Search

Infectious diseases (e.g., coronavirus disease 2019) dramatically impact human life, economy and social development. Exploring the low-cost and energy-saving approaches is essential in removing infectious virus particles from indoors, such as in classrooms. The application of air purification devices, such as negative ion generators (ionizers), gains popularity because of the favorable removal capacity for particles and the low operation cost. However, small and portable ionizers have potential disadvantages in the removal efficiency owing to the limited horizontal diffusion of negative ions. This study aims to investigate the layout strategy (number and location) of ionizers based on the energy-efficient natural ventilation in the classroom to improve removal efficiency (negative ions to particles) and decrease infection risk. Three infected students were considered in the classroom. The simulations of negative ion and particle concentrations were performed and validated by the experiment. Results showed that as the number of ionizers was 4 and 5, the removal performance was largely improved by combining ionizer with natural ventilation. Compared with the scenario without an ionizer, the scenario with 5 ionizers largely increased the average removal efficiency from around 20% to 85% and decreased the average infection risk by 23%. The setup with 5 ionizers placed upstream of the classroom was determined as the optimal layout strategy, particularly when the location and number of the infected students were unknown. This work can provide a guideline for applying ionizers to public buildings when natural ventilation is used.the Appendix is available in the online version of this article at 10.1007/s12273-022-0959-z.

Volatile organic compounds (VOCs) in urban areas are of great interest due to their significant role in forming ground-level ozone and adverse public health effects. Emission inventories usually compile the outdoor VOCs emission sources (e.g., traffic and industrial emissions). However, considering emissions from volatile chemical products (e.g., solvents, printing ink, personal care products) is challenging because of scattered data and the lack of an effective method to estimate the VOCs emission rate from these chemical products. This paper aims to systematically analyse potential sources of VOCs emission in Canada's built environment, including volatile chemical products. Also, spatial variation of VOCs level in the ambient atmosphere is examined to understand the VOC relationship with ozone and secondary organic aerosol formation. The study shows that VOCs level may vary among everyday microenvironments (e.g., residential areas, offices, and retail stores) depending on the frequency of product consumption, building age, ventilation condition, and background ambient concentration in the atmosphere. However, it is very difficult to establish VOC speciation and apportionment to different volatile chemical products that contribute most significantly to exposure and target subpopulations with elevated levels. Thus, tracer compounds can be used to identify inventory sources at the consumer end. A critical overview highlights the limitations of existing VOC estimation methods and possible approaches to control VOC emissions. The findings provide crucial information to establish an emission inventory framework for volatile chemical products at a national scale and enable policymakers to limit VOCs emission from various volatile chemical products.

Several research studies have ranked indoor pollution among the top environmental risks to public health in recent years. Good indoor air quality is an essential component of a healthy indoor environment and significantly affects human health and well-being. Poor air quality in such environments may cause respiratory disease for millions of pupils around the globe and, in the current pandemic-dominated era, require ever more urgent actions to tackle the burden of its impacts.\ud The poor indoor quality in such environments could result from poor management, operation, maintenance, and cleaning. Pupils are a different segment of the population from adults in many ways, and they are more exposed to the poor indoor environment: They breathe in more air per unit weight and are more sensitive to heat/cold and moisture. Thus, their vulnerability is higher than adults, and poor conditions may affect proper development.\ud However, a healthy learning environment can reduce the absence rate, improves test scores, and enhances pupil/teacher learning/teaching productivity. In this article, we analyzed recent literature on indoor air quality and health in schools, with the primary focus on ventilation, thermal comfort, productivity, and exposure risk. This study conducts a comprehensive review to summarizes the existing knowledge to highlight the latest research and solutions and proposes a roadmap for the future school environment. In conclusion, we summarize the critical limitations of the existing studies, reveal insights for future research directions, and propose a roadmap for further improvements in school air quality. More parameters and specific data should be obtained from in-site measurements to get a more in-depth understanding at contaminant characteristics. Meanwhile, site-specific strategies for different school locations, such as proximity to transportation routes and industrial areas, should be developed to suit the characteristics of schools in different regions. The socio-economic consequences of health and performance effects on children in classrooms should be considered. There is a great need for more comprehensive studies with larger sample sizes to study on environmental health exposure, student performance, and indoor satisfaction. More complex mitigation measures should be evaluated by considering energy efficiency, IAQ and health effects.

