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.
Display omitted
•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.
Display omitted
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.
The World Health Organization (WHO) announced that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may spread through aerosols, so-called airborne transmission, especially in a poorly ...ventilated indoor environment. Ventilation protects the occupants against airborne transmission. Various studies have been performed on the importance of sufficient ventilation for diluting the concentration of virus and lowering any subsequent dose inhaled by the occupants. However, the ventilation situation can be problematic in public buildings and other shared spaces, such as shops, offices, schools, and restaurants. If ventilation is provided by opening windows, the outdoor airflow rate depends strongly on the specific local conditions (opening sizes, relative positions, climatic and weather conditions).
This study uses field measurements to analyze the natural ventilation performance in a school building according to the window opening rates, positions, and weather conditions. The ventilation rates were calculated by the tracer gas decay method, and the infection risk was assessed using the Wells-Riley equation. Under cross-ventilation conditions, the average ventilation rates were measured at 6.51 h−1 for 15% window opening, and 11.20 h−1 for 30% window opening. For single-sided ventilation, the ventilation rates were reduced to about 30% of the values from the cross-ventilation cases. The infection probability is less than 1% in all cases when a mask is worn and more than 15% of the windows are open with cross-ventilation. With single-sided ventilation, if the exposure time is less than 1 h, the infection probability can be kept less than 1% with a mask. However, the infection probability exceeds 1% in all cases where exposure time is greater than 2 h, regardless of whether or not a mask is worn. Also, when the air conditioner was operated with a window opening ratio of 15%, power consumption increased by 10.2%.
Display omitted
•Appropriate window opening rates to prevent viral air infection were analyzed.•Under cross-ventilation, the ventilation rates were 6.51 h−1 for 15% opening ratio.•For single-sided ventilation, the ventilation rates were reduced by about 30%.•Infection probability was less than 1% by 15% window opening and wearing a mask.•Power consumption for air-conditioning increased by 10.2% under 15% opening ratio.
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.
Display omitted
•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.
Radon-222, a radioactive noble gas with a half-life of 3.8 days produced by radium-226, is a health hazard in caves, but also a powerful tracer of atmospheric dynamics. Here we show how airborne ...radon-222 can be analysed in a cave with multiple openings, the Pech Merle Cave in South-West France. This two-level cave hosts prehistoric remains and Gravettian paintings in its lower level. Radon concentration, monitored at 15 points with one-hour sampling intervals for more than one year, including two points for more than three years, showed mean values from 1274 ± 11 to 5281 ± 20 Bq m−3, with transient values above 15,000 Bq m−3. Seasonal variations were observed, with a weak normal cycle (low in winter) at two points in the upper level and a pronounced inverse seasonal cycle (low in summer) at the other points in the cave. The radon-222 source (effective radium-226 concentration, ECRa) was measured in the laboratory for floor deposits, soil and rock samples. While ECRa values obtained for rocks and speleothems are smaller than 1 Bq kg−1, most ECRa values for soils are larger than 10 Bq kg−1. Quantitative modelling confirms that the floor fillings inside the cave are responsible for the stationary lower concentrations, while the higher concentrations observed in winter are explained by percolation of outside air, which collects radon-222 as it passes through the soil layers. In addition, Stored Available Radon (SAR) is sufficient to account for transient variations. While air currents occur when visitors enter the cave or when the cave is deliberately ventilated, the climatic processes revealed by their radon-222 signatures appear to be essentially natural. These processes, enhanced by global climate change, could cause or accelerate the deterioration of prehistoric paintings. Radon-222 source analysis using ECRa-based modelling and SAR appears essential for the preservation of underground heritage.
Display omitted
•222Rn in air (RnA) monitored at 15 points in the two-level Pech Merle Painted Cave.•RnA has weak normal (upper level) and strong inverse (lower level) seasonal cycles.•The natural entrance at upper level competes with porous leakage at lower level.•Low RnA (~4 kBq/m3) in summer is accommodated by diffusive flux from the cave floor.•High RnA (>10 kBq/m3) in winter due to Rn-rich cold air seeping down from surface
•Natural ventilation potential is affected largely by ambient air pollution in China.•NV hours of 76 Chinese cities based on weather and ambient air quality are estimated.•Cooling energy savings and ...carbon reductions of 35 major Chinese cities are estimated.•8–78% of the cooling energy usage can be potentially reduced by NV.•Our findings provide guidelines to improve energy policies in China.
Natural ventilation (NV) is a key sustainable solution for reducing the energy use in buildings, improving thermal comfort, and maintaining a healthy indoor environment. However, the energy savings and environmental benefits are affected greatly by ambient air pollution in China. Here we estimate the NV potential of all major Chinese cities based on weather, ambient air quality, building configuration, and newly constructed square footage of office buildings in the year of 2015. In general, little NV potential is observed in northern China during the winter and southern China during the summer. Kunming located in the Southwest China is the most weather-favorable city for natural ventilation, and reveals almost no loss due to air pollution. Building Energy Simulation (BES) is conducted to estimate the energy savings of natural ventilation in which ambient air pollution and total square footage at each city must be taken into account. Beijing, the capital city, displays limited per-square-meter saving potential due to the unfavorable weather and air quality for natural ventilation, but its largest total square footage of office buildings makes it become the city with the greatest energy saving opportunity in China. Our analysis shows that the aggregated energy savings potential of office buildings at 35 major Chinese cities is 112GWh in 2015, even after allowing for a 43GWh loss due to China’s serious air pollution issue especially in North China. 8–78% of the cooling energy consumption can be potentially reduced by natural ventilation depending on local weather and air quality. The findings here provide guidelines for improving current energy and environmental policies in China, and a direction for reforming building codes.
PDF
