Natural ventilation is the process of supplying and removing air through an indoor space by natural means. There are two types of natural ventilation occurring in buildings: winddriven ventilation and buoyancy driven or stack ventilation. The most efficient design for natural ventilation in buildings should implement both types of natural ventilation. Stack ventilation which is temperature induced is driven by buoyancy making it less dependent on wind and its direction. Heat emitted causes a temperature difference between two adjoining volumes of air, the warmer air will have lower density and be more buoyant thus will rise above the cold air creating an upward air stream. Combining the wind driven and the buoyancy driven ventilation will be investigated in this study through the use of a windcatcher natural ventilation system. Stack driven air rises as it leaves the windcatcher and it is replaced with fresh air from outside as it enters through the positively pressured windward side. To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a three dimensional room fitted with a windcatcher based on the winddriven ventilation alone, buoyancy driven ventilation alone, and combined buoyancy and winddriven ventilation. Different wind speeds between 0 up to 2.5 m/s are applied and the total air flow rate through the windcatcher is investigated with and without temperature of 350 K applied at the windcatcher’s outlet wall. As the wind speed increased the efficiency of the solar windcatcher decreased.

Windcatcher has been used over centuries for providing natural ventilation using wind power, it is an effective passive method to provide healthy and comfortable indoor environment. The windcatcher’s function is based on the wind and on the stack effect resulting from temperature differences. Generally, it is difficult for wind to change its direction, and enter a room through usual openings, the windcatcher is designed to overcome such problems since they have vertical columns to help channel wind down to the inside of a building. The efficiency of a windcatcher is maximized by applying special forms of opening and exit. The openings depend on the windcatcher’s location and on its cross sectional area and shape such as square, rectangular, hexagonal or circular. In this study the effect of the inlet design is investigated to achieve better air flow and increase the efficiency of windcatchers. To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a three dimensional room fitted with a windcatcher based on the different inlet designs. The divergent inlet has captured the highest air flow with a difference of approximately 3% compared to the uniform inlet and 5% difference compared to the bulging-convergent inlet.

Solar chimney (thermal chimney) is a device which absorbs solar radiation to heat the air. The heated air, becoming buoyant, rises through the chimney’s passage and induces further air currents. When fitted to a building, solar chimney can thus induce fresh outside air to flow through the building for ventilation. Because only natural means (solar radiation here) are involved to cause the air flow, solar chimney is considered a natural-ventilation device. This work investigates computationally natural ventilation induced by a roof-mounted solar chimney through a real-sized 3-dimensional room, using a commercial CFD (Computational Fluid Dynamics) software package which employs the Finite Volume Method. Chien’s turbulence model of low-Reynolds-number K-ε is used in a Reynolds-Averaged Navier-Stokes (RANS) formulation. Computational domain that includes regions outside the room’s inlet opening and chimney’s exit allows for employing realistic boundary conditions for the computational model. Ventilation rate and air-flow pattern through the room are considered in terms of the location of the room’s inlet opening. It is found that while ventilation flow-rate through the room is higher with the room-inlet opening being located high on the wall opposite to the chimney’s entrance, a room-inlet opening being located near the ground results in better flow pattern with more flow through the living area in the lower part of the room.

Green walls are bio-filters developed to enhance air quality. Often, these walls form the base from which plants are grown; and the plant-wall system helps to remove both gaseous and particulate air pollutants. Green walls can be found indoors or outdoors and they are classified as passive or active systems. Their benefits include temperature reduction, improvement of air quality and reduction of air pollution, oxygen production as well as the social and psychological wellbeing. They can produce changes in the ambient conditions (temperature and humidity) of the air layers around them which create an interesting insulation effect. The effect of passive green wall modules on the air temperature and on humidity is investigated in this work. A closed chamber made of acrylic sheets is used to monitor the temperature and humidity variation caused by a green wall module placed at its center. Temperature and humidity are measured at different locations inside the chamber during operation for different modules with different plant species.

