2. Limitations and assumptions of the case study

#### 2.1. Experimental process of the research project

Experimental studies have been made on 17 separate opening configurations on the façade of a building not having (BSL-SUZ) openings on its mass that surrounds the courtyards preferred as reference building. The building has been evaluated as two stories as its original scale, whereby each storey has a height of 3.00 m, the external dimensions of the building are 14.00 14.00 6.00 m but courtyard dimensions are 6.00 6.00 6.00 m. 36 separate points of measurement have been determined on X and Y dimensions in the model courtyard; and measuring profiles with 36 measurement points have been found on Z dimension at each point of measurement.

disciplines [1]. Planners and designers have, for centuries, considered wind or air flow as innate data for construction of components at several levels which involve cities, regions and countries [2]. Miscellaneous passive or natural air-conditioning methods taking advantage of the wind are used by architects and city planners in order to reduce the costs of cooling in territories with high temperatures [3]. As a passive air-conditioning medium, the moving air may be precious for provision of ventilation within buildings, particularly when it comes to hot and humid climates. The traditional courtyard building form entailed by climates which are hot and dry ensures that air flow is due to wind pressure variations leading to some

74 Sustainable Buildings - Interaction Between a Holistic Conceptual Act and Materials Properties

Therefore, other openings of buildings which may cause a change on the efficacy of air movements resulting from the wind effect in courtyard buildings should be a subject for thorough study. There have been several studies, either numerical or experimental on the angle of insulation for buildings with courtyards. Nevertheless, wind effects have served as subject to a limited number of studies only. For instance, the wind attitude is to either flow over or circle in the courtyard if buildings are adjacent forming an open courtyard in a settlement area. Area of and openings position in courtyards in view of the wind (as well as openings width or total width) constitute variables that influence qualitative and quantitative wind character in courtyards [8, 9]. Outdoor layout and outdoor position have their effects on discomfort parameters for pedestrian spaces. The discomfort parameter is at its highest degree in areas subject to wind and at a medium degree in areas that are fully closed or subject to wind from a single direction [10–12]. Wind directions influence ventilation performance of buildings with courtyards and weaken if those courtyards are located in perpendicular to the wind [13]. In case buildings contain openings, openings in wind direction will cause highest speed of air flows as a number of parallel experiments have confirmed [14]. Studies demonstrate in the courtyards that maximum outdoor temperature is observed at noon time in summer of hot climates and

Courtyard depth is an effective variable for control of those parameters in buildings without openings [15–17]. The openings of buildings with courtyards on perpendicular areas, nevertheless, gain high significance particularly in hot/humid and moderate temperature/humid climatic territories, a parameter that is not true in hot/dry climate areas. In this study we tried to expound the effects of openings in the architecture of buildings with courtyards on airflow velocity in those courtyards. The outcomes depend on not only scale tests in the wind tunnel

Experimental studies have been made on 17 separate opening configurations on the façade of a building not having (BSL-SUZ) openings on its mass that surrounds the courtyards preferred as reference building. The building has been evaluated as two stories as its original scale, whereby each storey has a height of 3.00 m, the external dimensions of the building are 14.00 14.00 6.00 m but courtyard dimensions are 6.00 6.00 6.00 m. 36 separate points of

minimum outdoor temperature is experienced prior to sunrise.

2. Limitations and assumptions of the case study

2.1. Experimental process of the research project

but also CFD numerical analysis.

natural ventilation [4–7].

The building model in relation to the courtyard is modular to allow observation of the ventilation effects caused by the openings on the courtyard building. A reference model was made of empty Plexiglas material with dimensions of 4.00 4.00 4.00 cm to allow 17 separate configurations for courtyards. The model dimensions are 28.00 28.00 12.00 cm and dimensions for the internal courtyard are 12.00 12.00 12.00 cm.

Figure 1. Appearance at ground floor plan level of the configuration for the courtyard with 17 different openings experimented [10].

