Natural Ventilation In Buildings Research Articles

Quantification methods of natural ventilated building performance in preliminary design

ABSTRACTNatural ventilation can reduce the operational energy consumption of buildings in an energy-saving, environment-friendly and wholesome manner. This paper uses the existing ISO-standardized energy performance calculator and incorporates a dedicated controllable ventilation model to develop a method for the early design assessment of natural-ventilation-driven cooling with the aim of providing a technical support for studying the goal- and performance-oriented design of buildings adaptable to the regional climate. To facilitate application by architects, the normative model applies a certain degree of simplification, requiring only a small set of macroidentifiers for the considered building and assuming generic ventilation provisions in terms of the window opening size and control logic.

CFD analysis of the effect of uniformly sheared air flow on natural ventilation in building

ABSTRACT Air velocity and hence the temperature uniformity is essential for maintaining the required thermal environment inside poultry building. In this context, ventilation systems in poultry houses play a critical role to ensure appropriate indoor climatic conditions. The objective of this study was to assess the effect of inlet velocity with uniform shear on internal microclimate of poultry house in semi arid region. The main novelty of this work is to evaluate the capacity of the new and original technique of ventilation to supplies fresh air. Air velocities tested in this study is 0.68 m/s, air enters with uniform shear, (S = 1 s−1, S = 0.5 s−1 and S = 1.36 s−1) while the temperature is 22°C. The analysis is extended to wind speed enters without shear S = 0 s−1. Finally, evaluations were provided between the uniform velocity and velocity with uniform shear. The CFD results show a noticeable reduction in microclimate differences if using air flow with uniform shear for natural ventilation. The results showed also a uniformity and homogeneity of temperature and better distribution of air flow at the height of the broilers (0.2 m).

Data-driven model for cross ventilation potential in high-density cities based on coupled CFD simulation and machine learning

Effective urban ventilation through decent urban planning and building design can alleviate the deterioration of the urban built environment. However, natural ventilation requirements and guidelines in current building codes and standards are either qualitative or quantitative but subject to an absolute indoor airspeed threshold without considering the outdoor wind environment. To fill this gap, this paper develops an urban-scale coupled indoor and outdoor computational fluid dynamics (CFD) model and defines a novel ventilation index to assess natural ventilation potential. The index considers wind environments of both indoor and outdoor spaces. First, the coupled CFD model is developed to study wind-driven cross ventilation in high-density cities. A 3D isothermal CFD simulation is solved using the RNG k-ε turbulent model. The simulation results are compared with wind tunnel experiment data from literature. Second, six key design variables are used to generate 3840 parametric design variations for natural ventilation assessment. Third, a novel integrated index CIOIv (coupled indoor and outdoor interaction) is proposed to evaluate the wind speed ratio between the indoor area and outdoor reference area. For demonstration, CIOIv,F1 is used to represent CIOIv on the ground level. Data-driven CIOIv,F1 models are developed to predict indoor building ventilation potential for quick early design support. Compared with multivariate linear regression model, the Gradient Boosting non-linear model displays much higher prediction accuracy (mean absolute percentage error = 0.16 with R2 = 0.8). In early design stage, designers and engineers can skip the computational expensive CFD simulations and use this data-drive model to quickly check the building natural ventilation potentials of different design options in an urban environment.

Optimal control for the natural ventilation in buildings with large depth

This article proposes an optimal control method for the natural ventilation in buildings with large depth. Through designing control strategy, constructing building model, simulating the performance of natural ventilation under different control strategies, the optimal positions of the natural ventilation opening at different floors are decided to achieve the maximum free cooling and minimum cooling consumptions while ensuring the indoor air quality healthy. By using simulation, the cooling energy consumptions at three typical climate conditions, i.e. cool day, warm day, and moderate day, are simulated under two different control strategies, i.e. the proposed optimal control and traditional on/off control of natural ventilation opening. Based on the simulated energy consumptions at the three typical climate conditions, the annual total cooling energy consumptions are estimated. The annual total energy consumptions of optimal control can save cooling energy by 43.5% compared with the traditional on/off control, which shows the energy saving potential and the application prospective of the proposed optimal control method.

