This book contains twenty-one original papers and one review paper published by internationally recognized experts in the Atmosphere Special Issue "Recent Advances in Urban Ventilation Assessment and ...Flow Modelling", years 2017–2019. The Special Issue includes contributions on recent experimental and modelling works, techniques, and developments mainly tailored to the assessment of urban ventilation on flow and pollutant dispersion in cities. The study of ventilation is of critical importance, as it addresses the capacity with which a built urban structure is capable of replacing the polluted air with ambient fresh air. Here, ventilation is recognized as a transport process that improves local microclimate and air quality and closely relates to the term “breathability”. The efficiency with which street canyon ventilation occurs depends on the complex interaction between the atmospheric boundary layer flow and the local urban morphology.The individual contributions to this Issue are summarized and categorized into four broad topics: (1) outdoor ventilation efficiency and application/development of ventilation indices, (2) relationship between indoor and outdoor ventilation, (3) effects of urban morphology and obstacles to ventilation, and (4) ventilation modelling in realistic urban districts. The results and approaches presented and proposed will be of great interest to experimentalists and modelers, and may constitute a starting point for the improvement of numerical simulations of flow and pollutant dispersion in the urban environment, for the development of simulation tools, and for the implementation of mitigation strategies.
Different parameters could contribute to the performance of Building Integrated Semi-Transparent Photovoltaic/Thermal (BISTPV/T) systems, for example amount of incident radiation, the location, the ...degree of semi-transparency of the PV system, orientation of the collector surface, and the mode of ventilation of the air within the double-skin façade (DSF). Nevertheless, the performance of the system could not be solely depended on energy efficiency but has to be analyzed in its entirety. Thus, exergy efficiency must be examined as well. The present work studies the exergy, exergoeconomic and enviroeconomic analysis of BISTPV/T system by natural ventilation. For a given meteorological conditions, the energy and exergy efficiency, net and ratio loss rate, CO2 emission and enviroeconomic reduction are calculated by solving a set of energy and exergy formulations. The results depicted that the BISTPV/T exhibits greater energy and exergy efficiency than the opaque BIPV/T, thus creating lower loss rate and eventually better impact economy and environment.
Left: Prototype of the double skin PV façade. Right: single prism element showing PV and glazed surfaces. Display omitted
•Exergy, exergoeconomic and enviroeconomic analyses of a (BISTPV/T) system.•BISTPV/T exhibits greater exergy efficiency than the opaque BIPV/T.•BISTPV/T creates less CO2 emission and higher enviroeconomic reduction.
Seasonal and daily variations of gaseous emissions from naturally ventilated dairy cattle barns are important figures for the establishment of effective and specific mitigation plans. The present ...study aimed to measure methane (CH4) and ammonia (NH3) emissions in three naturally ventilated dairy cattle barns covering the four seasons for two consecutive years. In each barn, air samples from five indoor locations were drawn by a multipoint sampler to a photoacoustic infrared multigas monitor, along with temperature and relative humidity. Milk production data were also recorded. Results showed seasonal differences for CH4 and NH3 emissions in the three barns with no clear trends within years. Globally, diel CH4 emissions increased in the daytime with high intra-hour variability. The average hourly CH4 emissions (g h−1 livestock unit−1 (LU)) varied from 8.1 to 11.2 and 6.2 to 20.3 in the dairy barn 1, from 10.1 to 31.4 and 10.9 to 22.8 in the dairy barn 2, and from 1.5 to 8.2 and 13.1 to 22.1 in the dairy barn 3, respectively, in years 1 and 2. Diel NH3 emissions highly varied within hours and increased in the daytime. The average hourly NH3 emissions (g h−1 LU−1) varied from 0.78 to 1.56 and 0.50 to 1.38 in the dairy barn 1, from 1.04 to 3.40 and 0.93 to 1.98 in the dairy barn 2, and from 0.66 to 1.32 and 1.67 to 1.73 in the dairy barn 3, respectively, in years 1 and 2. Moreover, the emission factors of CH4 and NH3 were 309.5 and 30.6 (g day−1 LU−1), respectively, for naturally ventilated dairy cattle barns. Overall, this study provided a detailed characterization of seasonal and daily gaseous emissions variations highlighting the need for future longitudinal emission studies and identifying an opportunity to better adequate the existing mitigation strategies according to season and daytime.
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•Daily and seasonal CH4 and NH3 emissions were assessed in two consecutive years.•Both emissions increased in daytime and varied among seasons.•High intra-hour variability was observed during daytime for both gases.•NH3 emissions presented an emission peak in the middle day in all seasons.•The CH4 and NH3 emission factors were 309.5 and 30.6 g−1 day−1 LU−1.
