Evaluation of the indoor air quality minimum ventilation rate procedure for use in California retail buildings

This research assesses benefits of adding to California Title‐24 ventilation rate (VR) standards a performance‐based option, similar to the American Society of Heating, Refrigerating, and Air Conditioning Engineers ‘Indoor Air Quality Procedure’ (IAQP) for retail spaces. Ventilation rates and concentrations of contaminants of concern (CoC) were measured in 13 stores. Mass balance models were used to estimate ‘IAQP‐based’ VRs that would maintain concentrations of all CoCs below health‐ or odor‐based reference concentration limits. An intervention study in a ‘big box’ store assessed how the current VR, the Title 24‐prescribed VR, and the IAQP‐based VR (0.24, 0.69, and 1.51 air changes per hour) influenced measured IAQ and perceived of IAQ. Neither current VRs nor Title 24‐prescribed VRs would maintain all CoCs below reference limits in 12 of 13 stores. In the big box store, the IAQP‐based VR kept all CoCs below limits. More than 80% of subjects reported acceptable air quality at all three VRs. In 11 of 13 buildings, saving energy through lower VRs while maintaining acceptable IAQ would require source reduction or gas‐phase air cleaning for CoCs. In only one of the 13 retail stores surveyed, application of the IAQP would have allowed reduced VRs without additional contaminant‐reduction strategies.     

How home ventilation rates affect health: A literature review

This paper reviews studies of the relationships between ventilation rates (VRs) in homes and occupant health, primarily respiratory health. Five cross‐sectional studies, seven case‐control studies, and eight intervention studies met inclusion criteria. Nearly all studies controlled for a range of potential confounders and most intervention studies included placebo conditions. Just over half of studies reported one or more statistically significant (SS) health benefits of increased VRs. Wheeze was most clearly associated with VR. No health outcomes had SS associations with VRs in the majority of statistical tests. Most studies that reported SS health benefits from increased VRs also had additional health outcomes that did not improve with increased VRs. Overall, the number of SS improvements in health with increased VRs exceeded the anticipated chance improvements by approximately a factor of seven. The magnitude of the improvements in health outcomes with increased VRs ranged from 20% to several‐fold improvements. In summary, the available research indicates a tendency for improvements in respiratory health with increased home VRs; however, health benefits do not occur consistently and other exposure control measures should be used together with ventilation. The research did not enable identification of a threshold VR below which adverse health effects occur.     

Associations between indoor CO2 concentrations and sick building syndrome symptoms in U.S. office buildings: an analysis of the 1994-1996 BASE study data

Higher indoor concentrations of air pollutants due, in part, to lower ventilation rates are a potential cause of sick building syndrome (SBS) symptoms in office workers. The indoor carbon dioxide (CO2) concentration is an approximate surrogate for indoor concentrations of other occupant-generated pollutants and for ventilation rate per occupant. Using multivariate logistic regression (MLR) analyses, we evaluated the relationship between indoor CO2 concentrations and SBS symptoms in occupants from a probability sample of 41 U.S. office buildings. Two CO2 metrics were constructed: average workday indoor minus average outdoor CO2 (dCO2, range 6-418 ppm), and maximum indoor 1-h moving average CO2 minus outdoor CO2 concentrations (dCO2MAX). MLR analyses quantified dCO2/SBS symptom associations, adjusting for personal and environmental factors. A dose-response relationship (p < 0.05) with odds ratios per 100 ppm dCO2 ranging from 1.2 to 1.5 for sore throat, nose/sinus, tight chest, and wheezing was observed. The dCO2MAX/SBS regression results were similar.     

Do classroom ventilation rates in California elementary schools influence standardized test scores? Results from a prospective study

Limited evidence has associated lower ventilation rates (VRs) in schools with reduced student learning or achievement. We analyzed longitudinal data collected over two school years from 150 classrooms in 28 schools within three California school districts. We estimated daily classroom VRs from real‐time indoor carbon dioxide measured by web‐connected sensors. School districts provided individual‐level scores on standard tests in Math and English, and classroom‐level demographic data. Analyses assessing learning effects used two VR metrics: average VRs for 30 days prior to tests, and proportion of prior daily VRs above specified thresholds during the year. We estimated relationships between scores and VR metrics in multivariate models with generalized estimating equations. All school districts had median school‐year VRs below the California VR standard. Most models showed some positive associations of VRs with test scores; however, estimates varied in magnitude and few 95% confidence intervals excluded the null. Combined‐district models estimated statistically significant increases of 0.6 points (P = 0.01) on English tests for each 10% increase in prior 30‐day VRs. Estimated increases in Math were of similar magnitude but not statistically significant. Findings suggest potential small positive associations between classroom VRs and learning.     

