Natural Cross Ventilation Research Articles

Use of proper orthogonal decomposition and linear stochastic estimation technique to investigate real-time detailed airflows for building ventilation

As energy efficiency concerns grow for building heating, ventilation, and air-conditioning systems, more advanced mathematical models and methods may be needed for implementing more comprehensive building environmental monitoring practices. This work investigates the methodology of applying a coupled proper orthogonal decomposition (POD) and linear stochastic estimation (LSE) technique to provide detailed real-time velocity information for a single-room test environment under either mechanical ventilation or wind-driven cross natural ventilation with the support of limited on-site monitoring measurements. In addition, an example application of the proposed POD–LSE methodology with limited measurements to obtain real-time fluctuating wind-driven ventilation rates using a POD–LSE reconstructed velocity profile across a window opening is presented and shows very good agreement with the measured ventilation rates.

Performance-driven facades: Analysis of natural cross-ventilation in an indoor environment with Fast Fluid Dynamics and apertures optimization based on a genetic algorithm

One of the primary aims of performance-oriented design is to develop spaces that achieve acceptable levels of human comfort. Wind-induced airflow plays a significant role in improving occupants’ comfort in a building. This paper explores the extent to which simulation and evaluation of natural airflow can potentially be a contributing parameter in the conception of performance-aware designs. The authors employed Fast Fluid Dynamics simulation to study the natural ventilation performance of a pavilion and a genetic algorithm to optimize the shape of the pavilion’s facades’ openings. A performance analysis was conducted whereby an array of automated feedback loops carried out by a genetic algorithm produce a number of acceptable solutions. Hence the facade openings of these solutions are considered to be adequate to provide natural ventilation in the indoor environment. The study demonstrates the ability of the optimization model to yield design instances that fulfill a number of environmental criteria related to airflow and human comfort. In this light, the authors suggest that the aforementioned method can be used as an experimentation platform to influence and guide the designer during the initial stages of the design process towards a more performance-driven solution.

Natural cross ventilation in buildings on Mediterranean coastal zones

Abstract Natural ventilation of buildings is a common way to improve indoor air quality, thermal comfort in summer and reduce energy consumption due to air conditioning. However, efficiency of such a system is highly dependent on climatic conditions. This paper investigates the use of thermal breezes, characterized by moderate speeds and well-defined direction, to improve natural cross ventilation technique on Mediterranean coastal zones. The interest of this phenomenon is highlighted by the development of climate indicators with meteorological data from various places in Corsica (France). A statistical wind rose is used to give more information on main wind sectors and speed fluctuations. The natural ventilation potential is assessed by a radar plot which groups the main climate indicators for comfort ventilation and passive cooling. Tracer gas measurements on a seaside building in Corsica show that high air change rates are reached by cross ventilation during day (higher than 25 ACH). Night ventilation gives more moderate results for passive cooling with air change rates close to 10 ACH. As the comfort in building is related to the airflow, it is necessary to be able to control it. The issue of controlling openings to maintain a satisfying airflow is treated with the help of an empirical model. Due to the regularity of thermal breezes, it shows that even if the airflow varies greatly during the day, a minimal control on opening surface is sufficient to maintain the airflow rate on a comfortable range.

Effects of Lateral Window Position and Wind Direction on Wind-Driven Natural Cross Ventilation of a Building: A Computational Approach

Energy is saved when an effective natural ventilation system can provide comfort air to the occupants in a building by replacing a mechanical ventilation system. It also minimizes the risk of the environmental pollution and the global warming. A one story, full scale building was considered to carry out a comparative study of three different cases of wind-driven natural (WDN) cross ventilation with the help of computational fluid dynamics (CFD). In each case, the location of window was changed in lateral direction to predict the probable position for optimum ventilation performance and the angle of wind was varied to check the sensitivity of the wind direction on the flow field. After validating the current methodology through two satisfactory comparisons with the experimental investigations, the governing equations subjected to the corresponding boundary conditions were solved using commercial software and then the results were analyzed. A better location for the windows in each case was proposed. The ventilation purpose was served quite well even if the wind angle was changed in a moderate range from the original design. Furthermore, the velocity components, ventilation rate, surface pressure, ventilation time, and so forth in each case were investigated and compared extensively with those in other cases.