Latent heat storage systems using phase change materials (PCMs) store large amounts of thermal energy at a near-constant temperature in a compact space. However, PCMs possess relatively low thermal conductivity which prolongs their phase change process; consequently, their applications have been limited. To address this, a numerical investigation was conducted in this study on the heat transfer mechanism in a horizontal shell and multi-finned tube heat exchanger. Erythritol (melting point of 117 °C) was selected as the PCM and Therminol-55 was used as the heat transfer fluid. ANSYS Fluent v. 19.0 was used to numerically solve the governing equations. Once validated by comparing with experimental data, the developed numerical model was then used to investigate the effect of several design parameters regarding tubes and fins on the storage performance. It was found that number of tubes, fin height as well as rotation of fins and tubes significantly influence the melting process. Overall, the melting duration could be decreased by about 44% when the number of tubes increased from 5 to 9. Moreover, the melting time could be decreased by about 31% when the fin height increased from 6 to 15 mm.

Vacuum cleaner is known as a proper way to remove settled dust or aerosols from surfaces to protect building occupants against abiotic and biological particles. In fact, the act of vacuuming the su...

This article provides a state-of-the-art review on emerging applications of smart tools such as data analytics and smart technologies such as Internet-of-things (IoT) in case of design, management and control of energy storage systems. In particular, we have established a classification of the types and targets of various predictive analytics for estimation of load, energy prices, renewable energy inputs, state of the charge, fault diagnosis, etc. In addition, the applications of information technologies, in particular, use of cloud, IoT systems, building management systems (BMS) and building information modeling (BIM) and their contributions tomanagement of energy storage systems will be reviewed in details. The paper concludes by highlighting the emerging issues in smart energy storage systems and providing directions for future research. This article provides a state-of-the-art review on emerging applications of smart tools such as data analytics and smart technologies such as internet-of-things in case of design, management and control of energy storage systems. In particular, we have established a classification of the types and targets of various predictive analytics for estimation of load, energy prices, renewable energy inputs, state of the charge, fault diagnosis, etc. In addition, the applications of information technologies, and in particular, use of cloud, internet-of-things, building management systems and building information modeling and their contributions to management of energy storage systems will be reviewed in details. The paper concludes by highlighting the emerging issues in smart energy storage systems and providing directions for future research.

Utilization of PCM-to-Air Heat Exchangers (PAHXs) in building free cooling applications has been reporting the insufficient cooling charging energy during the PCM solidification, which affects the ...

Purpose One of the most critical infrastructures is a data center (DC) because of it having many servers, computers and other equipment. DCs provide online services for various companies in the information technology (IT) industry. DC facilities should provide reliable online services while addressing the required quality and performance level considering maximum reliability and availability. The purpose of this study is to represent and classify the main findings in this area and to identify the main research gaps and shortcomings from the perspective of research. Design/methodology/approach This paper provides an organized and systematic literature review focusing on topics regarding the operation and maintenance (O&M) management of DCs. Findings Although there are several studies on O&M management systems for industrial systems and facilities, a limited number of studies with few methods and models have focused on DCs so far and these facilities require more attention. This paper identifies the issues and challenges for DC buildings and facilities and provides a conclusion of the findings to highlight the main research limitations for discovering new potential methods as future research opportunities. Research limitations/implications The paper has highlighted the main practical issues of DCs in terms of maintenance management. Several research works have been discussed specifically for DC’s maintenance, which makes this paper a credible source for researchers, maintenance managers and companies involved in the area of DC. Because several of the reviewed literature were based on real case studies, decision-makers in the DC maintenance sector can take advantage of new research on maintenance scheduling to reduce the costs of maintenance. Originality/value The paper has presented a comprehensive list of frequent keywords in recent publications related to O&M management for DCs. It has provided a categorized list of publications based on by their topic, methodology and case study. Because this paper has discussed research works specifically for DC’s maintenance, it is a credible source for researchers, maintenance managers and companies involved in the area of DCs.

