A numerical investigation into the effect of windvent dampers on operating conditions

The United Kingdom has made a commitment to reduce buildings carbon emissions, placing a greater onus on sustainable energy sources. Therefore, an anticipated increase of usage of zero carbon technologies in new and existing building has led to the emergence of passive ventilation devices as an alternative to mechanical ventilation and air conditioning. The windvent is a commercially available passive ventilation device. The device is constructed from sheet metal and works on the principle of pressure differential. Whereby air rises, creating a low pressure in the receiving room, which then draws in the fresh air. The ensuing air delivery velocity is controlled by the dampers, installed at the room entry interface. The dampers are actuator operated, and form the basis of the control system for the device. The purpose of this paper is to investigate the control mechanism for the device and ascertain an optimum operating range. Numerical analysis is carried out using a commercial computational fluid dynamics (CFD) code, to investigate the effect of various damper angles (range 0–90°). The results show that optimum operating occurs at a damper angle range of 45–55°, at the UK average 4.5 m/s external wind speed. The operating range when considered in tandem with macro climatic influences is central to determining the overall control strategy for the fresh air supply. The results provide useful information for both engineers and architects when examining ways to reduce new and existing buildings running costs, and conform to new legislation.     

Investigation of a windvent passive ventilation device against current fresh air supply recommendations

Recent ecological and political developments have created an increased focus on sustainable energy sources. The purpose of this paper is to examine a passive ventilation device, the windvent, and evaluate its potential against current British Standards BS5952:1991 [British Standards, Ventilation principles and designing for natural ventilation, BS5925:1991 (1991)] recommended fresh air delivery rates. The results provide useful information for both engineers and architects when examining ways to reduce new and existing buildings running costs, and conform to new legislation. Numerical analysis is carried out using a commercial Computational Fluid Dynamics (CFD) code, to investigate the effect of various external wind velocities (1–5 m/s) and directions (concurrent and counter current) on the device performance. The results show that the windvent is capable of providing recommended rates of fresh air supply even at relatively low incident wind velocities. The performance indications show that the device warrants further analysis and provides a sustainable alternative ventilation system.     

A numerical simulation of wing walls using computational fluid dynamics

Larger window openings in the walls of a building may provide better natural ventilation. However, it also increases the penetration of direct solar radiation into indoor environment. The use of wing wall, one of the green features, is an alternative to create effective natural ventilation. Givoni conducted experiments in a wind tunnel to study the ventilation performance of wing walls. This paper presents a numerical study of the ventilation performance of wing walls using computational fluid dynamics (CFD). Two-dimensional and three-dimensional simulations are compared with the results of the experiments of Givoni. The results indicate that wing wall can promote natural ventilation by increasing the air change per hour and the mean indoor air speed relative to wind speed at various wind speeds and wind directions. The best performance of wing wall is at the wind angle of around 45°. The study also shows that 3D CFD simulation produces similar trend to the experimental results though there are some discrepancies.     

The assessment of the performance of a windcatcher system using computational fluid dynamics

Natural ventilation is increasingly being used in modern residential buildings to minimize the consumption of non-renewable energy and the reliance on active means for environmental control. Innovative green features such as the windcatcher has made use of natural ventilation in residential buildings for increasing ventilation rate. This paper presents a numerical study of assessment of the performance of windcatcher using computational fluid dynamics. A 500 mm square windcatcher system connected to the room has been modeled for different wind speeds in the range of 0.5–6 m/s and four different wind directions. The numerical results generally agree with the published experimental results of a wind tunnel experiment. The numerical results demonstrate that the windcatcher performance is greatly influenced by the external wind speed and direction with respect to the windcatcher quadrants. In all cases studied, the maximum velocity of air entering the room is close to the external wind speed and the windcatcher system is found to be an efficient way to channel fresh air into the room. The study also shows that the airflow rate of the air entering the room increases with the wind speed and slightly decreases with the wind incidence angle when the wind speed is lower than 3 m/s. In addition, the results show that the uniformity of air inlet decreases with increasing the wind speed and the incidence angle.     

