Natural Ventilation In Buildings Research Articles

Wind-driven and buoyancy effects for modeling natural ventilation in buildings at urban scale

Wind-driven and buoyancy effects for modeling natural ventilation in buildings at urban scale

Improving building natural ventilation simulation accuracy: calibration of standard k − ε closure coefficients using design of experiment

Abstract The objective of this study is to improve the accuracy of the standard k − ε (SKE) turbulence model for natural ventilation simulation, a critical component in the analysis and design of energy-efficient buildings. The methodology involves generating 17 design points for the four closure coefficients (C ɛ 1,C ɛ 2,C µ ,σ k ) for the SKE model using 2k full-factorial design of experiment (DOE) with a centre point. A sheltered single storey-building with windward and leeward openings is modelled and simulated using computational Fluid Dynamics (CFD) to obtain the Root Mean Square Error (RMSE) and Factor of two observation (FAC2) for each design point. Response models for RMSE and FAC2 are then generated, and optimization is employed to maximize FAC2, minimize RMSE, and the combination of both. The results are validated and compared with experimental and simulation data reported in existing literature. The findings indicate that the indoor velocity profiles with closure coefficients obtained by maximizing FAC2 are better aligned with the actual experimental results. Compared with the existing calibration method, the proposed calibration method can yield superior results with fewer sampling points, highlighting the efficiency of the proposed approach. The calibration framework developed in this study can be extended to other simulation scenarios, contributing to the robust and efficient modelling of natural ventilation systems in various contexts. This research presents a novel calibration method for the SKE model in natural ventilation simulation, providing a more accurate and efficient approach compared to existing methods. The results have important implications for researchers and practitioners working in the field of building energy simulation and sustainability.

Analyzing the thermal performance of walling systems in low-income housing through computational fluid dynamics approach

The thermal properties of wall materials have a direct impact on the thermal performance of the indoor environment, by also influencing the occupant’s well-being. Coupled with airflow dynamics, the thermal performance of wall materials influences the indoor air temperature distribution thereby impacting thermal comfort, particularly in naturally ventilated (NV) spaces. However, defining the relationships between the wall characteristics, airflow dynamics, and thermal comfort for selecting the appropriate wall material for low-income NV buildings is still not evident in the current literature. Therefore, this study proposes a simulation-based framework that considers the relationships between wall materials, airflow dynamics, and thermal comfort using a computational fluid dynamics (CFD) approach by spatially plotting the thermal comfort within the NV spaces.The study analyses locally accessible wall materials, subjecting them to different operating conditions within NV dwelling units of low-income housing in India. Out of the analyzed wall materials, aerated autoclaved blocks exhibited a significant indoor temperature reduction of 20.7 % compared to the compressed stabilized earth blocks, with constrained airflow exacerbating temperature fluctuations. The global implications of these findings are substantial for urban low-income dwellers experiencing excessive heat. Mass housing efforts worldwide can benefit from using thermally efficient materials in construction thereby improving living conditions, and mitigating the impact of climate change on thermal comfort and health.

Flow regimes in emptying–filling boxes with two buoyancy sources of differing strengths and elevations

Emptying–filling boxes have been studied in a wide range of configurations for decades, but the flow created in the box by two plumes rising from sources of arbitrary strength and elevation was previously unsolved. Guided by experiments and simplified analytical modelling, we reveal a rich array of two- and three-layer stratifications across seven possible flow regimes. The governing equations for these regimes show how the prevailing regime and stratification properties vary with three key parameters: the relative strength of the plumes, the height difference between their sources and a parameter characterising the resistance of the box to emptying. We observe and explain new behaviours not described in previous studies that are crucial to understanding emptying–filling boxes with multiple plumes. In particular, we demonstrate that the oft-assumed premise that $n$ plumes leads to a stratification with $n+1$ layers is not necessarily true, even in the absence of mixing. Two emptying–filling box models are developed: an analytical model addressing all combinations of the governing parameters and an extended model for three-layer stratifications that incorporates two mixing processes observed in the experiments. The predictions of these two models are in generally excellent agreement with measurements from the experimental campaign covering 69 combinations of the governing parameters. This study improves our understanding of emptying–filling boxes and could facilitate improvements to natural ventilation building design, as demonstrated by an example scenario in which occupants feel cooler upon the addition of a second source of heat.

