Shading Device Design Alternative

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SHADING DEVICE DESIGN ALTERNATIVE DECISION MAKING

by

MAJDI MUSTAFA AL SADEK

A Master Report for

CEM 6

I! "art#a$ F%$f#$$&e!t of t'e Re(%#re&e!ts

for t'e )e*ree

MASTER OF ENGINEERING

IN

CONSTRUCTION ENGINEERING AND MANAGEMENT

KING FAHD UNIVERSIT+

OF "ETROLEUM , MINERALS

D'a'ra!- Sa%)# Arab#a

Ja!%ary- ./


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ACKNOWLEDGEMENT

Acknowledgement is due to the King Fahd University of Petroleum & Minerals for

supporting this research.

I wish to epress my appreciation to Professor !sama "annadi who served as

my ma#or advisor. I also wish to thank my other supervisor $r. %aadi Assaf who

guided me through different su'topics of this report.

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TABLE OF CONTENTS

LIST OF TABLES.......................................................................................................v

LIST OF FIGURES.....................................................................................................vi

REPORT ABSTRACT................................................................................................x

CHAPTER 1. INTRODUCTION...................................................................................1

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*!A% A,$ !("/)1I4/%.......................................................................................5

M/12!$ !F A)2I/4/M/,1.................................................................................00

%)!P/ A,$ IMI1A1I!,%.....................................................................................06

%I*,IFI)A,)/ !F 12/ %1U$7.............................................................................03

CHAPTER 2. SHADING DEVICES PRINCIPLES AND CONSIDERATION.......................18

)IMA1/ )!,1+I(U1I!, 1! 2UMA,8% )!MF!+1................................................05

%2A$I,* $/4I)/% I, (UI$I,*%.........................................................................95

%2A$I,* $/4I)/% /FF/)1% !, (UI$I,* P/+F!+MA,)/.................................:;

)!,%I$/+A1I!, !F %2A$I,* $/4I)/%..............................................................6;

CHAPTER 3. PERFORMANCE EVALUATION OF SHADING DEVICES.........................51

)2A+A)1/+I%1I)% !F %U,I*21........................................................................;0

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LIST OF TABLES


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LIST OF FIGURES


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REPORT ABSTRACT

MA"$I MU%1AFA A %A$/K

%2A$I,* $/4I)/ $/%I*, A1/+,A1I4/ $/)I%I!, MAKI,*

)!,%1+U)1I!, /,*I,//+I,* & MA,A*/M/,1

"anuary 9@@0

1his report considers some effects of %un %hading $evices on uilding envelope

performance including thermal control noise control air flow and 4entilationB with

particular emphasis on daylight illumination and admission of solar radiant heat

energy. Cuantity of daylight admitted through three forms of shading devices

were assessed and evaluated through model study relative to eternal daylight

illuminance reference and to daylight illumination levels inside the model. %olar

radiant heat admission was evaluated on a relative asis under direct and

diffuse radiation eposures.

1he influence of shading devices on alternative design decision making process

is evaluated through assessment of costs associated with each alternative.

+esults and discussion indicates the usefulness of shading devices to control

direct solar radiation along with their ailities to admit useale daylight to efficient

room depths. +eduction in cooling loads and associated maintenance costs data

is used as a asis for alternative comparison using ife )ycle )osting.


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CHAPTER 1

INTRODUCTION

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(uilt environment is a mean for providing a suitale shelter for people needed

for fulfilling the reDuirements of comfort oth physically and psychologically. 1his

was a real motivation for mankind to seek out the most suitale indoor

environmental conditions that meet his needs satisfactorily. 2aving achieved that

people eperimented different themes trying to pursue further development in

their environment through acceptale improved environmental conditions. E0

2uman eings have always had the motivation and eagerness to improve their

environment and make it more suitale for living and that was the reason ehind

the success of early human eings to control the surrounding with which they

were in direct contact. In recent years air conditioning systems had een

efficient solution for providing and maintaining desirale temperature y cooling

indoor air to remove heat gained during summer seasons. Air conditioning

systems have ecome capale of controlling temperature moisture content

cleanliness air Duality as well as air circulation indoors as reDuired y the

occupants along with type of activities in the uilding.

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Air conditioning in its wider terminology that relates to various air Dualities in

uilding raised an important controversy regarding its contriution to the

conservation of natural resources. In other words people and scientists in

particular ecame aware of the fact that air conditioning systems reDuire large

amounts of energy to operate and demand high rate of power to e delivered y

power stations which has een a ma#or concern to energy conservation

enthusiasts. Air conditioning in this contet awakened specialists and energy

conservation enthusiasts to the energy consumption in the cooling process. 1hey

have noticed that esides its consumption to energy in a direct way these

systems cause pollution to the environment indirectly y continuous energy

demand supplied y power plants which considered to e unfriendly to the

environment.

1he awareness of energy conservation did in fact alert the specialists in uilding

24A) systems to the waste of energy in form of high energy'demanding cooling

systems operating continuously to achieve an acceptale thermal comfort

indoors. From economical point of view 24A) professionals considered the

factors affecting the thermal inconvenience indoors such as the temperature

uild'up. As a clue they have considered the factors and the means y which

heat is gained through the uilding envelope toward interiors as a start for their

demanding solution. ogically that was the key solution as to consider the factors

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different media. 1he rate at which energy is transferred to or generated within a

space is referred to as H2eat *ainH which is an important terminology when

talking aout cooling of indoor environment. As a result it ecomes essential to

remove this heat gain at a specific rate referred to as H Cooling Load', to achieve

the reDuired thermal comfort. E6

G)ooling oad8 is an important Duantity since it represents the amount of energy

to e removed in order to maintain the preferred level of temperature and

humidity. As this value gets larger the amount of energy needed to cool a

specific space increases and on the other etreme as this value ecomes

smaller we will e relieved to know that a reduction in energy consumption and

money saving is achieved and that8s our goal.

Up to this point we have determined our goals for minimiing energy

consumption in cooling indoors to e the reduction of the Gcooling load8 Duantity

which is 'as have een defined' a measure of heat gain characteriing the indoor

environment. 2eat gain is dependent upon the solar radiation received indoors

which in turn is dependent upon other factors such as the thermal properties of

materials constituting the uilding structural and architectural envelope solar

angle and altitude geometry colors and finishing. In accordance with this fact

and that we are trying to reduce the solar heat gain the most suitale solution to

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accomplish this would e to search for the uilding elements that are responsile

for the admission of solar heat. 1he elements we are talking aout are usually

fenestration elements that are in direct contact with the eterior. -alls floors

ceiling and glass windows are those fenestration elements of interest to us.

,evertheless glass windows represent the weakest element of all in accordance

with the fact that typical glass is transparent to the short'wave radiation emitted

y sun. E:

For further assessment in finding out the most suitale ways to control solar

radiation we have gathered the following facts which would lead us to the

appropriate solution >

2eat gains occur in such forms as solar radiation through openings heat

conduction through oundaries and radiation from inner surfaces

ventilation and infiltration latent heat gains generated within the space

and finally sensile heat> convection and radiation from internal o#ects.

+oofs and -indows represent the ma#or components of solar heat

gains.

*lass is a transparent material and when su#ected to short'wave

radiation it transmits much of the radiation from the sun falling on its

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surface. 1hus it represents the weakest interface element when heat

gain is concerned.

