Evaluation of air purifier and fan installation heights for enhancing indoor air quality in a plastic greenhouse

Environmental control of indoor biologic agents

Environmental control of indoor biologic agents

Students and teachers are exposed to harmful materials in the school where the students generate dusts when playing during the break time. Despite most schools adopting air purifiers in the classroom, the capability of the air purifier is not enough compared to natural ventilation. Therefore, this study proposed a smart air quality monitoring and purifying system for the school environment. The system consists of an outdoor air quality monitoring system, indoor air purifiers, and a server program running on PC. The proposed system allows teachers and students to choose when to use the air purifier or natural ventilation by comparing outdoor air quality and indoor air quality. In addition, the proposed air purifier system includes an intelligent operation that controls the speed of the fan and blower to make sure it does not generate noise that interfere with students in class. This paper also includes the performance evaluation of the air quality monitoring system. As a result, the system has less error than approximately 15% from the reference instrument.

Analyzing indoor air pollutants in naturally ventilated athletic facilities. A case of study

Mass COVID-19 infection cases in indoor spaces have been continuously reported since its global outbreak, generating increasing public interest in reducing the spread of the virus. This study considered a situation in which an infected individual continuously releases the virus into the air in a classroom, simulated by continuous injection of NaCl particles ≤ 5 μm, with heater operation during winter. The effects of applying natural ventilation and operating one or two air purifiers on the removal of virus-containing aerosols were experimentally compared and analyzed based on the spatiotemporal changes in NaCl concentration within the classroom. When a heater was operated with all windows shut, operating one and two air purifiers reduced the amount of the aerosol in indoor air by approximately 50 and 60%, respectively, compared to the case with no air purifier. Additionally, when the heater was operated with one or two air purifiers under natural ventilation, the amount of virus-containing aerosol in the air was reduced by 86–88% compared to the case with neither natural ventilation nor air purifier. Because natural ventilation significantly varies with weather conditions and particulate matter concentrations, combining natural ventilation with air purifiers in classrooms during winter needs to be adjusted appropriately.

A growing attention has been paid in the last years to the indoor pollutants’ concentrations. In particular, several European Administrations focused on the Particulate Matter with less than 2.5 µm in diameter, i.e., the PM2.5, since it can cause severe respiratory and other health hazards. In the early 2024, the European Union tightened IAQ standards by lowering the annual average PM2.5 threshold value from 25 to 10 µg/m3. Even if PM2.5 generation in the indoor environments is typically linked to printers and office appliances, a significant share is due to natural ventilation through openings adjacent to congested streets or factories.Recently, attention has been paid also to air purifiers, which can contribute to removal of PM2.5, reducing the need for window opening and, consequently, ventilation heat losses. Impact of air purifiers on the energy performance of naturally ventilated buildings, however, has not been investigated in detail, with primary focus put solely on IAQ.In order to discuss the potential of air-purifiers to improve IAQ while optimizing natural and hybrid ventilation strategies, in this research we analyzed a public office building located in Bolzano, Italy, representative of offices designed and constructed in the 1990s in the Italian northern regions. Although the building is equipped with mechanical ventilation system, this is operated only for the removal of pollutants one hour during lunch break, before and after occupancy. In the remaining worktime, employees rely on natural ventilation solutions to improve the IAQ conditions, increasing in such a way thermal losses during the heating season. Furthermore, part of the offices are adjacent to a congested street, meaning that windows opening may allow ingress of outdoor PM2.5 in those spaces. Given these premises, in this research we explored the potential of hybrid ventilation strategies based on optimal window opening schedule and installation of portable air purifiers to improve both IAQ and building energy performance.Whole annual building simulations with a calibrated TRNSYS and TRNFLOW model were performed to estimate energy consumption and CO2 and PM2.5 concentrations in all considered scenarios. Results confirmed that outdoor sources contribute significantly to the increase of indoor PM2.5 concentrations and internal air flows to their distribution to adjacent environments. Air purifiers proved to be effective in controlling PM2.5 in the room where placed, as well as to reduce energy consumption while keeping adequate air changes and CO2 concentrations, with an overall improvement compared to the current practice in the building.