Experimental and numerical study on natural ventilation performance of various multi-opening wind catchers

Wind catcher as a natural ventilation system is increasingly used in modern buildings to minimize the consumption of non-renewable energy and reduce the harmful emissions. Height, cross section of the air passages and also place and the number of openings are the main factors which affect the ventilation performance of a wind catcher structure. In this study, experimental wind tunnel, smoke visualization testing and computational fluid dynamic (CFD) modeling were conducted to investigate ventilation performance of wind catchers with different number of openings to find how the number of opening affects hydrodynamic behavior of wind catchers. To achieve this particular aim, five cylindrical models with same cross section areas and same heights were employed. The cross sections of all these wind catchers were divided internally into various segments to get two-sided, three-sided, four-sided, six-sided and twelve-sided wind catchers. The experimental investigations were conducted in an open circuit subsonic wind tunnel. For all these five shapes, the ventilated air flow rate into the test room was measured at different air incident angles. Numerical solutions were used for all these five configurations to validate the proposed measuring techniques and the corresponding wind tunnel results. The results show that the number of openings is a main factor in performance of wind catcher systems. It also shows that the sensitivity of the performance of different wind catchers related to the wind angle decreases by increasing the number of openings. Moreover, comparing with a circular wind catcher a rectangular system provides a higher efficiency.     

Reduced-scale building model and numerical investigations to buoyancy-driven natural ventilation

Similarities of a reduced-scale building model using air as the working fluid for buoyancy-driven natural ventilation have been analyzed and experiments were carried out using the scaled model for a common natural ventilation building, which has open office floor plans connected to a central atrium. Both open and closed cases have been investigated for the stack vents, located at the top of the atrium. Inputs for the scaled building model were taken from results measured in the prototype building by the authors. The parameters of the scaled building model's experiments thus were used as inputs into a computational fluid dynamics (CFD) simulation model to compare predicted and measured airflow patterns, temperatures and velocity distributions in the scaled building model.     

An analytical and numerical study of solar chimney use for room natural ventilation

The solar chimney concept used for improving room natural ventilation was analytically and numerically studied. The study considered some geometrical parameters such as chimney inlet size and width, which are believed to have a significant effect on space ventilation. The numerical analysis was intended to predict the flow pattern in the room as well as in the chimney. This would help optimizing design parameters. The results were compared with available published experimental and theoretical data. There was an acceptable trend match between the present analytical results and the published data for the room air change per hour, ACH. Further, it was noticed that the chimney width has a more significant effect on ACH compared to the chimney inlet size. The results showed that the absorber average temperature could be correlated to the intensity as: (T_w = 3.51I^0.461) with an accepted range of approximation error. In addition the average air exit velocity was found to vary with the intensity as (ν_ex = 0.013I^0.4).     

Full scale experimental study of single-sided ventilation: Analysis of stack and wind effects

Natural ventilation can contribute to the reduction of the air conditioning demand and to the improvement of thermal comfort in buildings. In this paper, the flow field and the air change rate generated by a simple configuration of natural ventilation, namely single-sided ventilation, are examined experimentally. The experiments are realized in a full scale building exposed to outdoor conditions, using several measurement techniques. The main features of the flow generated by stack and wind effect are examined for different outdoor conditions (temperature difference, wind speed and direction). Finally, measured air change rates are compared to those calculated by existing correlations in order to analyze their applicability to the experimental configuration. Results show that the wind generates turbulence diffusion at the opening, counteracting the stack effect. Moreover, in the case of windward opening, there is an additional effect, namely the effect of mixing layer, which tends to increase the airflow rate. Existing correlations give reasonably good results in the case of windward opening, while in the case of leeward opening they overestimate the airflow rate.     

Solar chimney—A passive strategy for natural ventilation

Passive ventilation systems are being increasingly proposed as an alternate to mechanical ventilation systems because of their potential benefits in terms of operational cost, energy requirement and carbon dioxide emission. Solar chimney is an excellent passive ventilation system which relies on natural driving force, that is, the energy from the sun. A significant amount of research work has been done on solar chimney since the 1990s. This article presents an overview of solar chimney research that has taken place in the last two decades. The review focuses on two main areas of research - the effects of geometry and inclination angle on the ventilation performance of a solar chimney. The experimental investigations of solar chimney have dominated the existing literature. However, numerical modelling of solar chimney using computational fluid dynamics (CFD) technique has attracted increasing attention. Moreover, this review found that solar chimney as a passive ventilation strategy has not been fully understood.     

Study of wind towers with different funnels attached to increase natural ventilation in an underground building

Finding ways to cool buildings by natural, passive techniques is crucial in the context of global warming. For centuries, wind towers (traditional windcatchers) have been used in the Middle East for cooling purposes. In this study, the use of funnels at the openings of wind towers for wind ingress and egress is proposed primarily to increase the mass flow captured by the wind tower. The use of funnels in the wind ingress openings increases the inlet area, improving the capture of wind. In parallel, the use of funnels in the egress openings modifies the wake of the tower, which aims to ease the exit of the flow from inside the building. Several design configurations are presented, where the length and width of the funnels are changed and tested separately by computational fluid dynamics (CFD). Results of over 120 CFD simulations are presented and compared. The volumetric flow entering the wind towers increases by 10.7% in several cases. These results indicate that adding funnels to wind towers could positively influence their performance. Changing the dimensions of the funnels affects their efficacy and can increase or decrease the airflow entering the tower.     