Utilizing periodic boundary conditions to save computational resources for assessing building natural ventilation in urban areas

For the first time in literature, we innovatively conducted CFD simulations with periodic boundary conditions to predict coupled indoor-outdoor airflows for a full-scale 3D six-floor residential building unit in urban areas with uniformly building clusters. A few influencing parameters on building ventilation performance are comprehensively analyzed, including the impacts of the surrounding buildings, wind incident angle (θ), external opening designs, cross or single-sided ventilation modes, and indoor facilities. Ventilation evaluation is contingent on factors including air change rate per hour (ACH), the corresponding ACH of purging flow rate (ACHPFR), and age of air (τ).Results show that the efficiency of natural ventilation on each floor differs from previous research conclusions after considering the impacts of surrounding buildings. Single-sided ventilation is significantly less effective than cross-ventilation in all scenarios. Most cross-ventilation cases have one-order greater ACH and ACHPFR values compared to those with single-sided ventilation. The window-to-wall ratio on the windward and leeward sides can affect the natural ventilation rate of the corresponding rooms. A large leeward opening helps to increase the ventilation rate, especially for the rooms on the upper floor, but it decreases the ventilation for the rooms near the ground. Indoor furniture has an insignificant impact on outdoor airflow and natural ventilation efficiency.

Influence of deflectors on indoor airflow velocity distribution under natural ventilation conditions

Deflectors offer a cost-effective solution for enhancing airflow distribution. The purpose of this paper is to investigate the effect of the deflector on the indoor airflow velocity distribution under natural ventilation conditions. The results obtained from numerical simulations are validated through experimental measurements using a reduced-scale model. Subsequently, the validated reduced-scale numerical model was extended to full-size rooms. A full-size numerical simulation method is used to analyze the effect of no deflector, deflectors with different opening width-to-height ratios and deflectors with different opening shapes on the percentage of indoor velocity partitions under natural ventilation conditions. The findings reveal that the judicious installation of deflectors can enhance indoor airflow velocity distribution and increase the percentage of the indoor comfort zone. Deflectors with different opening width-to-height ratios exert distinct influences on indoor airflow velocity distribution. When the deflector opening width-to-height ratio is set at 7/6, the indoor comfort zone percentage reaches its maximum at 75.98%. Furthermore, the shape of the deflector’s opening significantly affects indoor airflow velocity distribution, and when the opening shape is a rhombus shape of 4.00 cm × 9.00 cm, the proportion of indoor velocity comfort zone is the largest, which is 75.56%. This study provides a reference for the design and practice of natural ventilation in buildings.

Investigation of natural ventilation using a solar chimney in various solar cases

The high cost of conventional energy production, its uses, and its negative environmental impact led scientists to look for many ways to solve this problem. The main issues are environmental pollution, the high cost of air treatment, and the high cost of energy production. An essential solution is using renewable energy instead of traditional energy (petroleum, coal, natural gas, and electric power). As it is a permanent energy source, it causes no air pollution and is cheaper. In this work, an experimental study was conducted on using solar energy as an energy source in the natural ventilation of buildings and the factors affecting this ventilation. A solar chimney has been installed with and without storage materials to store energy for natural identity during sunrise and after sunset. In this work, the difference in air density with different temperatures is the main factor for energy production, which leads to a change in the airspeed (natural ventilation). The study indicates that indoor air velocity can remain higher than ambient air velocity during the day and at night for several hours. This reduces demand and dependence on conventional energy usage, which leads to cost reductions and a reduction in air and environmental pollution.

