Wind-driven 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.

A Verification and Validation Study of CFD Simulation of Wind-Induced Ventilation on Building with Single-Sided Opening

Wind-induced ventilation is widely acknowledged as one of the best approaches for inducing natural ventilation. Computational fluid dynamics (CFD) technique is gaining popularity among researchers as an alternative for experimental methods to investigate the behavior of wind-driven ventilation in building. In this present paper, Reynolds averaged Navier-Stokes equation (RANS) k-ε model approach is considered to simulate the airflow on a simplified cubic building with an opening on a single façade. Preliminary simulation using models from previous experiment indicates the reliability of OpenFOAM, the open source software that will be used in this study. The results obtained in this study will better define options for our future study which aims to explore how different buildings arrays modify the airflow inside and around a naturally ventilated building.

Evaluation of the Modified Chimney Performance to Replace Mechanical Ventilation System for Livestock Housing

The demand of poultry products and prices are increasing very rapidly. Therefore, modern poultry industry is using mechanical ventilation system in closed housing to support the increased growth rate of the birds. Ventilation system is used to produce the healthier and quality broiler by reducing indoor air pollutant concentration and temperature. Currently, the price of fossil fuel is increasing day by day; therefore, minimization of overall cost of poultry production needs reduction in energy consumption or introduction of cheaper and alternative energy sources. Although solar heating system is used in broiler industries during winter but limited research was done on natural wind-driven ventilation system. In the current study, natural draft chimney was modified with wire mesh screen and was designed for the enhanced ventilation. In laboratory, it was found that the modified chimney significantly minimized the draft losses and increased the ventilation rate up to 60 to 90 percent compared to the normal conventional chimney. The Computational Fluid Dynamics (CFD) showed that the chimney performance was significantly improved in the modified solar chimney than that in the normal one. It is suggested that modified solar chimney can be used to replace the mechanical ventilation system in poultry farming to reduce the production cost as well to meet the demand of animal protein for human beings.

Simulating Natural Ventilation in and Around Buildings by Fast Fluid Dynamics

Natural ventilation is a sustainable technology that can provide a well-built environment and also save energy. The application of natural ventilation to buildings requires a careful approach in the early design phase, and fast, simple design tools are greatly needed. Fast fluid dynamics (FFD) can provide useful airflow information at a speed much faster than CFD so that it is a potential design tool for natural ventilation. This study thus validated FFD with test cases representing different types of natural ventilation. The results showed that FFD was capable of predicting the main air flow feature and ventilation rate with reasonable accuracy for wind-driven or buoyancy-driven natural ventilation. FFD simulation can reflect the influence of wind direction and surrounding buildings on natural ventilation.

Comparison of Wind-Driven Natural Ventilation for Different Windows in a Room with a Single Opening

In order to get more effective natural ventilation into a room with a single sided opening or large depth, two new window types have been developed in the laboratory. These are based on three new patent developments. The first window is defined as a dual level ‘up-down folio’ window which consists of two pairs of openable sashes with one pair placed directly above the other. The second is a multi-sash mid-pivoted window with vertical deflectors. The performance of these new window designs were compared with a conventional side-hung window and sliding window by installing them, in turn, into a single sided opening space of a test room. Both spot measurements and CFD analysis were undertaken. Wind-driven ventilation performance was analysed in each case for three wind speeds 1 m/s, 2 m/s and 3 m/s and five wind angles 0°, 22.5°, 45°, 67.5° and 90°. It was concluded that for the single sided test case, the two new window designs provided room air velocities that were more uniform and with higher mass flow rates that occurred for the two conventional window types. However, further substantial studies are needed to improve these designs and popularise these new types of windows.

Performance evaluation of network airflow models for natural ventilation

The potential for natural ventilation in building design to reduce associated building cooling and fan energy consumption makes it an area of great interest. However, its increased use is dependent on the availability of accurate modeling tools to predict its impact on a given building design. Network airflow models have been developed to predict airflows within buildings and between indoor and outdoor, which usually require user-supplied thermal conditions in a space. Because of the dependency between airflow and space temperature in naturally ventilated buildings, network airflow models need to be incorporated into whole building energy simulation models. This study reviews existing network models that may be used for natural ventilation design and investigates the capability and accuracy of four prevalent network airflow models to simulate a wide range of natural ventilation scenarios, with varying combinations of geometry and natural ventilation driving forces. Comparison of predictions with measurements obtained from literature shows that the tools are generally able to predict natural ventilation rates within 35% except for the wind-driven single-sided ventilation case. The article indicates some significant needs for improvement of the network airflow model for natural ventilation applications.

