Natural Ventilation In Buildings Research Articles

The impact of building operations on urban heat/cool islands under urban densification: A comparison between naturally-ventilated and air-conditioned buildings

Many cities are suffering the effects of urban heat islands (UHI) or urban cool islands (UCI) due to rapid urban expansion and numerous infrastructure developments. This paper presents a lumped urban-building thermal coupling model which captures the fundamental physical mechanism for thermal interactions between buildings and their urban environment. The benefits of the model are its simplicity and high computational efficiency for practical use in investigating the diurnal urban air temperature change and its asymmetry in a city with both naturally-ventilated (NV) and air-conditioned (AC) buildings. Our model predicts a lower urban heat island and higher urban cool island intensity in a city with naturally-ventilated buildings than for a city with air-conditioned buildings. During the urban densification (from a low-rise, low-density city to a high-rise, high-density one), the increases in the time constant and internal heat gain give rise to asymmetric warming phenomena, which become more obvious in a city with air-conditioned buildings rather than naturally-ventilated ones. Unlike previous studies, we found that a low-rise, low-density city experiences a stronger urban cool island effect than a high-rise, high-density city due to less heat being emitted into the urban atmosphere. The urban cool/heat island effect will firstly increase/decrease, and then rapidly decrease/increase and ultimately disappear/dominate with increasing time constant in the process of urbanization/urban densification.

Wind tunnel investigations of sidewall opening effects on indoor airflows of a cross-ventilated dairy building

Well-understanding indoor air movement with respect to openings in naturally-ventilated buildings is essential to provide healthy and comfortable indoor climate for livestock. This study investigated the effects of the sidewall opening configurations on internal airflow fields and air velocity characteristics within the animal occupied zone (AOZ). Eight cases with varied opening ratios and locations were tested under 8 m•s-1 free wind speed and wind direction perpendicular to the sidewalls. The ‘up-jet’ airflow pattern was observed when the opening ratio was no greater than 62.71% and the openings located beneath the eaves. Air went across the AOZ without circulating with the surrounding air when no sidewalls were installed below the AOZ height. Both air speed and turbulent kinetic energy increased when the opening was bigger with Pearson's correlation coefficients of 0.8 and 0.9 respectively, but the relationship between the opening size and the turbulence intensity was more complex. Uniform air speed distributions were observed in the AOZ with high sidewalls on bottom. By contrast, the air speed heterogeneity in the AOZ was found when sidewall heights were below the AOZ height. We conclude that care should be taken when using these kinds of opening configurations during extreme cold windy weather conditions.

Transient investigation of stack-driven airflow process through rectangular cross-ventilated building with two vents in the absence of opposing flow in the upper opening

Natural ventilation of building provides improvement of internal comfort and air quality conditions leading to a significant reduction of cool-ing energy consumption. Design of natural ventilation systems for many types of building is based on buoyancy forces. However, external wind flow can have significant effects on buoyancy- driven natural ventilation. The paper was concerned with transient investigation of airflow through two vents in the absence of opposing flow in the upper opening. A flow of this type represents a new class of boundary- layer flow problems in the building. Moreover, this is an exact solution of the complete Navier- Stokes Equations (including, buoyancy force term), which were then Non Dimensionalised using some dimensionless parameters and then solved analytically by separation of variable methods in which, the behavior of parameters in the results were predicts the velocity, temperature profiles together with volumetric airflow and mass transfer. The results were then evaluated numerically for several sets of values of the parameters in order to ascertain the best for optimal ventilation.

Improving the performance of solar chimney by addressing the designing factors

Solar chimney is a reliable system totally based on solar energy to enhance natural ventilation in buildings, but challenge still exists to optimize its performance with the lowest cost. In this study, three designing factors, including configuration, installation conditions, and material usages, were reviewed to provide a technical guide for engineering applications. Regarding the configuration, the performance of solar chimney can be enhanced with a high cavity, an appropriate cavity gap (usually 0.2-0.3 m), equivalent inlet and outlet area, and height/gap ratio of 10-15. Regarding installation conditions, an optimum inclination angle of 45° was usually suggested, and large openings can enhance the performance while the increasing rate keeps decreasing. The principles of material usage are to maximum the heat absorption and reduce the heat losses, considering properties such as thermal conductivity, absorptivity, emissivity, transmissvity, and reflectivity.