According to the third edition of 'HVAC analysis and design' tet ook

eternal shading of a window is effective in reducing solar heat gain to a

space and may produce reductions of up to 5@ percent. E;

(ased on these facts we may initiate our research for minimiing heat transfer

into our prospected enclosed environment. )learly straightforward windows

comprise the main source of ecessive heat gain and for that reason we should

consider the means y which we can eternally shade windows. A shadow cast

y trees other uildings or even y any structural or architectural element of the

uilding itself may e sufficient. )onversely these accidental and uncontrolled

situations do not provide adeDuate shading to the windows or at least re#ect the

whole solar radiation throughout the daytime. (esides cooling loads calculations

can not e ased on such a variale circumstances. A mature decision to make

is to study the shading reDuirement of a uilding and to design the suitale

shading device that can control the solar radiation admitted y the window along

with other uilding performance characteristics as we will see later.

%uch a thing mentioned up could e achieved y using Shading Devices EFig.

0.9 0.: 0.6 which work as a screen eliminating direct solar radiation. In more

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precise words these devices prevent direct sun rays ' direct solar radiation '

from eing transmitted through the transparent material of the window.

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%hading devices eclude the direct component of solar radiation and filter it out

so that no energy transfer due to direct solar radiation is taking place. 1hey

eliminate the ma#or factor contriuting to the ecessive heat gain indoors. 1heir

placement would e most proaly outside glass windows in order to provide

shadow over these glaed areas and that would e good issue for inspection in

this report.

-indows are intended to provide occupants with daylight as well as eterior

views and cheerful reee whenever the situation permits. 1herefore shading

devices should e designed in accordance with certain guidelines for them not to

e interfering with the uilding functional characteristics.

)onsider for instance the natural ventilation in such a uilding where we

intending to apply the shading devices. -indows J as openings J represent the

inlet and mostly the outlet of air flow. -ith the eistence of an ostruction J

shading devices J the air flow inside that uilding would e altered and of course

will influence the ventilation system. !ther uilding characteristics that might e

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also influenced y the eistence of shading devices is the daylight. 1he

illumination levels received indoors is a function of openings of the uilding.

%hading devices in their role reduce solar radiation and conseDuently daylight.

Privacy and acoustical ehavior of the uildings and other uilding

characteristics will e also discussed as they might influence y shading devices.

1he decision to choose among alternative designs of a uilding element is very

complicated and crucial to the success of pro#ect whether investment of service

is intended. 1his report will focus on design decision scenarios in which two

alternatives will e presented for investigation with relative to pre'set criteria and

guidelines analysis. 1he case study eample should e ale to open a new era

for solar engineering application in uilding with great attention drawn to cost

engineering using life cycle costing.

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(uildings are intended to provide shelters for different creatures and particularly

for humans. 1heir role in any community might e social symolic artistic or

functional. 1o e functionally sustantial and satisfactory the uilding has to e

evaluated in term of indoor climatic conditions when thermal comfort oth

physiologically and psychologically is considered. Indoor thermal comfort is a

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measure of several factors that constitute a performance characteristic of an

indoor environment. As a fact that we have discussed several factors governing

the eternal'heat gain through uilding envelope and the thermal comfort

indoors you might guess that indoor thermal comfort is affected mainly y solar

radiation incident upon the glaed area of a uilding envelope.

,evertheless unsolved Duestions such as what makes indoors climate affected

y eternal climatic conditions and how is human8s comfort related to climatic

conditions remain with no answers until we have this su#ect rought up for an

insight analysis and comprehensive discussion. Along with the elements of

climate and its contriution to human8s comfort the first goal to e achieved is to

address issues and principles related to the thermal environment that illustrate

the interactive relation etween human eings their comfort and the climate

whether eternal or internal.

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!ur net o#ective will e the consideration of shading devices from functional

point of view. -e will clarify the way shading devices react to reduce heat gain

generated y solar radiation. Further eplanation to the su#ect of shading

devices is to e given through a rief introduction of their principles and design

methodology. 1heir impact on the other hand will e of a ma#or concern as it

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relates to the various performance characteristics of uilding envelope. -e will

consider how shading devices influence the thermal acoustical ehavior air flow

privacy and daylight admission as will as glare phenomena in uildings. From a

different prospective the su#ect of materials colors and geometry development

of shading devices will e discussed to draw attentions to such factors that might

affect the performance of shading devices consideraly as well as improving

their Dualities as a uilding elements that must e of a great effectiveness in

serving their roles.

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%un provides daylight in form of visile electromagnetic radiation that is sufficient

to provide illumination levels reDuired in order to carry out various visual tasks

during daytime. %hading devices on the other hand reduce the amount of direct

and diffuse daylight admitted indoors since they ostruct sun rays and some of

the sky vault that is considered to e the source of diffuse daylight. 2ow much of

daylight is eterminated ecause of shading devices and to which etents the

amount of daylight admitted inside relative to what is availale outdoor is

dependent upon the geometry and color of the shading device. For this reason

we will evaluate daylight and Duantify it y taking illumination measurements

indoors when shading devices of various geometry and colors are used.

Moreover the evaluation of shading devices for their contriution to thermal

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comfort has to e considered along with the daylight admission evaluation.

(asically this is essential in the view of the fact that daylight 'sunlight' is a form

of electromagnetic radiation energyL that is a ma#or contriute to solar radiant

heat gains. -e will aim to access a way to evaluate shading devices aility to

re#ect solar radiation incident upon them and we will try to correlate etween

shading device geometry and color with the amount of solar radiation admitted

indoors.

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1his o#ective will focus on assessing two design alternatives for an office

uilding in which the first alternative involves utiliing shading devices to reduce

heat gain through uilding envelope. 1he second alternative will investigate cycle

costs associated with etra head load when uilding envelope is su#ect to direct

solar radiation including windows and wall section.

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1he final o#ective will e concerned with coming up with conclusions and

recommendations regarding the usage of shading devices and other facts aout

their ehavior and performance characteristics. Attentions will e drawn to

selecting the most suitale colors along with some consideration to the geometry

and materials to e used.

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M/12!$ !F A)2I/4/M/,1

I1/+A1U+/ +/4I/-

1he general information to e presented in this report will e the digestion of a

comprehensive study and conceptual analysis of principles concepts and

historical literature otained from several references such as tetooks

periodicals and technical themes and papers along with a mature personal

eperience of the supervisor of this report.

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-e mean y theoretical concepts the innovative ideas developed in form of

drawings and diagrams descriing some of the possile application of shading

device as to e one of the uilding envelop integrated elements to enhance some

of the asic functions of this interface etween eternal and internal

environments.

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devices models ' of various geometry and color' and finally making other

accessories for assisting in measurement readings. 1he setup of this eperiment

however will e a carefully designed timetale and readings arrangement

schedule since the data collecting process will take several days during which

the measurements will e taken at different times on a daily asis.

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$A1A A,A7%I%

$ata analysis will e the final assignment where we will study the data collected

and analye them in accordance with the standards and recommended data

pulished in different references. )onclusion drawn out from the model studies

results will e considered with various applications and for that we might e ale

to add some overall guidelines regarding the design of fenestration of uildings.

1his analysis is very important and considered to e the output of the whole

report since it gives us a comprehensive evaluation of the shading devices from

daylight and solar radiant energy heat admission point of view along with other

characteristics and facts aout them.

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1he data analysis of the model studies along with the technical consideration of

shading devices in chapter 9 will e the su#ect of the last issue rought up in

this report. As a conclusion we will present a set of inferential points etracted

from the analysis of the data collected regarding the overall characteristics of

shading devices oth from daylight and solar radiation admission point of view.

(ased on these facts withdrawn from our conclusion we will try to recommend

some points to take care of when using shading devices such as their colors

geometry and other facts aout their orientation conseDuences and ehavior

when designed as a penetration elements.