A holistic approach to natural ventilation studies

Natural ventilation in buildings can increase thermal comfort and reduce air-conditioning use. However, it is very challenging today to accurately determine the natural ventilation rate through a building. This paper outlines a method to calculate the wind distribution around a building site from information obtained at a meteorological station miles away. This paper also discusses the influence of surrounding buildings on the wind flow around a target building at the site, and presents various geometrical models. In addition, the use of hour-by-hour wind velocity typically available from a meteorological station may give rise to some errors because of the large time step. A correlation method can be employed to convert the hour-by-hour wind velocity to minute-by-minute velocity. One can then use CFD to calculate the airflow around the building and wind-driven cross ventilation through an apartment simultaneously. However, prediction of single-sided natural ventilation is difficult because of the bi-directional flow at the room opening and the complex flow around buildings. This paper presents an empirical model that can predict the mean and fluctuating ventilation rates due to the pulsating flow and eddy penetration of wind-driven single-sided ventilation in buildings with three types of windows. One must use the correct strategy in a building in order to achieve the maximum benefits of natural ventilation.

Case study assessment for natural ventilation performance of heritage buildings in the Mediterranean city of Alexandria (Egypt)

Historic buildings are an important aspect of any city in their capacity to provide cultural reference points. Demonstrating capacity for better levels of energy efficiency and thermal comfort has become a critical challenge to such buildings’ survival. Wind driven natural ventilation in buildings is one way of reducing energy use by dependence on mechanical ventilation. This paper is a case study assessment of a nineteenth-century listed residential building located in the historic business district of the Mediterranean city of Alexandria (Egypt). From an architectural perspective, the European style courtyarded building offers good potential for healthy indoor air replacement, and the Mediterranean climate of the city provides enhanced possibilities for promoting indoor thermal comfort. Yet observation of the building today demonstrates that occupants rely heavily on mechanical ventilation (air conditioning) . It is clear that the building’s original layout has been modified. In this research, we use 3D RANS CFD simulation to investigate the potential for the original layout of the building to enable natural air flow patterns. Simulations are validated against air speed measurements in parts of the building. The results show a detailed natural ventilation deficiency performance in the case study building as modified today, and indicate potential for future improvement. This investigation can help in the understanding of conservation approaches that not only preserve the building’s cultural value but also reclaim its natural ventilation performance.

A holistic approach to natural ventilation studies

Natural ventilation in buildings can increase thermal comfort and reduce air-conditioning use. However, it is very challenging today to accurately determine the natural ventilation rate through a building. This paper outlines a method to calculate the wind distribution around a building site from information obtained at a meteorological station miles away. This paper also discusses the influence of surrounding buildings on the wind flow around a target building at the site, and presents various geometrical models. In addition, the use of hour-by-hour wind velocity typically available from a meteorological station may give rise to some errors because of the large time step. A correlation method can be employed to convert the hour-by-hour wind velocity to minute-by-minute velocity. One can then use CFD to calculate the airflow around the building and wind-driven cross ventilation through an apartment simultaneously. However, prediction of single-sided natural ventilation is difficult because of the bi-directional flow at the room opening and the complex flow around buildings. This paper presents an empirical model that can predict the mean and fluctuating ventilation rates due to the pulsating flow and eddy penetration of wind-driven single-sided ventilation in buildings with three types of windows. One must use the correct strategy in a building in order to achieve the maximum benefits of natural ventilation.

