Chapter 28Cooling by Effective Shading

28.1 Introduction

Passive cooling is based on the interface of the building and its surroundings.Before adopting a passive cooling strategy, we must be certain that it matches thelocal microclimate. Nowadays, this is called ‘‘passive cooling’’. Paradoxically,passive cooling is considered an ‘‘alternative’’ to mechanical cooling that requirescomplex refrigeration systems. By employing passive cooling techniques intocontemporary buildings, we can eliminate mechanical cooling or even to a smallextent decrease the size and cost of the equipment (Givoni and La Roche 2001).Buildings are cold mainly to enhance human comfort. There is a range of whatpeople actually define as comfortable, based on cultural expectation and clothing,as well as some rigorous scientific testing of human subjects. In the case ofcooling, the task is to promote heat rejection at the skin surface (Bahadori 1978).The body rejects heat by evaporation (sweat), convection (from moving air) and byradiation to cooler surface. It is worthwhile to distinguish between a method thatcools the building and a method that cools the person directly. The relative airvelocity will either increase or decrease the evaporative and convective cooling ofthe body. Where the temperature is above skin temperature, say 34�C, then anyincreases in air velocity will, by reducing the thermal resistance of the air filmaround the body, increase the convection heat gain from the environment and soincrease discomfort (Al-musaed 2004).

Before the advent of the new technology of passive cooling in hot climate,people kept cool using natural methods: breezes flowing through windows, waterevaporating from spring and fountains, as well as large amounts of stone and earthabsorbing daytime heat. These ideas were developed over thousands of years asintegral parts of the design of houses. Today, these are called ‘‘passive cooling’’(Butters 2002), in which the cooling operation is ensured by the transfer of energyfrom the space or air abounding the space, to reach a lower temperature and/orhumidity level than that of the natural ambience (Al-musaed 2004).

A. Almusaed, Biophilic and Bioclimatic Architecture,DOI: 10.1007/978-1-84996-534-7_28, � Springer-Verlag London Limited 2011

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The development of cooling processes has passed through several stages,starting from simple intuitive applications of natural openings of the buildings,which allowed for ample cross air movement and produced a significant coolingeffect. Even if the outdoor air is not at the desired temperature, air movementcreates a cooling sensation as it moves around the human body. Passive coolingencompasses natural processes and techniques of heat dissipation and modulation,and protection against overheating, as well as related building design techniques.It is a naturally occurring means without any form of energy input other thanrenewable energy sources or the use of other major mechanical systems. Passivecooling systems are also closely linked to the thermal comfort of occupants.Indeed, some of the techniques used for passive cooling do not remove the coolingload of the building itself, but rather extend the tolerance limits of humans forthermal comfort in a given space (The patrimony of passive cooling 1999).Therefore, increasing the effectiveness of passive cooling with mechanicallyassisted heat transfer techniques, which enhance the natural cooling processes,becomes possible. Such applications are called hybrid-cooling systems. Theirenergy consumption is maintained at very low levels, but the efficiency of thesystems and their applicability are greatly improved. The hybrid-cooling cover,besides the system of natural processes and techniques, also uses mechanicalsystems such as ventilators to a lesser extent (Fig 28.1).

The sustainable cooling system includes passive and hybrid-cooling with theapplication of more than one cooling system. We will further discuss this. Most

Fig. 28.1 The shading effecton a traditional façade in ahot climate (Baghdad city)

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importantly, all these systems must be created so as to integrate unique systems forany one particular place. The position of the building and the internal space layoutdetermine the exposure of the interior space to incident solar radiation, as well asto daylight and wind. The building shape controls both heat losses and heat gains,by reducing or increasing the ratio of the exposed surface to the volume. Theobjective is to limit thermal gains during the summer, from high outdoor airtemperatures and incident solar radiation. Thermal insulation can reduce the heatconducted through the building materials (Brown 1985). During summer, itreduces thermal gains, and during winter, it reduces energy losses. The concept ofenergy losses can also help to create an equilibrium in the change of energybetween inside and outside. In the following, we will discuss the cooling byintelligent sustainable systems that will use different cooling systems with acombination of many strategies, where the dominant method will be the one wewill talk about. All these systems would be competent in hot climate, and some ofthese can also be used for cold climate (Al-musaed 2004).Reradiated heat has adifferent wavelength and cannot pass out through the glass as easily. In mostclimates, trapping radiant heat is desirable for winter heating, but must be avoidedin summer. Shading of wall and roof surfaces is important to reduce summer heatgain, particularly if they are dark colored and/or heavyweight. Considering thefactor of cooling, we suggest the following (Al-musaed 2004):