Wind-Driven Natural Ventilation in an Areaway-Attached Basement with a Single-Sided Opening for Residential Purposes

This paper discusses the sustainability of the areaway-attached basement concept with the attentions focused on wind-driven single-sided natural ventilation. First, numerical simulations were performed on an areaway-attached basement with a single-sided opening. Two CFD approaches: Reynolds averaged Navier-Stokes (RANS) and large-eddy simulation (LES) were used and compared with the previous experimental results of effective ventilation rate. A good agreement between the measurement and LES model was found and RANS model tends to underestimate the ventilation rates. Furthermore, Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement was investigated for different wind incidence angles to examine the influences of wind direction on ventilation performances.

Modeling the neutrally stable atmospheric boundary layer for laboratory scale studies of the built environment

The properties of the atmospheric boundary layer (ABL) influence a range of physical phenomena in urban areas such as wind loading on buildings, wind-driven ventilation flows, pollution dispersion, and the lift off and transport of loose debris. In order to accurately model the ABL velocity profile at laboratory scale, it is important to establish the shear velocity u ∗, surface roughness z 0, and zero plane displacement d in either a wind tunnel or water flume. Current techniques for establishing these parameters are based on either an analysis of the boundary layer surface geometry or iterative curve fitting techniques that use mean velocity and/or turbulent kinetic energy profiles, occasionally combined with empirical correlations for z 0. A new curve fitting method for calculating these logarithmic velocity profile parameters is presented. This new method calculates u∗, z 0, and d directly from time-averaged velocity profile data in just two steps without any iteration. A comparison is presented between the results of the new method and other available methods applied to a range of velocity profile measurements in air and water. The comparison shows that, although the new method requires less data and fewer steps, it calculates u ∗ and z 0 with greater accuracy than existing techniques, and d with equivalent accuracy to existing techniques.

Probability analysis of wind-driven natural ventilation potential in areaway-attached basements

This article presents an exceedance probability analysis method to evaluate the natural ventilation potential in areaway-attached basements for residential purposes. This method can take the uncertainties associated with stochastic wind conditions into full account, and it uses the air change rate in the basement space as the evaluation index to calculate the exceedance probability distribution. A simple analysis approach is further proposed by extracting air change rates corresponding to the exceedance probabilities of 85% and 15% from the exceedance probability distribution curves. In order to determine the air change rate index for each wind direction accurately, a wind-tunnel experiment was performed on a two-story building scale model with an areaway-attached basement. A variety of parameters, including opening configuration, areaway plan area, building coverage ratio, orientation, and construction site of the model, were further investigated and analyzed in detail. The results demonstrate that the exceedance probability analysis is a useful tool for wind-driven natural ventilation potential analysis, and the findings of this article can provide quantitative information and guidelines for the design and application of areaway spaces.

Investigation of Ventilation Effectiveness for Wind-Driven Single-Sided Ventilated Buildings Located in an Urban Environment

This study employed large-eddy simulation (LES) to investigate wind-driven single-sided natural ventilation for an idealized building model located in an urban environment. Two ventilation cases, single-sided ventilation with an opening on the windward wall and with an opening on the leeward wall, were considered. The airflow rates through the single opening were calculated based on the mean flow fields and the transient flow fields, respectively. The comparisons showed that using only the information from the mean flow fields under-predicted the airflow rate and indicated the important role of fluctuating flow in the case of wind-driven single-sided ventilation. Using the homogeneous emission method, we further calculated the effective ventilation rates in the target indoor space and fairly good agreements were found in comparison with the measurements. The relationship between the airflow rate through the opening and the effective ventilation rate in the indoor space was studied by defining the ventilation efficiency for single-sided ventilation. This was 31.7% and 37.5% in the windward and leeward cases respectively, indicating a short-circuiting of fresh air at the opening. Based on a further analysis of the time-series data from LES, it was found that the variations of the airflow rate were significant while the variations of the effective ventilation rate were small.

Application of CFD in Modelling Wind-Induced Natural Ventilation of Buildings - A Review

This paper reviews the application of CFD for designing and parametric studies of wind-induced natural ventilation. The approaches employed in such applications of CFD are whole-domain and domain-decoupled CFD modelling. The domain-decoupled technique separately analyses the external airflow fields outside and internal flows inside a building. In the whole-domain approach, the outdoor and indoor airflow is modelled simultaneously and within the same computational domain. The review showed that the whole-domain approach has been more popular than the domain-decoupled approach, and with efficient computing algorithms, grid generation techniques and advances in hardware technology, can overcome the computational overhead it incurs during application. CFD has also allowed the concept of stream tube and the local dynamic similarity model (LDSM) to be used in practice. These concepts have helped in the fundamental understanding of wind-driven natural ventilation and in distinguishing flow through large openings from that of “cracks”. An important and practical approach for natural ventilation design and analysis is the integration of CFD with other simulation programs such as Building Simulation (BS) and Geographic Information Systems (GIS). Apparently, CFD is increasing its importance in sustainable building design and it is expected that more complex naturally ventilated buildings will be designed and analysed as CFD techniques continue to improve.

