Natural Ventilation Performance Research Articles

CFD Methodology Development for Singapore Green Mark Building Application

In the recent decade, investigation on the total building performance has become increasingly important for the environmental modelling community. With the advance of integrated design and modelling tool and Building Information Modelling (BIM) development, it is now possible to simulate and predict the building energy efficiency, air quality & health assessment, risk analysis& mitigation scenario for our urban planning analysis; all seamlessly in a single urban digital platform. In order to achieve the national goal of at least 80% of the buildings in Singapore to be green by 2030, Singapore Government has introduced the new BCA Green Mark 2015 scheme for accelerating the green building agenda. During the recent third Green Building Masterplan announced in 2015, it was decided to engage building tenants and occupants more actively to drive energy consumption behavioural change and to address the well-being of the people. Following up from this Masterplan, it is important for both the stakeholders and agency to jointly develop Performance Driven and Scientific Based Simulation Methodology and Evaluation Parameters as a frame work to evaluate the building design based on Singapore's hot and humid climate and densely-built-up urban areas for the Green Mark 2015 Scheme. In this paper, we will present the methodology and perform a baseline case study for the natural ventilation performance with the typical Non-Residential Building (NRB) industrial building. This can be resulted in the comprehensive CFD Quality Check List for the Environmental Sustainable Design (ESD) consultant in order to maintain modelling result accuracy. Demonstration on Indoor Air Quality (IAQ) using Air Exchange Effectiveness (AEE) as performance indicator will also be illustrated.

Prediction of the diffuse-field transmission loss of interior natural-ventilation openings and silencers.

The work reported here, part of a study on the performance and optimal design of interior natural-ventilation openings and silencers ("ventilators"), discusses the prediction of the acoustical performance of such ventilators, and the factors that affect it. A wave-based numerical approach-the finite-element method (FEM)-is applied. The development of a FEM technique for the prediction of ventilator diffuse-field transmission loss is presented. Model convergence is studied with respect to mesh, frequency-sampling and diffuse-field convergence. The modeling technique is validated by way of predictions and the comparison of them to analytical and experimental results. The transmission-loss performance of crosstalk silencers of four shapes, and the factors that affect it, are predicted and discussed. Performance increases with flow-path length for all silencer types. Adding elbows significantly increases high-frequency transmission loss, but does not increase overall silencer performance which is controlled by low-to-mid-frequency transmission loss.

Study of Natural Ventilation in wind Tunnels and Influence of the Position of Ventilation Modules and Types of Grids on a Modular Façade System

Natural ventilation requires no energy consumption, which can constitute 25% of a mechanically ventilated building, and both shape and position of inlets and outlets ventilation openings must be properly designed for better natural ventilation performance. Wind tunnel tests are a reliable tool for the determination of the effect of natural ventilation on buildings. This paper reports on results of wind tunnel tests conducted for the evaluation of the influence of the positioning and type of grid of ventilation modules on a façade system. Three ventilation modules were positioned below the window-sill (ventilated window-sill) and three were positioned above and below the façade. Ventilation modules with grid elements positioned vertically and horizontally were tested. Wind speed measurements that considered single-sided and cross ventilation were taken inside and outside the model for the different façade configurations for the evaluation of the best performance in relation to natural ventilation. The façade system proposed is movable and interchangeable, so that the same basic model can be used for the testing of possibilities for ventilation. The results show the use of six ventilation modules positioned below the window-sill and that form a “ventilated window-sill” with a horizontal grid is the best solution regarding natural ventilation. Such a configuration has proved the grid elements of ventilation modules exert a higher influence on the results than the positioning of modules on the façade. Therefore, better conditions of natural ventilation were obtained with a thin and horizontal positioning of the elements.

Assessment of Natural Ventilation System for a Typical Residential House in Poland

The paper presents the research results of field measurements campaign of natural ventilation performance and effectiveness in a residential building. The building is located in the microclimate whose parameters differ significantly in relation to a representative weather station. The measurement system recorded climate parameters and the physical variables characterizing the air flow in the rooms within 14 days of the winter season. The measurement results showed that in spite of proper design and construction of the ventilation system, unfavorable microclimatic conditions that differed from the predicted ones caused significant reduction in the efficiency of the ventilation system. Also, during some time periods, external climate conditions caused an opposite air flow direction in the vent inlets and outlets, leading to a significant deterioration of air quality and thermal comfort measured by CO<sub>2</sub> concentration and PMV index in a residential area.