• The most important consideration is the orientation of the aperture, which is tobe shaded. South-facing windows are easy to shade, because during summermonths, when shading is necessary, the angle of the sun is high. However, eastand west-facing windows are much more difficult to shade because the sun ismuch lower in the sky.

• Use plants to shade the building, particularly windows, to reduce unwanted glareand heat gain. Shading of roof and wall surfaces is important to reduce summerheat gain. Lighter colored shading devices reflect more heat. Internal shadingwill not prevent heat gain unless it is reflective.

• Shading on the building structure or outer spaces is not sufficient to cool theinside of the building. Shading can reduce the temperature between 5 and 10�C(Cook 1989). The solution lies in combining cooling systems such as evapo-rative cooling by water or trees and/or earth inertia cooling, ventilative cooling,etc., which can help us to create an efficient cooling system.

28.2 Shading Types

28.2.1 Shading by Agglomerate of Volumes

These types of shading are essential for cities with hot climate, where the archi-tectural creation concept starts from a shadow as a protective envelope against hightemperature, and a cooling source that covers all architectural creations (Fig. 28.2).

28.1 Introduction 335

Therefore, the first step toward an efficient cooling system by effectiveshading in architecture is how we can create different volumes, which help ingenerating a necessary shade for cooling and in the process of saving energy(Fig. 28.3).

The important and original space that can help us in a hot climate is thecourtyard, which is a consequential space of a combination of different volumesand space in the space concept.

28.2.2 Shading on Courtyard

The courtyard represents an effort to bring the forces of nature under partialcontrol. As pockets of space that are open to the sky, courtyards increase someaspects of the climate, such as daylight, and attenuate others, such as the heat. Thecourtyard can work well with existing shading, water and vegetation. It isimportant to make the courtyard with two floors for creating enough shading oncourtyard walls (Thompson and Steiner 1997). Shading or otherwise avoiding heatgain is the first rule of thermal comfort in the courtyard of buildings in hot climate.While the courtyard is by definition open to the sky, there are reasons, in additionto the hot sun, including dusty winds and bats or other forms of intruders, for atleast temporarily filtering this space (Al-musaed 2004) (Fig. 28.4).

Fig. 28.2 Different kinds of shading for bioclimatic buildings in hot climate

Fig. 28.3 Shading resultingfrom compact volumes

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The shading of the courtyard reduces significantly its effective temperature byneutralizing the element of radiation and by maintaining the external wall surfacessurrounding the courtyard at a relatively low heat (Fig. 28.5).

The result is a courtyard, which is very useful during most of the year, where alarge portion of the inhabitants’ activities can take place. Shading in courtyard canbe created by the structure of the building, but it is also preferable to create it withtrees (Al-musaed 2004).

28.2.3 Shading by Space in Space Concept

This concept considers the vital role of shading in architecture in hot climate. Theconcept consists of two volumes such as space in space concept. These volumeshave two different functions (Fig. 28.6).

Fig. 28.4 Courtyard from atraditional house in Damas-cus, Syria

Fig. 28.5 Bioclimatic houses project from Iraq

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The covering volume has a protective area exposed directly to sunlight,considered as the first line of defense against excessive heating. Covering spacecan include auxiliary functions such as service rooms, stores, flat green area forrecreation, flat plate, etc. The other volume includes the essential function: that is,protecting from the exterior heat overload.

28.2.4 Shading by Natural Elements (Vertical Plan)

Plants are very effective in blocking unwanted direct solar beam radiation,converting a great deal of the heat into stored biochemical energy in their leaves,while still providing an attractive view to the outdoor. The best method of shadingeast and west-facing windows is growing trees, shrubs or other vegetation spaced afew meters from the buildings.