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%)!P/ A,$ IMI1A1I!,%

-hile it8s essential to define the scope of this report it is difficult to pinpoint to

every task or o#ective to e achieved due to unepected conditions and

limitation especially in the eperiment part. ,evertheless ringing up the

limitation counteracting upon our interests might e helpful in realiing the scope

to which we will attenuate our elaoration. !f main concern the time factor and

the availaility of measuring devices are the ma#or limiting factors for achieving

the desirale goals. Unfortunately the time factor is a predominant element in

any academic research especially if it was eperimental. 2owever we could

coop with this fact and limit ourselves to some pre'estalished limited o#ectives.

(riefly here are some of the limitations the are epected to tie up our o#ectives

throughout the report>

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%ome facts and new concepts developed under this topic might not have any

eperimental confirmation. !therwise some will e rationalied y evidence from

literature to prove our points while other will e #ustified on a logical asis.

*enerally speaking most of these impact are to e considered as a theoretical

models.

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$A7I*21 IUMI,A,)/ +/A$I,*%>

All daylight illuminance measurements would e taken under actual sky

condition which is known to e instantaneously changing oth Dualitatively and

Duantitatively. 1herefore we epect to have some variation and inadeDuacy in

daylight illuminance readings among different sets of collected data. A more

consistence results and data would have een achieved if we could have had the

opportunity to make this daylight model study under artificial sky illuminance.

EFig. 0.; 0.3

In accordance with the fact that we have taken the daylight illuminance readings

during %eptemer we were not ale to take the internal daylight illuminance

measurements for a north facing shading device under the direct solar radiation

condition as long as we know that no direct solar radiation falls upon north facing

facades during %eptemer for 96° latitude on the northern hemisphere.

%!A+ +A$IA1I!, M/A%U+/M/,1 >

Actual measurements of solar radiation would e denied ecause of the

unavailaility of devices for such measurements. Accordingly we will measure

the illumination intensities and correlate these values to the solar radiation as to

e eplained in appendi A.

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)!!I,* !A$ )A)UA1I!,

1he case study presented in chapter 6 will illustrate the guidelines followed to

workout the reDuired chiller sie for our uilding when shading devices are used

to eclude direct solar radiation from striking windows and penetrating the

uilding envelope. 2owever we have used and assumed average solar intensity

values for our calculation due to lack of actual data radiation for $hahran.

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%ignificance of the study underlies in the eperimental results and otained

daylight illuminance data. 1hese are clearly valued when we come to the

eperimental part in chapter :. *enerally speaking the daylight illuminance

readings can e used as a direct daylight design reference under specific

conditions as to e eplained in appendi A. 1he whole issue of investigating

shading devices on the other hand would draw attention to uildings envelope

and the way its elements react together to enhance the uilding envelope

performance.

$ata presented in chapter 6 should e a great potential for further investigations

y incorporating data outcomes in other sets of variale in order to assess actual

real'life situations. *enerally speaking these calculation can assist in making

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decision in selecting the most economical uilding envelope8s element using life

cycle costing with these data as input.

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CHAPTER 2

SHADING DEVICES PRINCIPLES AND CONSIDERATION

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Although the purpose of uilding as a shelter is to provide a safe and secured

enclosed environment having its own controlled elements of climate to achieve

an internal isolated environment nevertheless the eternal climate is considered

as a medium which surrounds and penetrates ' y heat transfer fenestration '

through this enclosed environment. 1hus eternal climate is continuos with the

internal one found indoors. As a matter of fact human eings can not survive in a

totally isolated artificial 'man controlled' environment and moreover whenever

we leave an artificial and overly conditioned climate and walk outside into

amient conditions that are much different we will eperience the metaolic

shock that cause us a lot of struggling to adopt our odies to the current

conditions and that may lead to illness. E63

1he issue therefore is to provide and maintain alances of internal ody

functions which operate efficiently at certain climatic conditions and to control

eternal climatic factors and manipulate them to meet the acceptale

comfortale environmental conditions. (efore we do so however we have to

study the interactive relation etween humans and their environment and the

way they response to climatic changes. E3

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2UMA,8% +/%P!,%/ 1! )IMA1/

1he way in which human eings interact with their environment is rather comple

and instantaneous at the same time. 1hat is ecause humans ody maintains a

constant internal temperature needed to energie all reactions and processes

taking place in various human systems. A continuous echange of heat etween

human odies and their surrounding take place in four physical different ways

that are >

)onduction

)onvection

+adiation

/vaporation Fig. 9.0

1his heat echange is dependent upon the environmental factors. In other words

human eings are strongly influenced y the climatic conditions y which they

are surrounded. 1heir thermal comfort along with other critical processes needed

for their survival is also affected y various climatic and environmental factors.

-hich means that human8s psychological and physical comfort is associated with

their surrounding climatic conditions. E3

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1o measure the climatic effects on humans eings in general however we have

to analye the >

,egative effects on human eings.

)onditions in which productivity are at its highest.

and y which we can decide upon the etent to which various climatic factors can

affect human comfort. In actual fact recent studies indicated that temperature

and climatic factors have a ma#or impact on health and some from day to day

climatic changes stimulate our activities while other depress us. E0

As far as we have talked aout climate and human8s response to climatic factors

and conditions we did not give decent definition of the climate itself. 1hereof

net section will deal with the climatic terminology along with the elements of

climate and their relation with each other and the impact they have on the

thermal performance of uildings.

//M/,1% !F 12/+MA )IMA1/

1hrough the previous lines we have realied the direct impact the climate has on

human eings and the interaction that eists etween climatic changes and

human comfort. In the forthcoming paragraphs we will give a rief introduction to

the factors that determine the status of climate.

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-hen talking aout elements of climate that contriute to the overall thermal

comfort of an environment we might consider those elements as two categories

according to their influential scale point of view. 1hat is we can regard the

elements or factors that affect the G*loal climate8 on one hand and consider the

factors which affect some local environmental condition that we call

GMicroclimate8 on the other hand. %un movement solar radiation temperature

wind and humidity are those climatic factors affecting the gloal condition. !n the

microclimatic scale however sun and shade along with the temperature wind

and humidity are the only factors determining the climatic conditions in any local

environment. E=

In general the climatic elements that are of interest when human comfort and

uilding design are concerned are solar radiation temperature humidity wind

precipitation and special characteristics such as lightning dusts etc. 1he ones

of ma#or concern of these elements is the Solar Radiation and Temperature

factors which have a direct impact on human8s comfort and contriute to the

thermal performance of uilding in the first place.

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!ur planet G/arth8 is one of the nine planets oriting the sun. !ur nearest

star 'the sun' is a power plant providing energy y a nuclear fusion reaction.

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%olar energy is the source of energy and life on earth in form of coal wood

gas wind and other forms of energy utilied y human eings. 1he amount

of energy received on earth from sun is enormous and it8s estimated that

the amount of energy sun is athing over earth each hour eDuals the

amount of energy contained in over 90 illion tons of ituminous coal. 1he

energy received at the outer space of earth which is called the

Getraterrestrial8 radiation is 69? (1UhrsD.ft. 2owever what reaches the

surface of the earth is around ::@ (1Uhr.sD.ft. though to the reflection

and asorption y air particles. 1his value on the other hand varies with

the geographic location altitude and weather. E6

1he intensity of the solar radiation received at earth is dependent upon two

factorsB the atmospheric conditions amount of dust particles water vapor

oone content and atmospheric pressureL and the solar altitude. E5

-hat happens actually to the solar radiation as it enters the earth

atmosphere ' Fig. 9.9 ' could e categoried into three components of solar

radiation. Portion of incoming solar radiation inside earth sphere is reflected

y the surface of the clouds and part of which is asored y atmospheric

ingredients such as water vapor and oone which constitute the first

component. A certain amount of the remaining radiation is scattered y

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molecules in the atmosphere ut some of this is re'gained as diffuse

radiation. 1his second component of solar radiation is altered in direction

due to the reflection and scattering y water vapor molecules dust particles

and other air molecules. 1he portion of solar radiation that have een

unaltered in direction is the third component of the solar radiation. E05

At the earth level part of the radiation received at ground is reflected y the

earth8s surface leaving the larger portion asored y different o#ects.

