with WHMV reported they did not know how to operate it, and only half of the systems were properly labeled. Two-week homes had lower formaldehyde, radon, CO2 and NO (NOX-NO2) when operated with WHMV, and had faster PM2.5 decays following indoor emission events. Overall IAQ satisfaction was similar in Oregon and Colorado, but more Colorado participants (19% vs 3%) felt their IAQ could be improved and more reported dryness as a problem (58% vs. 14%). The collected data indicate that there are benefits of operating WHMV, even when continuous use may not be needed because outdoor pollutant concentrations are low and indoor sources do not present substantial challenges.

Today, the fan pressurization method is the most frequently used method to evaluate a building's airtightness. However, the localization and quantification of leaks remain difficult. In this paper, an acoustic method is introduced to estimate the leakage size of single leaks. Acoustic and airflow measurements were conducted and compared in laboratory tests within the same boundary conditions. This work aims to investigate if various leak sizes can be predicted using acoustic measurement methods. The test apparatus consists of two chambers, separated by a test wall. This wall represents a single characteristic air leakage path. Various types of wall structures with different slit geometries, wall thicknesses, and insulation materials were investigated. The acoustic measurements were performed with a sound source placed in one chamber and ultrasonic microphones located in both chambers. These results were compared to measured airflows through the test wall to provide estimates of uncertainty in the acoustic approach, which indicate a linear trend. Finally, these laboratory measurements were compared to the same measurements at a real office building. Although the acoustic measurement uncertainty is still significant (greater than +/- 50%), the acoustic method has the potential to give an order of magnitude of single leak sizes.

The evolution of SARS-CoV-2 virus has resulted in variants likely to be more readily transmitted through respiratory aerosols, underscoring the increased potential for indoor environmental controls to mitigate risk. Use of tight-fitting face masks to trap infectious aerosol in exhaled breath and reduce inhalation exposure to contaminated air is of critical importance for disease control. Administrative controls including the regulation of occupancy and interpersonal spacing are also important, while presenting social and economic challenges. Indoor engineering controls including ventilation, exhaust, air flow control, filtration, and disinfection by germicidal ultraviolet irradiation can reduce reliance on stringent occupancy restrictions. However, the effects of controls-individually and in combination-on reducing infectious aerosol transfer indoors remain to be clearly characterized to the extent needed to support widespread implementation by building operators. We review aerobiologic and epidemiologic evidence of indoor environmental controls against transmission and present a quantitative aerosol transfer scenario illustrating relative differences in exposure at close-interactive, room, and building scales. We identify an overarching need for investment to implement building controls and evaluate their effectiveness on infection in well-characterized and real-world settings, supported by specific, methodological advances. Improved understanding of engineering control effectiveness guides implementation at scale while considering occupant comfort, operational challenges, and energy costs.

Tracer gas experiments were conducted in a 158 m 3 room with overhead supply diffusers to study dispersion of contaminants from simulated speaking in physically-distanced meeting and classroom configurations.The room was contained within a 237 m 3 cell with open plenum return to the HVAC system.Heated manikins at desks and a researcher operating the tracer release apparatus presented 8-9 thermal plumes.Experiments were conducted under conditions of no forced air and neutral, cooled, or heated air supplied at 980-1100 cmh, and with/out 20% outdoor air.CO2 was released at the head of one manikin in each experiment to simulate small (<5 µm diameter) respiratory aerosols.The metric of Exposure Relative to perfectly-Mixed (ERM) is introduced to quantify impacts, based on measurements at manikin heads and at three heights in the center and corners of the room.Chilled or neutral supply air provided good mixing with ERMs close to one.Thermal stratification during heating produced higher ERMs at most manikins: 25% were ≥2.5 and the highest were >5× perfectly mixed conditions.Operation of two within-zone air cleaners together moving ≥400 cmh vertically in the room provided enough mixing to mitigate elevated exposure variations.

This report presents a simulation-based analysis that estimates the magnitude of indoor air pollutant concentration changes that could result from the proposed energy conservation standards. The analysis was conducted for a 1568 ft2, double-wide MH with variations in heating and cooling equipment (either furnace + air conditioner or heat pump) and various types of whole-house mechanical ventilation (continuous exhaust fan or central fan integrated supply), in three locations with varying climate conditions: Chicago IL, Fresno, CA; and Houston TX. The simulations tracked four air pollutants that can reach levels exceeding established safe target levels in homes: acrolein, formaldehyde, fine particulate matter (PM2.5), and nitrogen dioxide (NO2). The simulations considered acrolein and formaldehyde emitted from continuous indoor sources; acrolein, NO2 and PM2.5 from cooking; PM2.5 from dispersed occupant activities; and NO2 and PM2.5 from outdoors, using historical data to identify typical levels. The impacts in homes operating or not operating whole-house mechanical ventilation equipment, kitchen and bath exhaust fans, and window opening as ventilation approaches were examined.