Particulate matter (PM) related ambient pollution has emerged as one of the most significant environmental and human health issues during the last decades. Thus, ambient PM concentration levels have been widely investigated through several studies. On the contrary, investigation of indoor microenvironments, where people spend most of their time, air quality conditions is rather limited.In this study, indoor and outdoor air quality conditions were analyzed across different areas with distinct characteristics towards a better understanding of the complex relationships between indoor and outdoor air quality levels and the mechanisms governing infiltration factors. Simultaneous PM2.5 concentration measurements were conducted, using particle sensors, providing useful information for the identification of Indoor Air Quality (IAQ) variation due to sharp changes in outdoor conditions.The dynamics of PM infiltration factor, the fraction of ambient particles that infiltrate indoors either by mechanical or natural ventilation, that provoked degraded indoor air quality conditions, have also been evaluated. Moreover, an algorithm is developed, based on regression models, to estimate the infiltration factor, through IO (indoor/outdoor) ratios. The estimated infiltration factor would facilitate the quantification of the fraction of the indoor generated particles to the total indoor concentrations.The integration of several parameters such us as building characteristics, ventilation systems, air exchange rates, indoor activities and meteorological conditions will elucidate the mechanisms that affect relationship between outdoor and indoor measurements. These findings could provide substantial knowledge to the relationship between infiltration factor and IAQ that is crucial for promoting healthier indoor environments. The study mainly focuses on time periods where outdoor PM2.5 concentrations are dominant, to model more accurately the infiltration factor and the corresponding IAQ at each measurement site. Overall, the synergy of in situ, outdoor and indoor air quality, measurements and  physical modelling will enhance the knowledge on IAQ and could engage the adoption of better IAQ systems and practices.

Air curtain is an effective control for separating air spaces and reducing the cross-transfer of air, heat, and contaminant between different zones. Studies show that displacement ventilation is better for indoor air quality than mixed ventilation. However, displacement ventilation may be susceptible to a phenomenon called lock-up, whereby contaminants are held in a lower stratified portion of the space and increase infection potential. This study investigates whether indoor air curtain and circulation fan can reduce the lock-up phenomenon for spaces with displacement ventilation and thus reduce infection risk across the breathing zone. Specially, numerical test is conducted to explore if a side-wall diffuser-integrated vertical slot air curtain would be sufficient for reducing infection risk. Additionally, circulation fans above the occupants are applied to explore if they would reduce the lock-up phenomenon. The conclusions are that neither a side air curtain slot nor circulation fans is/are adequate to reduce infection risk. In fact, all methods tested increased infection risk. This increase in infection risk is contrary to previous research and is due to changing air flow patterns throughout the space that disrupted thermal plumes and created contaminant leakage from one side of the room to the other. Circulation fans provided the promising results while further optimization should be conducted in terms of the ideal quantity, location, flow rate, orientation, and size of fans throughout a given space.

This paper assesses, through an extensive literature review, the use of ventilation and High-Efficiency Particulate Air (HEPA) purifiers as practical mitigation strategies for reducing the spread of aerosolized COVID-191 virus. HEPA is a well-defined standard by the U.S. Department of Energy for filters. The focus of the literature review was on indoor air quality (IAQ) and COVID-19, with a particular emphasis on classroom settings. The start of the review, January 2020, was chosen to coincide with the first cases of COVID-19 in North America. Although children under the age of 12 are currently not yet vaccinated, there is mounting pressure for a return to normal by the start of the new school year, 2021. Also, many classrooms lack pre-installed mechanical ventilation systems (Olsiewski et al., 2021); therefore, mitigation in classrooms often falls solely in the hands of teachers and students. Research shows that ventilation and air purification are essential tools to counter aerosolized transmission (Curtius et al. (2020), the inhaled dose of particles containing virus RNA is six times lower when using air purifiers with an ACH (air changes per hour) of 5.7. However, ventilation and air purifiers are not replacements for masks, which remain vital for countering droplet (>5 μm) transmission. In addition, occupancy (i.e., number and proximity of people present in a given area) and group activity levels (e.g., talking, shouting, singing) play a critical role in viral transmission. Although natural ventilation by opening windows can be an essential strategy to help counter the spread of the virus, the level of ventilation offered by opening windows is largely uncontrollable as it is subject to weather conditions and building design. One must also consider the energy implications (i.e., loss of heat) that this strategy carries. Scientific evidence shows that varying levels of continuous and/or intermittent ventilation, either mechanical or natural, combined with the use of HEPA air purifiers, can provide a higher degree of protection than window access alone (Curtius et al., 2020). Systematic deployment of a hybrid mitigation strategy incorporating both ventilation and HEPA air purification in schools, offices, or other facilities offers a practical way to establish a safe re-opening of society in Canada.

In this paper, we use a path model to study natural ventilation in classrooms and research the link between air change rate, occupancy, and both outdoor and indoor physical variables. In general, the path model is derived from the building physics and occupant behavioral considerations via structural equation modeling (SEM), and allows for the use of continuous observable and unobservable factors. The latter are often employed in behavioral and social sciences to represent personal and group attributes. The path model is validated with data gathered during two consecutive academic years from four classrooms of a Portuguese school. The results confirm indoor and outdoor air temperature as major drivers of classroom ventilation, with standardized total path coefficients of approximately 0.55. Solar energy, precipitation, and occupancy are also significant drivers of classroom ventilation, with standardized total path coefficients of 0.24, −0.18, and 0.17, respectively. These results contribute to our understanding of the relative importance of occupancy as well as to identifying the most relevant environmental determinants of natural classroom ventilation. In spite of the statistical significance of the path model as a whole and its detailed causal relationships (direct, indirect, and feedback), only 58% of classroom ventilation variance is explained by the selected input variables. Because naturally ventilated classrooms depend significantly on occupants’ interactions with the built environment, i.e., opening/closing windows and blinds, extending path modeling to include additional personal and context-related drivers of occupants’ behavior would allow for further insights into the complex multi-domain topic of natural classroom ventilation.