1hat asored energy changes to heat as the o#ects which asored it re'

radiate that energy as a long'wave radiation in form of heat that raises the

temperature of the air ground and surrounding o#ects whether humans

vegetation or uildings. E6

N2eat energy cannot e lostO. 1hat was a well known principle in physics

which states also that energy can e converted to another form of energy

such as electrical chemical or mechanical or remains as heat. It can e

converted stored asored moved gained and son on. 2eat flows from

one place to another due to the temperature difference etween two points

and its direction according to the second law of thermodynamics is to the

cooler point or o#ect. In other words heat flows from hot point or o#ects

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towards the cooler one until the two o#ects reaches the state of eDuilirium

at which they would have the same temperature. E65

%olar radiation is a form of energy and thus it transforms from one state to

another move e gained or asored. Its transformation from one place to

another is of interest to us. G2eat8 transfer occurs asically through three

different modes>

)onduction

)onvection

+adiation Fig. 9.:

Conduction heat transfer occurs through direct contact etween two

different o#ects. -hile in Convection the heat transfers etween two

discrete places via a fluid such as gas or liDuid. Radiation heat transfer is

somewhat similar to the convection mode ecept that there is no medium

through which heat transfers such as electromagnetic waves until eing

asored or reflected. E6

In general heat transfer via radiation represents a ma#or mode of heat

transfer that affects our uildings. !f radiation the %olar +adiation is the

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ma#or source of heat acting upon our environment. 1here are four channels

of radiant heat transfer affecting uildings which are>

$irect short'wave radiation from the sun.

$iffused short'wave radiation from the sky vault.

%hort'wave radiation reflected from surroundings.

ong'wave radiation from heated ground. E3

1he mechanism y which heat get indoors is simply illustrated y having

insight view of what happens to the short'wave high temperature energy in

form of solar radiation emitted from the sun. 1his energy affects uildings in

two ways. First this energy enters through windows and it is asored y

internal o#ects and surfaces such as furniture people and walls and in

turn these o#ects emit long'wave or infrared low temperature radiation to

the surrounding. %econd this energy may e asored y outside surface

of the uilding creating heat input a large portion of which is conducted

through the structure and emitted to the interior. In either ways the short'

wave emission from sun enters through the glass window 'which is

transparent to short wave radiation' and when asored and re'radiated y

interior o#ects as a long'wave radiation is trapped inside since it can not

escape through glass windows toward outside. (y these two effects

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together we have a heat input toward inside environment which yield a high

temperature uild up that cause the thermal inconvenience. E3

1he fact that glass windows are opaDue to long'wave radiation and they

don8t allow for transmission of long'wave radiation creates the phenomena

of greenhouse effect which was a good applied physical principle that

allowed agriculturists to raise their crops even in cold climates .

1he thermal forces acting on the outside of a structure are cominations of

radiation and convection impacts. 1he radiation component consists of

incident solar radiation and of radiant heat echange with outdoor

surrounding and air temperature and may e accelerated y air motion

which will e discussed in a while.

AI+ 1/MP/+A1U+/ A,$ 12/+MA )!MF!+1

Air temperature is a climatic element that varies according to location time

and other climatic factors. 1he description of comfort temperature is

su#ectively relative and people usually can not agree upon the etent to

which their environment is hot or cold. A lot of other people also argue aout

how cold or hot their surrounding is when talking aout thermal comfort

while others do not realie the importance of temperature for human

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survivals. !ne fact is that air temperature is one of the climatic elements

that have an instantaneous effect on human eings and their productivity.

1hey can eperience temperature effect instantaneously as they walkout

from one place to another having different temperature reading. Air

temperature influence can e oserved through human8s >

%urvival

)omfort

Performance

2ealth

Psychological social and economic factors. E=

(y now we realie that 1hermal comfort can not e measured in terms of

psychological factors. 1herefore the most suitale methodology to e

adopted in order to provide a thermally comfortale environment is to

maintain the thermal alance etween human ody and the surrounding.

Maintaining such alance implies keeping internal human temperature

within a certain range at which it can function efficiently and with minimum

efforts and energy wasted. 1hat can e achieved y controlling the

surrounding temperature !perative 1emperatureL which is a measure of

oth edian Radiant Temperature and Am!ient Air Temperature. 2uman

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odies eperience the heat produced y the Radiant and Am!ient

temperature to produce what is called %ol'Air temperature which is

influenced y the outdoor air temperature solar radiation asored y the

ody and the long'wave radiation heat echange with environment. E3

2aving reached the forth mentioned state of alance we will e in a thermal

comfort or what we call the )omfort one. In other words arriving at

conditions at which minimum ependiture of energy is needed to ad#ust

with environment whereas most of energy is freed for productivity we will e

in a comfort one. E0

%2A$I,* $/4I)/% I, (UI$I,*%

It8s ovious from our previous discussion that heat gain from solar radiation is the

most important factor affecting the indoor temperature uild up. 1his is caused y

direct sunlight falling upon the glaed area of a uilding which might also create

a glare prolem. A fact is that heat gain and glare from direct solar radiation can

e controlled y preventing direct sunlight from falling upon the glaed areas of

the uilding facade. At this stage we can say that a shading device is the tool to

eliminate the incident solar radiation to provide a thermally comfortale

environment while reducing the cooling load significantly. 1hat is shading

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devices re#ect the direct radiation and allow the diffuse component only to e

admitted through in. E5

From functional point of view shading devices are intended to provide an

adeDuate thermally comfortale climate with enough lighting levels to perform

various anticipated tasks while managing the utiliation of daylight illumination

as well as their contriution to glare and solar heat gain control when well

designed. (ased on their geometry color and materials shading devices reduce

contrast etween glaed areas and right sky pass reees filter light allow

controlled views and cast interest playful shadow patterns that change

continuously. !f these characteristics control of solar heat gain thermal controlL

constitutes the principal role of shading devices since their effectiveness could

e appreciated from thermal comfort efficiency and economic point of view.

A good point etracted from our introduction to the solar radiation climatic

element could e that solar radiation from sunlight accounts for the solar heat

gain indoors. -e have talked aout the heat transfer from outdoor toward

uilding interiors and that the primer cause to such a transfer was the

temperature difference etween the indoors and the local environment outdoors.

,evertheless the solar radiation is not the only factor causing the temperature

uildup indoors outside air temperature as well as the internal heat gain light

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sources human eings and process workL also have a role in the play. !ther

factors could e the rate of ventilation and the relative humidity of air ut to some

etent. E5

1o these facts we add that the uilding envelope represent the interface

oundary etween the interior and the eternal climate and it stands for the heat

gained through the roof windows and walls elements. !f these windows and

walls elements contriute to the ma#or heat gain and they must receive our focus

and attention to provide them with the suitale defense against solar heat gain

since they are the weakest fenestration elements. 2ow this can e achieved is

the su#ect of the net section.

)!,1+! !F %!A+ +A$IA1I!,

%o far we have talked aout shading devices their functions the thermal

comfort and we have introduced the solar radiation and its impact on uilding

thermal performance. (esides we noticed that the sun is the factor determining

our thermal environment and that the amount of solar radiation received indoor

y direct penetration of sunlight through windows is usually the greatest source

of solar heat gain. E5

1o overcome this prolem we usually cool the indoor y using one of our

sophisticated air conditioning systems availale on the market nowadays. ,ot to

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mention the fact that these air conditioning system are capale not only of

providing the desired air temperature ut also they provide the desirale climatic

condition with the a whole set of climatic elements fully controllale. Air

conditioning systems are efficient solution although it8s an epensive and costly

for operating. !n the other hand these air conditioning systems actually remove

heat that has een gained and trapped indoors and do not reduce heat gain in

the first place in addition to the waste of energy and the pollution pumped out to

the environment that they cause. E?