The Numerical Simulation Study of Pumping Airflow Driven by Wind Pressure for Single- and Multi-Room Buildings

Pumping airflow occurs in single-sided natural ventilation buildings when the openings are located on the leeward side; the direction of airflow through the building then changes periodicity. In order to propose a calculation method of the ventilation rates for single-room buildings and analyze the pumping ventilation for multi-room buildings, the CFD method with an SST k-ω turbulence model was used to conduct numerical simulation in this study, which is verified by other experimental results. Firstly, the qualitative and quantitative characteristics of pumping ventilation were investigated for a single-room building with two openings. The results show that the steady-state method underestimates the ventilation flow rates, and the unsteady-state method captures the microstructures of the flow better. Secondly, the vortex-shedding and indoor airflow oscillation frequencies were analyzed based on transient simulation for a single-room building. It was found that both of them increase with air speed. Then, the factors affecting ventilation flow rates were analyzed. A calculation method for dimensionless ventilation rates is proposed. Finally, the pumping ventilation for a multi-room building was numerically simulated. The ventilation rate for a middle room is greater than that for a corner room, and the ventilation rate for any room in a multi-room building is greater than the single-room building given the same room size and the same incoming wind speed. The findings of this paper are helpful for the design and evaluation of natural ventilation.

Experimental evaluation of airflow guiding components for wind-driven single-sided natural ventilation: A comparative study in a test chamber

Single-sided ventilation is a frequently employed ventilation strategy in contemporary structures, yet its effectiveness is often mediocre, underscoring the need for solutions to enhance its performance. To evaluate the effect of louvres and guide vanes on the effective ventilation rate, 21 different louvre configurations and four guide vane designs were compared with a plain opening for single-sided ventilation in a full-scale experimental test chamber under three different magnitudes of local wind velocity. Ventilation rates were measured using the tracer gas decay method with 12 NDIR CO2 sensors. The findings, obtained under specific test conditions, indicate that deeper openings result in a decline in ventilation rate performance. It was observed that wider guide vanes lead to higher ventilation rates, suggesting their potential to enhance SSV performance. The results reveal that, in most cases, louvres contribute to a decline in the system's performance. However, the ventilation rate is influenced by the angle and number of louvres, with optimal performance observed at specific angles and fewer louvres. These findings provide valuable insights for optimizing the design of airflow-guiding components in wind-driven single-sided ventilation systems, enabling the development of more efficient and customized solutions for natural ventilation in buildings.

Impact of roof shape on indoor gaseous pollutant level for natural ventilation buildings in a street canyon: Numerical simulation

Introduction: Coupling the indoor and outdoor airflow of roadside buildings in a street canyon, the impact of flat and triangular roofs on indoor air pollutant concentration and ventilation rates of naturally ventilated buildings is studied using numerical simulation methods.
 Materials and methods: The flow and pollutant diffusion control equations are solved by using ANSYS Fluent. In simulation, RNG k-ε turbulence model is adopted. The numerical model is validated using the three-dimensional street canyon test data from the wind tunnel experiment at University of Karlsruhe.
 Results: The flow and pollutant concentration distributions under different roof shapes are obtained. The ventilation rates with different air flow resistances and pollution level indoors are provided.
 Conclusion: Ventilation direction through windows of roadside buildings determines the level of indoor air polluted by vehicle emissions in street canyon. When the building main height equals to the width of the street, flat roofs make the indoor concentration basically consistent with that near the external walls of the canyon. The higher the triangular roofs, the higher the ventilation rate and the lower the indoor concentration. The ventilation rate is influenced not only by roofs, but also by the floor location and indoor ventilation resistance.v

Thermal Comfort and Microclimate in Indoor Spaces of Low-rise Residential Buildings in Dry Tropical Climate

The aim of this research is to analyze thermal comfort and microclimate for indoor spaces in low-rise residential buildings in dry tropical climate. The study area is the municipality of Palmar de Varela in northern Colombia. The experimental methodology is based on measuring three microclimatic parameters: air temperature (Ta), relative humidity (RH) and natural ventilation (W). The study assessed the thermal sensation in indoor spaces based on Thermal Sensation Vote (TSV) and Predicted mean vote (PMV). Data gathered from surveys were analyzed with data mining technologies. The findings suggest that suspended ceilings and ceramic tiles aid to the thermal equilibrium of the building, resulting in a 1.1 °C decrease in indoor air temperature. Likewise, the correlation between temperature and wind (r = -0.72; -0.56) indicates that natural ventilation in buildings can alleviate thermal discomfort. Based on the thermal sensation evaluation, the predominant feeling reported by interviewees in indoor spaces was warm (2) in S1 and S2, and slightly warm (1) in S3. In addition, the correlation between air temperature and comfort sensation in indoor spaces (r = 0.64; 0.44) suggests that temperature has a direct impact on thermal sensation votes.