Airflow assessment in cross-ventilated buildings with operable façade elements

This paper presents an experimental study of basic cross-ventilation flow characteristics that are essential inputs for accurate natural ventilation modelling and design. The study focuses on a generic single-zone building model tested in a wind tunnel under isothermal flow conditions (wind-driven ventilation). An advanced experimental method based on particle image velocimetry (PIV) was developed to investigate the air velocity field in buildings with cross-ventilation. It was found that airflow patterns in rooms with cross-ventilation are complex and cannot be predicted by simplified macroscopic models such as the orifice equation. Inlet-to-outlet ratio and relative location of openings on a building façade are important parameters to be considered, in addition to the wall porosity. This study provides new insights that enable improved design and control of operable façade elements to enhance space cooling using natural ventilation.

A methodology to assess the influence of local wind conditions and building orientation on the convective heat transfer at building surfaces

Information on the statistical mean convective heat transfer coefficient ( CHTC SM) for a building surface, which represents the temporally-averaged CHTC over a long time span (e.g. the lifetime of the building), could be useful for example for the optimisation of the performance of solar collectors and ventilated photovoltaic arrays or for preservation analysis of cultural heritage sites. A methodology is proposed to estimate the CHTC SM for a building surface, by combining local wind climate information and information on the CHTC, namely CHTC-U 10 correlations, where U 10 is the mean wind speed at a height of 10 m above the ground. This methodology is applied to a cubic building for a specific wind climate, where the CHTC-U 10 correlations are obtained by means of CFD simulations (CFD code Fluent 6.3, realizable k-ɛ turbulence model). It is shown that the CHTC SM varied significantly with the orientation of the building surface due to the rather anisotropic wind conditions, where high values are found for surfaces oriented towards the prevailing wind directions, thus for windward conditions. Moreover, the evaluation of the CHTC SM for other wind climates clearly shows that the local wind conditions also can have a significant impact on the overall magnitude of the CHTC SM, where differences up to a factor 4 are found in this study. Different levels of complexity for determining the CHTC SM value are also evaluated and it is found that the required number of CFD simulations can be reduced significantly by using more simplified methods to calculate the CHTC SM, without compromising its accuracy. The applicability of the proposed methodology for other building-related applications is also discussed, for example to assess statistical mean pressure coefficients, wind-driven ventilation rates or convective mass transfer coefficients.

Prediction of wind environment in different grouping patterns of housing blocks

The idea of utilising natural ventilation for passive cooling has increasingly attracted the attention of researchers. In urban areas, this is intended to improve the outdoor and indoor thermal conditions without compromising the principles of sustainable building design. This study investigates the effect of building grouping pattern on the resulting wind environment in the outdoor spaces and the resulting ventilation potential of these buildings. A parametric three-dimensional modelling study has been carried out using computational fluid dynamics (CFD). Several configurations of housing blocks exposed to different wind directions have been modelled and compared considering the hot climate of Gaza. It has been found that grouping pattern of buildings as well as their orientation with respect to wind has a dramatic effect on the resulting airflow behaviour and pressure fields. Configurations that contain a central space articulated by buildings and oriented towards the prevailing wind can offer better exposure to air currents and better containment of wind. Such configurations are recommended for better wind-driven ventilation, where the main design objective is passive cooling.

Wind Modulation of Dissolved Oxygen in Chesapeake Bay

A numerical circulation model with a simplified dissolved oxygen module is used to examine the importance of wind-driven ventilation of hypoxic waters in Chesapeake Bay. The model demonstrates that the interaction between wind-driven lateral circulation and enhanced vertical mixing over shoal regions is the dominant mechanism for providing oxygen to hypoxic sub-pycnocline waters. The effectiveness of this mechanism is strongly influenced by the direction of the wind forcing. Winds from the south are most effective at supplying oxygen to hypoxic regions, and winds from the west are shown to be least effective. Simple numerical simulations demonstrate that the volume of hypoxia in the bay is nearly 2.5 times bigger when the mean wind is from the southwest as compared to the southeast. These results provide support for a recent analysis that suggests much of the long-term variability of hypoxia in Chesapeake Bay can be explained by variations in the summertime wind direction.

The loss factors of building openings for wind-driven ventilation

This study used wind tunnel experiments to determine the loss factors of building openings for wind-driven ventilation. It is found that the loss factor is a function of internal porosity, but independent of Reynolds number. The loss factor of a partially open door increased as the door angle decreased. In addition, the influence of thickness ratio on the loss factor is much smaller than the internal porosity. The present study also derived the relationship between the loss factor and the discharge coefficient used in the orifice equation. The experimental results demonstrate that the ventilation rate of wind-driven cross ventilation can be predicted by a resistance model, once the loss factors of the openings and external pressure coefficients are known. Besides, it was found that the flow resistance of the internal opening dominated the ventilation rate when the external openings are large. But the resistance of external opening is the governing parameter when the external openings are small.