Comparative evaluation of the link between measured and perceived indoor environmental conditions in naturally and mechanically ventilated office environments

This paper uses a case study-based approach to comparatively evaluate the relationship between measured and perceived indoor environmental conditions in two office buildings, one naturally ventilated (NV) and one mechanically ventilated (MV) located in southeast England. Environmental parameters (indoor and outdoor relative humidity (RH), CO2 and indoor and outdoor temperature) were continuously monitored at 5 minute intervals over a period of 19 months (March 2017 to September 2018). During the monitoring period, occupant satisfaction surveys (snapshot and longitudinal) were conducted to record occupant perceptions of their working environment, including thermal comfort, resulting in approximately 2600 survey responses from each case study.In the NV office, CO2 levels were high (>2000ppm) and indoor temperature was both high (>27°C) and variable (up to 8°C change). The MV office environment was found to operate within much narrower indoor temperature, RH and CO2 bands. This was evident in the little seasonal variation observed in the indoor CO2 levels in the MV office; whereas in the NV office, CO2 concentrations were over 1400 ppm for 20% of the working hours during the heating seasons and decreasing to 3% in the non-heating seasons, when windows were frequently opened. Occupants were found to have different levels of tolerance to measured indoor temperatures - neutral thermal sensation votes corresponded to a higher indoor temperature in the NV building, indicating the role of adaptation. Insights from the study can help in improving indoor environments of NV and MV offices.

Thermal Comfort in Naturally Ventilated Classroom: A Literature Review

A phenomenon of global climate change and global warming led to an increase of study on indoor thermal comfort as it causes an increase in air temperature in both outdoor and indoor environments. Thermal comfort of indoor condition had a significant impact on occupants' performance, especially in the educational building. The impact is more crucial in a natural ventilated building as it is influenced by both outdoor and indoor condition. This paper presents an overview of a study on thermal comfort over the past ten years in the classroom that use the passive ventilation system. The study is divided into two sections; the first reviews the variables that are measured to determine thermal comfort and the second section reviews the other factors that could influence the thermal comfort. The factors that have been reviewed include climatic condition, design of ventilation system of the building, building envelope design and occupants behaviour that had influence the thermal comfort in the building, hence influenced the occupants' performance. Most of the studies had found that the occupants were dissatisfied with the indoor environment and the results of the studies found that thermal comfort is not in the comfort range, as stated in the standards. The ventilation factor has been highlighted in most studies to be the crucial factor that influences the indoor environment and thus influence the thermal comfort of the building.

Climate responsive buildings: a comfort assessment of buildings on KNUST campus, Kumasi

Purpose The ever-increasing demand and consumption of energy and the effects of global warming with its long-term comrade, climate change, is obvious today than ever before. In today’s world, naturally-ventilated buildings hardly provide the satisfaction that occupants need and wish for. It’s on this backdrop that the study aims to investigate how responsive buildings on the Kwame Nkrumah University of Science and Technology, Kumasi, Ghana campus are to its warm humid climate and assess students thermal comfort levels. Design/methodology/approach Quantitative approach was adopted for the study. Empirical investigation was carried out using the survey approach. In total, 14 buildings (offices, classrooms and halls of residences) were assessed using the Mahoney Tables. Again, subjective thermal perceptions of occupants in the halls of residences was sought. A total of 214 valid questionnaires were used for the analysis. Findings Adaptive principles like the Mahoney Tables are not followed in recent years. Even where these principles have been followed, indoor spaces were still found to be uncomfortable. In total, 58 per cent of the occupants in all the three halls of residence voted in the comfort band: an indication unacceptable sensations. Warm sensation votes (44 per cent) was more than cool sensation votes (29 per cent). In warm sensation, 39 per cent of the subjects preferred cooler environment. The occupants felt that opening windows and the use of fans could keep them comfortable. Moreover, 48 per cent of the subjects voted that their fans and windows were effective. Originality/value The papers contribution to the body of knowledge is the provision of empirical evidence in the field of adaptive designs and thermal comfort. There is a strong indication from the results that human activities in terms of blatant disregard for laid down design principles coupled with the worsening situation of global warming is making interior spaces ever uncomfortable.