The Effects of Void on Natural Ventilation Performance in Multi-Storey Housing

Enhancing natural ventilation performance in multi-storey housing is very important for the living environment in terms of health and thermal comfort purposes. One of the most important design strategies to enhance natural ventilation in multi-storey housing is through the provision of voids. A void is a passive architectural feature, which is located in the middle of deep plan buildings. It is very crucial to consider the configurations of voids in the buildings for enhancing natural ventilation, especially for multi-storey housing. In this study, Malaysian Medium Cost Multi-Storey Housing (MMCMSH), which is an example of multi-storey housing located in a suburban area, has been selected in this study. This study aims to investigate the potential of void for enhancing natural ventilation performance in multi-storey housing by the comparison of two different void configurations. Field measurement of MMCMSH has been conducted to validate Computational Fluid Dynamic (CFD) model and Atmospheric Boundary Layer (ABL) is an important parameter for setting up the CFD Model’s domain. Ventilation rate (Q), which is necessary for comfort and health reasons, is an important parameter for the comparison of the different void configurations. This study revealed that the provision of void can enhance natural ventilation performance in multi-storey housing with an increase in the value of Q, from 3.44% to 40.07%, by enlarging the void’s width by 50% compared to the existing void.

Natural Ventilation Building Design Approach in Mediterranean Regions—A Case Study at the Valencian Coastal Regional Scale (Spain)

Environmental awareness has led to an increased concern about low carbon technologies implementation. Among these technologies, the following research is focused on the natural ventilation effect evaluation in buildings prior to its construction. The aim is to select the most suitable architectural solution to ensure comfortable indoor environment in the most efficient way in the early building design stage. The design approach takes into account the wind conditions in the region and the building surroundings to evaluate the façade opening distribution impact on natural ventilation performance. The design approach is based on computational fluid dynamics (CFD). In this article, a case study located in the Valencian Community (Spain) is depicted. The Valencian Community coastal climatic conditions are evaluated to assess the low carbon technology energy saving potential. Moreover, the main drivers and barriers involved in the design approach implementation in the region are discussed. The conclusions show that the natural ventilation design approach can improve up to 9.7% the building energy performance respect an initial building design, in which natural ventilation has not been considered. The results contribute to an assessment of the complete low carbon technology effect in the region.

Numerical investigation of wind-driven natural ventilation performance in a multi-storey hospital by coupling indoor and outdoor airflow

This study employed two ventilation indexes: local mean age of air and air change rate per hour, to investigate wind-induced natural ventilation of 260 wards of a multi-storey hospital building in suburb of Guangzhou using computational fluid dynamics simulations. Using the surface-grid extrusion technique, high-quality hexahedral grid cells were generated for the coupled outdoor and indoor airflow field. Turbulence was solved by the renormalisation group k-ɛ model validated against experimental data with grid independence studies. Homogeneous tracer gas emission was adopted to predict room age of air. The air change rate of cross ventilation and single-sided ventilation can reach 30–160 h−1 and 0.5–7 h−1, respectively. Due to different locations of room openings on the balconies, natural ventilation of a room can be greatly better than its neighbouring room. The wind-induced cross ventilation highly depends on the distance from the room opening to the stagnation point and on the resulting pressure distribution on the target building surface. Furthermore, it is significantly influenced by the upstream buildings, the bent shape of the target building, and the prevailing wind directions. The coupled computational fluid dynamics methodologies with integrated ventilation indexes are useful for assessing the natural ventilation performance in other complex built environments.