Natural ventilation is the process of supplying and removing air through an indoor space by natural means. Windcatcher has been used over centuries for providing natural ventilation using wind power, it is an effective passive method to provide healthy and comfortable indoor environment by decreasing moisture content in the air and reducing pollutants concentration. The windcatcher’s function is based on the wind and on the stack effect resulting from temperature differences. Generally, it is difficult for wind to change its direction, and enter a room through usual openings, the windcatcher is designed to overcome such problems since they have vertical columns aimed at helping wind to channel down to the inside of a building. The efficiency of a windcatcher is maximized by applying special forms of opening and exit. The openings depend on the windcatcher’s location and on its cross sectional area and shape such as square, rectangular, hexagonal or circular. In this study the effect of different wind speeds on the total air flow captured by different inlet designs is investigated. To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a two dimensional room fitted with a windcatcher applying wind speeds from 1 m/s up to 14 m/s and based on different inlet designs such as a uniform inlet, a divergent inlet and a bulging-convergent inlet.

Green or living walls are active bio-filters developed to enhance air quality. Often, these walls form the base from which plants are grown; and the plant-wall system helps to remove both gaseous and particulate air pollutants. They can be classified as passive or active systems. The active systems are designed with ventilators which force air through the substrate and plant rooting system, therefore the air is purified and filtered through a bio-filtration process which also acts as a natural cooling system. Their benefits include temperature reduction, improvement of air quality and reduction of air pollution, oxygen production as well as the social and psychological wellbeing. They can produce changes in the ambient conditions (temperature and humidity) of the air layers around them which create an interesting insulation effect. The effect of green wall modules on the air temperature and on humidity is investigated in this work. A closed chamber made of acrylic sheets is used to monitor the temperature and humidity variation caused by a green wall module placed at its center. A fan positioned at the back center of the module drives air at ambient conditions and direct it into the module. Temperature and humidity are measured at different locations inside the chamber during operation for different modules with different plant species. The effect of changing the surrounding ambient conditions is also investigated.

Green or living walls are active bio-filters developed to enhance air quality. Often, these walls form the base from which plants are grown; and the plant-wall system helps to remove both gaseous and particulate air pollutants. They can be classified as passive or active systems. The active systems are designed with ventilators which force air through the substrate and plant rooting system, therefore the air is purified and filtered through a bio-filtration process which also acts as a natural cooling system. A fan positioned at a central opening on the module’s back face drives air through the medium-plant-roots mix and then onward through the plants’ canopy; and these would help to remove both gaseous and particulate pollutants from the air. Pressure drop across the module, air flow distribution through it as well as the total flow rate have been obtained. The effect of different fan speeds on the total air flow and on its distribution through the module is investigated in this study in order to optimize the energy consumption of the fans whilst maintaining the modules biofiltration efficiency.

Natural ventilation is the process of supplying and removing air through an indoor space by natural means. Windcatcher has been used over centuries for providing natural ventilation using wind power, it is an effective passive method to provide healthy and comfortable indoor environment by decreasing moisture content in the air and reducing pollutants concentration. The windcatcher’s function is based on the wind and on the stack effect resulting from temperature differences. Generally, it is difficult for wind to change its direction, and enter a room through usual openings, the windcatcher is designed to overcome such problems since they have vertical columns aimed at helping wind to channel down to the inside of a building. The efficiency of a windcatcher is maximized by applying special forms of opening and exit. The openings depend on the windcatcher’s location and on its cross sectional area and shape such as square, rectangular, hexagonal or circular. In this study the effect of the inlet design is investigated to achieve better air flow and increase the efficiency of windcatchers. To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a two dimensional room fitted with a windcatcher based on different inlet designs such as a uniform inlet, a divergent inlet and a bulging-convergent inlet.