The measuring axis perpendicular to the wind tunnel observation section "AB, B, C, D, E, F" lateral surface was in the wind direction. The points of measurement "1, 2, 3, 4, 5, 6" were placed on the axis perpendicular to the direction of the wind. At the courtyard, 36 points of measurement in total have been set with distances of 2.00 cm between directions of the X and Y axis. As to the points of measurement in dimension Z, profiles with 34 points of measurement have been placed at differing intervals in a way to be closer to the ground, to the roof and the opening edges that are to be organized on the model courtyard surfaces (Figures 1–3). At each measurement profile, nine points of measurement from 0 to 4 cm have been set at 0.5 cm intervals; 6 of them were placed at 1.00 cm intervals in the section as far as the following 10.00 cm; 14 have been placed at 0.5 cm intervals through the area between 10.00 and 17.00 cm; and another out-of-the-model 5 between 17.00 and 22.00 cm.

2.2. Modeling and simulation in numerical analysis

the flow as well as the thermal areas available in detail.

Computational Fluid Dynamics have been utilized in prediction of the transfer of convective heat on the exterior of building surfaces [13–15]. The main advantages of CFD in this practice has been that: (1) it allows for analysis of a specific and complex building or building configuration; (2) it provides high data on spatial resolution; (3) it makes consideration of high Reynolds number flows for atmospheric conditions possible and (4) it makes information on

Optimization of Building Facade Voids Design, Facade Voids Position and Ratios - Wind Condition Relation

http://dx.doi.org/10.5772/intechopen.72697

77

Figure 3. The wind velocity and air flow at 0.25H level for courtyard options between BSL-5-BSL-8.

Those former studies made possible the analysis in detail of: the Correlation over building surfaces of the distribution of the Heat Transfer Factor; the effect of turbulence in addition to the wind direction; correlation with various reference wind velocities; the thermal boundary layer, etc. Nevertheless, we need to highlight some important limitations of the numerical

Figure 2. The wind velocity and air flow characteristics of courtyard options between BSL-SUZ-BSL-4 at 0.25H plane.

Optimization of Building Facade Voids Design, Facade Voids Position and Ratios - Wind Condition Relation http://dx.doi.org/10.5772/intechopen.72697 77

Figure 3. The wind velocity and air flow at 0.25H level for courtyard options between BSL-5-BSL-8.

#### 2.2. Modeling and simulation in numerical analysis

The measuring axis perpendicular to the wind tunnel observation section "AB, B, C, D, E, F" lateral surface was in the wind direction. The points of measurement "1, 2, 3, 4, 5, 6" were placed on the axis perpendicular to the direction of the wind. At the courtyard, 36 points of measurement in total have been set with distances of 2.00 cm between directions of the X and Y axis. As to the points of measurement in dimension Z, profiles with 34 points of measurement have been placed at differing intervals in a way to be closer to the ground, to the roof and the opening edges that are to be organized on the model courtyard surfaces (Figures 1–3). At each measurement profile, nine points of measurement from 0 to 4 cm have been set at 0.5 cm intervals; 6 of them were placed at 1.00 cm intervals in the section as far as the following 10.00 cm; 14 have been placed at 0.5 cm intervals through the area between 10.00 and 17.00 cm;

Figure 2. The wind velocity and air flow characteristics of courtyard options between BSL-SUZ-BSL-4 at 0.25H plane.

and another out-of-the-model 5 between 17.00 and 22.00 cm.

76 Sustainable Buildings - Interaction Between a Holistic Conceptual Act and Materials Properties

Computational Fluid Dynamics have been utilized in prediction of the transfer of convective heat on the exterior of building surfaces [13–15]. The main advantages of CFD in this practice has been that: (1) it allows for analysis of a specific and complex building or building configuration; (2) it provides high data on spatial resolution; (3) it makes consideration of high Reynolds number flows for atmospheric conditions possible and (4) it makes information on the flow as well as the thermal areas available in detail.