Association of classroom ventilation with reduced illness absence: a prospective study in California elementary schools

Limited evidence associates inadequate classroom ventilation rates (VRs) with increased illness absence (IA). We investigated relationships between VRs and IA in California elementary schools over two school years in 162 3rd–5th‐grade classrooms in 28 schools in three school districts: South Coast (SC), Bay Area (BA), and Central Valley (CV). We estimated relationships between daily IA and VR (estimated from two year daily real‐time carbon dioxide in each classroom) in zero‐inflated negative binomial models. We also compared IA benefits and energy costs of increased VRs. All school districts had median VRs below the 7.1 l/s‐person California standard. For each additional 1 l/s‐person of VR, IA was reduced significantly (p<0.05) in models for combined districts (?1.6%) and for SC (?1.2%), and nonsignificantly for districts providing less data: BA (?1.5%) and CV (?1.0%). Assuming associations were causal and generalizable, increasing classroom VRs from the California average (4 l/s‐person) to the State standard would decrease IA by 3.4%, increase attendance‐linked funding to schools by $33 million annually, and increase costs by only $4 million. Further increasing VRs would provide additional benefits. These findings, while requiring confirmation, suggest that increasing classroom VRs above the State standard would substantially decrease illness absence and produce economic benefits.     

Transport of particulate and gaseous pollutants in the vicinity of a human body

A uniform pollutant concentration in indoor environments can be an inappropriate representation of breathing concentration. This is especially true when local airflow in the vicinity of an occupant is dominant in transporting pollutants. The present study investigates the airflow in the vicinity of a human body, effects of respiration on breathing concentration of particulate and gaseous pollutants, and inhalation exposure in relation to source position and overall airflow patterns. It is based on experiments with a human simulator in a full-scale environmental chamber. Airflow and pollutant concentrations in the vicinity of a thermal manikin are monitored, while varying parameters including breathing, arm/hand movements, and ventilation system. Results show that breathing of a sedentary manikin has a measurable influence on the airflow in breathing zone, whereas it has very small impacts on occupant thermal plume. Also, localized hand motions have insignificant effects on the thermal plume. The results indicate that overall airflow pattern affect the inhaled particle concentrations. With highly mixed airflow in the space, relatively uniform concentration patterns occur in the occupant vicinity. However, with stratified airflow patterns, non-uniform concentration patterns are observed due to the occupant thermal plume. With a particle source at floor level and in near proximity to an occupant, inhaled particle concentrations are up to four times higher than the ambient concentrations. This finding implies that occupant thermal plume may play a significant role in transporting pollutants from floor level to the breathing zone. The non-uniform concentration observed with stratified flow also suggests caution in estimating inhalation exposure using a “well-mixed” mass balance model.     

Use of personalized ventilation for improving health,comfort, and performance at high room temperature and humidity

The effect of personalized ventilation (PV) on people's health, comfort, and performance in a warm and humid environment (26 and 28°C at 70% relative humidity) was studied and compared with their responses in a comfortable environment (23°C and 40% relative humidity). Thirty subjects participated in five 4‐h experiments in a climate chamber. Under the conditions with PV, the subjects were able to control the rate and direction of the supplied personalized flow of clean air. Subjective responses were collected through questionnaires. During all exposures, the subjects were occupied with tasks used to assess their performance. Objective measures of tear film stability, concentration of stress biomarkers in saliva, and eye blinking rate were taken. Using PV significantly improved the perceived air quality (PAQ) and thermal sensation and decreased the intensity of Sick Building Syndrome (SBS) symptoms to those prevailing in a comfortable room environment without PV. Self‐estimated and objectively measured performance was improved. Increasing the temperature and relative humidity, but not the use of PV, significantly decreased tear film quality and the concentration of salivary alpha‐amylase, indicating lower mental arousal and alertness. The use of PV improved tear film stability as compared to that in a warm environment without PV.     