A computational fluid dynamics study of air mixing in a naturally ventilated livestock building with different porous eave opening conditions

Computational fluid dynamics models of wind-dominated and wind and buoyancy-influenced ventilation in a naturally ventilated livestock building were developed to investigate the mixing characteristics of the building and to determine its ventilation efficiency when different cladding materials are used at the eave openings. Firstly, CFD was used to provide insight into the air mixing characteristics of the building during wind-driven and wind and buoyancy-influenced ventilation. Secondly the relationship between an eave opening’s resistance to airflow and indoor air mixing during wind-dominated ventilation was quantified, and finally the effect of eave opening conditions (i.e. eave cladding type, porosity, height) on building ventilation rate was analysed for a range of wind speeds. Overall, this study found the porosity of the eave opening cladding system heavily influenced the mixing of indoor air during wind-driven ventilation, with the low porosity cladding significantly enhancing the building’s ventilation efficiency.

Measurements of the performance of a wind-driven ventilation terminal

This paper presents the results of the measured ventilation flow rates through a roof-mounted inflow/outflow natural ventilator and of the wind pressures measured on the terminal under real conditions. The experiments were conducted at full scale at the former Silsoe Research Institute wind engineering test site using a 6 m cubic test building, referred to as the Silsoe cube, and using a test house. Ventilation rates and free-stream wind speed were measured using ultrasonic anemometers. The nominally 800 mm × 800 mm ventilation terminal on the Silsoe cube achieved a peak ventilation rate of 0·06 m3/s per m/s wind speed although the data also indicated periods when the ventilation rate dropped to approximately zero for a specific wind direction due to the vent then being in the position of flow re-attachment following separation at the windward leading edge of the roof. This has led to better knowledge in relation to the siting of such terminals. A similar terminal monitored on the test house achieved a peak ventilation rate of nearly 0·1 m3/s per m/s wind speed. The ventilation unit proved to be an effective means of providing natural ventilation and is likely to broaden the application of natural ventilation. The results of pressure measurements on the terminal louvres and the internal pressure in the cube, coupled with the measurements of the corresponding ventilating flow rate mechanisms, provide unique data with which to establish procedures for the rational design of such terminals, which is also outlined in the paper.

Prediction of performance of a wind-driven ventilation device

The paper presents the aerodynamic design of a ventilation device suitable for remote open areas, such as desert terrains. The device is attached to the top of an enclosure roof and employs wind energy to create a partial vacuum in a specially designed duct to draw out the stale air from within the enclosure. The design is developed with the aid of fluid flow simulation software that is employed to predict the flow details corresponding to different geometric shapes so that an efficient shape may be found. The software is also employed to predict the performance of the adopted shape for different operating conditions and the results are presented in the form of characteristics curves and a correlation equation. Reliability of predictions is backed by results of experimental validation presented elsewhere, and by performing a detailed grid-dependence study, as well as a domain extent sensitivity analysis.

Analysis of the role of sidewall vents on buoyancy-driven natural ventilation in parral-type greenhouses with and without insect screens using computational fluid dynamics

Computational fluid dynamics (CFD) was used to study the effect of greenhouse sidewall vents on buoyancy-driven natural ventilation, which is the most difficult situation for greenhouse cooling. A CFD model was validated and then used to compare roof ventilation with combined roof and sidewall vents. The effects of the distance between opposing sidewall vents and the presence of anti-insect screens were investigated and quantified. In a 20 span greenhouse with a distance of 152 m between the sidewalls, combining roof and sidewall vents gave a ventilation rate per unit ground area that was twice that with only roof vents. In a 3 span greenhouse with 22.8 m between sidewalls but with the same roof vent area per unit ground area, seven times more ventilation was obtained with combined ventilation compared to only roof ventilation. In the 7 and 20 span greenhouses with roof ventilation, 79% and 48.3%, respectively, of the cross sectional area had a temperature difference between inside and outside the greenhouse greater than 4 °C, whereas with combined ventilation, these areas were 23.4% and 36.1%. In the latter case, these hot areas were located in the centre of the houses. These results show that, with buoyancy-driven ventilation, the contribution of the sidewall vents is important even for quite large greenhouses but is more critical for greenhouses with a small number of spans. Numerical simulations with an anti-insect screen having a porosity of 25% showed that the air exchange rate with combined ventilation was reduced by 77–87%, depending on greenhouse size. These reductions were much larger than those obtained for wind-driven ventilation. It was concluded that, to maximise ventilation when wind speeds are low, combined roof and sidewall ventilation should be used. Also, large greenhouses should be relatively narrow to make better use of the sidewall vents.