Those former studies made possible the analysis in detail of: the Correlation over building surfaces of the distribution of the Heat Transfer Factor; the effect of turbulence in addition to the wind direction; correlation with various reference wind velocities; the thermal boundary layer, etc. Nevertheless, we need to highlight some important limitations of the numerical models applied, taking into consideration the building shell in assessment of thermal comfort and energy performance of buildings with a courtyard, as also studied in CFD. The wall section is made of several layers in various thicknesses and with miscellaneous physical properties. The external surface is subject to solar radiation (Is), convection heat transfer (qc,o) and an exchange of radiation from the sky (qr,o). The internal surface is affected by a combination of convection and radiation heat transfer (qi) in turn being relevant directly to the air-conditioning load necessary to preserve the inside design temperature (Tf,i). The following assumptions have been utilized in formulating the mathematical model:


Taking as a basis the aforementioned assumptions,

Reynolds number:

Air intensity r = 1225 kg/m<sup>3</sup>

Wind speed (average) V = 30 m/s

Dynamic viscosity μ = 1.7894e-05 kg/(m�s)

Building Length D = 14 m

Reynolds number has been found 28,75.106 in view of the reference values. The flow has turbulence since the value is greater than 106.

Mach number:

$$\mathbf{M} = \frac{\mathbf{V}}{\mathbf{C}} \tag{1}$$

• perpetual

Preservation equations

Momentum Equation:

2.3. Boundary conditions

• realized in 3 dimensions (x,y,z cartesian coordinate system).

Perpetuity equation: (for perpetual flow)(for incompressible flow)

in case of constant intensity and viscosity in Newtonian flow (because the air is Newton type fluid): the flow is perpetual and gravity acts in negative z direction turning the equation into:

Optimization of Building Facade Voids Design, Facade Voids Position and Ratios - Wind Condition Relation

Entering right boundary conditions in CFD is highly important to solve equations correctly. Those conditions having being determined, necessary surfaces should be designated before the analysis process to read them for analysis and post-analysis. Fluids contacting to the solid surface adheres to the surface due to viscose effect, and velocity is zero on the surfaces. Consequently, those surfaces should, for correct solution, be determined in our model.

ð2Þ

79

http://dx.doi.org/10.5772/intechopen.72697

ð3Þ

ð4Þ

ð5Þ

ð6Þ

ð7Þ

Sound velocity c ≈ 340 m/s

Wind velocity (average) V = 30 m/s

Mach number has been found as 0.09 in view of the reference values. Because the value is smaller than 0.3, the flow has been deemed incompressible.

Furthermore, because the properties at any point within the flow do not vary in time, the flow is defined as perpetual. According to those results, the flow is:


• perpetual

models applied, taking into consideration the building shell in assessment of thermal comfort and energy performance of buildings with a courtyard, as also studied in CFD. The wall section is made of several layers in various thicknesses and with miscellaneous physical properties. The external surface is subject to solar radiation (Is), convection heat transfer (qc,o) and an exchange of radiation from the sky (qr,o). The internal surface is affected by a combination of convection and radiation heat transfer (qi) in turn being relevant directly to the air-conditioning load necessary to preserve the inside design temperature (Tf,i). The following

iv. Relatively small thickness of composite roof in comparison to other dimensions. One-

v. Constant convection factor based on the heat flow direction and daily average of wind

Reynolds number has been found 28,75.106 in view of the reference values. The flow has

Mach number has been found as 0.09 in view of the reference values. Because the value is

Furthermore, because the properties at any point within the flow do not vary in time, the flow

assumptions have been utilized in formulating the mathematical model:

78 Sustainable Buildings - Interaction Between a Holistic Conceptual Act and Materials Properties

dimensional temperature variation has been thus assumed.

ii. Fine contact of layers, resulting in interface resistance being negligible.

i. Lack of heat generation.

velocity.