A comparison between CFD and Network models for predicting wind-driven ventilation in buildings

The aim of this paper is to compare the implementation of computational fluid dynamics (CFD) and Network models for airflow rate estimation in buildings. The CFD software used is Fluent 5.5. Comparison between the predicted and simulated airflow rate is suggested as a validation method of the implemented CFD code, while the common practice is to compare CFD outputs to wind tunnel or full-scale measurements. This could be useful for studies that have no access to laboratory or full-scale testing facilities. Results obtained from testing a number of cases have been compared and analysed, considering normal and oblique wind directions. The comparison held between mathematical and CFD results generally showed a good agreement, which seems to justify the use of CFD code for predicting natural ventilation in buildings.     

Evaluating the influence of openings configuration on natural ventilation performance of residential units in Hong Kong

Natural ventilation performance of a residential dwelling is affected by a combination of internal and external factors. External factors are often subject to constraints beyond the control of site planners and architects. Internal factors include the openings configuration, which site planners and architects are free to design the way they deem proper. However, little information is available in this regard. In this study, a case study was conducted by tracer-gas measurements at a carefully selected residential unit for Computational Fluid Dynamics (CFD) model validation. A hypothetical residential unit was formulated to represent the characteristics of typical residential units in Hong Kong. CFD simulations were performed based on the hypothetical unit to evaluate the influence of different openings configurations on natural ventilation performance using the mean age of air. Openings configuration is defined by many parameters. Among the three studied parameters, evaluation results indicate that natural ventilation performance of residential units was most affected by the relative position of the two window openings groups (i.e. bedroom windows and living room windows), followed by building orientation and doors positions. It was found that better natural ventilation performance could be achieved when the two openings groups were positioned in opposite directions or perpendicular to each other. The combined effect of the three parameters was evaluated. It was found that varying two parameters at the same time offered positive improvements in natural ventilation performance, but varying all three parameters did not result in any improvement because of the counter-effects of changes in doors positions.     

A venturi-shaped roof for wind-induced natural ventilation of buildings: Wind tunnel and CFD evaluation of different design configurations

Wind tunnel experiments and Computational Fluid Dynamics (CFD) are used to analyse the flow conditions in a venturi-shaped roof, with focus on the underpressure in the narrowest roof section (contraction). This underpressure can be used to partly or completely drive the natural ventilation of the building zones. The wind tunnel experiments are performed in an atmospheric boundary layer wind tunnel at scale 1:100. The 3D CFD simulations are performed with steady RANS and the RNG k-? model. The purpose of this study is twofold: (1) to evaluate the accuracy of steady RANS and the RNG k-? model for this application and (2) to assess the magnitude of the underpressures generated with different design configurations of the venturi-shaped roof. The CFD simulations of mean wind speed and surface pressures inside the roof are generally in good agreement (10–20%) with the wind tunnel measurements. The study shows that for the configuration without guiding vanes, large negative pressure coefficients are obtained, down to −1.35, with reference to the free-stream wind speed at roof height. The comparison of design configurations with and without guiding vanes shows an – at least at first sight – counter-intuitive result: adding guiding vanes strongly decreases the absolute value of the underpressure. The reason is that the presence of the guiding vanes increases the flow resistance inside the roof and causes more wind to flow over and around the roof, and less wind through it (wind-blocking). As a result, the optimum configuration is the one without guiding vanes.     

Experimental investigation of heat transfer during night-time ventilation

Night-time ventilation is seen as a promising approach for energy efficient cooling of buildings. However, uncertainties in the prediction of thermal comfort restrain architects and engineers from applying this technique. One parameter essentially affecting the performance of night-time ventilation is the heat transfer at the internal room surfaces. Increased convection is expected due to high air flow rates and the possibility of a cold air jet flowing along the ceiling, but the magnitude of these effects is hard to predict. In order to improve the predictability, heat transfer during night-time ventilation in case of mixing and displacement ventilation has been investigated in a full scale test room. The results show that for low air flow rates displacement ventilation is more efficient than mixing ventilation. For higher air flow rates the air jet flowing along the ceiling has a significant effect, and mixing ventilation becomes more efficient. A design chart to estimate the performance of night-time cooling during an early stage of building design is proposed.     

A review on wind driven ventilation techniques

Natural ventilation has gained prominence in recent times as a bespoke method of ventilating buildings. The two fundamental principles of natural ventilation are stack effect and wind driven ventilation. This paper reviews miscellaneous wind driven ventilation designs with respect to traditional means such as wind towers and more modern techniques including turbine ventilators and wind catchers. A distinction is made between specific types of wind driven ventilation techniques depending on their operation and mode of engagement with the wind. For example, a static wind catcher is classified as passive; a rotating wind cowl as a directed passive technique and a rotating turbine ventilator is classified as outright active due to its constant rotation with the wind. A table summarising the review is presented at the end with corresponding references.     