The Investigation of Indoor Air Temperature Effects for Different Types of Window Dimensions Using CFD Simulation

Windows plays an important role in heat transfer and natural ventilation in buildings. In the field of building design, the challenge is to provide a thermally comfortable indoor environment that requires the least energy consumption to maintain. One of the energy reduction alternatives that can be incorporated into modern building design is the installation of efficient windows. The windows should allow thermally acceptable indoor air quality and have a pleasant design while being energy efficient. Good thermal conditions in school buildings, especially learning spaces, promote the educational process. Unfulfilling comfort levels can reduce the lecturers’ and students' physical and intellectual performance. One of the variables that affect the thermal comfort condition is indoor air temperature. The purpose of this study is to investigate the effect of window size on indoor air temperature by using Computational Fluid Dynamics (CFD) simulation. The selected classroom at Universiti Teknologi MARA (UiTM) Permatang Pauh, Pulau Pinang will be used as a case study. The field measurement result can be used to validate the simulation result. The simulation result will be compared to standard regulations set by the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) Standard 55-2017. Three different sizes of windows have been chosen in this study which are double, triple, and quadruple-glazed windows. The validation result shows the percentage difference in indoor air temperature between the experimental and simulation is 1.04 %. The result found double and triple-glazed windows show the value of temperature under the range set by ASHRAE Standard 55-2017. The selection of triple-glazed windows is more suitable because the brightness of the classroom meets the criteria for the absence of direct solar radiation. In conclusion, the size of the window shows the performance in terms of heat transfer and indoor air temperature of the classroom.

Designing and testing the applicability of a natural green ventilation building block in an Egyptian Climatic zone using waste materials

Natural ventilation is one of the ways used to enhance building spaces' indoor air quality, especially after the COVID-19 pandemic. It also saves energy by utilizing natural wind forces to provide internal building spaces with fresh air instead of energy-consuming mechanical systems. For a multiple-floor building, adding external wall ventilation blocks can improve natural cross ventilation by catching and directing fresh air from the external prevailing wind into its internal spaces. This research aimed to enhance the building's natural ventilation by using environmentally friendly blocks. This was done by designing a green block using marble and granite waste materials as a partial substitute for conventional materials in the block. Styrofoam beads were added to the block’s mixture to reduce its weight. The block’s shape was designed to direct fresh air through building side walls by the use of natural wind pressure. The block was developed from the initial shape of the standard hollow block to a block with a wind catcher. Ventilation block shape simulations were done using (ANSYS fluent) computational fluid dynamics (CFD) software to determine the best inlet angle, catcher angle, and catcher length. The study revealed that by increasing the block inlet angle more than 45°, the block outlet air velocity starts to decrease due to the flow separation in the front part of the block inlet. The catcher angle ranged from 65° to 85°, and the catcher’s ability to redirect the airflow is decreased at a catcher angle greater than 85°. The best nondimensional catcher length-to-block length ratio (height /length) h/L was 0.625. Substitution of 5% of cement by granite in the presence of 0.15 Kg of Styrofoam (C5G) produced a lightweight green ventilation block of weight 19.3 kg. Whereas, the substitution of 15% of sand for marble in the presence of 1 Kg of Styrofoam (S15M) produced a lightweight green ventilation block of weight 15.9 kg. The produced block was tested in a building located in New Cairo City (a region currently having a tremendous increase in the building construction sector) as a study sample representing one of the Egyptian Climatic zones. The research concluded that it is preferred to allocate the building corners towards the prevailing wind direction to prevent airflow separation and to magnify the quantities of air along the building sides.