The applications of PCM-to-air heat exchangers (PAHXs) face operational challenges regarding the local climatic conditions. One of the main issues is the insufficient cooling potential during the phase change material (PCM) solidification process. In order to increase the cooling charging power of the system, in this study, a unique PAHX type is proposed for building envelope applications. The objective is to magnify the thermal radiation losses from the PCM panels to the nocturnal sky during the solidification process. Two real-scale prototypes were designed and constructed to monitor the effect of radiative cooling on the PAHX thermal behavior during solidification. Accordingly, the cooling performance was investigated for different operational scenarios. In addition, specific key performance indicators were defined to analyze the system charging performance. The experimental results proved that exposure to the clear sky during solidification increases the charging power of the system due to the maximized thermal losses by radiation. The results confirmed that the sky condition and the ambient air temperature profile are key factors in determining the cooling potential of the system. It was shown that making use of the radiation thermal loss to the clear sky increased the charging energy by up to 22% of the proposed PAHX application.

Industrial expansion and increased water consumption have created water scarcity concerns. Meanwhile, conventional wastewater purification methods have failed to degrade recalcitrant pollutants efficiently. The present review paper discusses the recent advances and challenges in photocatalytic processes applied for industrial effluents treatment, with respect to phenolic compounds degradation. Key operational parameters including the catalyst loading, light intensity, initial pollutants concentration, pH, and type and concentrations of oxidants are evaluated and discussed. Compared to the other examined controlling parameters, pH has the highest effect on the photo-oxidation of contaminants by means of the photocatalyst ionization degree and surface charge. Furthermore, major phenolic compounds derived from industrial sources are comprehensively presented and the applicability of photocatalytic processes and the barriers in practical applications, including high energy demand, technical challenges, photocatalyst stability, and recyclability have been explored. The importance of energy consumption and operational costs for realistic large-scale processes are also discussed. Finally, research gaps in this area and the suggested direction for improving degradation efficiencies in industrial applications are presented. In the light of these premises, selective degradation processes in real water matrices such as untreated sewage are proposed.

Photocatalytic oxidation is a promising technology to control air pollution. However, the formation of hazardous by-products hinders the commercialization application of this technology. This paper reports the development of a novel by-products predictive model considering the mass transfer of the pollutant in the gas phase and kinetic reaction in the solid phase. Two challenge compounds from ketone group (acetone and methyl ethyl ketone) were examined for model validation in a continuous Photocatalytic Oxidation (PCO) reactor with TiO2 coated on silica fiber felts. A possible reaction pathway for degradation of each challenge compound was proposed based on identified by-products using analytical methods (GC-MS and HPLC). Formaldehyde, Acetaldehyde, Propionaldehyde, Ethanol, and acetic acid were detected as by-products of the Acetone and Methyl Ethyl Ketone in the PCO reactor. Different possible reaction rate scenarios were evaluated to find the best expression fitted to experimental data at the steady-state condition. The obtained reaction coefficients were then used to validate the model under various operating conditions, namely concentration, relative humidity, irradiation, and velocity variations. Higher concentration and irradiation, as well as lower relative humidity and velocity, resulted in more by-products generation. It was also observed that with enhancing residence time, mineralization efficiency (or CO2 formation) and by-products generation increases through PCO reaction. The model validation provided acceptable accuracy for both steady-state and transient conditions. Finally, the Health Risk Index was used to investigate the implications of generated by-products on human health under varying operating conditions.

During the normalized phase of COVID-19, droplets or aerosol particles produced by infected personnel are considered as the potential source of infection with uncertain exposure risk. As such, in densely populated open spaces, it is necessary to adopt strategies to mitigate the risk of infection disease transmission while providing sufficient ventilation air. An example of such strategies is use of physical barriers. In this study, the impact of barrier heights on the spread of aerosol particles is investigated in an open office environment with the well-designed ventilation mode and supply air rate. The risk of infection disease transmission is evaluated using simulation of particle concentration in different locations and subject to a number of source scenarios. It was found that a barrier height of at least 60cm above the desk surface is needed to effectively prevent the transmission of viruses. For workstations within 4m from the outlet, a 70cm height is considered, and with a proper ventilation mode, it is shown that the barriers can reduce the risk of infection by 72%. However, for the workstations further away from the outlet (beyond 4m), the effect of physical barrier cannot be that significant. In summary, this study provides a theoretical analysis for implementing physical barriers, as a low-cost mitigation strategy, subject to various height scenarios and investigation of their effectiveness in reducing the infection transmission probability.