Theoretical and experimental investigation of impinging jet ventilation and comparison with wall displacement ventilation

This paper focuses on evaluating the performance of a new impinging jet ventilation system and compares its performance with a wall displacement ventilation system. Experimental data for an impinging jet in a room are presented and non-dimensional expressions for the decay of maximum velocity over the floor are derived. In addition, the ventilation efficiency, local mean age of air and other characteristic parameters were experimentally and numerically obtained for a mock-up classroom ventilated with the two systems. The internal heat loads from 25 person-simulators and lighting were used in the measurements and simulations to provide a severe test for the two types of ventilation systems. In addition to a large number of experimental data CFD simulations were used to study certain parameters in more detail. The results presented here are part of a larger research programme to develop alternative and efficient systems for room ventilation.     

Breathing architecture: Conceptual architectural design based on the investigation into the natural ventilation of buildings

This study explores architectural design by examining air, fluid mechanics, and the natural ventilation of buildings. In this context, this research introduces a new way of dealing with the process of architectural synthesis. The proposed way can be used either to create new architectural projects or to rethink existing ones. This study is supported by previous investigation into the natural ventilation of buildings via computational and laboratory simulation (Stavridou, 2011; Stavridou and Prinos, 2013). The investigation into the natural ventilation of buildings provides information and data that affect architectural design through various parameters. The parameters of architectural synthesis that are influenced and discussed in this paper are the following: (i) inspiration and analogical transfer, (ii) initial conception of the main idea using computational fluid dynamics (digital design), (iii) development of the main idea through an investigatory process toward building form optimization, and (iv) form configuration, shape investigation, and other morphogenetic prospects. This study illustrates the effect of natural ventilation research on architectural design and thus produces a new approach to the architectural design process. This approach leads to an innovative kind of architecture called “breathing architecture.”     

The effects of night ventilation technique on indoor thermal environment for residential buildings in hot-humid climate of Malaysia

This study investigates the effectiveness of night ventilation technique for residential buildings in hot-humid climate of Malaysia. This paper firstly presents the results of a survey on usage patterns of windows and air-conditioners in typical Malaysian residential areas. Secondly, the effects of different natural ventilation strategies on indoor thermal environment for Malaysian terraced houses are evaluated based on the results of a full-scale field experiment. The results show that the majority of occupants tend to apply not night ventilation but daytime ventilation in Malaysian residential areas. It can be seen from the field experiment that night ventilation would provide better thermal comfort for occupants in Malaysian terraced houses compared with the other ventilation strategies in terms of operative temperature. However, when the evaporative heat loss of occupants is taken into account by using SET*, the night ventilation would not be the superior technique to the others in providing daytime thermal comfort mainly due to the high humidity conditions. Therefore, the indoor humidity control during the daytime such as by dehumidification would be needed when the night ventilation technique is applied to Malaysian terraced houses. Otherwise, full-day ventilation would be a better option compared with night ventilation.     

Experimental and computational investigation into suppressing natural convection in chilled ceiling/displacement ventilation environments

The combination of chilled ceiling and displacement ventilation systems can cause destruction of the displacement flow pattern in some circumstances. This paper reports on the performance of a new technique for achieving stable conditions for displacement airflow in the presence of a chilled ceiling system. The technique is based on the attachment of a honeycomb slat system to the underside of a chilled ceiling, thereby suppressing downward cool natural convection. Investigations were carried out using both computational and experimental methods for a range of typical office environment conditions. The results showed that a slat depth to width ratio of 10 could suppress the natural convection by more than 80% when the Rayleigh number reached 7 × 10⁶. This confirms that the technique is capable of minimising downward cool air currents, resulting in preservation of the displacement flow pattern in the presence of the chilled ceiling. The proposed slat system can raise the general air temperature in the space allowing some displacement flow pattern to occur. The outcome of this study is the emergence of a honeycomb slat-based approach for improving the performance, together with provision of general advice for designers as regards the combination of radiant cooling/displacement ventilation systems.     

天窗及挡风板几何特性对厂房自然通风效果的影响

运用CFD软件模拟分析了矩形天窗及挡风板几何特性对采用天窗进行自然通风的一南北向厂房的影响,结果表明天窗宽高比为1.8时厂房的自然通风量最大,通风效果最好;挡风板高度增加,自然通风量有所增加,但增量较小;自然通风量随挡风板与天窗间距的增大以对数规律增加。