APPLIED CLIMATOLOGY (ARC 810) DEPARTMENT OF ARCHITECTURE, FEDERAL

APPLIED CLIMATOLOGY (ARC 810) DEPARTMENT OF ARCHITECTURE, FEDERAL

APPLIED CLIMATOLOGY (ARC 810) DEPARTMENT OF ARCHITECTURE, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE, NIGERIA ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria Shading Devices ARC 810: Building Climatology

Department of Architecture, Federal University of Technology, Akure, Nigeria 1. Introduction. 2. Types of shading devices. 3. Various Shading Devices and their Geometries. 4. Design of shading devices. 5. Overheated and underheated periods. 6. Using the Effective Temperature Nomogram. 7. The Hourly Temperature Calculator. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria

. 8. When Is Shading Required? 9. Sun-Shading Periods. 10. Determination of the sun's position. 11. Superimposing the sun-shading periods. 12. The shadow angle protractor. 13. Examples of shading devices. 14. References.

ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria INTRODUCTION Windows may contain several elements including shading devices. The design of these elements reflect various functions including thermal control. There are three types of shading devices - vertical, horizontal and egg-crate.

ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . The design of sunshading devices for thermal comfort involves four steps: 1. determination of when shading is required; 2. determination of the position of the sun at the times when shading is required. 3. determination of the dimensions and proportions of the

required shading device, and 4. finally the architectural and structural design of the shading device. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 2. Types of Shading Devices. Openings, especially windows, greatly influence the thermal conditions within a building. Windows usually contain several elements, some of which are adjustable. These elements perform various functions, including the

following: ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . 1. ventilation 2. daylighting 3. provision of privacy and security 4. prevention of glare

5. exclusion of rainfall 6. allowing a view out 7. exclusion of dust, noises, pollution and insects 8. exclusion of direct solar radiation. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria External shading devices are only one of these elements. Others include curtains, glass, solid or louvered shutters, security bars and mosquito screens. The functions of external shading devices include:

1. allowing a view out 2. protection from rain 3. protection from direct solar radiation 4. protection from sky glare ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 3. Various Shading Devices and Their Geometries. There are three types of sun-shading devices, They are:

1. Vertical devices. 2. Horizontal devices. 3. Egg-crate devices. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria Windows without shading devices have some shading characteristics measured by their horizontal and vertical shading angles. See figure 1. In describing the characteristics of shading devices it should be noted that

the window and the shading device are considered as one unit. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria Figure 1: Shading characteristics of a simple window. Shading chart indicating the areas of the sky which are shaded by the thickness of the wall . ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria

Vertical Shading Devices Vertical Shading Devices consist of pilasters, louvre blades or projecting fins in a vertical position. Their performance is measured by the horizontal shadow angle (delta). They are commonly referred to as fins and are most effective on western and eastern elevations. See figure 2. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria

. Figure 2: A vertical shading device. Shading chart indicating the additional areas of the sky which are shaded by a vertical shading device on one side of the window only ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria Horizontal Shading Devices Horizontal Shading Devices are usually in the form of canopies, long verandas, movable horizontal louvre blades or

roof overhangs. They are best suited to southern and northern elevations and their performance is measured by the vertical shadow angle (epsilon). See figure 3. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . Figure 3: A horizontal shading device. Note that it projects beyond the window on plan to prevent the sun reaching the window from the ends of the shading device. Shading chart

indicating the additional areas of the sky which are shaded by a horizontal shading device. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria Egg-Crate Devices. Are combinations of vertical and horizontal devices. They are usually in the form of grill blocks or decorative screens. Their performance is determined by both the horizontal and vertical shadow angles and (delta and epsilon). ARC 810: Building Climatology

Department of Architecture, Federal University of Technology, Akure, Nigeria . Figure 4: A shading device with vertical and horizontal elements. Shading chart indicating the additional areas of the sky shaded by a combination of horizontal and vertical projections. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 4. Design of Shading Devices.

There are certain steps to be followed in the design of shading devices. Step 1: It is necessary to determine when shading is required, that is at what times of the year and during what hours of the day. This is usually done by defining the overheated and underheated period Step 2: The position of the sun at the times when shading is required must be established. This is usually done with the aid of a sun-path diagram.

ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . Step 3:The dimensions and proportions of the shading device that will provide shading during the period earlier defined is found. This is done with the aid of a shadow angle protractor. Step 4:The choice of prefabricated devices or the design of new ones. The design of shading devices takes not only the required

geometry into consideration but also aesthetic and structural factors. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 5. Overheated andUnderheate Periods. The overheated and underheated periods are determined with the aid of a thermal index. Such an index should be able to indicate for given climatic conditions whether there i s cold discomfort, comfort or

hot discomfort. This process is explained with the aid of the Effective Temperature index using Zaria as an example. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . The climatic data needed are the monthly minima and maxima of dry-bulb and wet-bulb temperatures as well as the mean monthly wind velocity. The wet-bulb temperatures are

not always available and in such a case they should be calculated from the monthly minima and maxima of relative humidity. This was done for Zaria with the aid of the psychometric chart. See table 1. Alternatively, the computer program PSYCHRO may be used ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . Figure 5: The Effective Temperature nomogram for persons wearing

normal clothes. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 6. Using the Effective Temperature Nomogram. The Effective Temperature nomogram is used to obtain the Effective Temperatures. In the example, the nomogram for persons wearing normal business clothing is used and an air velocity of 1.0 m/s is assumed. The maximum DBT and the maximum WBT are used to obtain the maximum ET while the minimum DBT and the minimum WBT are used to obtain the

minimum ET. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . The computer program EFFECT may be used for this purpose. We have now obtained the monthly minima and maxima of Effective Temperature. The comfort limits 22 -27 degrees Celsius

are provisionally assumed for the Effective

Temperature index in Nigeria. The calculated Effective Temperature should be compared with the comfort limits to determine the thermal stress and hence the period when shading is required. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 7. The Hourly Temperature Calculator. The hourly temperature calculator is used to determine the diurnal temperature variation. See figure 6

It is based on the sinusoidal character of temperature variation with the minimum temperature around 6.00 am and the maximum around 2.00 pm. To use the hourly temperature calculator, the minimum and maximum temperatures are marked. These two points are joined by a straight line and results are read off the line. For example, given a minimum temperature of 20 degrees Celsius and a maximum of 30 degrees Celsius, . ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria

. Figure 6: The hourly temperature calculator ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . The temperature at 12 noon is about 28.5 degrees Celsius and the temperature rises to 26 degrees Celsius at 10.00 a.m. and

falls back to the same 26 degrees Celsius at about 6.40 pm. It is possible to construct a complete effective temperature isopleth showing the underheated, comfortable

and overheated periods using the hourly temperature calculator and the calculated effective temperatures. For our purposes however, it is usually enough to determine when shading should start and when it should stop. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 8. When Is Shading Required?

Shading is required both during the overheated period and when conditions are comfortable. The reason for this is that if solar gain is permitted during comfortable periods the excess heat thus gained may cause hot discomfort. Thus the lower limit of comfort is used to establish when shading should start. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria

. Table 1: Sunshading periods using the Effective Temperature nomogram for Zaria. Note: F = full shading required, N = no shading required ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 9. Sun-Shading Periods. Take the minimum and maximum Effective Temperatures for January. Using a lower comfort limit of 22 degrees Celsius,

determine the time of the day when the temperature rises to 22 degrees Celsius. This represents when shading should start. Shading should stop when the temperature falls back to 22 degrees Celsius. When the temperature is always above the lower comfort limit then full shading is required throughout. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria Consequently, when the temperature is always below the lower comfort limit no shading is required. See table 1. Repeat the

process for the remaining months of the year and tabulate the data. If required, plot the sunshading periods thus obtained on a graph. The sunshading periods can be obtained from basic climatic data using the computer program SHADE. Plots of the thermal stress (overheated and underheated periods) are made by the computer program COLDHOT. An example of such a plot is presented in figure 7. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria Figure 7: Plot of the thermal stress for Zaria by the computer program

COLDHOT ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 10. Determination of the sun's position. The next step in the design of sun-shading devices is to determine the position of the sun at the times when shading is required. The position of the sun is defined by two angles -the solar altitude s (beta, measured from 0 to 90 degrees above the horizon) and the solar azimuth (theta). The solar azimuth is

measured from the south and is measured from 0 to -180 degrees (westward) and 0 to +180 degrees (eastward).See figure 8. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . Figure 8: Solar angles for vertical, sloping and horizontal surfaces. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria

. The position of the sun can be determined in five ways: 1. By Calculation. The solar azimuth and altitude can be calculated given the latitude, date and time from mathematical formulae. In fact the vertical and horizontal shading angles can be calculated directly for various orientations. This method is usually too tedious for architectural purposes. 2. By a computer program. There are various computer programs that can make the necessary calculations and present the results

graphically, sometimes even in the form of plots. Such programs are now available on microcomputers and are becoming more ARC 810: Building Climatology popular. Department of Architecture, Federal University of Technology, Akure, Nigeria . 3. From tables: A good alternative is the use of almanacs where the necessary solar angles are tabled. These tables undergo

minor revisions yearly. 4. Experimental methods: Complex and lengthy research on the sun-earth relationship is often carried out experimentally using the heliodon, the solarscope or some other device. See figure 9. These studies are carried out on models and are very popular in teaching. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria ,

Figure 9: The solarscope. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . 5: Sun-path diagrams: These are graphical representations of the movement of the sun across the sky throughout the day and the year. They owe their popularity to simplicity. The sun-path diagram is used in this text and is described in more detail. The

sunpath diagram is a projection of the hemisphere of the sky. The observer is assumed to be in the centre of this hemisphere and the sun to travel on the surface of the hemisphere ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . There are two types of projections used to obtain sunpath diagrams. The first is a stereographic projection of the hemisphere onto a horizontal circle. This is the most

common projection and is most useful in visualizing the movement of the sun across the sky. See figure 10. The hemisphere can also be projected onto a vertical surface. This gives an orthogonal sun-path diagram useful in the analysis of shading angles, glare and diffuse light from the sky. See figure 11. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria .

Figure 10: Stereographic sunpath diagram for latitude 0. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria Figure 11: Orthogonal sunpath diagram for latitude 0. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 11. Superimposing the sun-shading periods.

The date and the time when shading should start and stop should be marked on the sunpath diagram: these points should be joined and the enclosed area shaded. In doing this there are usually instances where the sun passes over the same part of the sky at different times requiring different shading. It is left to the designer to choose between overheating, underheating or a little of both. See figure 10. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria

. The shaded area represents the position of the sun in the sky when shading is needed. The sun-shading device should be so designed that it will block this part of the sky. The required geometry i s determined using a shadow angle protractor. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria

. Figure 12: The overheated period for Zaria shown on the sunpath diagram. Shading this part of the sky gives no underheating and partial overheating. Figure 13: The overheated period for Zaria shown on the sunpath diagram. Shading this part of the sky gives no overheating and partial underheating.

ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 12. The ShadowAngle Protractor. The shadow angle protractor is used to determine the horizontal and vertical shading angles of the shading device. See appendix A.7 and A.11. There are two types, one for each of the projections of the hemisphere, either onto a horizontal or vertical surface. The shading angles can be determined for only

one orientation at a time. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . Thus if we are designing shading devices for a building with elevations facing N-E, S-E, S-W and N-W, we must take the four orientations one by one and establish the shading angles. This gives us four sets of horizontal and vertical shading angles. It is

common to find that the shading mask defined by these angles do not cover the required portion of the sky. Some areas are left uncovered while other areas are covered unnecessarily. The designer should choose such angles that will be optimal. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . Figure 14: Orthogonal shadow

angle protractor. Figure 15: Stereographic shadow angle protractor. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria 13. Examples of Shading Devices. The horizontal and vertical shading angles only give an

indication of the required geometry of the shading device. The design of the actual shading device is based on structural and aesthetic factors and several designs can be made in conformity with the shading angles. One important decision is whether to use a single large element or several small elements. See figures 18, 17 and 18. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria .

Large elements are usually made of concrete while small elements may be made from various metals, plastics and wood. The shading devices may be designed as adjustable and the need for a view out is often important. A great challenge to an architect is posed by aesthetics. A good design should be functional, structural and reflect our culture. Examples of sunshading devices on existing buildings (located at Ahmadu Bello University, Zaria) are shown in plate 1. ARC 810: Building Climatology

Department of Architecture, Federal University of Technology, Akure, Nigeria . Figure 16: Example of horizontal shading devices with the same shading mask. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . Figure 17: Example of horizontal shading devices with the same shading mask.

ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria . Figure 18: Examples of shading masks for vertical shading devices. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria

. Plate 1: Examples of sunshading devices on existing buildings. ARC 810: Building Climatology Department of Architecture, Federal University of Technology, Akure, Nigeria

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