Thermal energy storage in phase change materials (PCMs) received considerable attention due to the capability of tackling the time mismatch between energy supply and demand, especially for renewable energy sources. Nevertheless, PCMs suffer from some drawbacks preventing their widespread commercialization. In this study, a geometrical heat transfer enhancement technique was investigated to increase the rate of heat transfer from the heat transfer fluid (HTF) to the PCM in a shell-and-tube heat exchanger. The performance of two designs of single and multiple (five) tube heat exchangers (i.e. STHX and MTHX, respectively) were experimentally investigated and compared in terms of average PCM temperature, liquid fraction and stored heat during a complete charging and discharging cycle. It was found that the MTHX out-performed the STHX in terms of phase change duration and stored heat. Furthermore, the validity of a common simplifying assumption in numerical investigation of MTHXs which is considering an artificial cylindrical boundary around each tube was experimentally investigated. This assumption was found to result in inaccuracy meaning that it should no longer be considered in future numerical studies.

In this study, a method to track the melting front of phase change materials (PCMs) is developed under simultaneous charging and discharging (SCD) inside horizontal triplex tube heat exchangers. For SCD, the heat transfer mode of internal heating and external cooling is investigated. According to the heat transfer mechanism within the PCMs, two models of pure conduction (PC) and combined conduction and natural convection (CCNC) are developed and solved using ANSYS Fluent (version 17.2). Generally, during charging (i.e. melting), the buoyancy forces induce the liquid PCM to move upwards; therefore, the upper section of the storage is affected. However, this motion is limited during SCD due to the simultaneous cooling from the outer tube. Therefore, a front tracking method is developed assuming that natural convection only contributes melting to the upper section of the storage unit. On the other hand, it is assumed that the melting front for the lower section behaves similar to the PC model. In this study, three PCMs are used in three geometries to develop the correlations using two dimensionless numbers; i.e. liquid fraction of the PC model and the storage radius ratio. Another PCM is then used to verify the method. The correlations can provide results in the range of ±15% discrepancy.

A novel hydrothermal route was developed to synthesize crystalline and hierarchically porous TiO2 at mild conditions under acidic/basic reaction environments. A good control over the key features of catalysts could be achieved by varying the pH of the starting solution (pH = 2–12) and type of acid during preparation. Crystalline, textural, and optical properties of photocatalysts were characterized in order to explore the connections between catalysts’ features and photoactivity. The activities of catalysts were evaluated for decomposition of methyl ethyl ketone (MEK) in a continuous flow photoreactor. To gain insight into the impact of main operating conditions on photocatalytic oxidation (PCO) processes, experiments were conducted at wide ranges of inlet concentration, relative humidity, and residence time. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that yielded titania samples possess good crystallinity and mainly consist of anatase polymorph. Results of X-ray photoelectron spectroscopy (XPS) indicated that the population of hydroxyl groups on the surface of TiO2 declines as the acidity of hydrothermal solution increases. Hierarchical porous structure with ultra-long parallel macrochannels and large macropores (> 0.5 μm) could be directly observed in scanning electron microscopy (SEM). The multimodal porous structure offers higher light utilization, enhanced mass transport, and superior adsorption capacity for air pollutants. Photoluminescence spectroscopy revealed that the enhancement in crystallinity has an impact on the separation of photo-induced charge carriers. Moreover, a satisfactory linear correlation between the ability of photocatalysts to generate •OH and crystallinity could be found. Under the harshest operating condition (residence time = 0.012 s, relative humidity = 50%, concentration = 1000 ppb), the TiO2 synthesized in nitric acid (pH = 4) achieved the highest MEK removal efficiency, 36.9%, which substantially surpassed that of P25, 14.5%. Hierarchical porosity, optimum trade-off between surface area and crystallinity, existence of meso- and macropores, small crystal size, and high •OH generation ability could account for the superior performance. A tentative reaction pathway for MEK photodegradation and a health-risk index were put forward considering the by-products detected in the gas phase.