Anti-short-circuit device: A new solution for short-circuiting in windcatcher and improvement of natural ventilation performance

Windcatcher is an effective technique for naturally ventilating a space and improving indoor air quality. A common problem for modern and traditional windcatchers is air short-circuiting. Air-short-circuiting in windcatchers occurs when the air entering through the supply channel immediately exits through the exhaust channel without circulating and mixing inside the enclosed space. Several previous works on windcatchers have observed the “short-circuiting” effect and concluded that it has a negative impact on the ventilation performance however, no work have provided a solution to eliminate this effect. The present study will address this issue by incorporating a component called the anti-short-circuiting device (ASCD) and investigating its potential to eliminate air short-circuiting in windcatchers and improve ventilation performance. Two methods were employed in this research: experimental and Computational Fluid Dynamics (CFD) study. For the experimental work, three scaled models were studied in a wind tunnel. The CFD modelling was validated using the air velocity measurements and good correlation was observed with average error below 10%. The results showed that the ASCD windcatcher with angles between 20° and 80° prevented air-short-circuiting while supplying up to 40–51 l/s per occupant, which is higher than the minimum recommendations of ASHRAE62.2 and BS5925. In addition, the windcatcher without ASCD showed 8% higher CO2 concentration in the room, indicating that the ASCD windcatcher was more effective in removing stale air out of the room. Furthermore, the average air velocity in the room at sitting height with the ASCD windcatcher was 19–28% higher than windcatcher without ASCD.

A Case study on the Energy Conservation Strategies in Factory Building

Increasingly strict energy policies, rising energy prices, and a desire for a positive corporate image currently serve as incentives for multi-national corporations to reduce their factories’ energy consumption. In the current study, performance of energy conservation strategies focusing on natural ventilation has been evaluated. In this regard, energy saving strategies related to natural ventilation performance has been derived and then the energy saving factors that can be applied to the base buildings have also been evaluated using air network model in EnergyPlus simulation program. According to the evaluation results, 5.41% of total energy in the base building can be saved compared with a base building.

Possibility of using roof openings for natural ventilation in a shallow urban road tunnel

Naturally ventilated urban vehicular tunnels with multiple roof openings have increased in China. Unnecessary gas (polluted air or fire smoke) are expected to be exhausted out through openings. Whether its safety standards can be satisfied or not still needs to be verified. In this paper, a safe CO concentration was firstly discussed, and a heat risk level of very high to extreme up to 46°C was given. Secondly, a real 1410m tunnel was proposed, and a 1/10 scale model tunnel was reproduced. Ambient winds of 0.95m/s in prototype and 0.3m/s in model were considered. Under normal traffic test, a track circuit was constructed with model vehicles moving on it to form traffic wind, and once the air velocity was larger than 0.31m/s, the airflows were found to be not relevant to the Reynolds number. The traffic winds were weakened by openings. For three of all tested traffic, the actual air velocities were larger than the required ones, so its air qualities were satisfied. In firing test, two sets of burning experiments were conducted with which the heat release rates (HRR) were 8.35kW and 13.7kW. Large amounts of smoke were exhausted out of openings, and the high-temperature was not significant. Full-scale numerical simulations were carried out to verify the experimental results respectively using Fluent 6.0 for normal traffic and FDS 4.07 for firing. The simulations were compared well with the experiments. Further FDS simulations show that the openings’ mass flow rates are influenced little by ambient temperature; with the increasing length of the buried section, much smoke accumulate inside leading to a high temperature; having 4–5 openings in one shaft group is oversize in the actual engineering design.

Effects of “wall angularity of atrium” on “buildings natural ventilation and thermal performance” and CFD model

Standpoints about atrium design have been revolutionized. Nowadays, design of atrium is not only for shine of light, but is also for natural ventilation as well. In high rise building, residents have not a same advantage of buoyancy-driven ventilation that arising from existence of atrium. One strategy to more equalize ventilation and thermal comfort in different levels, is designing building with various opening area in different heights.Present study aims to overcome the problem by changing the atrium shape. Thus, the atrium's wall angularity is changed in different case studies and these shapes are compared with each other in order to find the relations between atrium wall angularity and thermal performance. Each case study comprises equal opening area for all floors. CFD models are implemented to compare the cases together. Results show that converging tilted walls in tall atrium space only enhances thermal comfort for stories that are located lower than neutral pressure level and deteriorates thermal comfort for upper stories. No advantage was observed for diverging walls in atrium. Results indicates that a combination of vertical and tilted wall yield the best performance whenever the tilted walls are used for lower stories and vertical walls are used for upper stories.