Associations of indoor carbon dioxide concentrations,air temperature,and humidity with perceived air quality and sick building syndrome symptoms in Chinese homes

The indoor environment influences occupants’ health. From March 1, 2018, to February 28, 2019, we continuously monitored indoor temperature (T), relative humidity (RH), and CO₂ concentration in bedrooms via an online system in 165 residences that covered all five climate zones of China. Meanwhile, we asked one specific occupant in each home to complete questionnaires about perceived air quality and sick building syndrome (SBS) symptoms at the end of each month. Higher CO₂ concentration was significantly associated with a higher percentage of perceived stuffy odor and skin SBS symptoms. Higher relative humidity was associated with higher percentage of perceived moldy odor and humid air, while lower RH was associated with a higher percentage of perceived dry air. Occupants who lived in residences with high RH were less likely to have mucosal and skin SBS symptoms (adjusted odds ratio (AOR): 0.73–0.78). However, the benefit of high humidity for perceived dry air and skin dryness symptoms is weaker if there is a high CO₂ concentration level.     

Thermal comfort,perceived air quality,and cognitive performance when personally controlled air movement is used by tropically acclimatized persons

In a warm and humid climate, increasing the temperature set point offers considerable energy benefits with low first costs. Elevated air movement generated by a personally controlled fan can compensate for the negative effects caused by an increased temperature set point. Fifty‐six tropically acclimatized persons in common Singaporean office attire (0.7 clo) were exposed for 90 minutes to each of five conditions: 23, 26, and 29°C and in the latter two cases with and without occupant‐controlled air movement. Relative humidity was maintained at 60%. We tested thermal comfort, perceived air quality, sick building syndrome symptoms, and cognitive performance. We found that thermal comfort, perceived air quality, and sick building syndrome symptoms are equal or better at 26°C and 29°C than at the common set point of 23°C if a personally controlled fan is available for use. The best cognitive performance (as indicated by task speed) was obtained at 26°C; at 29°C, the availability of an occupant‐controlled fan partially mitigated the negative effect of the elevated temperature. The typical Singaporean indoor air temperature set point of 23°C yielded the lowest cognitive performance. An elevated set point in air‐conditioned buildings augmented with personally controlled fans might yield benefits for reduced energy use and improved indoor environmental quality in tropical climates.     

Sick building syndrome—A case study in a multistory centrally air-conditioned building in the Delhi City

Recently, airtight envelope system has become popular in the design of office buildings to reduce heating and cooling loads. Maintaining allowable indoor air quality (IAQ) for such airtight buildings totally depends on mechanical ventilation systems. Subsequently, poor operation of the ventilation system in such office buildings causes ineffective removal of polluted indoor air, and displays a sign of “sick building syndrome” (SBS). User's perception is an important parameter for evaluating IAQ. A questionnaire study was carried out to investigate the prevalence of the SBS at a multistory centrally air-conditioned Airport Authority of India (AAI) building in the New Delhi city. Quantification of the perceptions of the users regarding IAQ was done by converting their responses to a SBS score. The quantified answers were then subjected to statistical analysis. Qualitative analysis of the questionnaire was carried out to evaluate relationships between SBS score and carbon dioxide (CO₂) and other parameters related to building and work environment. Quantitative analysis of IAQ was also conducted by monitoring indoor concentrations of four pollutants, namely, nitrogen dioxide (NO₂), sulphur dioxide (SO₂), suspended particulate matter (SPM) and carbon monoxide (CO). Concentrations of pollutants were complying with IAQ standards as given by ASHRAE and WHO. The SBS was higher on the third floor as compared to other floors and the control tower. The main symptoms prevailing were headache (51%), lethargy (50%), and dryness in body mucous (33%). The third floor and the control tower were affected by infiltration, mainly from entrance doors. A direct relation between the average SBS score and CO₂ concentration was found, i.e., the average SBS score increased with CO₂ concentration and vice versa, clearly signifying the usefulness of SBS score in IAQ.     