Field measurement of natural ventilation rate in an idealised full-scale building located in a staggered urban array: Comparison between tracer gas and pressure-based methods

Currently, no clear standards exist for determining urban building natural ventilation rates, especially under varying realistic meteorological conditions. In this study, ventilation rates are determined using tracer gas decay and pressure-based measurements for a full-scale (6 m tall) cube. The cube was either isolated (2 months of observations) or sheltered within a staggered array (7 months), for both single-sided and cross ventilation (openings 0.4 m × 1 m). Wind speeds at cube height ranged between 0.04 m s−1 and 13.1 m s−1. Errors for both ventilation methods are carefully assessed. There is no discernible linear relation between normalised ventilation rates from the two methods, except for cross ventilation in the array case. The ratio of tracer gas and pressure derived ventilation rates is assessed with wind direction. For single-sided (leeward opening) cases it approached 1. For cross ventilation the ratio was closer to 1 but with more scatter. One explanation is that agreement is better when internal mixing is less jet-dominated, i.e. for oblique directions in the isolated case and for all directions for unsteady array flows. Sheltering may reduce the flushing rate of the tracer gas from the cube relative to internal mixing rate. This new dataset provides an extensive range of conditions for numerical model evaluation and for understanding uncertainty of ventilation rates. Knowledge of the latter is critical in building design.

Statistical analysis of wind data using Weibull distribution for natural ventilation estimation

Incorporating natural ventilation in buildings can have significant benefits. Nevertheless, realistic wind conditions continually change. Airflow rate estimation methods that assume wind speed and direction as being constant are thus error-prone. To elucidate wind variability and its effect on airflow rate estimation, the Weibull distribution was used in the current study to represent high-resolution historical wind data, statistically, for a 1-year period. A preliminary investigation was carried out on categorizing the wind by its statistical characteristic, and two distinct wind speed distributions were found by applying the K-means algorithm in the categorization process. The yearly distribution of days in two different clusters showed seasonal changes. The wind data from the same clustering was grouped and utilized to estimate the airflow rate in the form of probability density. The results were in good agreement with the full-scale experiment measurements of a 10-day test in Austin, Texas. The proposed method could be used to characterize wind speed variances, especially with a small time step wind data and enables building designers to do a statistical analysis of airflow.

Thermal Assessment of a Novel Combine Evaporative Cooling Wind Catcher

Wind catchers are one of the oldest cooling systems that are employed to provide sufficient natural ventilation in buildings. In this study, a laboratory scale wind catcher was equipped with a combined evaporative system. The designed assembly was comprised of a one-sided opening with an adjustable wetted pad unit and a wetted blades section. Theoretical analysis of the wind catcher was carried out and a set of experiments were organized to validate the results of the obtained models. The effect of wind speed, wind catcher height, and mode of the opening unit (open or closed) was investigated on temperature drop and velocity of the moving air through the wind catcher as well as provided sensible cooling load. The results showed that under windy conditions, inside air velocity was slightly higher when the pad was open. Vice versa, when the wind speed was zero, the closed pad resulted in an enhancement in air velocity inside the wind catcher. At wind catcher heights of 2.5 and 3.5 m and wind speeds of lower than 3 m/s, cooling loads have been approximately doubled by applying the closed-pad mode.

Air infiltration rates in the bedrooms of 202 residences and estimated parametric infiltration rate distribution in Guangzhou, China

This study investigates the overnight air infiltration rates of 202 natural ventilated bedrooms, measured in August to September 2016 (cooling season) in Guangzhou, China. The rates were calculated and analyzed based on a single zone mass balance equation, using CO2 produced by the sleeping occupants as tracer gas source. It was found that additional ventilation is required to satisfy the Chinese building code, where only 16% had the minimum required amount of ventilation. The air infiltration rates fit a log-normal distribution (R2 = 0.85) ranging from 0.05 to 1.32 h−1, with an arithmetic mean of 0.41 h−1. None of these parameters had an effect on the air infiltration rate distribution: Absolute indoor and outdoor temperature difference, window age, building type (two different window standards), floor level of bedroom and openable window area. The provided data can be used in analyzing cooling energy and indoor air quality from outdoor pollution in natural ventilated residential buildings in south China.