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Acceptable indoor air quality (IAQ) is one of the most relevant aspects of a healthy home environment. Despite advances in mechanical and hybrid ventilation systems, natural ...ventilation still constitutes a crucial intervention to improve IAQ in existing homes; especially in older and/or vulnerable ones. The challenge, however, is optimizing natural ventilation strategies so IAQ is reached while thermal discomfort (and potentially associated energy consumption) is minimized.
The complexity of identifying factors that may determine the possibilities of natural ventilation in existing homes has traditionally hindered the efforts from the scientific community to communicate straightforward answers for end-users. This work develops a methodology that, based on real case studies and through a series of simulations, provides simple, context-specific criteria and recommendations in order to reach acceptable IAQ through natural ventilation strategies in existing homes. The use of a minimum ventilation time (MVT) indicator, alongside considerations for different seasons and housing types, are translated into step-by-step guidelines aimed at helping the end-user to (i) gain knowledge regarding the opportunities and limitations for natural ventilation in the dwelling, and (ii) identify which specific actions should be carried out under different conditions to maintain minimum IAQ.
The conceptual framework and methodology presented, while illustrated for the case of Barcelona, can be replicated for different cities or regions with differing housing characteristics and climatological conditions, and can easily accommodate other locally relevant factors.
Advanced control strategies are central components of smart buildings. For model-based control algorithms, the quality of the model that represents building systems and dynamics is essential to ...guarantee satisfactory performance of smart building control and automation. For the model predictive control of the heating, ventilation, and air conditioning systems in buildings coupled with natural ventilation, a high-fidelity model is necessary to reliably predict the thermal responses of the building under various environmental and operational conditions. This task can be accomplished by using a deep neural network, which can capture the dynamics of complicated physical processes, such as natural ventilation. Training a deep neural network requires the collection of a large amount of data; however, in practice, the target building may not have enough operational data available. This study demonstrates how transfer learning could help with this dilemma. By freezing most layers of a deep neural network model with 42,902 parameters that are pre-trained on multi-year data from a source room in Beijing, the model can be re-trained with only 200 trainable parameters on only 15 days of data from the target room in Shanghai that has entirely different floor area, building material, and window size. The proposed transfer learning model achieves high accuracy predicting both indoor air temperature and relative humidity for a time horizon from 10 minutes to 2 hours, showing the mean squared error almost one magnitude smaller than the comparison model that is only trained on source data or target data. This methodology can be applied to the design of the control system in a new building which reduces the required amount of data for the training of the model, thus saving costs in control system design and commissioning.
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•ASHRAE et al. recommends increasing indoor fresh air supply to mitigate COVID-19 spread.•Increased fresh air supply may double energy costs when operating a conventional HVAC ...system.•We propose an HVAC solution which couples novel radiant systems with natural ventilation.•We estimate this solution would address thermal comfort needs in all major climate zones.•Where adopted, this solution could reduce building HVAC energy demand by 10–45%.
Radiant cooling-assisted natural ventilation is an innovative technical approach that combines new radiant cooling technology with natural ventilation to increase fresh air delivery into buildings year-round with minimal energy cost and improvment of air quality. Currently, the standard paradigm for HVAC (heating, ventilation and air conditioning) is based on central air systems that tie the delivery of heating and cooling to the delivery of fresh air. To prevent heat loss, the delivery of fresh air must be tightly controlled and is often limited through recirculation of already heated or cooled air. Buildings are designed with airtight envelopes, which do not allow for natural ventilation, and depend on energy-intensive central-air systems. As closed environments, buildings have become sites of rapid COVID-19 transmission. In this research, we demonstrate the energy cost of increasing outdoor air supply with standard systems per COVID-19 recommendations and introduce an alternative HVAC paradigm that maximizes the decoupling of ventilation and thermal control. We first consider a novel analysis of the energy costs of increasing the amount of conditioned fresh air using standard HVAC systems to address COVID-19 concerns. We then present an alternative that includes a novel membrane-assisted radiant system we have studied for cooling in humid climates, in place of an air conditioning system. The proposed system can work in conjunction with natural ventilation and thus decreases the risk of indoor spread of infectious diseases and significantly lowers energy consumption in buildings. Our results for modeling HVAC energy in different climates show that increasing outdoor air in standard systems can double cooling costs, while increasing natural ventilation with radiant systems can halve costs. More specifically, it is possible to add up to 100 days’ worth of natural ventilation while saving energy when coupling natural ventilation and radiant systems. This combination decreases energy costs by 10–45% in 60 major cities globally, while increasing fresh air intake.