Analysis of Natural Cross-Ventilation in Buildings Driven by Wind and Buoyancy Forces

In order to investigate natural cross-ventilation in buildings driven by combined wind and thermal buoyancy forces, computational fluid dynamics (CFD) with the DES model is applied. The aim of this paper is to investigate the influence of thermal buoyancy force on natural ventilation in buildings under different heating conditions. The simulation results indicate that the thermal effect has a significant impact on airflow structure and airflow rate of building at low Froude numbers, however, the thermal effect can be neglected when Froude number value is greater than 6.

Numerical Simulation of Cross-Ventilation in Buildings Affected by Surrounding Buildings with Different Separation Distances

In order to investigate natural cross-ventilation in buildings, computational fluid dynamics (CFD) with the DES model is applied. The aim of this paper is to investigate the influence of surrounding buildings on natural ventilation in target building under different separation distances. The simulation results indicate that surrounding buildings has a significant impact on airflow structure and airflow rate of the target building. The flow characteristics in target building is determined by the flow regime in street canyon.

Flow visualization, PIV measurement and CFD calculation for fluid-driven natural cross-ventilation in a scale model

A building that is equipped with a natural ventilation system gives greater physical comfort for its occupants and saves on electricity consumption. The flow structure of fluid-driven natural cross-ventilation is studied using three techniques: flow visualization, Particle Image Velocimetry (PIV) measurement and Computational Fluid Dynamics (CFD). Four specific cases are chosen to study the effect of the number of windows and the window configuration on cross-ventilation performance. A comparative discussion of these cases is provided and the significant advantages and disadvantages for each case, with regard to ventilation, are reported. There is satisfactory agreement between the results obtained from computation and those from the experiment, which provides an effective guideline for CFD users for the validation of future numerical approaches. A novel numerical technique is used to provide an insight into the quantification of the movement of entering air. The three dimensionality, turbulence and the replacement of the indoor fluid are visualized. The overall performance is significantly affected by the specific design of the cross-ventilation system. It is found that a larger volumetric flow rate does not always ensure better replacement of the indoor air, and vice versa.

Natural ventilation of buildings due to buoyancy assisted by wind: Investigating cross ventilation with computational and laboratory simulation

In this paper cross natural ventilation due to buoyancy assisted by wind is investigated with computational and laboratory simulation. The impact of the outlet's opening position is investigated, forming cross ventilation of variable distance h – namely, the vertical distance between midpoints of leeward and windward opening –, for three initial Froude numbers: (i) Fr0 = 1.15, (ii) Fr0 = 2.79, (iii) Fr0 = 4.85. For the computational simulation a fluid dynamic software is used and the problem is solved by solving the 3D unsteady Reynolds Averaged Navier Stokes (RANS) equations in conjunction with the energy equation and the turbulence model RNG k-ε. The laboratory simulation took place in an open channel and the experimental model represents a building form of orthogonal shape. The interior of the experimental model is filled with solution of ethanol at conditions of normalized gravity, but also with salted water at conditions of inversed gravity. The time taken for the indoor space to empty is calculated numerically and experimentally. Based on Froude number dynamic similarity, the experimental and computational results are characterized by good agreement and the functional process of natural ventilation is being explicated. In addition, the suggestion of using ethanol solution for the density difference between interior and exterior fluid in laboratory simulation of natural ventilation is verified successfully, as the results with use of ethanol solution are in good agreement with those using salted water.

A Wind Channel Passive Ventilation System for Deep-Plan, High-Rise Residential Buildings

In a world where energy conservation in buildings is an important target, natural ventilation is an important field in which carbon footprint reductions can be achieved. This paper investigates the possibility of creating horizontal channels to deliver natural cross ventilation passively in deep-plan buildings that otherwise would suffer from a lack of fresh air ventilation. The research objective has been to find a new system in which the depth of buildings is no longer an issue when it comes to natural ventilation. If applied on a large scale this would help in creating healthier communities and a more sustainable built environment. The system was designed, simulated using CFD, and tested at full scale. The CFD simulation showed good potential in delivering an average of 1.95 m/s of fresh air at 4 m/s wind speed.