Wind tunnel study of natural ventilation of building integrated photovoltaics double skin façade

The paper presents a wind tunnel experimental analysis of a small-scale building model (1:30). The objective of the study is to determine the wind influence on the ventilation of a double skin façade channel (DSF) and the cooling effect over integrated photovoltaic panels. The tests were achieved by conceiving and implementation of an experimental program using a wind tunnel with atmospheric boundary layer. The effect of the wind over the ventilation of the horizontal channels of double skin façades is evaluated for different incident velocities. The results are generalized for the average steady state values of the velocities analysed. The experimental results put in evidence the correlation between the reference wind velocity and the dynamics of the air movement inside the double skin façade. These values are used to determine the convective heat transfer and the cooling effect of the air streams inside the channel upon the integrated photovoltaic panels. The decrease of the photovoltaic panels temperature determines a raise of 11% in efficiency and power generated.

History of Building Natural Ventilation Research in Japan - A Review

History of Building Natural Ventilation Research in Japan - A Review

Analysis of Airflow and Cooling Effect according to Opening Area of ​​Building Natural Ventilation

Analysis of Airflow and Cooling Effect according to Opening Area of ​​Building Natural Ventilation

The Study Natural Ventilation by Using Buildings Windows: Case Study in a Hot Dry Climate, Ghardaïa, Algeria

Natural ventilation in buildings can create a comfortable and healthy indoor environment, and save energy used in the mechanical ventilation systems, have an important role on the balance between heating and cooling needs, It is also necessary to study the possible combinations with natural resources.With natural ventilation the internal building structure is cooled through open windows and/or air vents, in order to provide a wind induced flow or stack effect. It is dependent on natural forces to move air through a building: so the disadvantage is that there is no direct control of the ventilation, but on the other hand it delivers low running costs and low energy usage by reducing the electrical energy used for air-conditioning.The building design must implement simple principles based on common sense and have proven their effectiveness in traditional constructions. It must be adapted to seasonal needs (warm in winter, cool in summer) and promote maximum passive solar gain and minimize lossesIn the first part of this article, the building geometry, its operation and the thermo-aerodynamics numerical model are developed under the TRNSYS-CONTAM environment are presented. In the second part, the simulation is performed for both cases; with ventilation natural night and without natural ventilation. The study will ensure the night ventilation door and window of the cell which are open from 20 pm until 8 am.

Wind-induced single-sided natural ventilation in buildings near a long street canyon: CFD evaluation of street configuration and envelope design

Wind-induced single-sided natural ventilation in buildings was widely investigated based on isolated buildings. However, owing to the presence of surrounding buildings, the wind flow pattern around a building in an urban area becomes very different from that around an isolated building. Considering an urban context, this study investigates the wind-induced single-sided natural ventilation in buildings near a long street canyon under a perpendicular wind direction using CFD method. Four aspect ratios (AR) of the street canyon, from 1.0, 2.0, 4.0 to 6.0, are investigated to examine the influence of street configuration, while eight envelope features are compared to explore the possibility of envelope design in improving natural ventilation performance of urban buildings. Ventilation rate of rooms in buildings is particularly analyzed. AR influences ventilation rate and its distribution among rooms along height of buildings. The percentage decrease of ventilation rate of buildings reaches 67% when AR of a street canyon is increased from 1.0 to 6.0. Envelope design provides a possibility to enhance the adaptability of buildings to dense urban environments. A good envelope design, such as a horizontal feature at the middle of an opening, can break effectively the along-facade flow and thus create a large pressure difference to drive ventilation. The findings of this study are intended to increase the understanding of natural ventilation performance in urban buildings and thus provide information for urban planning and building design.