• First-time indoor/outdoor black carbon (BC) concentrations reported in hospitals. • Lung-deposited surface area (LDSA) infiltration factors varied between 0.04 and 0.64. • Indoor BC, LDSA, and PM 2.5 concentration varied by factor of 100 between hospitals. • Air cleaners reduced indoor/outdoor ratios of particulate pollution by 70–90 %. • Air purifiers are effective in both mechanically and naturally ventilated spaces. In healthcare facilities, maintaining a controlled, contaminant-free environment is essential. This involves eliminating airborne contaminants and ensuring a continuous supply of clean air. The objectives of this study were to understand the differences in the indoor and outdoor characteristics of particulate matter pollution (fine particle mass (PM 2.5 ), lung-deposited surface area (LDSA), and black carbon mass (BC) concentrations) and environmental conditions (air temperature, relative humidity and carbon dioxide concentration) in hospital buildings in Romania and Finland. Additionally, the effectiveness and impact of ventilation and air cleaning technologies on the indoor air quality were assessed. The highest mean concentrations of outdoor PM 2.5 , LDSA, and BC were observed in Bucharest, with values of 32.7 µg/m³, 59.4 µm²/cm³, and 3.3 µg/m³, respectively. The use of air cleaners effectively reduced indoor particulate concentrations in both naturally and mechanically ventilated buildings. In the naturally ventilated hospital in Bucharest, Romania, the use of air cleaners resulted in reductions of up to 93.8 % and 89.3 % in the median PM 2.5 and LDSA indoor/outdoor (I/O) ratios, respectively. In the mechanically ventilated hospital in Espoo city in Finland, corresponding I/O-ratio reductions were 78.6 % and 69.9 %. These results highlight that indoor air quality is influenced by both indoor and outdoor air characteristics, as well as the building's ventilation and filtration systems. In addition, reduction in indoor concentration values emphasize the effectiveness of using portable air cleaners as a local solution for reducing particulate pollution when integrated with an appropriate natural or mechanical ventilation system.

The characteristics of a hybrid air-conditioning system, utilising natural and mechanical “task” ventilation, are investigated in an office setting. The characteristics of the indoor environment are examined by means of CFD (Computational Fluid Dynamics) simulations under various conditions of incoming outdoor air. The control of the task air conditioning system (VAV system) is included in the calculation through changing the supply air volume to keep the task zone‘s temperature at a target temperature. Results show that the thermal environment at the task zone is maintained comfortably with the aid of mechanical air conditioning and indoor air quality is achieved by providing natural ventilation through window opening. When the temperature of the in-flowing outdoor air rises and the vertical width of the window opening that lets in the air decreases, the inflow jet flows deeper into the room and therefore mixes easily with the indoor air. When the in-flowing outdoor air volume increases, the inflow jet exhibits a 3-dimensional aspect in a room. A vertical temperature gradient appears at the task zone with the increase of the temperature and volume of the in-flowing outdoor air. The distribution of the age of air is strongly influenced by the flow fields. The average age of air at the task zone depends mainly on the natural ventilation rate.

Building ventilation systems are used to mitigate occupant exposure to airborne pollutants such as particulate matter (PM), carbon dioxide and total volatile organic compounds. Building rating systems such as Leadership in Energy and Environmental Design promote the use of natural ventilation to reduce building energy consumption while improving occupant satisfaction. A number of investigations have attempted to compare indoor air quality (IAQ) between spaces with natural or mechanical ventilation without reaching a consensus regarding quantitative impacts. This work provides direct quantitative comparison of the IAQ of a single office space designed for operation with either mechanical or natural ventilation. Natural ventilation has been shown to maintain pollutant accumulation below current standards governing IAQ but is subject to significant airflow variability. In contrast, the mechanical ventilation was shown to result in lower levels of indoor pollution and provide tight control of pollutant levels. The correlation between natural ventilation air exchange rate and concentration of total volatile organic compounds was −0.66 compared to no significant correlation for mechanical ventilation. Average indoor to outdoor PM2.5 ratios were found to be 0.87 and 0.5 for natural and mechanical ventilation, respectively. These results show difficulty in controlling indoor pollutants using prescriptive standard ventilation strategies and that performance-based hybrid ventilation systems provide the most flexibility in meeting IAQ needs.

Solar-assisted naturally ventilated double skin façade for buildings: Room impacts and indoor air quality

Thermal environment of rural residential buildings in Hengyang, China: A two-year on-site study