Butterfly valves are typically used as emergency closure devices in dam penstocks; these valves must be capable of closing if a penstock bursts. This paper summarizes a 3D CFD (Computational Fluid Dynamics) study that was conducted on the water flow across a sizable butterfly valve (1.6m in diameter) in a dam penstock with 57m of water head. The main aim is to determine the maximum torque required to close the valve. Thus semi steady flow conditions across the valve at various degrees of closure were investigated and the corresponding torque calculated. A maximum torque of about 87 700 N-m has been obtained, occurring at valve angle 40° (with valve totally closed at 0°, and fully open at 90°). Visual results were analyzed at each valve angle to understand the nature of the flow through the butterfly valve using various 2D contours and streamline images. The CFD software ANSYS Fluent has been used employing a Finite Volume Method. The RANS (Reynolds-Averaged Navier-Stokes) approach with Realizable K-epsilon turbulence model was employed. A grid independence study with up to 10 million cells has also been carried out, resulting in the adoption of 7.5 million cells in all models. Comparison with other available data was also completed, adding to the reliability of the computational results. Distribution of pressure, flow velocity, and turbulence parameters are also presented.

Natural ventilation is the process of supplying and removing air through an indoor space by natural means. There are two types of natural ventilation occurring in buildings: winddriven ventilation and buoyancy driven ventilation, or stack ventilation. The most efficient design for natural ventilation in buildings should implement both types of natural ventilation. Stack ventilation which is temperature induced is driven by buoyancy making it less dependent on wind and its direction. Heat emitted causes a temperature difference between two adjoining volumes of air, the warmer air will have lower density and be more buoyant thus will rise above the cold air creating an upward air stream. Combining the winddriven and the buoyancy driven ventilation will be investigated in this study through the use of a windcatcher natural ventilation system. Stack driven air rises as it leaves the windcatcher and it is replaced with fresh air from outside as it enters through the positively pressured windward side. To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a two dimensional room fitted with a windcatcher based on the winddriven ventilation alone and on the combined buoyancy and winddriven ventilation.

Green or living walls are active bio-filters developed to enhance air quality. Often, these walls form the base from which plants are grown; and the plant-wall system helps to remove both gaseous and particulate air pollutants. A green wall can be found indoors as well as outdoors, and could be assembled from modules in an arrangement similar to tiling. The module is a rectangular plastic box (dimensions about 500 mm × 500 mm × 130 mm) that holds a permeable bag containing a plant-growing medium (replacement for soil). The front face of the module has multiple openings for plants to protrude out from the bag inside. Plant roots are imbedded in the medium. A fan positioned at a central opening on the module’s back face drives air through the medium-plant-roots mix and then onward through the plants′ canopy; and these would help remove both gaseous and particulate pollutants from the air. Volatile Organic compounds (VOCs) and particulate matters PMs are both reduced by passing through the plant-growing medium, thus reducing the percentage of air flow that passes through the open top face of the module is essential to maximize the capacity of bio-filtration. Drip-irrigation water is dispensed from a tube running along the open top-face of the module. The module has also a small drainage hole on its bottom face. Pressure drop across the module as well as air-flow rate through it have been obtained in a previous work [1], air-flow distribution through the module and the effect of introducing a cover to the module’s open top face are investigated in this work to improve the design of the module and achieve more appropriate flow rate and flow distribution. The top cover essentially includes small holes of 10 mm diameter to allow the necessary irrigation. The measurements help to determine the pattern of flow resistances which in turn will be used in a future CFD (Computational Fluid Dynamics) analysis.