28.2.4.1 Shading by Trees

Trees with high canopies are useful for shading roofs and large portions ofbuilding structure. Trees offer an excellent natural cooling. They provide shadeover the walls and roof. They also will shade driveways, sidewalks and patiosthat can reflect heat to the building. Since big trees, such as palm trees in hotclimate and spruce in temperate climate, give more shade than little ones, wemust devise a site plan that preserves as many existing trees as possible(Al-musaed 2004) and plant new trees immediately after construction. Treesprovide a cooling bonus. To keep themselves cool, trees pump water from theground into their leaves (Moore 2001). As this water evaporates from the surfaceof the leaves, it cools the tree. This ‘‘evaporative cooling’’ cools the surroundingarea, too. Deciduous trees are best for south-facing yards, because their canopiesare broad and dense (Fig. 28.7).

When the leaves fall in the winter, many deciduous trees allow solar heat toreach the building. Evergreens can work well for north and northwest yards.

Fig. 28.6 Shading by spaceon space concept

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Passive cooling is also achieved by planting trees and bushes around buildings tocreate a thermal break.

28.2.4.2 Shading by Shrubs

Shrubs offer less shading, but they have several other advantages. They usuallycost less, reach mature size more quickly and require less space. Shrubs can shadewalls and windows without blocking roof-mounted solar panels.

28.2.5 Shading by Devices (see Movable Insulation)

The drawing of shading device is a rather complicate mission with manyparameters implicated, from solar geometry to esthetics or maintenance. Shadingdevice can be internal or external (Fig. 28.8).

The control or otherwise of solar radiation is an important part of buildingdesign. In a relatively hot climate; it represents one of the most important sourcesof potential summer heat gains. Even in a relatively cold climate, direct solarradiation can be a source of extreme local discomfort, equivalent to a 1000 Welectric bar radiator for every square meter of exposed window. Both external andinternal shades control heat gain (Fig. 28.9).

28.2.5.1 Internal Shading Device

All interior shading devices are less effective than exterior shading devices.In addition, the user must adjust the interior shading device to reduce solar heatinfiltration. Interior shading devices should be designed to be durable and shouldbe light colored to minimize glare, especially if these are the only shading devices.

Fig. 28.7 Shading by usingtrees

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Interior shades, such as roller shades, blinds and drapes, can reduce heat gain.However, interior shades do not block sunlight as well as exterior shades. Interiorshades work in three ways (Al-musaed 2007).

Interior shades reflect sunlight back out of the window before it can turn into heat.They block the movement of hot air from the area around the window into the roomand insulate the room from the hot surfaces of the window glass and frame.

28.2.5.2 External Shading Device

Principally, external shading devices are designed to provide protection againstdirect sunlight, although they can also offer protection against glare from a brightovercast sky. The categories include fixed canopies and overhangs, intended asintegral parts of the structure, attached screens (Beckett 1974), etc. Well-plannedexternal shading is the most effective method of reducing solar heat gain.In addition, it offers possibilities for incorporating lighting during day and passive

Fig. 28.8 Shading by differ-ent forms of devices

Fig. 28.9 The effects oninternal heat flow of externalagainst internal shades

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heating. The most important benefit with external shades of all categories is thatthe solar heat absorbed by them is dissipated into the open and is not releasedindoors as with internal shades. The decorative model shape of the permanentexternal shading system is able to add to the necessary architectural temperamentof the exterior.

In cold and temperate climates, the major disadvantage with fixed opaqueshading devices is the supplementary reduction in the transmission of diffusedaylight, particularly on cloudy days. Changeable shades are better in this respect,but have to be easy to operate, sturdy and able to endure strong winds. Even withchangeable shades, on days with irregular sunshine the necessity for regularreadjustment of the shades arises. The property of sun control devices on the daylighting of rooms can be worked out for individual cases from first principles usingestablished methods of daylight calculation (Beckett 1974).