Kajian Kebutuhan Ventilasi Alami Ruangan pada Bangunan Gedung

The Indonesian National Standard (SNI) 6572:2001 on natural ventilation in buildings has not been updated in the last 20 years, while similar standards in other countries have been periodically improved. The development of science and technology, environmental conditions, coupled with the COVID-19 pandemic that affects the entire world are the basis for consideration of the adjustment of related standards. The purpose of this study is to look at the standards for natural ventilation in several countries, namely the United States, Singapore, Malaysia, and Australia, as well as identify criteria that can be applied according to conditions in Indonesia. The results showed that the need for natural ventilation in buildings in Indonesia by 5% has met the existing conditions. However, further studies regarding the need for natural ventilation that are adjusted based on the function of the room as determined by ASHRAE 62.1 need to be carried out.

Model predictive control of short-term winter natural ventilation in a smart building using machine learning algorithms

Natural ventilation in buildings has the potential to reduce building energy consumption and the incidence of sick building syndrome. However, controlling natural ventilation is often challenging. For instance, natural ventilation through operable windows may cause cold draughts for the occupants in winter. This paper presents the key findings of a novel machine learning-based model predicted control of single-sided natural ventilation in a retrofitted four-story smart building in Cambridge, Massachusetts, in the northeast region of the United States. A data-driven methodology is used to realize this natural ventilation modeling, including data collection, system dynamics identification, and control formulation. The prediction model of indoor CO2 and room air temperature is built through a learning process. The model predictive control (MPC) formulation step combines thermal comfort and indoor air quality requirements. Finally, the natural ventilation MPC is tested in the real building, and the results showed that indoor air quality and thermal comfort are maintained successfully, without increasing significantly the heating energy consumption in winter. This scalable data-driven methodology can potentially be applied to natural ventilation in smart buildings.

Assessment of exhaled pathogenic droplet dispersion and indoor-outdoor exposure risk in urban street with naturally-ventilated buildings

Assessment of exhaled pathogenic droplet dispersion and indoor-outdoor exposure risk in urban street with naturally-ventilated buildings

Feasibility of applying an electrostatic precipitator integrated with a naturally ventilated double-skin façade in residential buildings

One of the main advantages of applying a double-skin façade (DSF) is allowing natural ventilation. As concerns about high outdoor particle concentrations increase, maintaining comfortable indoor air quality through natural ventilation in buildings with DSFs becomes difficult. An electrostatic precipitator (ESP) integrated with a DSF (EPID) has been proposed for maximizing the natural ventilation in buildings with polluted outdoor air. In this study, the particle removal performance and ozone generation of the EPID were experimentally evaluated to determine the feasibility of applying it in residential buildings. An EPID prototype was constructed, and laboratory experiments were performed to measure the single-pass particle removal efficiency and concentration of ozone, a byproduct of the ESP. The results showed that the average particle removal efficiency (77.4 ± 5.5%) at the upper ESP position is similar to that at the lower ESP position (78.5 ± 11.6%) for 0.25–1.82 μm particles at 9 kV applied voltage and 0.5 ms−1 inlet air velocity. When the inlet air velocity increases to 2.0 ms−1, the particle removal efficiency decreases to 39.7% depending on the ESP position. Moreover, the ESP position significantly influences the particle removal efficiency because it changes the inlet air velocity, especially at low applied voltages. Our results highlight the importance of determining the appropriate ESP position in the EPID for residential applications because low-voltage operation is recommended for the safety of occupants and reduction in ozone generation. In addition, at 0.5 ms−1 inlet air velocity, at which the EPID has excellent removal performance, the net ozone concentrations are 33.0 ppb and 35.7 ppb at 6 kV and 9 kV, respectively, which are all lower than the threshold (50 ppb), regardless of the ESP position. The results of this study verify the feasibility of applying the EPID and have important implications for future EPID designs and developing control strategies to improve the indoor air quality of naturally ventilated residential buildings with DSFs.