Unintended Infiltration in buildings is responsible for a significant portion of the global housing stock energy demand. Today, the fan pressurization method, also known as blower-door test, is the most frequently used measurement method to evaluate the airtightness of buildings and determining the total air change rate of a building or a building element. However, the localization and quantification of single leaks in the building envelope remain difficult and time-consuming. In this paper, an acoustic method is introduced to estimate the leakage size of single leaks in buildings. Sound transmission measurements and measurements of airflow have been conducted in a laboratory test apparatus. The objective of this investigation is to compare acoustic measurements with airflow measurements of leaks under the same boundary conditions. The test apparatus consists of two chambers, which are separated by a test wall. This test wall represents a single characteristic air leakage path in the building envelope. Various types of wall structures with different slit geometries, wall thicknesses and insulation materials have been investigated. The acoustic measurements have been performed with a sound source placed in one chamber and ultrasonic microphones located in both chambers. The results of the acoustic measurements were compared to airflows through the test wall measured using a flow nozzle to provide estimates of the uncertainty in the acoustic approach.

This paper presents pollutant concentrations and performance data for code-required mechanical ventilation equipment in 23 low-income apartments at 4 properties constructed or renovated 2013-2017. All apartments had natural gas cooking burners. Occupants pledged to not use windows for ventilation during the study but several did. Measured airflows of range hoods and bathroom exhaust fans were lower than product specifications. Only eight apartments operationally met all ventilation code requirements. Pollutants measured over one week in each apartment included time-resolved fine particulate matter (PM2.5), nitrogen dioxide (NO2), formaldehyde and carbon dioxide (CO2) and time-integrated formaldehyde, NO2 and nitrogen oxides (NOX). Compared to a recent study of California houses with code-compliant ventilation, apartments were smaller, had fewer occupants, higher densities, and higher mechanical ventilation rates. Mean PM2.5, formaldehyde, NO2, and CO2 were 7.7 mu g/m(3), 14.1, 18.8, and 741 ppm in apartments; these are 4% lower, 25% lower, 165% higher, and 18% higher compared to houses with similar cooking frequency. Four apartments had weekly PM2.5 above the California annual outdoor standard of 12 mu g/m(3) and also discrete days above the World Health Organization 24-hour guideline of 25 mu g/m(3). Two apartments had weekly NO2 above the California annual outdoor standard of 30 ppb.

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The California residential building code requires kitchen exhaust ventilation to protect indoor air quality. The requirement can be met with a kitchen exhaust fan or a range hood that conforms to airflow and sound specifications based on certified, standard test results. Appliances that integrate an exhaust fan with an over the range microwave (OTRs) are popular for their space saving utility; but for years there were none with the certified performance data required for building code compliance. This project, initiated during that period, aimed to evaluate OTR models found in new California homes and compare their performance to range hoods that minimally met code requirements. The study aimed to expand on limited information available about OTR performance with a particular focus on measuring the fraction of cooktop-generated air pollutants that are captured and removed by the exhaust devices, a parameter called “capture efficiency”. Airflow and capture efficiency (CE) were measured in a simulated kitchen in Berkeley Lab’s FLEXLAB facility. Airflows were measured using several variations of a balanced-pressure flow method (Walker et al. 2001) including a protocol that had been used in the California Healthy Efficient New Gas Homes (HENGH) field study. Measurements were made for six OTRs observed in the field study, including three with certified test results (published after the start of this project) for airflow and sound. Measurements were also made on two standard range hoods with comparable airflows and costs to the OTRs, when accounting for the microwave functionality. CE was measured using the CO2 emitted from burners while heating pots of water (POW) as a tracer and calculating the ratio of added CO2 in the exhaust flow over the total CO2 generated from burning fuel. Results show that OTRs generally met the California code requirements for airflow, which are the same as those of the residential ventilation standard of ASHRAE. It was determined that the field protocol used in HENGH study homes was biased low by ~14% on average. The CE performance of OTRs tested in this study were consistent with those tested under controlled conditions in prior studies, showing CE increasing with airflow and being higher for emissions occurring at the back cooktop burner(s) compared with front burner emissions. The measured CE covered a range of 40% to 85% for the front burners and 60% to 100% for the back burners. The relationship of CE to airflow for OTRs was within the range of those found for standard range hoods in this study and prior studies, with the key caveat that OTRs appear to have more consistent CE performance for emissions on the front burner.