In order to provide satisfaction for a uilding8s occupants through the provision of

thermally comfortale climate we have to seek the ways in which we can reduce

the impact of solar radiation that causes heat gain. 1o start with we have to

search for the uilding elements that are responsile for the admission of heat.

1hese are usually fenestration elements which are in direct contact with the

eterior. -alls floors ceiling and glass are the elements constituting the point

through which heat transfers. !rientation of the uilding itself also contriutes to

the amount of solar heat gained. ,evertheless the window represents the

weakest element of all since it8s transparent to the short'wave radiation emitted

y sun. In recent decades a lot of studies and researches were made to

investigate the ways in which we can reduce the solar impact on windows and

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one of these studies reference E5 came up with the following actions to reduce

the solar impact>

!rienting the uilding in such a way that the facades with large

openings face towards the directions which receive less sunlight.

Using special glasses which act as heat filters.

Using shading devices such as screens overhangs louver

systems linds etc. in front of the windows.

Another research reference E6 came up with some guidelines which are not

applicale in all situations one of which was that the first line of action to reach a

very thermally comfortale indoor climate is to shade the eternal internal and

the surrounding of the structure. $oing this we will e ale to reduce the

temperature uild up due to amient air and solar radiation incidence. 2owever

this is rather an impractical solution since we can not isolate our uildings

completely and shade them from the eterior and interior.

For housing and residential uildings glass windows represents a small portion

of the wall area if they were well designed and oriented to avoid ecessive heat

gain. In commercial and office uildings where glaing component is responsile

for ;@Q of the cooling load the situation however is different. 1hese glaed

elements represent a ma#or admission of solar radiation and additional cooling

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load is acDuired. In that case the shading strategies are Duiet important to the

reduction of these cooling loads. E0@

%hading devices take over in this scene and play their role impressively to

reduce the ecessive cooling loads. As mentioned efore shading devices re#ect

the direct solar radiation and filter it out so that no energy transfer due to direct

solar radiation is taking place. In other words shading devices are intended to

eclude the direct radiation component of the solar radiation which contriutes to

the ma#or heat gain. (ased on this point it seems logical to place the shading

device at the eternal part of the uilding envelope. E0

!ne fact states that eternal arrangement of shading devices is more effective

than internal arrangement although efficiency depends also on orientation. 1hat

is ecause on the inner side of the uilding envelope the shading device

intercepts solar energy that have #ust passed though glass surface. It eliminates

only that portion of radiant energy which can e reflected through the glass

again. 1hat is energy is asored convected and radiated into the room for an

interior shading devices. And as we know aout the green house effect this

solution would still yield a temperature uild up indoors since the admitted energy

would e trapped inside.

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A second situation represents a shading device placed at the surface of the

glass. At this instance part of the energy will e reflected ack at the entry layer.

Part of it will e transmitted while other part will e asored. 1his last portion

which is asored will e convected and radiated oth to the outside and into the

interior of the uilding.

A final situation is where the shading devices are eterior ones that act as a

protecting shading devices that dispose the convected and radiated portion of

energy to the outdoor air since no incident energy reaches the surface of the

glass. 1his solution seems to e the most suitale one ecause having the

shading device in front of the glass window will prevent any direct radiation from

eing transmitted through in. E0

P+I,)IP/% A,$ $/%I*,

Although eyond the scope of this thesis we will try to guide the reader to the

principles that govern the design of shading devices along with the asic

principles and considerations that should e taken into account in design to get

the optimal result. 1he designer of a shading device should e familiar with the

solar geometry which is an essential ackground knowledge needed for the

design. *eometry of solar movement includes the knowledge of the terrestrial

latitude and longitude the celestial sphere enith nadir and horion celestial

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poles the coordinate systems relation etween horiontal and eDuatorial

systems sun8s apparent motion time eDuation of time local and standard time

and most important the calculation of solar altitude and aimuth. 1he foregoing

knowledge will Dualify the designer to estalish the asic geometry of the

shading device ased on the data values of solar altitude and aimuth. E5 %ome

monographs have een devoted for this particular su#ect concerned with the

design of shading devices. (asically ones start y otaining the horiontal and

vertical shadow angles for a specific orientation and particular month of year from

a solar chart with the help of a protractor. 1hese angles constitute the first step

toward the completion of design of a shading device y pro#ecting these angles

from plane and section elevation for a window where we are interested to use

shading device. 1he rest will e a matter of otaining the intersection of these

pro#ected lines to form the asic geometry of the shading device.

%AMP/ $/%I*,

1his section includes two different shading devices that are going to e

used in the daylight study conducted in chapter three. First shading device

is for a north facing window that designed to eclude all direct solar

radiation throughout the year. 1he other shading device is for a south facing

window that eclude direct solar radiation from Feruary through to !ctoer.

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,orth Facing %hading $evice. For a north oriented shading device

figure 9.6 shows the asic geometry otained y pro#ecting solar

vertical and horiontal shadow angle otained from the solar chart and

protractor Fig. 9.;. 1he figure also indicates the horiontal and

vertical shadow angles at different times during the day. 1his shading

device guarantees that no direct solar radiation would e admitted all

around the year. 1he geometry is simple and it provides a great deal

of daylight since it ostructs a little portion of the sky vault.

%outh Facing %hading $evice. 1he other figure. 9.3 shows a south

facing shading device along with the horiontal and vertical shadow

angles at different time during the day. 1his type of shading device

ecludes the solar radiation from Feruary through to !ctoer. (ased

on the geometry it8s ovious that this shading device will admit less

daylight compared with the shading device designed for the north

facing window.

%2A$I,* $/4I)/% /FF/)1% !, (UI$I,* P/+F!+MA,)/

1he foregoing sections were mainly concerned with the shading devices from

functional point of view. At that time it was not suitale to present the shading

devices impact on uildings and the way they influence various characteristics of

uildings envelope. Meanwhile it8s time to deal with five ma#or impacts that

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shading devices have on uildings envelope performance. 1hermal comfort

daylight and glare are those impacts of importance to the occupants who sense

their effects instantaneously. 2ow Duiet the uilding is and its aility to provide

the acceptale level of privacy is also of great concern to occupants. !ther

characteristics affected y having an eterior ostruction outside the window

'such as a shading device' is the ventilation and air flow around and inside the

uilding itself. /ach of these impact will e dealt with separately in this section.

12/+MA )!,1+!

1oday8s technology has taken a lot of forms in which it has een displayed and

promoted for eager customers who are looking always for all new technical

developments. -indows8 technology has received its dole of attention in a form

of larger and larger glaed areas in uilding facades which have an impressive

image that noody can deny. !n the other etreme the design of very large

windows are now eing tempered y the realiation of the environmental

prolems created y such large areas of glaing. 1he first of these environmental

prolems to e recognied is the ecessive solar heat gain eperienced y

uildings having such large areas of glass with no mean of protection or shading.