The impact of temperature difference of the sunny and shady yards on the natural ventilation of the vernacular buildings

Natural ventilation is the process of replacing the air in a building with fresh air outside the building, without using ventilating machines, which consume fossil fuel. Natural ventilation is crucially important in the northern region of Iran due to its humid climate. Throughout history, the residents of this region have created airflow in their buildings by producing differential pressure. To do this, they have one shaded yard in the north of their homes and a sunny yard in the southern part of the building; due to temperature difference, the air moves from the high-pressure area to the low-pressure area, passing through the building and ventilating it. The yards are located in proper the parts of the building to change the temperature and pressure in hot seasons.This study aims to examine the effect of southern and northern yards on three properties in the northern region of Iran, in terms of improving natural ventilation in buildings. To do so, the temperatures of yards were simulated in different months of the year using simulation software. In the next step, the rates of ventilation of these buildings and their relationships with the temperatures and the geometrical shapes of the yards were evaluated by employing Computational Fluid Dynamics (CFD). The results show that building 1 had the lowest and the most suitable average indoor temperature and the highest indoor velocity in the daytime, building 2 had the lowest and the most suitable nighttime indoor temperature, and the velocity increased in building 3 indoor at night. By doing this, the more suitable one in natural ventilation was identified. The results of this study can be utilized as a new method for ventilating buildings in densely populated cities.

The Effect of Ventilation Strategies on Indoor Air Quality and Energy Consumptions in Classrooms

Most of the school buildings in Italy are high energy-demanding buildings with no ad-hoc ventilation systems (i.e., naturally-ventilated buildings). Therefore, reducing the heat losses of schools represent the main aspect to be dealt with. Nonetheless, the indoor air quality of the building should be simultaneously considered. Indeed, to date, energy consumptions and air quality are considered as incompatible aspects especially in naturally-ventilated buildings. The aim of the present paper is to evaluate the effect of different ventilation and airing strategies on both indoor air quality and energy consumptions in high energy-demanding naturally-ventilated classrooms. To this purpose, an Italian test-classroom, characterized in terms of air permeability and thermophysical parameters of the envelope, was investigated by means of experimental analyses and simulations through CO2 mass balance equation during the heating season. The air quality was assessed in terms of indoor CO2 concentrations whereas the energy consumptions were evaluated through the asset rating approach. Results clearly report that not adequate indoor CO2 concentrations are measured in the classroom for free-running ventilation scenarios even in low densely populated conditions (2.2 m2 person−1), whereas scheduled airing procedures can reduce the indoor CO2 levels at the cost of higher energy need for ventilation. In particular, when airing periods leading to the air exchange rate required by standards are adopted, the CO2 concentration can decrease to values lower than 1000 ppm, but the ventilation losses increase up to 36% of the overall energy need for space heating of the classroom. On the contrary, when the same air exchange rate is applied through mechanical ventilation systems equipped with heat recovery units, the ventilation energy loss contribution decreases to 5% and the overall energy saving results higher than 30%. Such energy-saving was found even higher for occupancy scenarios characterized by more densely populated conditions of the classroom typically occurring in Italian classrooms.

CFD simulations of natural cross ventilation through an apartment with modified hourly wind information from a meteorological station

Natural ventilation in buildings can improve indoor air quality and thermal comfort and reduce air-conditioning use except for highly polluted area. Traditionally, the inflow boundary conditions for calculating natural ventilation used weather data from a meteorological station that is often in a suburb. The use of hour-by-hour wind velocity from the station may give rise to some errors because of the large time step. This investigation proposed a correlation method for converting the hour-by-hour wind velocity from a meteorological station to minute-by-minute velocity, using data measured on the rooftop of the building of interest. A CFD simulation with the coupled modeling method using the unsteady RNG k-ɛ model was performed to calculate airflow around the building and airflow in an apartment simultaneously. The computed outdoor wind velocity and indoor ventilation rate were compared with the corresponding experimental data. The results showed that the simulations calculated the outdoor wind velocity on the building rooftop and the cross-ventilation rate through the apartment with acceptable accuracy.