Field Measurement & Research on Natural Ventilation Performance of the New East-main Building of China Academy of Building Research (CABR)

Present the natural ventilation design for the New East-Main Building of China Academy of Building Research (CABR) at the corridor linking Building A and Building B, theoretical calculation during the design phase, and field measurements after the building's completion. The theoretical analysis show that indoor air change rate can reach up to more than 4.4 h-1 as long as temperature difference between indoor and outdoor greater than 1°C or outdoor air velocity greater than 0.4m/s, so that could remarkably improve comfort during the transitional seasons in Beijing; but the field measurement results show 3.37 h-1 when temperature difference is 1.2°C and outdoor air velocity is about 0.3∼1.5m/s, which tells a considerable difference compared to the design value, which has a greater impact on the air exchange efficiency of the room. The author conducts a comprehensive analysis of possible factors, and obtained preliminary conclusions and recommendations.

Coupled Natural Ventilation Modeling for Contextual Parametric Design Decision Support

It is important to study the interactions between indoor and outdoor environments for natural ventilation assessment. A 3D isothermal cross ventilation of a high-rise building with surrounding buildings is solved with RNG k-ɛ turbulent model. Openings on four floors are created on north and south walls of the target building. Steady state simulations are performed in a commercial CFD code, scSTREAM, using multi-block method to integrate high-resolution mesh in a neighborhood scale. 72 CFD models are built for parametric analysis to support decision making for early design by evaluating indoor natural ventilation performance in terms of wind directions, building block layouts and opening sizes.

Influence of radiation on predictive accuracy in numerical simulations of the thermal environment in industrial buildings with buoyancy-driven natural ventilation

This paper investigates the effects of radiation on predictive accuracy in the numerical simulations of industrial buildings. A scaled experimental model with a high-temperature heat source is set up and the buoyancy-driven natural ventilation performance is presented. Besides predicting ventilation performance in an industrial building, the scaled model in this paper is also used to generate data to validate the numerical simulations. The simulation results show good agreement with the experiment data. The effects of radiation on predictive accuracy in the numerical simulations are studied for both pure convection model and combined convection and radiation model. Detailed results are discussed regarding the temperature and velocity distribution, the buoyancy force and the ventilation rate. The temperature and velocity distributions through the middle plane are presented for the pure convection model and the combined convection and radiation model. It is observed that the overall temperature and velocity magnitude predicted by the simulations for pure convection were significantly greater than those for the combined convection and radiation model. In addition, the Grashof number and the ventilation rate are investigated. The results show that the Grashof number and the ventilation rate are greater for the pure convection model than for the combined convection and radiation model.

The Sound Insulation of Double Facades with Openings for Natural Ventilation

Natural ventilation represents a potentially sustainable scheme for the provision of good indoor air quality and free cooling in buildings. Noise pollution is an impediment in this case, as buildings under noise exposure cannot effectively deploy the natural (window) ventilation option. The present contribution focuses on a double-leaf facade solution, which offers sufficient sound insulation while facilitating natural ventilation. The impact of various variables of such a system (e.g., the size of the opening, location of the openings, the relative displacement of the openings in the two layers, the cavity sound absorption) were examined via parametric laboratory sound transmission measurements using an experimental modular double-leaf wall. An empirically-based equation and a simple analytical one were developed for the prediction of the sound insulation of double-leaf facades with openings for natural ventilation. The results of these computational estimations are compared with the measurements results to discuss the potential and limitations of their predictive performance.

Estimating the Sound Insulation of Double Facades with Openings for Natural Ventilation