1he prolem of solar heat gain was discussed efore in earlier sections

however we want to stress that even when heat asoring glass or any other

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special type of glass are used to reduce the impact of solar radiation the result is

still unsatisfactory and the efficiency is limited to some etents. E00

In the situation using reflective glass we will encounter another type of prolem

which is that these types of glass will reflect the incident sunlight away to neary

uildings and traffics Fig. 9.=. 1his in turn will cause heat gain concentration on

other uildings not to mention the glare caused y these large glaing reflecting

sunlight toward pedestrian and traffic. %hading devices y their role protect

typical clear glass from direct solar radiation and hence they eliminate the ma#or

factor causing the ecessive solar heat gain in uildings. Moreover y selecting

the suitale material for shading devices to e made of we can further reduce

the impact of convected heat from air in contact with the glass windows and y

providing a mean of ventilation so that the hot air flows away. 1o further illustrate

the impact of shading devices in providing a more thermally comfortale climate

indoors we will consider two situation in which the first represents a glass

window having no eternal sun'protection such as a shading device while in the

other situation we will recognie what effects does shading device fied at the

eterior side of a glass window has see Fig. 9.5.

:?


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,!I%/ )!,1+!

1he fore mentioned fact that the development in windows8 technology lead to

larger and larger areas of glaed facade did in fact alert us to other

environmental prolems as a result of using such a large glaing in uildings. As

ecessive solar heat gain was one of the prolems of these glaed areas the

increasing traffic noise that contriutes to discomfort eperienced y the

occupants is another prolem. 1ypical and average cost glass used for glaing is

not a good insulator for noise especially for high freDuency noises. For this

reason it ecomes essential for seeking out some solutions to the noise

penetration prolem. E09

(efore we try estalishing a solution we have to identify the nature of noise and

the physical principles that govern its transmission. *enerally speaking noise is

unwanted sound caused y a virating medium acting on the ear. 1he source of

viration could e natural or man'made. ,atural viration causing noise could e

wind water rain etc. while on the other hand man'made virating sources

include machines motors traffic etc. Physically noise is a form of a series of

compression and contraction of air particles that set the air in motion. It travels in

a spherical wavefront and is usually forced to reflect diffract diffuse or asored

depending on the surface and sie of o#ects it is striking. !ne of the facts

known aout noise impact on human eings is that it produces oth

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psychological and physiological effects. -orking efficiency is dropped when

people are eposed for sustained period to a noise level of 5@ d( d(> unit for

measuring the noise level L. E09

1he first solution to e thought of in order to reduce the noise transmission to the

interiors would e to reduce the areas of glaing. 1hat is ased on the fact that

windows component of the uilding skin admit most of the noise ecause their

surface weight is much ellow that of the eterior walls that known to e opaDue

surfaces and good reflectors to the eterior noise. 2owever this solution is not

desired since the purpose of having such a large glaed areas is to provide a

wide vision angle to the occupants and admitting most of availale daylight.

2aving shading devices fied outside the glaed areas to control the solar heat

gain we can utilie them as an ostructing elements in the uilding envelope that

are capale of reflecting asoring and reducing the noise effect on the interior.

E09

In this prospective we have to consider the ways in which we can manipulate

shading devices and develop them to accomplish our acoustical reDuirements.

*eometry materials and orientation of shading devices must e considered in

order to e ale to control the penetration of sound waves of various freDuencies.

1ake the orientation of shading devices for instance the direction they are facing

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contriutes to the solution of the prolem. Fig. 9.? shows different orientations of

the same shading device. )onsider the three situation and notice that the first

situation represents the correct direction of the shading devices in which they act

as a shelter and protect the window from the noise waves either y reflecting the

noise waves or asoring them if it were taken into account when selecting the

shading device material. -hile in the other two situations the direction of shading

devices magnify the penetration of noise as they act like a collectors of noise.

1he other three figures 9.0@ 9.00 9.09 illustrate a practical application that

utilies shading devices as an acoustical elements in the uilding envelope.

1hese figures shows noise transmission and its ehavior when it meets the

uilding envelope. In each figure there are graphical interpretation of different

noise freDuency that may eist in any noise source such a comination of low

medium and high freDuencies that can eist in the noisy sound of an air #et.

AI+ M!4/M/,1 ' 4/,1IA1I!, )!,1+!

Prior to the invention of air conditioning systems people had the intuition to

utilie the desirale air movement 'especially in hot seasons' to cool and

ventilate their homes. For that they knew how and when air movement should e

activated Fig. 9.0:. 1hey knew that in hot seasons they had to create an air flow

inside their homes in order to reduce the impact of high temperature and humid

air and that they had to avoid any air movement indoors in cold seasons. From

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my point of view I think that at those days people wondered what forces acted to

produce the natural ventilation system they utilied. At the time eing the answer

is clear and simply there are two types of forces that produce natural ventilation

in uildings and can e categoried as >

Air movement produced y pressure difference or simply wind

forces.

Air change caused y difference in temperature. E0

-hat have shading devices to do with all of this anywayR. In actual fact shading

devices produce type of forces similar to the first category. %hading devices are

regarded as an ostructing elements around the windows which produce

pressure concentrations around the window and cause air to flow in an altered

patterns. !n the other hand shading devices are not the only factor affecting the

air flow patterns around windows openings. !rientation as well as placement of

windows are another factors y which air flow pattern is influenced. For instance

the air will flow at higher level than that of the normal level when seeping through

a window on the tenth floor while the air will flow at lower levels when it passes a

window on the first floor. 1he two factors mentioned aove do not contriute

much to the air flow patterns in low uildings with respect to the shading device

influence on air movement whenever they are used. For high rise uildings

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however this effect is remarkale in determining what flow pattern air will have

around as well as inside the uilding depending on the geometry and scale of

shading devices used. E0

Inlet attachment such as a shading device is an influential element as far as air

movement is concerned Fig. 9.06. $ifferent configuration of opening along with

shading devices in different locations are presented in Fig. 9.0; 9.03 9.0=.

$ifferent case is encountered in Fig. 9.05 which illustrates two situations in which

we are trying to control the air flow patterns indoor to ring it down to the

desirale levels.

P+I4A)7

At the time when we were talking aout shading devices impact on the thermal

performance of uildings we have mentioned types of glass used to provide a

mean to control solar heat gain. 1he reflected glass type in particular is widely

used to re#ect a percentage of incident solar radiation. $uring daytime reflected

glass acts as mirrors so no one can see through in and thus it provides privacy

for the uilding occupants. 1hat is true as far as it is daytime. 2owever this type

of glass act in the opposite way at night where the larger amount of light will e

inside the uilding itself. A lot of us have eperienced the lack hole effect in

office and commercial uildings glaed with reflected type of glass during night

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time. -e see our images on these reflected glass type instead of the eterior

scene. For an oserver standing outside the uilding this glass would e

transparent and he can see eyond the glassed facade at night whenever the

light is on. Fig. 9.0?

It is ovious that any type of glass can not stand y itself to provide the privacy

acDuired y the occupants. 1he privacy issue is relative and su#ected to various

factors such as the culture purpose utility and tasks performed in the uilding

along with the time these activities take place. In our culture the privacy is one of

the main characteristics that must e one of the uilding8s if it is to e

satisfactory especially for residence uildings. %hading devices reduce solar

radiation admitted indoors in ecause they ostruct some of the sky vault the

window eposed to. 1herefore one should epect that shading devices also

reduce the view or in other words control it and allow for controlled vision in and

out through them Fig. 9.9@. 1o make the su#ect more familiar we might

correlate etween nowadays shading devices and the NMashraiyahO used y

Islamic architects to provide a mean for privacy reducing temperature uild up

ventilation and to add an interesting element to the facade. %hading devices

might e thought of as a developed and more sophisticated version of

NMashraiyahO for which we might consider the addition and modification of

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finishing to keep the traditional characteristic of old NMashraiyahO along with its

superior provision of privacy.