External shading is much easier to integrate into the design of a new building,that is, it can be retrofit. Fixed shading devices have some inherent disadvantages,the first of which is due to their inability to allow synchronization between theheating season and the altitude of the sun. If a fixed shading device is designed forhot climate, for example, to prevent overheating in September, the result is thatsolar energy will be rejected to the same extent in March. March, unlikeSeptember, has a relatively high demand for solar heating and such control wouldbe unwelcome. Fixed shading devices will also usually cast a shadow on a portion,albeit a small portion, of the collection window for most of the heating season(Givoni 1992). This is expensive in terms of cost of glass and higher energy lossesthan gain over this area of shaded window. External shading devices can be of thefollowing types.

Shading by Overhangs System

Overhangs may be solid, louvered, supportive vegetation or a combination of all ofthese aspects. Some shutters, eaves, trellises, light shelves and awnings serve thesame purpose as an overhang. Most buildings have a built-in shading device.

Overhangs block the high-angle summer sun, but allow the lower winter sun tostrike the building. Fixed overhangs will always be a compromise, since the sun’sangle is the same in spring and autumn. We might want solar gain in March, butnot in September. We can use overhangs also in combination with bioclimaticsolution in hot climates.

Shading by Awnings

Awnings work like the visors on baseball caps by blocking high-angle sunlight.Awnings on buildings can cover individual windows or sections of outside walls.They are most effective on the south side of the house. Some awnings stay in afixed position. Others can be rolled up in the winter to allow low-angle sun to

28.2 Shading Types 341

reach the living space in the building. In some bioclimatic solutions, we cancombine the awning function with water or/and vegetation to enhance the physicalcomfort in living spaces. So, awnings function in shading and ameliorating theenvironments of living spaces (Fig. 28.10).

Awnings and overhangs are the most effective means of solar control since theyprevent sunlight from striking the windows. Movable systems are adjustableaccording to season, but are more prone to failure or mistreatment. Fixed over-hangs are more dependable, but their design must account for daily and seasonalvariation of the sun’s path.

Shading by Trellises

Trellises are permanent structures that partly shade the outside of a building.Clinging vines growing over the trellis add more shade and evaporative cooling.Fast growing vines create shade quickly, while trees can take years to provideuseful shade. Trellises and climbing plants are design solutions that areattractive and flexible. Trellises can be used on flat roofs in hot climates toshade sleeping places, or to shade the roof surface during the hot period ofsummer (Fig. 28.11).

Fig. 28.10 Different types of awnings

Fig. 28.11 Trellises, out-ward appearance

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Shade Screens

Outside shade screens prevent sun from entering a window. We must place theseonly on windows exposed to direct sunlight. These devices are often called sun-screens or solar shields (Fig. 28.12).

The screens are made of aluminum or plastics, which are lightweight, durableand easy to install. New forms of solar cells can be used such as shade screens inthe south orientation also for the vital function of producing electrical energy.

References

Al-musaed A (2004) Intelligent sustainable strategies upon passive bioclimatic houses.Arkitektskole in Aarhus, Denmark

Al-musaed A (2007) Shading effects upon cooling house strategy in Iraq, 2nd PALENCConference and 28th AIVC Conference on Building Low Energy Cooling and AdvancedVentilation Technologies in the 21st Century, September 2007, Crete island, Greece

Bahadori MN (1978) Passive cooling systems in Iranian architecture, Scientific American, vol238, no 2

Beckett HE (1974) Windows, crosby lockwood staples. London, p 181Brown GZ (1985) Sun, wind and light: architectural design strategies. Wiley, pp 65–67Butters C (2002) Architects in the time and space, understanding sustainability. UIA Congress,

BerlinCook J (ed) (1989) Passive cooling. MIT Press, CambridgeGivoni B (1992) Comfort, climate analysis and building design guidelines, energy and buildingsGivoni B, La Roche P (2001) Radiant cooling systems for developing countries. Accepted for

ISES 2001, Adelaide AustraliaMoore S (2001) Living homes: sustainable architecture and design. Chronicle books, San

Francisco, p 36The patrimony of passive cooling (1999) Proceeding of the symposium on Mosque. The

environmental control in Mosque architecture. King Saudi University, Riyadh, Kingdom ofSaudi Arabia, pp 1–14

Thompson GF, Steiner FR (1997) Ecological design planning.Wiley, New York

Fig. 28.12 Shade screens

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