People spend most of their time indoors. A comfortable indoor environment is thus essential for the occupants’ good health and productivity. Buildings are responsible for about half of a modern society’s total energy consumption. HVAC (Heating, Ventilation and Air-Conditioning) which is often used to provide thermal comfort to the occupants, in turn accounts for a major proportion of this energy demand. Minimising HVAC energy consumption will thus result in great economic benefits. It also contributes beneficially to the issue of sustainable future and climate change, by reducing fuel burning. Natural ventilation can be used to help reduce significantly HVAC energy demand. Solar chimney (thermal chimney) is a device which absorbs solar radiation to heat the air. The heated air, becoming buoyant, rises through the chimney’s passage and induces further air currents. When fitted to a building, solar chimney can thus induce fresh outside air to flow through it for ventilation. As a very useful ventilation device, solar chimney has been the subject of many studies. However, due to the complex non-laminar, non-isothermal flow and heat transfer involved, there are still many factors affecting a solar chimney’s performance (measured by the induced flow rate of air, for instance) not yet considered, especially regarding 3-dimensional computational modelling in real-sized building settings. This work thus investigates computationally natural ventilation induced by a roof-mounted solar chimney through a real-sized 3-dimensional room, using a commercial CFD (Computational Fluid Dynamics) software package which employs the Finite Volume Method. Chien’s turbulence model of low-Reynolds-number K-ε is used in a Reynolds Averaged Navier-Stokes (RANS) formulation. Thus, the full set of Reynolds-Averaged governing equations pertaining to non-isothermal, buoyancy induced, incompressible, steady, turbulent flow of air near standard conditions at sea level, coupled with equations describing the Chien’s turbulence model, are solved, with appropriate boundary conditions. No further simplifying assumptions are made. Grid convergence tests are conducted to make sure that the grid patterns used are appropriate. Adequate numerical convergence is allowed; this often requires that relative changes in the successive iterated solutions be less than 0.0001. Accumulation errors resulting from massive or lengthy computation are also carefully monitored and minimized. 64-bits precision is used throughout. It is found that entrance geometry to the chimney’s channel affects significantly the ventilation rate, especially at higher solar heat flux, with rounded entrance resulting in higher rate. But these entrance-geometry effects also vary significantly with location of the room’s inlet-opening which in its turn affects the flow path before the chimney’s entrance.

Ventilation is a process of changing air in an enclosed space. Air should continuously be withdrawn and replaced by fresh air from a clean external source to maintain internal good air quality, which may referred to air quality within and around the building structures. In natural ventilation the air flow is due through cracks in the building envelope or purposely installed openings. Its can save significant amount of fossil fuel based energy by reducing the needs for mechanical ventilation and air conditioning. Numerical predictions of air velocities and the flow patterns inside the building are determined. To achieve optimum efficiency of natural ventilation, the building design should start from the climatic conditions and orography of the construction to ensure the building permeability to the outside airflow to absorb heat from indoors to reduce temperatures. Effective ventilation in a building will affects the occupant health and productivity. In this work, computational simulation is performed on a real-sized box-room with dimensions 5 m × 5 m × 5 m. Single-sided ventilation is considered whereby openings are located only on the same wall. Two opening of the total area 4 m 2 are differently arranged, resulting in 16 configurations to be investigated. A logarithmic wind profile upwind of the building is employed. A commercial Computational Fluid Dynamics (CFD) software package CFD-ACE of ESI group is used. A Reynolds Average Navier Stokes (RANS) turbulence model & LES turbulence model are used to predict the air’s flow rate and air flow pattern. The governing equations for large eddy motion were obtained by filtering the Navier-Stokes and continuity equations. The computational domain was constructed had a height of 4H, width of 9H and length of 13H (H=5m), sufficiently large to avoid disturbance of air flow around the building. From the overall results, the lowest and the highest ventilation rates were obtained with windward opening and leeward opening respectively. The location and arrangement of opening affects ventilation and air flow pattern.

A Computational Fluid Dynamics (CFD) software package is used to investigate numerically a 3-dimensional rectangular-box room installed with heat pipes heat exchanger (HPHE). Heat pipe heat exchanger utilizing refrigerant by mean of working fluid is installed on top of a room. The air-side heat transfer and the flow pattern of a thermo-siphon heat pipes is studied with a natural driven ventilation of a building. Different opening of the inlet and outlet air where the heat pipe was installed are tested with round edges opening as well as sharp edges. The standard RANS k –ε turbulence model is used. Results with different setting of heat pipe and opening characteristic, air flow rate and flow pattern as well as its temperature effects are examined.