$A7I*21 *A+/ A,$ 4I%UA )!MF!+1

ight is important for human communication since it represents the asic element

in the visual sense which human eings depend upon as a mean for interaction

with the surrounding environment. %un provides visile light as a part of its

electromagnetic radiation. 1he amount of these radiation which lies in the visile

spectrum is indeed large and sufficient for all tasks and activities needed to e

done indoors and outdoors.

1he need for sunlight in uildings depend on climatic regions and tasks

undertaken in different places. iving areas in houses need to receive a lot of

sunlight to e psychologically comfortale relative to edrooms and relaation

areas. In hot climate the sunlight is welcomed ut to some etents and in certain

periods. ,evertheless it8s always welcomed in cold regions and all around the

year. E5

-e know that shading devices eliminate the direct solar radiation although they

influence the amount of light getting inside which is sometimes desirale in case

of glare. %hading devices may reduce the illumination ecessively and that what

usually happens. 2owever they compensate for the daylight loss y providing a

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more visually and thermally comfortale environment. -ell designed shading

devices can provide most of the daylight incident upon them y reflecting the

sunlight toward the interior and y which they make up for lost sunlight that

would have een admitted indoors. 1hat can e achieved y providing the

shading devices with louvered tops or roofs using light colored finishing and

furthermore developing the geometry of the shading devices as to chop off any

unneeded volumes 'redundancies' to eliminate any additional lockage of

sunlight as indicated in Fig. 9.90. E0:

(eing visile through a window sun8s disc can cause ecessive glare and that

can even happen when it produces huge contrasts upon falling on a work ench

or chalkoard. 1here are two types of glare namely $iscomfort glare and

$isaility glare. 1he discomfort glare can e uncomfortale and sometimes

painful however it does not reduce aility to perform visual tasks significantly.

-hat affect the discomfort glare is the rightness conditions within the entire field

of vision. $isaility glare reduces the aility to perceive visual information needed

for task performance. It is influenced y o#ect rightness. *lare prolem

ecomes apparent in office uilding and very disturing in correlation with the

fact that large glaed areas permit the scene of a great deal of the right sky

from most parts of the room. 1his acDuires human8s eye a considerale effort to

ad#ust from the rightness of the room to the higher rightness of the sky. E0006

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1he solution to all of this lies in the considerale and conceptual understanding

of the variales which control the prolem. !rientation of windows should e

considered in relation to the times of day when sunshine is reDuired. 1he effect of

the direction of sunlight shall also e under consideration. (linds or curtains

ehind the glass windows may e effective in reducing glare although they may

lock the whole view and still admitting solar radiant heat. %hading devices

having the right material and color would increase the amount of daylight that

could e reflected off them. E00

1hose was some of the impact shading devices have on the performance of

uildings from different prospective. Fig. 9.99 gives a comprehensive summary of

the role and impact of shading devices on uilding envelope performance.

)!,%I$/+A1I!, !F %2A$I,* $/4I)/%

-e have noticed throughout the previous pages how shading devices affect the

performance of uilding envelope though the alteration of daylight admission

esides the noise transmission and other functional characteristics of uilding

envelope.

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*/!M/1+7 $/4/!PM/,1

1he principle of thermal'solar sun control is to let sun8s energy into the uilding

during winter and intercept it during summer when additional heat gain is

undesirale. For this reason while designing a shading device we have to

consider that principle and give careful consideration to the shading device in

relation with the fact that we need to>

Minimie the heat gain during summer.

Allow winter sun to come in.

Interfere as little as possile with windows views. E0;

1o illustrate how simple consideration in design of a shading device can e

effective in improving some of its performance characteristics consider for

instance the south facing shading device presented in the previous section Fig.

9.;. -e might consider further development in the asic geometry to increase

the daylight admission for instance. If we eliminate the roof which is small

enough to e functionally disturing when removed we would epect that the

daylight admission will increase 'as we will see in the daylight study in chapter :

Fig. 9.9:.

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Another #ustification for eliminating the roof could e ased on the fact that

surface temperature of sunlit materials will e higher than that of air. 1herefore

air movements over these eposed surfaces will reduce the eternal heat impact.

In our case this can e achieved e providing an air channel through the

shading devices such that hot air will flow up and cool the hot surfaces windows

and walls. /liminating the roof element of the shading device would achieve this

result and air channel could e a mean for ventilating the enclosed volumes

inside the shading devices whenever the geometry of the shading device

permits. Fig. 9.96 E0

MA1/+IA% A,$ FI,I%2/%

1he su#ect of selecting the suitale materials for shading devices is eyond the

scope of this thesis since it8s su#ected to so many factors governing the

structural architectural thermal and visual performance of the shading devices

and the uilding envelope itself. In this section we were intending to draw

attention to the impact of materials used for making shading devices on their

performance and the contriutions those materials have on the uilding

envelope itself as we will see in a while.

)onsideration of materials can e regarded from two points of view in which the

first takes into account what impact does the selected material have on shading

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devices with respect to their performance. In other words material selection

might affect the shading devices aility to function well last longer look etter

cost less to maintain and so on. In this sense we are looking for materials that

can stand for different forces acting on them such as the wind forces and those

materials which resist deterioration and last longer and any other suitale

materials that might e considered in making such an industrial piece. !n the

other hand the second point is concerned with the impact that materials might

have on the uilding itself. (ased on the fact that shading devices are placed

outside glass windows at a close distance to the uilding surface we shall

consider the interaction etween these shading devices and the uilding

envelope especially the windows.

,owadays technology have reached eyond many epectations and the

industrial field have received its dole of this technology. It ecame no more a

prolem to come up with new designs of any mechanical structural or even

architectural element that could e readily converted into industrial piece. For this

reason the first point we have mentioned aove represents a solved issue for

which there are many eperts who could help and assist in the decision making

of selecting the most suitale materials. 2owever the designer of shading

devices is the one who should decide upon the material to e selected in

accordance with the second point of view. For this an epert in uilding

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engineering should consider the selection of materials. As a matter of fact poor

choice of material might lead to ecessive heat gain through uilding envelope.

Fig. 9.9; 9.95

-hen impact of materials on thermal performance is concerned we have to

select the preferred asorption and emissivity of materials. -hat is preferred are

the materials which reflect rather than asor radiation and readily release the

asored Duantity as thermal radiation will cause lower temperatures within the

structure. *enerally speaking material and finishes for shading devices has to

e considered for its emissivity surface conductance reflection teture ' in the

way it affects the surface conductance' duraility easiness of maintenance and

many other factors that determine the performance Duality of these shading

devices. Fig. 9.93 E0

1ake for instance the type of material used for finishing the surface of a shading

device whether it was a paint or a rough finishing or the structural material of the

shading device. If we were to use a polished surface as a finishing we have to

consider the conseDuences in view with the fact that polished surfaces are glossy

and cause a specular reflection of light. 1hat might cause glare to oth occupants

of the uilding ' if the inner surface of the shading device has the same finishing'

and viewer outside the uilding. -hereas rough finishing provide diffuse

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reflection that is more desirale for viewer outdoors and might increase the

daylight admitted through shading devices indoors if were designed to get enefit

of that. Fig. 9.9=

)!!+%

)olors of the shading devices is very important factor affecting the daylight

admission indoors as well as the Duantity of solar radiation gained. It8s well'

known that light colors reflect incident light and dark ones asors them. In other

words light colored shading devices of the same geometry are epected to

provide more daylight indoors along with an increased admission of solar

radiation while dark colored shading devices will reduce the amount of daylight

admitted through in and maintain a good alance of solar radiation admitted

indoors. For this reason we have considered the color of shading devices to e

one of our variale in evaluating the daylight and solar radiation admission

through shading devices indoors as we will see in chapters : and 6. Fig. 9.95 E0

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CHAPTER 3

PERFORMANCE EVALUATION OF SHADING DEVICES

1his chapter investigates the impact of shading devices on solar radiation

admitted indoors with accordance to the fact presented in chapter two that

shading devices actually reduce and control solar radiant heat admitted indoors.

