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Historically air constituents have been assumed to be well mixed in indoor environments, with single point measurements and box modeling representing a room or a house. Here we demonstrate that this fundamental assumption needs to be revisited through advanced model simulations and extensive measurements of bleach cleaning. We show that inorganic chlorinated products, such as hypochlorous acid and chloramines generated via multiphase reactions, exhibit spatial and vertical concentration gradients in a room, with short-lived ⋅OH radicals confined to sunlit zones, close to windows. Spatial and temporal scales of indoor constituents are modulated by rates of chemical reactions, surface interactions and building ventilation, providing critical insights for better assessments of human exposure to hazardous pollutants, as well as the transport of indoor chemicals outdoors.

CO2–based demand controlled ventilation (DCV) can save energy while maintaining acceptable indoor air quality. CO2 concentration may vary within an occupied space and it is unclear how sensor location influences the ventilation and energy performances. The objective of the present study is to investigate the effect of CO2 sensor position on the performance of DCV systems under mixing and displacement ventilation. Experimentally validated computational fluid dynamics (CFD) models were simulated under representative indoor ventilation and occupancy conditions. The results show that the ventilation strategy, occupancy level, and air change rate have notable impacts on the CO2 sensing performance. Under mixing ventilation, CO2 sensors placed at the room exhaust can meet the requirements of sensor accuracy defined by ASTM E741 and California Title 24. However, the sensor errors associated with sensor location can be higher than the acceptable threshold under displacement ventilation, which exhibits vertical CO2 stratification with two separated zones (lower transition zone and upper uniform zone). The dividing height of the two zones is highly sensitive to the occupancy level. In such cases, exhaust sensors can overestimate the breathing zone concentration and result in additional energy consumptions for thermal conditioning as well as fan operation, especially for densely occupied buildings. The study findings suggest that for ensuring good performance of CO2–based displacement ventilation, it is necessary to develop quantitative relationships between CO2 concentrations at the breathing height and the room exhaust considering ventilation strategies.

The utilization of portable air cleaners (PACs) is a recommended supplemental approach to help remove airborne pathogens and mitigate disease transmission in learning environments. To improve PAC effectiveness, science-based information is needed to optimize their implementation strategies such as the deployment location, height, and number of PACs. In this study, we developed a Computational Fluid Dynamics (CFD) model to assess how PACs perform in occupied classrooms equipped with displacement and mixing ventilation systems. The results show that PACs with a flow rate of 2.6 h−1 reduce the mean aerosol intake of all students by up to 66%. A key benefit of using PACs is to facilitate air mixing and movement in indoor environments with inadequate ventilation, thereby effectively reducing high aerosol concentrations near the infector. Furthermore, our results highlight the impact of PAC location on its performance. PACs achieve the best effectiveness when placed closed to the infector (within a distance <3 m). In the absence of knowing who is infected, deploying a PAC at the center of the room is recommended. Moreover, adjusting PAC flow discharge height to the breathing height of occupants (e.g., 0.9–1.2 m for seated people) can enhance their effectiveness in spaces with poor air mixing. [ABSTRACT FROM AUTHOR]

Draft is defined as unwanted local convective cooling. Existing draft risk models, developed in the 1970s, focus on air movement at the neck. The purpose of the present study is to experimentally evaluate ankle draft risk for women with uncovered ankles because of current widespread use of displacement ventilation and underfloor air distribution systems and changes in dress customs. Thirty female university students participated in nine double-blind randomized tests. The subjects wore sandals with lower legs, ankles and feet uncovered. Exposures occurred in an environmental chamber resembling an office environment. The operative temperature at 1.1 m above the floor was maintained at 24.1 ºC. The measured air speeds at the ankle varied between 0.16 and 0.59 m/s and the air temperature at the ankle varied between 18.0 and 21.7 °C. Subjective responses were obtained to assess these parameters: thermal acceptability, comfort, preference and sensation, air movement acceptability and preference, local thermal sensation and comfort, and perceived air quality. Subjects were more sensitive to ankle draft than expected. For all the tested conditions, between 20 and 37% of the subjects found the overall thermal environment not acceptable, while between 23 and 57% of the subjects found air movement at the ankle unacceptable. These dissatisfaction percentages are higher than those of international, American and European standards, indicating the need to develop a draft risk model for displacement ventilation and underfloor air distribution systems.