NUMERICAL ANALYSIS OF CIRCULATION AND DISPERSION OF POLLUTANTS IN VENTILATED BUILDINGS UNDER NON-ISOTHERMAL CONDITIONS

Air quality, thermal comfort and internal circulation in urban areas are closely linked to the promotion of natural ventilation in buildings. In this sense, the main objectives of the present work are to study the effect of internal circulation in buildings with different openings and the phenomenon of pollutant dispersion in naturally ventilated buildings under non-isothermal conditions using a numerical model for incompressible flows with heat and mass transport. For the flow simulation, a semi-implicit Characteristic-Based Split (CBS) scheme is used in the context of the Finite Element Method (FEM), where linear tetrahedral elements are used for spatial discretization. Turbulence is treated using the Large Eddy Simulation (LES) methodology and thermal effects are considered in the momentum balance equation through buoyancy forces, which are calculated taking into account the Boussinesq approximation. Classical examples are analyzed to verify the numerical model proposed here, as well as the forms of natural ventilation and, finally, a numerical investigation is carried out considering the dispersion of pollutants and the thermal effects simultaneously. In addition to ensuring air exchange while maintaining a healthy environment, ventilation helps to disperse pollutants and promotes thermal comfort, both inside the building and in the street canyon, as indicated by results obtained.

Towards a Wind Urbanism in Tropical Environments

One of the conditions for the proper functioning of passive comfort in humid tropical environments is access to natural ventilation in buildings. This notion of access to natural ventilation has taken on its full meaning during the current health crisis.
 Based on this observation established by a rich literature, we asked ourselves how to ensure the sustainability of the good functioning of natural ventilation in a humid tropical environment of a building in a built complex? This questioning led us to show the importance of the context through various dimensions: the chain of natural ventilation, the programmatic context, the climatic and geographical context, the regulatory context.
 Taking these parameters into account has allowed us, in the context of a case study, the eco-district Cœur de ville de La Possession, on the island of La Réunion, to develop a new conceptual approach associating urban planning and aeraulic engineering from the beginning of the design process for maximum efficiency.
 To this end, we initiated a new approach based on: co-design, the use of physical wind tunnel simulation at different scales, the integration of environmental, architectural and landscape recommendations at the scale of the district and of the buildings making up this district, in an enforceable urban planning regulation. This has enabled us, within the framework of this eco-district, to develop the concept of the right to natural ventilation, of the windy city and of the guarantee over time of the preservation of this potential.
 The transcription of this approach in other eco-neighbourhoods in a tropical environment seems to us to be a major challenge to be considered and which could even be extended to other climatic zones, in the context of current global warming.

A new design to create natural ventilation in buildings: Wind chimney

The global warming crisis and the increase in urban population are significant issues for human society. It has required using passive solutions in various industry sectors, particularly construction. The primary purpose of this study was to propose a novel and creative passive element for creating natural ventilation in buildings in coastal areas and areas with a prevailing wind flow. This novel element works according to the aerodynamics law and the difference in air pressure due to wind flow, called wind chimney. CFD was used in Comsol Multiphysics software for simulation to achieve this aim, and data validation was performed using the wind tunnel. Initially, the wind chimneys with nine different aerodynamic forms for two cases of buildings in the coastal area of Bushehr, Iran, were simulated as case studies. In building A, the wind chimney was located on one side. In building B, it was situated in the middle of the building. The performance of the wind chimneys has been compared to obtain the best aerodynamic form for each building. The results showed that case seven of aerodynamic form for building A, and case three of aerodynamic form for building B had the best performance in terms of natural ventilation. In addition, the parametric optimization of the aerodynamic form was performed in terms of location and angle. The best performance case was proposed for buildings A and B to utilize in buildings as an innovative passive element. The air flow rate of the wind chimney's output for buildings A and B was 3.66 m2/s and 13.2 m2/s, respectively, which was 116.5% and 98.8% higher than wind chimneys without aerodynamic form, respectively. Moreover, the ACH of building A with an optimized wind chimney was 117.9% higher than building without it, and this amount for building B was calculated at 98.7%.