Venting range hoods can control indoor air pollutants emitted during residential cooktop and oven cooking. To quantify their potential benefits, it is important to know how frequently and under what conditions range hoods are operated during cooking. We analyzed data from 54 single family houses and 17 low-income apartments in California in which cooking activities, range hood use, and fine particulate matter (PM2.5) were monitored for one week per home. Range hoods were used for 36% of cooking events in houses and 28% in apartments. The frequency of hood use increased with cooking frequency across homes. In both houses and apartments, the likelihood of hood use during a cooking event increased with the duration of cooktop burner use, but not with the duration of oven use. Actual hood use rates were higher in the homes of participants who self-reported more frequent use in a pre-study survey, but actual use was far lower than self-reported frequency. Residents in single family houses used range hoods more often when cooking caused a discernible increase in PM2.5. In apartments, residents used their range hood more often only when high concentrations of PM2.5 were generated during cooking.

Advances in particle sensor design and manufacturing have enabled the development of low-cost air quality monitors (LCMs). The sensors use light scattering to estimate mass concentration and thus require evaluation for aerosols of varied composition and size distribution. We tested the performance of six LCMs designed for home use and having a retail price under US$300 in October 2018. We assessed their performance by comparing their output to reference PM2.5 and PM10 measurements from 21 common residential sources and from infiltrated outdoor PM2.5. Reference data were obtained by using gravimetric measurements to adjust time-resolved output from an aerosol spectrometer with both electrical mobility and optical particle sensors. Compared by linear regression to reference measurements, LCMs had negative intercepts and slopes of 1-2 for infiltrated outdoor PM2.5. Semi-quantitative responses (similar to 50-200% of actual PM2.5) were obtained for varied aerosols including minerals (ultrasonic humidifier, vacuuming, test dust); combustion products (incense, mosquito coil, extinguished candles); microwave popcorn; and cooking involving frying or grilling. LCMs had low or no response to sources for which all mass was in particles smaller than 0.25 mu m, including steady candle flames and cooking without frying or grilling. PM10 data from LCMs was more variable than PM2.5.

Air quality monitors using low-cost optical PM2.5 sensors can track the dispersion of wildfire smoke; but quantitative hazard assessment requires a smoke-specific adjustment factor (AF). This study determined AFs for three professional-grade devices and four monitors with low-cost sensors based on measurements inside a well-ventilated lab impacted by the 2018 Camp Fire in California (USA). Using the Thermo TEOM-FDMS as reference, AFs of professional monitors were 0.85 for Grimm mini wide-range aerosol spectrometer, 0.25 for TSI DustTrak, and 0.53 for Thermo pDR1500; AFs for low-cost monitors were 0.59 for AirVisual Pro, 0.48 for PurpleAir Indoor, 0.46 for Air Quality Egg, and 0.60 for eLichens Indoor Air Quality Pro Station. We also compared public data from 53 PurpleAir PA-II monitors to 12 nearby regulatory monitoring stations impacted by Camp Fire smoke and devices near stations impacted by the Carr and Mendocino Complex Fires in California and the Pole Creek Fire in Utah. Camp Fire AFs varied by day and location, with median (interquartile) of 0.48 (0.44–0.53). Adjusted PA-II 4-h average data were generally within ±20% of PM2.5 reported by the monitoring stations. Adjustment improved the accuracy of Air Quality Index (AQI) hazard level reporting, e.g., from 14% to 84% correct in Sacramento during the Camp Fire.

Cooking activities are a major source of indoor air pollutants. To control pollutants generated from cooking activities, a range hood is commonly used in residential kitchens. Several building codes require that a range hood be installed in new homes to control pollutants from cooking, and the required airflow rates for range hoods are specified by indoor air quality standards. However, airflow alone does not show how much of the cooking pollutants are exhausted by the range hood. A better metric to evaluate range hood indoor air quality performance is capture efficiency—the fraction of contaminants emitted during cooking that are exhausted directly to the outside via the range hood. The current article summarizes the development of a range hood capture efficiency test method for use in laboratory testing and equipment rating.