Elevated tropospheric ozone concentrations are associated with increased morbidity and mortality. Indoor ozone chemistry affects human exposure to ozone and reaction products that also may adversely affect health and comfort. Reactive uptake of ozone has been characterized for many building materials; however, scant information is available on how diurnal variation of ambient ozone influences ozone reaction with indoor surfaces. The primary objective of this study is to investigate ozone-surface reactions in response to a diurnally varying ozone exposure for three common building materials: ceiling tile, painted drywall, and carpet tile. A secondary objective is to examine the effects of air temperature and humidity. A third goal is to explore how conditioning of materials in an occupied office building might influence subsequent ozone-surface reactions. Experiments were performed at bench-scale with inlet ozone concentrations varied to simulate daytime (ozone elevated) and nighttime (ozone-free in these experiments) periods. To simulate office conditions, experiments were conducted at two temperatures (22 °C and 28 °C) and three relative humidity values (25%, 50%, 75%). Effects of indoor surface exposures were examined by placing material samples in an occupied office and repeating bench-scale characterization after exposure periods of 1 and 2 months. Deposition velocities were observed to be highest during the initial hour of ozone exposure with slow decrease in the subsequent hours of simulated daytime conditions. Daily-average ozone reaction probabilities for fresh materials are in the respective ranges of (1.7-2.7) × 10-5, (2.8-4.7) × 10-5, and (3.0-4.5) × 10-5 for ceiling tile, painted drywall, and carpet tile. The reaction probability decreases by 7%-47% across the three test materials after two 8-h periods of ozone exposure. Measurements with the samples from an occupied office reveal that deposition velocity can decrease or increase with time. Influence of temperature and humidity on ozone-surface reactivity was not strong.

Providing sufficient amounts of outdoor air to occupants is a critical building function for supporting occupant health, well-being and productivity. In tropical climates, high ventilation rates require substantial amounts of energy to cool and dehumidify supply air. This studyevaluates the energy consumption and associated cost for thermally conditioning outdoor air provided for building ventilation in tropical climates, considering Singapore as an example locale. We investigated the influence on energy consumption and cost of the followingfactors: outdoor air temperature and humidity, ventilation rate (L/s per person), indoor airtemperature and humidity, air conditioning system coefficient of performance (COP), andcost of electricity. Results show that dehumidification of outdoor air accounts for more than 80% of the energy needed for building ventilation in Singapore’s tropical climate. Improved system performance and/or a small increase in the indoor temperature set point would permit relatively large ventilation rates (such as 25 L/s per person) at modest or no cost increment.Overall, even in a thermally demanding tropical climate, the energy cost associated with increasing ventilation rate up to 25 L/s per person is less than 1% of the wages of an office worker in an advanced economy like Singapore’s. This result implies that the benefits ofincreasing outdoor air ventilation rate up to 25 L/s per person—which is suggested to provide for productivity increases, lower sick building syndrome symptom prevalence, and reduced sick leave—can be much larger than the incremental cost of ventilation.

Draft is defined as an unwanted local convective cooling of the body caused by air movement (Fanger, 1977). The main factors that affect draft are air temperature and velocity (Houghten et al., 1938), air turbulence (Fanger et al., 1988), body parts exposed and clothing insulation level, and overall thermal comfort (Toftum et al., 2003). Historically, the literature on draft has focused on thermal discomfort at the neck, which was considered the most sensitive part of the body, especially as the majority of mechanical systems supplied air from the ceiling. Now, owing to the widespread use of floor-level air distribution systems (underfloor air or displacement) and dress customs in which ankles could be uncovered, the need to assess draft risk for the ankle has emerged (Sekhar and Ching, 2002). The purpose of the present study is to experimentally evaluate local draft risk for uncovered ankles associated with displacement ventilation and underfloor air distribution.