The effect of structures on indoor humidity--possibility to improve comfort and perceived air quality

The research presented in this paper shows that moisture transfer between indoor air and hygroscopic building structures can generally improve indoor humidity conditions. This is important because the literature shows that indoor humidity has a significant effect on occupant comfort, perceived air quality (PAQ), occupant health, building durability, material emissions, and energy consumption. Therefore, it appears possible to improve the quality of life of occupants when appropriately applying hygroscopic wood-based materials. The paper concentrates on the numerical investigation of a bedroom in a wooden building located in four European countries (Finland, Belgium, Germany, and Italy). The results show that moisture transfer between indoor air and the hygroscopic structure significantly reduces the peak indoor humidity. Based on correlations from the literature, which quantify the effect of temperature and humidity on comfort and PAQ for sedentary adults, hygroscopic structures can improve indoor comfort and air quality. In all the investigated climates, it is possible to improve the indoor conditions such that, as many as 10 more people of 100 are satisfied with the thermal comfort conditions (warm respiratory comfort) at the end of occupation. Similarly, the percent dissatisfied with PAQ can be 25% lower in the morning when permeable and hygroscopic structures are applied.     

Understanding employee resourcing in construction organizations

In recent years the literature on employee resourcing has consistently advocated the importance of adopting a holistic, strategic approach to employee deployment decision making rather than adopting a reactive needs‐based approach. This is particularly problematic in construction where the multi‐project environment leads to constantly changing resource requirements and to changing demands over a project's life cycle. This can lead to inappropriate decisions, which fail to meet the longer‐term needs of both construction organizations and their employees. A structured and comprehensive understanding of the current project team deployment practices within large construction organizations was developed. Project deployment practices were examined within seven case study contracting firms. The emergent themes that shaped the decision‐making processes were grouped into five broad clusters comprising human resource planning, performance/career management, team deployment, employee involvement and training and development. The research confirms that a reactive and ad hoc approach to the function prevails within the firms investigated. This suggests a weak relationship between the deployment process and human resource planning, team deployment, performance management, employee involvement and training and development activities. It is suggested that strategic HR–business partnering could engender more transparent and productive relationships in this crucial area.     

Particulate Matter Intervention Study: A Causal Factor of Building-Related Symptoms in an Older Building

Abstract Five floors of a 20-year old 6-story office building were investigated using an integrated step-by-step investigation strategy. This involved a walkthrough inspection, an occupant questionnaire, and targeted environmental monitoring of indoor air quality and comfort parameters. The initial questionnaire survey revealed a high occurrence of building-related symptoms. The walkthrough inspection and environmental monitoring identified deposits of surface dust (indoor surface pollution – ISP) on carpets and hard surfaces, and elevated levels of carbon dioxide and respirable suspended particulate matter (RSP) throughout the building. An intervention study (blinded to the occupants) was targeted at reducing ISP levels by replacing normal carpet cleaning practices with higher performance vacuum cleaners and improved cleaning practices. The intervention reduced ISP levels and significantly lowered RSP concentrations by approx. 80% from initial values and against control floors. A follow-up SBS questionnaire revealed significant reductions in all but two of the symptoms. The most significant reductions occurred with symptoms of eye irritation, throat irritation, dry unproductive cough, and nose irritation. The study showed that in older buildings with poor ventilation, a build-up of ISP, and elevated RSP levels, using higher performance carpet cleaning practices can reduce RSP to acceptable levels and can reduce SBS symptoms.     

Modeling the Evacuation of the World Trade Center Towers on September 11, 2001

Multiple evacuation models were used to simulate different WTC tower evacuations, subject to a number of assumptions. The goal of the modeling was to frame an understanding of actual evacuation findings on September 11, 2001. Simulations demonstrated that a phased evacuation (occupants of the emergency floor, the occupants on the floor above, and the occupants on the floor below were to evacuate to three floors below the emergency floor) would have taken between 4 min to complete (without delays in evacuation initiation) and 11 min to complete (with evacuation initiation delays between 0 min and 10 min). Total evacuation of a tower assuming a full occupant load would have required from 92 min to 142 min. NIST estimated that approximately 14,000 occupants would have been unable to evacuate from WTC 1 and WTC 2 on September 11, 2001 had the starting building population in each tower been 19,800, i.e., a full occupant load without visitors.     