A study on terraced apartments and their natural ventilation performance in hot and humid regions

Terraced apartments as a typology of the buildings are new approaches to meet energy conservation targets. This principle in the form of interactive spaces contributes to an incorporation of interior and exterior, daylight addition and exploitation of natural ventilation. This study mainly investigates the natural ventilation exploitation of a terraced apartment in the hot and humid region. One solid block and 4 porous apartments with different terrace depths (TD) are evaluated using computational fluid dynamics (CFD) analysis. The k-e turbulence model was adapted to simulate airflow in and around a mid-rise building with 42 residential blocks. CFD analysis compares the effect of permeability in the form of terraces on wind behaviour and natural ventilation efficiency in a mid-rise building. Ventilation assessment parameters such as mean air velocity and mean age of air are measured to compare the natural ventilation performance. The simulation results clearly indicate that the implementation of permeability in the form of terraces can enhance building natural ventilation performance significantly. However, it is proved that some physical configurations such as terrace depth can influence this performance greatly. According to the results, increasing the terrace depth up to 1.2 meters will enhance the mean wind velocity 40%–88% inside the room, 10.61%–12.29% near the window and 63.44% on the openings. Velocity diagram follows a descending process after TD 1.2. The mean wind speed decreases to 25.53% inside the room, 15.09% inside terraces and 1.09% near the window. The average wind velocity on the openings is revealed to be 1.54 to 1.64 times larger in the porous models than the solid one. On the other hand, porous cases indicate lower values for the mean age of air compared to the solid model. This study provides proper guidelines to predict ventilation performance and to improve the design of naturally ventilated mid-rise buildings in hot and humid regions.

Natural Ventilation of Buildings through Light Shafts. Design-Based Solution Proposals

This work analyses how the built environment affects the quality of the air to be introduced into buildings from light shafts. Several factors such as urban environment and building design intervene in the ability of the light shaft to produce its air change process. Urban areas continuously pollute the air in cities which affects the human health and the environment sustainability. Poor air quality outside buildings supposes a big energy waste to promote an acceptable air quality inside buildings. That requires a large flow rate to maintain the indoor air quality which is translated to an energy efficiency term.The main objective focuses on the impact of standardized architecture design in the quality of the indoor air dependent on the air change in the light shaft. The air change capacity of the outdoor space is numbered analysed using the concept of air change efficiency (ACE). ACE is determined by the built environment, the wind conditions and the design of the building containing light shafts. This concept is comparatively evaluated inside a control domain virtually defined to obtain the mean age of the air for a known air volume.The longer the light shaft in the wind direction is, the better the ACE is compared with other options. Light shafts up to 12 metres high are the most suitable in order to obtain acceptable efficiency results. Other studied cases verify that assumption.Different simplified tools for the technicians to evaluate the design of buildings containing light shafts are proposed. Some strategies of architectural design of buildings with light shafts to be used for ventilation are presented.

Understanding User Satisfaction Evaluation in Low Occupancy Sustainable Workplaces

This paper presents the findings of a post-occupancy evaluation (POE) applied to a building in the UK. The design of the building was generated through an externally funded research project over two years from 2005 to 2007. The construction of the building was completed in 2010. After a period of occupancy, a POE of the building was carried out in 2015. The POE offered an opportunity to investigate the effect of occupant behaviour on the performance of the building and their level of comfort and satisfaction. We adopted a field survey method to evaluate the comfort and satisfaction of users by asking them a series of questions to analyse how they felt in different parts of the building throughout the course of the year. In our analysis, the users were prompted to provide a subjective measure of the building regarding a range of internal conditions such as air temperature, humidity, air movement, air quality, daylight, artificial light, and noise. The analysis supports the notion that in naturally-ventilated buildings some users may find the building to be hot in summer while cold in winter. The high level of control the users have over the operation of the building contributes to their comfort and satisfaction. The users demonstrated a tendency to be satisfied despite environmental factors and to forgive some aspects of the building which are not performing as they should. The paper offers a perspective on statistical user satisfaction in a low occupancy building and attempts to explain the role of workplace wellbeing on occupant perception of comfort in this case.