Post-occupancy evaluation and experimental feedback of a net zero-energy building in a tropical climate

Located in the French tropical Island of La Reunion in the Indian Ocean, the ENERPOS building was inaugurated in January 2009. The building is located in the Saint Pierre Campus of the University of Reunion Island. It was designed to be a net zero-energy building with mixed-mode air-conditioning systems in some areas (natural ventilation, ceiling fans, air conditioning) and efficient passive solutions sets usually used in tropical areas – i.e. efficient solar protection coupled with cross natural ventilation. This article reports the results of a recent user survey of the staff and students who use the building, and relates the users’ perceptions to some of the environmental control systems installed. Indications are that the users have been able to achieve thermally comfortable conditions for much of the year without recourse to the air-conditioning systems. However, there is still the need for more readily available information on how to get the best from the windows and the ceiling fan systems for the ever-changing groups of students, and staff who may only use the classrooms intermittently. For the more permanent staff group, preliminary indications are of improved health and productivity by comparison with their experience of other buildings.

Ventilação natural como estratégia para o conforto térmico em edificações

Uma circulação natural de ar adequada dentro de um ambiente construído, além de auxiliar na diminuição do gradiente térmico, contribui para a renovação do ar interno. Este, dependendo do perfil de ocupação do ambiente, pode ser prejudicial à saúde. Uma circulação natural pode se constituir em uma alternativa eficiente na redução do consumo de energia no condicionamento de edificações. Nesse trabalho, estuda-se a ventilação natural, dirigida pela ação combinada das forças do vento e térmicas num ambiente. Avalia-se a eficiência da ventilação unilateral e cruzada, utilizando-se o método numérico de elementos finitos, por meio do software ANSYS. O modelo numérico é utilizado na determinação dos efeitos das forças do vento e das forças térmicas combinadas, obtendo-se o fluxo de ar e a distribuição de temperatura dentro do ambiente. Os resultados obtidos são comparados com resultados de modelos empíricos, observando-se que a eficiência da ventilação cruzada fica em torno de 3,5 vezes maior do que a ventilação unilateral, aumentando os vórtices no fluxo de ar no interior do ambiente.

CFD simulation of cross-ventilation flow for different isolated building configurations: Validation with wind tunnel measurements and analysis of physical and numerical diffusion effects

Computational Fluid Dynamics (CFD) has become one of the most important tools for the assessment of natural cross-ventilation of buildings. To ensure the accuracy and reliability of CFD simulations, solution verification and validation studies are needed, as well as detailed sensitivity studies to analyse the impact of computational parameters on the results. In a previous study by the present authors, the impact of a wide range of computational parameters on the cross-ventilation flow in a generic isolated single-zone building was investigated. This paper presents the follow-up study that focuses in more detail on validation with wind tunnel measurements and on the effects of physical and numerical diffusion on the cross-ventilation flow. The CFD simulations are performed with the 3D steady Reynolds-Averaged Navier–Stokes (RANS) approach with the SST k–ω model to provide closure. Validation of the coupled outdoor wind flow and indoor airflow simulations is performed based on Particle Image Velocimetry (PIV) measurements for four different building configurations. The analysis of numerical diffusion effects is performed in two parts. First, the effect of physical diffusion is analysed by changing the inlet profiles of turbulent kinetic energy within a realistic range. Second, the effect of numerical diffusion is investigated by changing the grid resolution and by applying both first-order and second-order discretisation schemes. The results of the validation study show a good to a very good agreement for three of the four configurations, while a somewhat less good agreement is obtained for the fourth configuration. The results of the diffusion study show that the effects of physical and numerical diffusion are very similar. Along the centreline between the openings, these effects are most pronounced inside the building, and less pronounced outside the building. The velocity-vector fields however show that increased physical and numerical diffusion decreases the size of the upstream standing vortex and increase the spread of the jet entering the buildings. It is concluded that diffusion is an important transport mechanism in cross-ventilation of buildings, and that special care is needed to select the right amount of physical diffusion and to reduce the numerical diffusion, using high-resolution grids and using at least second-order accurate discretisation schemes.