A series of porous TiO2 photocatalysts are prepared, by systematically varying the preparation conditions (time, temperature, or pressure (i.e. filling ratio)), characterized, and evaluated in photocatalytic oxidation of toluene and methyl ethyl ketone (MEK) to explore preparation-property-performance relationships. A detailed characterization has been conducted via X-ray diffraction (XRD), N2 adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and UV–vis spectroscopy. Furthermore, hydroxyl radical ( OH) generation on the surface of TiO2 is measured by a photoluminescence (PL) method using terephthalic acid (TA) as probe molecule. All the hydrothermally-prepared samples possessed good crystallinity (79.5–89 %), large surface area (134.9–237.2 m2/g), small crystal size (5.9–10 nm), and mesoporous structure. SEM images revealed presence of macropores and marcochannels, and N2 adsorption-desorption and TEM analyses indicated a significant amount of mesopores. PL and XRD results demonstrated a good proportionality between surface area normalized OH generation and crystallinity. The complex interplay among various properties (especially crystallinity and surface area) led to appearance of activity optimums. Photocatalyst prepared at 12 h, 200 °C, and 80% filling ratio exhibited the best toluene and MEK removal efficiencies, which surpass those of P25 by factors of 2.08 and 1.85 times, respectively. The superior photocatalytic activity of developed TiO2 catalysts might be attributed to high surface area and existence of meso-/macropores that provide a large number of active sites, and facilitate light penetration and pollutants diffusion. The presented property-activity relationships can be utilized as potential design criteria for the development of new TiO2 photocatalysts for air purification.

In this study, a thermal storage system for residential buildings in a Northern climate is developed for electrical peak shifting and shaving. To facilitate implementation, only commercially available products are used for the system in conjunction with common construction methods. A thermal model is created within TRNSYS simulation software and validated using data from a two-year monitoring campaign. The thermal model is used to identify key system parameters and propose system design guidelines. It is determined that, for residential buildings with a footprint varying between 80 m2 to 200 m2, the basement floor slab can be used for thermal storage with electrical heating cables and that the entire basement heating load can, during the peaks, be shifted to off-peak periods. The best assembly for the basement floor is composed of 102 mm of extruded polystyrene insulation followed by 152 mm of concrete. The electric heating cables are positioned at the bottom of the concrete layer. This assembly can be controlled with the air set point temperature (ASPT). The ASPT of basement rooms during charging needs to be 2 °C higher than the ASPT during normal operating conditions. The required charging time for building footprints of 80, 120 160 and 200 m2 corresponds to 6.00, 5.51, 5.05 and 4.66 h, respectively. The main achievement of this study is the determination of key parameters for a low cost and easily implementable electrical activation method for concrete slabs to achieve peak shifting.

Evidence from a various research suggests that buildings hold a vital role in climate change by significantly contributing to the global energy consumption and the emission of greenhouse gases. Considering the trend of higher energy consumption in the building sector, it is important to influence this sector by decreasing its energy demand. District generation and cogeneration systems integrated with the energy storage system have been suggested as a potential solution to achieve such planned goals. Unlike the older generation of the DHS, where the focus of the design was on minimizing the system heat loss, in 4th generation DHS, achieving higher system efficiency is made possible by picking the optimal equipment size as well as adopting the appropriate control strategy. Designers have adopted different design methods for selecting the equipment size, however, finding the optimal size is a challenging task. This paper reports the development of a simplified methodology (dynamic optimization) for a hybrid community-district heating system (H-CDHS) integrated with a thermal energy storage system by coupling the simulation and optimization tools together. Two, existing and newly built communities, have been considered and the results of the optimization on the equipment size of both communities have been studied. The results for the newly built community is later compared with the one obtained from the conventional equipment size methods whereas static optimization methods and potential size reduction with the conventional method has been obtained.