In buildings, energy is primarily consumed by mechanical air conditioning systems. Low energy alternatives, such as natural ventilation, are needed. However, they need to be able to cope with ...increasing heatwaves and pollution, particularly in warm climates. This review paper looked at the ability of natural ventilation to provide adequate thermal comfort, resilience against heatwaves, and good Indoor Air Quality in warm climates. Single-sided ventilation demonstrates the poorest ability to provide thermal comfort, while cross ventilation highlights better performance in terms of reducing indoor air temperatures compared to outdoor. However, windcatchers and solar chimneys displayed even better performance by producing relatively high ventilation rates. During heatwaves and future climatic scenarios, natural ventilation, by cross-ventilation, was not able to meet internal thermal comfort standards. A potential low energy solution could be combining solar chimneys or windcatchers with water evaporation cooling. A critical synthesis of the literature suggests that these systems can generate high ventilation rates and keep indoor temperatures around 8 °C cooler than outdoor temperatures in warm weather (>35 °C). However, no studies were found testing these systems against future climate scenarios, and further studies are recommended. The literature supported natural ventilation being effective in removing pollution generated indoors due to adequate ventilation rates. However, using unfiltered natural ventilation for areas with high outdoor pollution can increase the indoor deposition of harmful particulate matter. With increasing air pollution, further studies are urgently required to investigate filter enabled natural ventilation, particularly with solar chimney/windcatcher incorporated.
•Single-sided or cross ventilation won't meet thermal comfort in future warm climate.•Windcatcher and solar chimney show promise for good Indoor Air Quality in hot climate.•Natural ventilation with evaporative cooling can be resilient to heatwaves.•Further studies required on heatwave resilient natural ventilation in warm climates.•Research on filter enabled natural ventilation for pollution control is lacking.
Combination of natural ventilation approaches is a new trend for free space cooling/heating in buildings. A critical review was then undertaken to provide an overview of the combined technologies ...that hope to initialize new ideas and promote future endeavors. The advantages of the integrated natural ventilation systems can be summarized into several principles, including achieving beyond the existing performance by single system, maintaining indoor temperature stability, realizing heat energy recovery, overcoming the inadequacy of a single system, and providing a more comprehensive and useful energy-saving scheme. Most of the existing studies on combined systems are found based on thermal buoyancy, while only a small amount dealt with the combination of wind-driven and buoyancy-induce due to the complexity. Parametric studies in most previous studies focused on several major ones, so a systematic analysis is critically needed to address the performance of the overall combination to achieve stable and durable performance. A thoughtful investigation is also required to avert unpredictable delivery of air flow, such as through the manipulation of external wind forces. The related research focuses should also be shifted following the trend of multi-storey buildings under the rapidly growing population. No guideline was found that arranges these natural ventilation systems in terms of performance and applicability for their practical selections and usages. Also, the thermal bridge breaking in cold winter and condensation in summer may compromise the natural ventilation performance and durability, and longevity of buildings. The studies on the coupling between different natural ventilation systems are still insufficient, requiring quite a bit of effort in future works.
•Combined natural ventilation systems in single building were reviewed.•Advantages of combined natural ventilation systems were summarized.•Existing systems much reply on thermal buoyancy but not combined buoyancy and wind.•Research focuses should be shifted following the trend of multi-storey buildings.•Studies on coupling different natural ventilation systems are still insufficient.
This paper has analysed the influence of cross-sectional area and aspect ratio of shaft on natural ventilation in urban road tunnel fires by Large Eddy Simulation (LES). Results have shown that the ...performance of smoke exhausting process displays different smoke extraction modes with the increasing of the cross-sectional aspect ratio. When the cross-sectional aspect ratio increases to a certain value, the hot smoke will be adhered to the upstream wall of the shaft and be exhausted through the upstream region. In this case, the cold air from tunnel bottom penetrates the vertical shaft leading to the smoke exhausting process inefficiently. The 2-D line plume in near region could be used to predict the process of hot smoke exhausting by shaft upstream after penetration and the predicted values give a good agreement with the simulated values. It comes to conclusion that the shaft with larger cross-sectional aspect ratio should be divided into several smaller shafts in order to exhaust as much smoke as possible and avoid overmuch entrainment of fresh air.
Outdoor ventilation is very important for a healthy and livable urban environment. It is strongly influenced by wind speed and direction, which in turn are affected by urban morphology. This paper ...first provides a detailed review of the literature for CFD studies of outdoor ventilation for generic urban configurations. The review indicates that there is a clear lack of studies for urban configurations where not all parallel streets have equal street widths. Next, the paper presents Computational Fluid Dynamics (CFD) simulations of outdoor ventilation for generic configurations with parallel streets of equal and unequal street widths. The 3D steady RANS equations with the standard k- model and the passive scalar transport equation are used to calculate the effective local mean age of air at pedestrian level as an indicator of pollutant removal efficiency. The study is based on grid-convergence analysis and on validation with previously published wind-tunnel measurements. The influence of a central and wider main street on the wind-velocity pattern and on the effective local mean age of air of the surrounding area is analyzed for different wind directions. For wind directions oblique or perpendicular to the main street, the presence of this main street generally improves the ventilation efficiency because the main street acts as a sink of clean air. However, this is generally not the case for the parallel wind direction, where the higher flow rate through the main street reduces the flow rates through the parallel narrower streets, negatively affecting their ventilation efficiency.
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