Reynolds number:

Air intensity r = 1225 kg/m<sup>3</sup>

Building Length D = 14 m

Sound velocity c ≈ 340 m/s

• incompressible, • with turbulence

Wind velocity (average) V = 30 m/s

Mach number:

Wind speed (average) V = 30 m/s

Dynamic viscosity μ = 1.7894e-05 kg/(m�s)

turbulence since the value is greater than 106.

smaller than 0.3, the flow has been deemed incompressible.

is defined as perpetual. According to those results, the flow is:

iii. Negligible variation of thermal properties.

Taking as a basis the aforementioned assumptions,

• realized in 3 dimensions (x,y,z cartesian coordinate system).

Preservation equations

$$\frac{\partial \rho}{\partial t} + \nabla \cdot \left(\rho \vec{V}\right) = 0\tag{2}$$

Perpetuity equation: (for perpetual flow)(for incompressible flow)

$$\nabla \cdot \left( \rho \vec{V} \right) = \begin{array}{c} \begin{array}{c} \\ \end{array} \tag{3} \end{array} \tag{3}$$

$$\nabla \cdot \vec{V} = 0\tag{4}$$

$$\frac{\partial \mathbf{u}}{\partial \mathbf{x}} + \frac{\partial \mathbf{v}}{\partial \mathbf{y}} + \frac{\partial \mathbf{w}}{\partial \mathbf{z}} = \mathbf{0} \tag{5}$$

Momentum Equation:

$$
\rho \cdot \mathbf{g} - \nabla P + \nabla \tau\_{\mathcal{Y}} = \rho \frac{d\mathcal{V}}{dT} \tag{6}
$$

in case of constant intensity and viscosity in Newtonian flow (because the air is Newton type fluid): the flow is perpetual and gravity acts in negative z direction turning the equation into:

$$-\frac{\partial P}{\partial \mathbf{x}} + \mu \left( \frac{\partial^2 u}{\partial \mathbf{x}^2} + \frac{\partial^2 u}{\partial \mathbf{y}^2} + \frac{\partial^2 u}{\partial z^2} \right) = \mathbf{0}$$

$$-\frac{\partial P}{\partial \mathbf{y}} + \mu \left( \frac{\partial^2 v}{\partial \mathbf{x}^2} + \frac{\partial^2 v}{\partial \mathbf{y}^2} + \frac{\partial^2 v}{\partial z^2} \right) = \mathbf{0} \tag{7}$$

$$\rho \cdot \mathbf{g}\_z - \frac{\partial P}{\partial z} + \mu \left( \frac{\partial^2 w}{\partial \mathbf{x}^2} + \frac{\partial^2 w}{\partial \mathbf{y}^2} + \frac{\partial^2 w}{\partial z^2} \right) = \mathbf{0}$$

#### 2.3. Boundary conditions

ð1Þ

Entering right boundary conditions in CFD is highly important to solve equations correctly. Those conditions having being determined, necessary surfaces should be designated before the analysis process to read them for analysis and post-analysis. Fluids contacting to the solid surface adheres to the surface due to viscose effect, and velocity is zero on the surfaces. Consequently, those surfaces should, for correct solution, be determined in our model. The ground on which the fluid moves and the surfaces of the courtyard buildings being set as Wall, non-slippery condition will be applied on those surfaces. Because the flow takes place outdoors, Symmetry boundary condition will be selected for upper and lateral boundaries.

comfort and then to serve as a background for a more comfortable environment through comparison of achieved findings; the information from the measurements in the existing wind tunnel and the data from the analyses with CFD were examined and interpreted in detail.

Optimization of Building Facade Voids Design, Facade Voids Position and Ratios - Wind Condition Relation

http://dx.doi.org/10.5772/intechopen.72697

81

With the experimental study; it was aimed to find out the effect on velocity profiles of the rates of opening placed on the building surface, the effects of the flow types on turbulence, and the comfort conditions that can be deducted from human-climate data. The results of the measurements were compared via charts to the average velocity and turbulence values gained from measurements at heights of 0.00H–0.25H–0.50H–0.75H–1.00H–1.25H–1.50H–1.75H at 36 different pre-set points within the courtyard in the pre-set courtyard building configuration with 17 different openings. All openings were opened at ground floor level and the BSL-SUZ configuration accepted as