Ventilation and health in non-industrial indoor environments: report from a European multidisciplinary scientific consensus meeting (EUROVEN)

Scientific literature on the effects of ventilation on health, comfort, and productivity in non-industrial indoor environments (offices, schools, homes, etc.) has been reviewed by a multidisciplinary group of European scientists, called EUROVEN, with expertise in medicine, epidemiology, toxicology, and engineering. The group reviewed 105 papers published in peer-reviewed scientific journals and judged 30 as conclusive, providing sufficient information on ventilation, health effects, data processing, and reporting, 14 as providing relevant background information on the issue, 43 as relevant but non-informative or inconclusive, and 18 as irrelevant for the issue discussed. Based on the data in papers judged conclusive, the group agreed that ventilation is strongly associated with comfort (perceived air quality) and health [Sick Building Syndrome (SBS) symptoms, inflammation, infections, asthma, allergy, short-term sick leave], and that an association between ventilation and productivity (performance of office work) is indicated. The group also concluded that increasing outdoor air supply rates in non-industrial environments improves perceived air quality; that outdoor air supply rates below 25 l/s per person increase the risk of SBS symptoms, increase short-term sick leave, and decrease productivity among occupants of office buildings; and that ventilation rates above 0.5 air changes per hour (h-1) in homes reduce infestation of house dust mites in Nordic countries. The group concluded additionally that the literature indicates that in buildings with air-conditioning systems there may be an increased risk of SBS symptoms compared with naturally or mechanically ventilated buildings, and that improper maintenance, design, and functioning of air-conditioning systems contributes to increased prevalence of SBS symptoms.     

Are We Measuring the Relevant Indoor Pollutants?

Abstract Concentrations of volatile organic compounds (VOCs) measured indoors may exceed their odor thresholds, but are usually far below TLV estimates. Even applying additivity to eye and airway irritation effects, it is difficult to rationalize increased sick building syndrome (SBS) symptoms by exposure to generally chemically inert VOCs in the indoor environment. Several studies suggest that chemical reactions in indoor air are linked with SBS symptoms and the examination of these reactions may be necessary in order to understand the role of VOCs as causative agents of SBS symptoms. The usual evaluation of odor annoyance of VOCs based on odor thresholds should be modified, taking into account the large variation of individual human odor thresholds for single substances, and specific additivity phenomena even at subthreshold levels of VOCs. The conclusion of this review is that chemical reactions between oxidizable VOCs and oxidants, such as ozone and possibly nitrogen oxides, can form irritants which may be responsible for the reported symptoms. Compounds adsorbed to particles may also contribute to SBS symptoms. The individual effects of indoor pollutants may act in concert with temperature and relative humidity. New analytical methods are required to measure the oxidative and reactive species or specific markers thereof in indoor air.     

Ventilation rates in recently constructed U.S. school classrooms

Low ventilation rates (VRs) in schools have been associated with absenteeism, poorer academic performance, and teacher dissatisfaction. We measured VRs in 37 recently constructed or renovated and mechanically ventilated U.S. schools, including LEED and EnergyStar‐certified buildings, using CO₂ and the steady‐state, build‐up, decay, and transient mass balance methods. The transient mass balance method better matched conditions (specifically, changes in occupancy) and minimized biases seen in the other methods. During the school day, air change rates (ACRs) averaged 2.0±1.3 hour^?1, and only 22% of classrooms met recommended minimum ventilation rates. HVAC systems were shut off at the school day close, and ACRs dropped to 0.21±0.19 hour^?1. VRs did not differ by building type, although cost‐cutting and comfort measures resulted in low VRs and potentially impaired IAQ. VRs were lower in schools that used unit ventilators or radiant heating, in smaller schools and in larger classrooms. The steady‐state, build‐up, and decay methods had significant limitations and biases, showing the need to confirm that these methods are appropriate. Findings highlight the need to increase VRs and to ensure that energy saving and comfort measures do not compromise ventilation and IAQ.     