The natural ventilation contributes the improvement of internal thermal comfort and internal air quality when applied properly. An investigation of single-sided double opening was performed to a 3-dimensional rectangular-box room using a commercial Computational Fluid Dynamics (CFD) software package of ESI group. Sixteen models with different location of double-openings were investigated. The large eddy simulation (LES) turbulence model was used to predict the air’s flow rate and air flow pattern. The governing equations for large eddy motion was obtained by filtering the Navier-Stokes and continuity equations. From the overall results, the lowest and the highest air flow rates were obtained to be 1.14 × 10 −3 m 3 /s and 2.12 × 10 0 m 3 /s respectively. The location & arrangement of opening influences the air flow rate and air flow pattern.

A windcatcher is a structure placed on the roof of a building for providing natural ventilation for interior space working by wind power. It draws out the inside stale air to the outside and supplies the outside fresh air for the building’s interior space. In this paper, the effect of different types of windcatcher’s inlet\outlet on the air flow, flow velocity and flowrate through a three-dimensional room fitted with a two-sided windcatcher is observed numerically, using a commercial computational fluid dynamics (CFD) software package. The standard RANS K-ε CFD method is used in the simulations. The flow pattern, flow velocity and flowrate of the inside ventilation flow is considered for the six different types of a two-sided windcatcher’s inlet\outlet. It is found that the shape of the inlet\outlet of windcatcher strongly affects flow pattern, flow velocity and flowrate and the performance of square windcatcher is higher than the circular one specially in ventilating the living area (lower part) of a room.

A commercial Computational Fluid Dynamics (CFD) software package is used to investigate numerically a 3-dimensional rectangular-box room with rounded edges. The room has all its window openings located on one wall only. The standard K-ε turbulence model is used. Air’s flow rate and flow pattern are considered in terms of wind speed and the openings’ characteristics, such as their number, location, size and shape. Especially, comparison with ventilation rate corresponding to when the room edges are sharp is made; and thereby the effects of the edges being rounded are examined.

Natural-ventilation flow induced in a real-sized rectangular-box room fitted with a solar chimney on its roof is investigated numerically, using a commercial CFD (Computational Fluid Dynamics) software package. The chimney in turn is in the form of a parallel channel with one plate being subjected to uniform solar heat flux. Ventilation rate and air-flow pattern through the room are considered in terms of the heat flux for two different locations of the room’s inlet opening. Chien’s turbulence model of low-Reynolds-number K-ε is used in a Reynolds-Averaged Navier-Stokes (RANS) formulation. It is found that ventilation flow rate increases quickly with solar heat flux when this flux is low, but more gradually at higher flux. At low heat flux, ventilation rate is not significantly affected by location of the inlet opening to the room. On the other hand, at high heat flux, ventilation rate varies substantially with the opening’s location. Location of the inlet opening to the room also affects strongly the air-flow pattern. In any case, ample ventilation rate is readily induced by the chimney.

The past few decades have seen a considerable change in terms of technological innovation. The recent technological trend is a shift towards the incorporation of natural processes such as hydro, solar and wind in design and implementation. For the purpose of this report, a miniaturised solar chimney test rig was constructed which utilises the principles of natural ventilation. Analysis of similar types of technologies was conducted and various ideas considered in the construction of the test rig. Computational fluid dynamics software was also used in conjunction with the experiment to see the similarities associated with the experiment and software package, taking into account the limitation of various instruments. A comprehensive experimental and theoretical approach was developed and reported.

Influence of temperature on the performance of slider bearings of infinite width but having corrugation of limited extent is investigated numerically, using a commercial Computational Fluid Dynamics (CFD) software package. Lubricant is assumed to be a fluid of power-law type with temperature-dependent viscosity. Over a range of the power-law index, combined effects of temperature and the corrugated section’s location on load-supporting capacity F y of the bearing’s fluid film are considered. Influence of the bearing-gap surfaces’ thermal boundary condition is also examined. Compared with isothermal situation, thermal effects result in significant reduction in F y , especially with shear-thickening lubricants. This reduction in F y is also affected significantly by the corrugated section’s location.