The opening rates on the courtyard building models with experimented 17 different openings are as follows. Openings were formed at a rate of 1/20 of the total ground floor area for BSL1, at a rate of 1/10 of the total ground floor area for BSL2, at a rate of 3/20 of the total ground floor area for BSL3, at a rate of 1/5 of the total ground floor area for BSL4, at a rate of 1/4 of the total ground floor area for BSL5, at a rate of 3/20 of the total ground floor area for BSL6, at a rate of 1/5 of the total ground floor area for BSL7, at a rate of 1/10 of the total ground floor area for BSL8, at a rate of 1/20 of the total ground floor area for BSL9, at a rate of 1/10 of the total ground floor area for BSL10, at a rate of 3/20 of the total ground floor area for BSL11, at a rate of 3/20 of the total ground floor area for BSL12, at a rate of 1/5 of the total ground floor area for BSL13, at a rate of 1/5 of the total ground floor area for BSL14, at a rate of 3/10 of the total ground floor area for BSL15, at a rate of 2/5 of the total ground floor area for BSL16 (Figure 1).

Although the opening rates of some courtyard building configurations are of the same value, the air velocity and turbulence values within the courtyard were found at different levels. The reason why different values have been found is the position to the wind and opening dimen-

In BSL-SUZ courtyard building configuration, the average wind speed in the courtyard is 1.50 m/s. While turbulence values were between approximately 50 and 60% as far as 1.25H level, they have showed a decrease after 1.25H level. Although turbulence values exhibit an unstable appearance going up and down at 0.25H level, high turbulence values have been

The opening rate at BSL-1-BSL-9 courtyard building configurations is 1/20. It has been seen upon comparison of the velocity values in BSL1 configuration and the values in the configuration of BSL-SUZ, the reference building, that velocity values in the courtyard show an increase. The average velocity in reference building courtyard H height is 1.50 m/s compared to BS1, which rises to 2.50 m/s. As to the windward points with opening, that rate reaches values of 4.50–5.00 m/s. Laminar flow type has been observed considering the flow values at 0.00H- and 0.50H levels. Turbulence air flow type has been observed at other levels. BSL9 configuration shows similarity in terms of lack of windward opening, yet measurements in the courtyard came out differently. The average wind velocity in courtyard at the side of the windward area

sions rather than same opening rates.

reached at other levels.

reference building consists of a total of 40 4.00\*4.00\*4.00 cm boxes on ground floor level.

#### 2.4. Modeling of courtyard configurations

Separate geometries were formed for each of the 17 different courtyard configurations in Fluent Design Modeler. In choosing the control volume to be calculated, attention was paid to selection of a domain where all necessary geometric and flow properties can be captured. Sensitivity was paid at a few important points for mesh and analysis in forming those geometries.

The first one of those is to make independent from the control volume the analysis in the solution area to be formed around the building. Recommendations from some resources were used to this end. It is generally recommended that if the height of the building is H and width is W, then the control volume should be at least 5H in height and 10W in width, and 2H for upward flow and 10H for the downward flow of the building. [Tutorials: Fluent Introduction - Cell Zone and Boundary Conditions] Another recommendation suggests that the upward flow value should be at least 5H and the downward flow value at least 15H [18].

An average interval was elected among those recommended values and the height of the building which was designed in dimensions of 28.00 28.00 12.00 cm at the scale of 1/200 (H = 12 cm, W = 28 cm), was set 100 cm in height, 200 cm in width, 100 cm in upward flow and 200 cm in downward flow.

The second important point is that the geometry was divided into as many parts as possible to increase the number of structural meshes in the mesh procedure. Although a structural mesh is easier to approach a solution, they still are hard to shape in complex geometries. Therefore, the geometry may require elimination of unnecessary details and division into an adequate number of smooth parts. In our model, the geometry was divided into an adequate number of parts in view of the same. Furthermore, "form new part" option was used to define under a single form to allow mesh element nodes capturing each other among respective parts.