Assessing effects of wind speed and wind direction on discharge coefficient of sidewall opening in a dairy building model – A numerical study

The discharge coefficient (Cd) of an opening is an important parameter in the application of the orifice equation to calculate the airflow rate of naturally-ventilated buildings. It is questionable to regard Cd as a constant under varied external airflows for large openings that are often applied in dairy buildings. This study investigated the impact of external wind speed and wind direction on the discharge coefficient of the windward sidewall opening with various opening sizes for a scaled naturally-ventilated dairy building model. The investigations were performed with Computational Fluid Dynamics (CFD) simulations. A set of data from wind tunnel experiments with a building model was used for the CFD model validation. The simulation results indicated that the discharge coefficient was almost unaffected by outdoor wind speed but varied considerably with the wind direction. Lower Cd values were observed for smaller wind angles. The pressure distributions on sidewalls were non-uniform. It is concluded that in the application of the orifice equation in oblique wind directions and large openings, the discharge coefficient is required to be specified instead of using the constant value, and it is necessary to distribute enough pressure taps along the horizontal direction to obtain the representative pressure difference.

Effect of Solar Chimney and PCM cooling ceiling to the air flow inside a naturally-ventilated building

Computational fluid dynamics (CFD) gives significant contributions to building design fields. Building ventilation is the most common problem to simulate in CFD software. 2D and 3D simulation can be used to simulate cross ventilation within the building. ANSYS Fluent is commonly used CFD software, and it has been used in this study to assess the environment of an atrium building under buoyancy-driven natural ventilation and wind-driven natural ventilation. Buoyancy is one of the main forces driving flows. Buoyancy effect happened when the moving fluid is lighter or heavier than surrounding fluid. This paper will elaborate the use of ANSYS Fluent in assessment the environmental performance of a building. Some cases on a building were set in this study. The aim is to simulate accurately buoyancy-driven air flow inside a building for natural ventilation, visualize and analyse simulation results, provide architectural/engineering solution to natural ventilation of buildings. Cooler air appears from ceilings and creates cooling to the room down. Meanwhile, solar chimney generates wind flow across the building due to temperature differences within the chimney.

An approach of calculation and analysis of pulsating flow rate of single-sided ventilation due to unsteady wind pressure

Natural ventilation of buildings has received considerable attention aiming to reduce the energy consumption and CO2 emissions. The flow rate of a single-sided ventilation building due to unsteady wind pressure consists of two elements: mean ventilation rate and fluctuating ventilation rate. To design an efficient ventilation system, an accurate model that is capable of considering the variation of fluctuating flow needs to be developed. In this paper, a novel and simple model was developed that can predict the fluctuating ventilation rate due to the pulsating flow of single-sided, wind-driven natural ventilation in buildings. The model of the pulsating ventilation rate is derived based on the theory of wind engineering, the air compressibility, and inertia of air at the opening. The indoor and outdoor fluctuating wind pressure was constructed using a transfer function. It is found that there was an acceptable relative error of 13.9% compared with Haghighat’s model, which proved that the calculation method is reasonable. Finally, the model had also been used to analyze the effect of influencing parameters such as opening area, room volume, mean wind speed, turbulence intensity of the wind, and power spectrum density analysis on the pulsating ventilation rate.

BIM-based framework to analyze the effect of natural ventilation on thermal comfort and energy performance in buildings

Buildings use significant amount of energy worldwide, with mechanical air-conditioning systems accounting for a large proportion of the total energy consumed. Utilizing natural ventilation can achieve a comfortable indoor thermal environment while reducing the use of air-conditioning and building energy consumption. However, previous studies mainly focused on either thermal comfort or energy conservation by utilizing natural ventilation. The correlation between thermal comfort and energy performance due to the effect of natural ventilation is important, but has not been studied thoroughly in literature. Moreover, natural ventilation in buildings is greatly affected by building geometry, material property, outdoor environmental condition and occupancy, which were not fully incorporated in the previous studies. This paper presents a framework based on building information modeling (BIM) to study the effect of natural ventilation on the correlation between thermal comfort and energy performance. BIM provides 3D building models with detailed geometric and material information as well as the building location and type that help determine the outdoor environmental condition and occupancy, thereby improving the accuracy of natural ventilation simulation. A case study was conducted using the proposed framework, aimed at investigating the natural ventilation in a residential flat in Hong Kong at different seasons. The results show that utilizing natural ventilation cannot always achieve thermal comfort. Natural ventilation brings cool air in late spring (April) during which the indoor temperature can be controlled at a comfortable level and the energy use for mechanical ventilation can be saved. The proposed framework helps evaluate the natural ventilation in buildings for maintaining indoor thermal comfort at minimal energy use, thereby creating a more sustainable built environment.