INDOOR THERMAL COMFORT ASSESSMENT OF NATURALLY VENTILATED ATRIUMS IN SINGAPORE

This research looks into the aspect of Thermal Comfort (TC) in naturally ventilated (NV) buildings, in this case NV atriums. Compared to fully air-conditioned buildings, NV buildings tend to have better indoor air quality (IAQ), but worse TC. Therefore, this research investigates the range of acceptable temperature and wind speed in order to achieve thermal comfort for naturally ventilated atriums. Data was collected through field survey in three different buildings of NV atriums and were used to develop and validate the TC model. The data collected from field survey represent visitors’ TC perception in atrium environment, and in-situ environmental measurement also records the characteristics of NV atrium in each area, such as solar radiation, air temperature, relative humidity, and intermittent wind. At the same time with the indoor field survey, a weather station was installed on the roof of the building to measure the micro-meteorological condition. Thermal comfort prediction model was developed from the statistical analysis of the field survey data. The acceptable range to achieve thermal comfort for NV atrium was analyzed. The air temperature of 31°C was determined as the boundary condition. Based on the result of Predicted Mean Vote (PMV) formula, PMV 1 is the highest acceptable value with wind speed required is 0.51 m/s and PMV 0.8 is recommended to achieve the best thermal comfort with wind speed required is 0.78 m/s.

Performance Evaluation of a Modular Design of Wind Tower with Wetted Surfaces

Wind towers or wind catchers, as passive cooling systems, can provide natural ventilation in buildings located in hot, arid regions. These natural cooling systems can provide thermal comfort for the building inhabitants throughout the warm months. In this paper, a modular design of a wind tower is introduced. The design, called a modular wind tower with wetted surfaces, was investigated experimentally and analytically. To determine the performance of the wind tower, air temperature, relative humidity (RH) and air velocity were measured at different points. Measurements were carried out when the wind speed was zero. The experimental results were compared with the analytical ones. The results illustrated that the modular wind tower can decrease the air temperature significantly and increase the relative humidity of airflow into the building. The average differences for air temperature and air relative humidity between ambient air and air exiting from the wind tower were approximately 10 °C and 40%, respectively. The main advantage of the proposed wind tower is that it is a modular design that can reduce the cost of wind tower construction.

The Effect of Balcony to Enhance Natural Ventilation in Local Houses in Mazandaran Province

<p>Utilization of natural ventilation in buildings has a long history. Architecture has been trying to response to weather conditions all the time. Wind catcher, mashrabiya, portico and iwan are some examples of climate designs in vernacular architecture which have shown the importance of natural ventilation since a long time ago. The efficiency scope of natural ventilation when used with other cooling techniques will be more widespread. Today, designing desirable buildings using natural ventilation requires knowing theoretical foundations and a detailed study based on new knowledge regarding the feasibility of the use of components design and equipment related to natural ventilation. The present research aims to offer architects some design solutions in order to take advantage of natural ventilation in buildings using the vernacular architecture. Through matching features of functional spaces in local houses with climatic characteristics of regions around the Caspian sea (Mazandaran province) and determining the pattern used in these spaces in housing areas, the present study seeks to answer this question: “Are types of local houses in regions with moderate and humid climate in Iran (Mazandaran) consistent with regional climate in terms of patterns applied in internal functional spaces? How do regional climate features affect physical form of houses?”</p><p>The results show that there is a direct and consistent relationship between vernacular architectural features of Mazandaran province and climate classification and regional climate. It also enhances home comfort in summer and finally, it can be concluded that local houses are built based on the climate classification and environment context, and natural ventilation is the most important factor affecting the conditions which improve environmental comfort. The present research provides some guidelines for the architectural design of residential buildings in regions with moderate and humid climate with the aim of achieving maximum level of natural ventilation. Also, in order to exploit the potential of natural ventilation, the results of the research will help architect select optimal designing parameters in harmony with the regional climate. </p>

The Application of CFD Technology in Analysis of Wind Environment

The need of natural ventilation in buildings has placed more emphasis on site planning in order to find the relationship between natural ventilation and the layout of architecture. This can reduce the energy consumption and the adverse effects of outdoor wind, to improve the living environment, quality of life and create a harmony between human and the nature. In this paper, we use Air-Pak to simulate the wind environment of an area. Through analyzing and simulating the airfield that forms when the wind blows around the buildings using Air-Pak, the advantage of combining computer simulation software and residential area planning is explained Through the simulation of the outdoor environment’s effects on buildings, some advice is given regarding the layout of the site early in the planning stage.