Fuzzy Cellular Automata Model for Signalized Intersections

At signalized intersections, the decision‐making process of each individual driver is a very complex process that involves many factors. In this article, a fuzzy cellular automata (FCA) model, which incorporates traditional cellular automata (CA) and fuzzy logic (FL), is developed to simulate the decision‐making process and estimate the effect of driving behavior on traffic performance. Different from existing models and applications, the proposed FCA model utilizes fuzzy interface systems (FISs) and membership functions to simulate the cognition system of individual drivers. Four FISs are defined for each decision‐making process: car‐following, lane‐changing, amber‐running, and right‐turn filtering. A field observation study is conducted to calibrate membership functions of input factors, model parameters, and to validate the proposed FCA model. Simulation experiments of a two‐lane system show that the proposed FCA model is able to replicate decision‐making processes and estimate the effect on overall traffic performance.     

Effects of pollution from personal computers on perceived air quality, SBS symptoms and productivity in offices

In groups of six, 30 female subjects were exposed for 4.8 h in a low-polluting office to each of two conditions--the presence or absence of 3-month-old personal computers (PCs). These PCs were placed behind a screen so that they were not visible to the subjects. Throughout the exposure the outdoor air supply was maintained at 10 l/s per person. Under each of the two conditions the subjects performed simulated office work using old low-polluting PCs. They also evaluated the air quality and reported Sick Building Syndrome (SBS) symptoms. The PCs were found to be strong indoor pollution sources, even after they had been in service for 3 months. The sensory pollution load of each PC was 3.4 olf, more than three times the pollution of a standard person. The presence of PCs increased the percentage of people dissatisfied with the perceived air quality from 13 to 41% and increased by 9% the time required for text processing. Chemical analyses were performed to determine the pollutants emitted by the PCs. The most significant chemicals detected included phenol, toluene, 2-ethylhexanol, formaldehyde, and styrene. The identified compounds were, however, insufficient in concentration and kind to explain the observed adverse effects. This suggests that chemicals other than those detected, so-called 'stealth chemicals', may contribute to the negative effects. PRACTICAL IMPLICATIONS: PCs are an important, but hitherto overlooked, source of pollution indoors. They can decrease the perceived air quality, increase SBS symptoms and decrease office productivity. The ventilation rate in an office with a 3-month-old PC would need to be increased several times to achieve the same perceived air quality as in a low-polluting office with the PC absent. Pollution from PCs has an important negative impact on the air quality, not only in offices but also in many other spaces, including homes. PCs may have played a role in previously published studies on SBS and perceived air quality, where PCs were overlooked as a possible pollution source in the indoor environment. The fact that the chemicals identified in the office air and in the chamber experiments were insufficient to explain the adverse effects observed during human exposures illustrates the inadequacy of the analytical chemical methods commonly used in indoor air quality investigations. For certain chemicals the human senses are much more sensitive than the chemical methods routinely used in indoor air quality investigations. The adverse effects of PC-generated air pollutants could be reduced by modifications in the manufacturing process, increased ventilation, localized PC exhaust, or personalized ventilation systems.     

Energy and comfort performance of thermally activated building systems including occupant behavior

In building simulations it is common practice to use standardized occupant behavior and internal gains. Although this is a valid approach for designing systems, the probabilistic nature of these boundary conditions influences the energy demand and achieved thermal comfort of real systems. This paper analyzes the influence of occupant behavior on the energy performance and thermal comfort of a typical office floor equipped with a thermally activated building system (TABS). A multi-zone TRNSYS model with 10 adjacent zones per orientation for a typical moderate Belgian climate is set up. First, the energy performance and thermal comfort of thermally activated building systems (TABS) are compared with the performance of idealized cooling with standardized user behavior. TABS are able to deliver good thermal comfort but show to have a higher energy demand. Secondly, probabilistic occupant behavior was implemented in the TABS simulations. The influence of the occupancy rate, the shading device use and switching of the lights are analyzed by defining user profiles. It is shown that occupant behavior may have an important influence on the cooling demand and thermal comfort. However, as long as good solar protection is foreseen and operated in a correct way, TABS are able to cope with different user behavior modeled in this paper. In this case, normal daily stochastic processes do not considerably affect the cooling demand and thermal comfort during summer.