CFD simulation of cross-ventilation for a generic isolated building: Impact of computational parameters

Accurate CFD simulation of coupled outdoor wind flow and indoor air flow is essential for the design and evaluation of natural cross-ventilation strategies for buildings. It is widely recognized that CFD simulations can be very sensitive to the large number of computational parameters that have to be set by the user. Therefore, detailed and generic sensitivity analyses of the impact of these parameters on the simulation results are important to provide guidance for the execution and evaluation of future CFD studies. A detailed review of the literature indicates that there is a lack of extensive generic sensitivity studies for CFD simulation of natural cross-ventilation. In order to provide such a study, this paper presents a series of coupled 3D steady RANS simulations for a generic isolated building. The CFD simulations are validated based on detailed wind tunnel experiments with Particle Image Velocimetry. The impact of a wide range of computational parameters is investigated, including the size of the computational domain, the resolution of the computational grid, the inlet turbulent kinetic energy profile of the atmospheric boundary layer, the turbulence model, the order of the discretization schemes and the iterative convergence criteria. Specific attention is given to the problem of oscillatory convergence that was observed during some of these coupled CFD simulations. Based on this analysis, the paper identifies the most important parameters. The intention is to contribute to improved accuracy, reliability and evaluation of coupled CFD simulations for cross-ventilation assessment.

Environmental Prospective of Passive Architecture Design Strategies in Terrace Houses

Conventional terraced houses in Malaysia have deep floor plans which limit natural cross ventilation. Inevitably, certain rooms are subject to solar gain and cause thermal discomfort to occupants who then dependent on mechanical cooling; thus incur high operational energy cost. This paper advocates Passive Architecture (PA) terraced house which design strategies create natural thermal comfort for occupants. The indoor thermal comfort in the two hypothetical schemes, i.e., conventional and PA terraced houses is simulated. The result shows that PA terraced house has a definite environmental prospective to house owner/occupant and offer a positive returns to the developer.

Wind tunnel investigation on influence of fluctuating wind direction on cross natural ventilation

The performance of wind driven natural ventilation is influenced significantly by the boundary conditions set for the wind. In real conditions the wind direction is fluctuating constantly so it is important to consider this fluctuation in experiments and simulations. This paper investigates the influence of fluctuating wind direction on cross-ventilation using wind tunnel experiments with the aim of improving the evaluation accuracy for natural ventilation. A periodically fluctuating wind direction was designed and reproduced in the experiment. Rapid Response FIDs (Flame Ionization Detector) were used to monitor the concentration of tracer gas. An index named diluting flow rate (DFR) is introduced to evaluate the ventilation performance of this kind of experiment. The results indicate that the DFRs of fluctuating cases are approximately 65–100% of the maximum airflow rate and DFR is influenced by the wind speed, the opening size and the wind direction fluctuation. Informed by the experimental data the mechanism of this combined influence is discussed in this paper.

Emissions of ammonia and methane from a livestock building natural cross ventilation

Agriculture, especially animal husbandry, is a major source of the greenhouse gas methane as well as the gas ammonia. In order to develop reduction measures for emissions and immissions, two factors prove to be: firstly, to determine the emission mass flow from livestock buildings, and secondly, to understand the dispersion processes in its surroundings. The quantification of emissions from livestock buildings with naturally ventilation is a particularly difficult task. The experimental uncertainties are largely unknown but are expected to be considerable. Using poor quality emission data as model input in dispersion studies (wind tunnel or numerical simulations) will produce results with limited significance. Accordingly a field study has been conducted to quantify the emission mass flow from naturally ventilated livestock buildings. During two field campaigns in summer tracer gas experiments and measurements of gas concentrations within and around two naturally ventilated cow sheds in Mecklenburg-Vorpommern were carried out, in order to estimate the emission mass flow. It was found that the measured concentrations within the livestock building strongly depend on outside conditions such as e.g. the wind direction. Large uncertainties also arise from estimates of the air ventilation rate, which determines the emission mass flow. The data analysis shows high estimated ventilation rates of 1280―1380 m 3 /h/LU (1 LU = 500kg body weight) for cow shed 1 and 1140―1180 m 3 /h/LU for cow shed 2. These results suggest ammonia emission mass flow rates of about 4 g/h/LU for cow shed 1 and about 2 g/h/LU for cow shed 2, respectively.

BASIC STUDY ON THE EVALUATION METHOD OF THERMAL COMFORT BY CROSS VENTILATION

Natural ventilation has the effect on improving the comfort of the indoor environment. However, this effect has not been clarified since it is difficult to artificially reproduce the same airflow as natural cross ventilation. In this study, the psychological and physiological effects of fluctuating airflow on the human body in hot summer environment were evaluated. The subjective experiments were carried out in a climatic chamber with fluctuating airflow generator, which can generate three airflows with different properties. The following results were obtained. (1)The thermal comfort is obtained by the natural cross ventilation most. Even after the airflow stops, the thermal comfort can be maintained. (2)The allowable environment can be reproduced by using the fluctuating airflow in a hot environment. Especially, the natural cross ventilation is psychological and physiological effective.