In order to assist in determining this impact and to get a practical understanding

of thermal control as an element in uilding design we have designed an

eperiment in which heat gain will e measured when using shading devices.

)2A+A)1/+I%1I)% !F %U,I*21

+adiant energy emitted from sun is a whole range of electromagnetic waves

having different freDuencies that contains light as a very small part of this

spectrum. /clusively light has an action on the eye that result in vision and the

variation in wavelengths of this radiant energy is what gives rise to the sensation

of different colors that we see. 1his light what our eyes detect within the visile

range of the radiant energy spectrum is what we call the G$aylight8. E00

$aylight is different from artificial lighting in that it is dependent upon outdoor

climatic conditions. In fact daylight is variale in Duantity and in color

continuously throughout the day though to the earth revolution aout the sun and

the sky conditions. And this is one of the things that makes daylighting design

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difficult and unreliale although on cloudy days daylight Duantity and color

would remains constant. ,evertheless Ndaylight has predicta!le daily and

seasonal variations and unpredicta!le patterns "rom cloud cover, atmospheric

pollution, and other climatic variations#$ %ky condition is the most climatic factor

influencing the Duantity and Duality of daylight received at a certain point. As the

figures show there are three asic sky conditions which are>

)lear %ky > which produces intense direct light from sun and

diffuse light from sky.

Partly )loudy %ky > produces constantly changing intense diffuse

light.

!vercast %ky > produces diffuse light. E06 Fig. :.0

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are the shading device geometry orientation and color for oth shading devices

and the interior floor.

1/+M% A,$ $/FI,I1I!,%

%ince we are concerned with daylight measurements whether we have shading

devices mounted on the windows or not we have to consider some asic terms

and definitions of daylight. %ome of the very important photometric concepts and

units are presented in tale :.0. !f these units lumen and l are of great

importance to us.

UMI,!U% FU< GF8 ' UM/,

1he light 'previously discussed' is a from of electromagnetic radiation and

the rate of emission of any radiation of any kind including light from a

source may e measured in watts. ikewise the rate of reception of

radiation on a surface may e measured in watts or in watts per sDuare

meter of area of the surface. 1herefore the lumen may e looked upon as a

unit which is of the same kind as the watt. 1he difference etween them is in

their magnitudes. 1his is ecause in measuring light as distinct from other

kinds of radiation it is necessary to take account of the way in which the

human eye responds to the various colors of light. 1o put it in another way

the lumen can e considered as a unit of light'producing power of a light

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source. 1he rate at which light falls on one sDuare foot of surface area one

foot from a source of one candlepower can e defined as a one lumen. E03

Fig. :.6 aL

IUMI,A,)/ G/8 ' U<

1he other very important unit in light measurement is the Glu8 which is a

unit for measuring the illuminance. 1his concept is derived from the lumen

that is a Glu8 is the Duantity of light 'or illumination level' on one sDuare

meter of surface area one meter away from the light source. In other words

the illumination of a surface is the luminance received on that surface over

the area of that surface lumenm9. E03 Fig. :.6 L

$A7I*21 )!MP!,/,1%

1he daylight reaching a point indoors can e thought of as a sum of light

eams coming from different sources. %ources are either self'illuminated

Gsun8 or light'reflecting surfaces such as the surfaces of internal and

eternal o#ects which reflect ack the light incident upon them. 1his is an

important attriute of light that should e taken into the account since we

are going to measure the daylight illuminance indoors at certain locations

along the depth of the room. *enerally components of daylight reaching a

certain point indoors are>;=


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direct light from the sky. %)L

light reflected from eternal surfaces. /+)L

light reflected and inter'reflected from internal surfaces. I+)L

$irect light from the sky 'sky component %)L' contriutes for the ma#or part

of total daylight admitted inside especially in an unostructed field.

/ternally reflected component /+)L represents the light reflected from

eternal surfaces and of significance when the area under consideration is

heavily uilt'up or in the situation where we have sort of ostruction outside

windows as the case with shading devices. 1he internally reflected

component I+)L includes all the light which reaches the reference point

indoors after multiple internal reflections that is light from sky eing

reflected from the floor and then from walls and ceiling. E00. Fig. :.;

$A7I*21 FA)1+!+ G$F8

1he daylight availale indoors is not measured in asolute values of lu as

we might think ut as a ratio Gdaylight "actor 8 of the total daylight availale

outdoors. 1hat is the $aylight Factor epresses the total interior illumination

' the light which reaches the interior directly from the sky y reflection from

outside ostruction and y inter'reflection from the surfaces within the

room' as a percentage of that availale outdoors.

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1he concept of daylight factor is valuale for two reasons first of which is

that human8s eyes adapt readily to changes in the luminance of the sky and

hence to changes of daylight illuminance in a room thus the illumination

indoors measured as a ratio 'daylight factor' remains constant as the sky

luminance changes. 1hat is this ratio of the interior to the eterior light is a

measure which to some etent takes into account the eye adaptation effect.

-hile the second reason is that Ndaylight "actor is an arithmetic

convenience !ecause it is not only a measure o" the lighting which accords

well enough with the visual e""ect on the eye, !ut it is also a %uantity which

can !e e&pressed in terms o" the sie and position o" the windows relative

to the re"erence point, the re"lectance o" the internal and e&terior sur"aces,

and angular o!structions o" these e&terior sur"aces, all o" which are

measura!le physical %uantities which can !e "ed into an appropriate

computing "ormula to ena!le the daylight "actor to !e calculated with the

design o" the !uilding .O E00

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well as illumination levels. Most light meters are cosine'corrected and a lot

of them are also color'corrected. light meters 'or the photoelectric cells' are

part of a group of devices which are more commonly known as the radiation

detectors. 1he name photoelectric implies that the electrical characteristics

of the cell material are changed when radiation is incident upon its surface

and that the range of wavelengths which produce this change is in the

visile spectrum. 1he cell is provided with suitale contacts y means of

which it is connected to an eternal electric circuit. +adiation incident upon

the cell causes a direct current to flow in that circuit and measurement of

this current forms the asis of the system to measure the incident radiation.

+eadings measured using light meter are epressed in Gu8.

M!$/%

1he o#ective of this eperiment is to evaluate and measure daylight

admitted indoors through windows openings having shading devices fied

over them. Actually we will not take illuminance measurements inside an

actual full'sie room. 1hat is ecause we can not afford uilding full'scale

shading devices of different geometry and colors to e fied over windows.

As an alternative we will make a prototype model of a room with opening to

a scale to represent a typical room with a window. In addition we will

construct a shading device models to represent different geometry that we

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are intending to analye. %cale dimension and various aspects of each

model is listed elow.

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Arch. Fig. :.= shows an arch'shaped cardoard model. 1his arch was

made to cast shadow over the photoelectric cell when taking

measurements of diffused daylight illuminance as well as direct

daylight illuminance to make sure that no ground'reflected daylight

would greatly affect our readings. It has no specific dimensions

nevertheless you should consider the height of the arch as to e at a

distance aove the photoelectric cell such that reflection from the

surface of the arch would not affect the readings.

+oom Protoype. Model room is simply a o'shaped cardoard with

one opening at its front to represent the window. Another opening was

provided at the other end to e ale to access the photoelectric cell

inside the model. Model scale and dimensions are shown on Fig. :.5

aL and L. +egarding the color of the inner surfaces of the model all

should e white corresponding to the actual color to e used in reality.

$epth of the room in model'scale should e marked on the floor for

every meter as to guide us

Shading Device Design Alternative

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