Natural ventilation represents a potentially sustainable scheme for the provision of good indoor air quality and free cooling in buildings. However, its application is frequently hindered due to outdoor climatic conditions, air pollution, or noise pollution. The later impediment represents one of the main motivations behind the research presented in this paper, as buildings under noise exposure cannot effectively deploy the natural (window) ventilation option. To address this problem, the potential of building envelope solutions that could offer sufficient sound insulation while facilitating natural ventilation is of critical importance. Specifically, the present contribution focuses on the sound insulation properties of double facades with openings for natural ventilation. Thereby, a generic double-leaf façade was conceived and installed between two adjacent reverberant chambers in the acoustic laboratory of the Department of Building Physics and Building Ecology at the Vienna University of Technology. This experimental modular double-leaf wall allows for various configurations of open elements. Multiple opening combinations were studied, such that the impact of various system parameters (e.g., the size of the opening, location of the openings, the relative displacement of the openings in the two layers) could be assessed both empirically and computationally. Furthermore, various levels of sound absorption in the double wall cavity (realized with absorber panels) were considered and tested. The resulting comprehensive set of parametric configurations was subject of systematic sound transmission measurements. Using the results of the measurements, multivariable analysis and curve-fitting techniques were deployed toward developing empirically-based equations for the prediction of the sound insulation of double-leaf facades with openings for natural ventilation. Furthermore, a simple analytical model was proposed that could be also applied toward predicting the sound transmission of such constructions. The results of empirically-based and analytical models are compared with the measurements results to discuss the potential and limitations of their predictive performance.

Thermal Performances of Traditional Houses in Dry Hot Arid Climate and the Effect of Natural Ventilation on Thermal Comfort: A Case Study in Damascus

Traditional houses in hot arid climate of Mediterranean area consist of rooms around one or more courtyards giving a general good comfort conditions especially in hot summer periods. This paper aims to contribution to evaluate the influence of thermal performance of building structures and natural ventilation (cross ventilation, single side ventilation) on the indoor thermal comfort for traditional houses and courtyard located in Damascus old city. The paper shows results of several monitoring data (air temperature, humidity and air velocity) acquired during a summer period, in parallel with occupancy survey for the evaluation of comfort conditions.

Performance Assessment of Ancient Wind Catchers - an Experimental and Analytical Study

Wind catchers – “Baud-Geers” in Persian– are the main component of the traditional buildings in the hot regions of Iran. A Baud-Geer is a tower linked to a building that uses wind to provide natural ventilation and passive cooling. This passive renewable strategy offers the opportunity to improve the ambient comfort conditions in buildings whilst reducing the energy consumption of air-conditioning systems. In this research the natural ventilation performance of a typical wind tower in a hot dry central region of Iran -Yazd city- is studied. The tower is equipped with wind, temperature, air-velocity and solar sensors to acquire a climatic database. Using the measured data, the theoretical values of the ventilation rates are estimated and analysed to assess the performance of the wind tower. Additionally the data collected from the on-site measurements will assist in the validation of a CFD computer model. Finally the findings from this field study will lead to a discussion on the potential of Baud-Geers in achieving thermal comfort. This can contribute to energy savings for cooling and to the reuse and reappraisal of wind towers in Iran.

Assessment of Natural Ventilation within Buildings Located on Hot-temperate and Mild-temperate Regions

This work presents an energy assessment of the natural ventilation performance within buildings located on both hot-temperate and mild-temperate conditions such as the existing along the central region of Mexico. With the assistance of a coupled thermal-airflow simulation program, simulations are run without and with natural ventilation, respectively. Thereby, the consumption of air-conditioning presented in this region is validated with data from literature when natural ventilation is not applied. Results show that when natural ventilation is used thermal comfort is achieved more than 90% of the assessed time. Therefore, the cooling demand supplied by air-conditioning could be virtually avoided, especially when the building has high thermal capacity, feature presented on a great part of the building stock.

Combined thermal and daylight analysis of a typical public rental housing development to fulfil green building guidance in Hong Kong

This paper presents a combined daylight, airflow network and building energy simulation of a Public Rental Housing (PRH) development in Hong Kong to fulfil the requirement of the local green building guidance. The numerical modelling results are partly validated by on-site measurements during the period with the highest monthly average outdoor temperature. Different ventilation control strategies are simulated to optimize natural ventilation performance. The simulation results show that the full-day ventilation strategy contributes to a lower average and peak indoor temperatures compared to the non-ventilation and night-ventilation scenarios. The indoor operative temperature of a worst-case vacant flat lies under the upper 80% acceptability limits in ASHRAE 55 during 67.5% of the modelled period in July. On the other side, at least 95.6% of the habitable area in the case buildings is predicted to experience a higher average daylight factor of 1% compared with the local green building guidance. Furthermore, the energy saving potential of the combined natural ventilation and daylight strategies is anticipated to be 51.9% for air-conditioning and 8.3% for lighting compared to a baseline building, respectively.