Overview of natural cross-ventilation studies and the latest simulation design tools used in building ventilation-related research

High-performance insulation, draught stripping and double glazing have effectively sealed off the fresh air routes and have made adequate natural ventilation impossible inside the modern energy-efficient home nowadays. Cross ventilation, a passive cooling method for buildings, is a major type of natural ventilation. Various study approaches have been reported; however, there is still no appropriate simulation tool that can predict the indoor thermal environment of natural ventilation. The typical building energy simulation for investigating a naturally ventilated building adopts thermal simulation and an airflow network. However, the airflow network approach for airflow estimation in building energy simulation cannot accurately predict indoor airflow by solving the pressure-flow algebraic equation, the mass balance equation and hydrostatic pressure variations. Recent advances in computer performance and computational fluid dynamics (CFD) software integrated with building energy simulation have made it possible to improve the accuracy to assess the performance of natural ventilation and also to give more realistic predictions of airflow in buildings. This chapter overviews and discusses various network airflow models integrated with CFD in the natural ventilation of buildings. Examples of results obtained with this approach are given to demonstrate the significant effects of such a coupling programme on natural ventilation prediction accuracy.

Review of Cross-Ventilation Research Papers - from the Working Group for Natural Ventilation and Cross-Ventilation of the Architectural Institute of Japan

A working group for natural ventilation and cross-ventilation at the Architectural Institute of Japan (AIJ) was established in 2005 by researchers and designers with an interest in this topic. One of the tasks of the working group is to review and classify related research papers. This paper introduces the activities of the working group and presents some results of the review work. As examples of the review work, this paper concentrates on the area cross-ventilation rate and the interference coefficient concept of the cross-ventilation phenomenon that solves the problem of the remaining dynamic pressure inside a room.

Economic assessment of Operational Energy reduction options in a house using Marginal Benefit and Marginal Cost: A case in Bangi, Malaysia

Abstract Energy Efficient (EE) appliances such as Compact Fluorescent Light (CFL) bulbs and Renewable Energy (RE), namely solar Photovoltaic (PV) can help to reduce Operational Energy (OE) in a house. In addition, a house should also incorporate Passive Architecture (PA) design strategies which in the hot and humid tropical climate, mean avoiding direct heat gain, encouraging natural cross ventilation and optimising the abundant daylight. Nevertheless, reducing OE must also mean economic gain to households to encourage their participation. Common economic gauges such as Return on Investment, Payback Period, Cost Benefit Analysis, Life Cycle Assessment and Life Cycle Cost are not suitable to validate OE options in households. These economic gauges approach economic assessment as an end-result on the cost side of the product and may result for good intention to be shelved, primarily because EE equipment and RE have high capital cost compared with the alternatives. On the other hand, reducing OE in houses is actually a continual progression from the status quo and there is always a marginal gain in doing so. The challenge is to know how much is the marginal benefit against the marginal cost of investing in EE and RE. In Economics, the ratio of Marginal Cost (MC) and Marginal Benefits (MB) measure additional benefits of every additional costs of investment at a specific level of production and consumption; and Economists suggests that effective gain and loss should be compared to the status quo, i.e., Relative Position (RP). The Economics theories of MC, MB and RP are being adapted to measure the progression of reducing OE. The living/dining area in two types of houses: with and without PA design strategies are simulated to use conventional incandescent light bulbs and CFL as well as solar PV in lieu of the mains electricity supply. The power requirement for artificial lighting in every case is translated into monetary value and the ratio of MB against MC for each case shows the gain or loss in investment to reduce OE in a 30-year period. The result suggests that the value of MB/MC is high when both houses use CFL, i.e., approximately (Ringgit Malaysia) RM2.5 gain for every RM1 cost. It is also found that investment in solar PV benefits the most in the PA case that uses superior CFL bulbs, i.e., approximately RM2 gain for every RM1 cost. Despite the high capital cost of EE equipment and RE, MB/MC approach seems to make economic sense for household to invest in reducing OE at certain stages.