Bioclimatic modeling for determining the minimum area of natural ventilation in buildings for the wet processing of coffee

Este estudio tuvo como objetivo encontrar el área mínima de ventilación natural necesaria para instalaciones de beneficio húmedo de café con secado mecánico en su interior, con el fin de preservar la calidad de café a través de un ambiente bioclimático que propicie la inocuidad biológica, este estudio se realizó con ayuda de simulaciones computacionales en el programa EnergyPlusTM. Se encontró que a medida que se incrementa la capacidad de secado, y por ende la potencia de las máquinas de secado, la temperatura y la humedad relativa interna tienden a aumentar. Por otra parte, se encontró una correlación lineal inversa entre el área de ventilación natural y las variables temperatura y humedad relativa. Por último, se encontraron relaciones de área mínima de ventilación natural con la capacidad de secado, con el fin de obtener un ambiente bioclimático adecuado para la preservación del café pergamino.

Acoustical Perceptions of Building Occupants on Indoor Environmental Quality in Naturally-Ventilated Building Façades

Accelerated growth of urban population and motor vehicles has resulted in constant exposure to urban traffic noise that is one of the significant environmental stressors in urban environments. The aim of this research as a preliminary study is to evaluate acoustical perceptions of building occupants on their dwelling satisfaction with outdoor traffic noise through naturally-ventilated glazed building facades in the Seoul metropolitan area. This area has the highest population density among the largest countries of Organization for Economic Co-operation and Development (OECD). First, quantitative data of the A-weighted equivalent continuous sound levels (LAeq) at six sites in the Seoul metropolitan area were analyzed, showing that LAeq exceeded the thresholds of noise level standards, 65 dB(A) for day-time (06:00 AM to 10:00 PM) and 55 dB(A) for night-time (10:00 PM to 06:00 AM) respectively. Second, a questionnaire survey was conducted to find the environmental impacts of urban noise transmission on building occupants’ comfort and their ventilation behaviors. It showed that approximately 87% of building occupants (n = 92) used mechanical ventilation systems rather than window ventilation methods. Eighty-two percent of participants have experienced sick building syndrome (SBS)-related symptoms such as skin irritations or coughs. Thirty-three percent of the respondents were deterred from opening windows for natural ventilation due to outdoor traffic noise transmission, and 49% of respondents complained mostly of poor task productivity. The survey outcomes propose the importance of acoustically-treated ventilation openings in naturally-ventilated glazed building facades for building occupants’ indoor environmental quality in high-noise urban areas.

Optimization of window type and vent parameters on single-sided natural ventilation buildings

The residential building sector is one of the major areas to reduce energy demand. In this study, the single-sided top vent-based natural ventilation parameters are optimized using Taguchi technique. The computational fluid dynamics tool is used to simulate the room model. The grid sensitivity analysis is executed to predict more precise results. The operating parameters for top vent and window-based ventilation investigated are top vent width, top vent height, the location of the top vent, the number of top vents and window type with different levels. The orthogonal array, L8, is selected for the conduct of experiments. The signal-to-noise ratio and analysis of variance technique are used to optimize the results. The optimized results showed that the maximum top vent width, top vent height and more number of vents with higher window opening area reduce the maximum indoor air temperature and increase the mass flow rate of a single-sided residential room. Of all, around 60.64% numbers of top vents contributed to indoor temperature reduction. In addition, thermal exergy is also investigated on various vent sectional planes.