Daylight Respondent Envelope Design

Daylight Respondent Envelope Design

Master Graduation ReportBuilding Technology Department

Faculty of ArchitectureTU Delft

Juan Manuel Dávila Delgado

Foreword

The current document is the final Building Technology research

report; part of my double master graduation project in Architecture

and Building Technology (A+BT).

The main mentor for the Building Technology research was Dr. ir. R.

Stouffs; the tutors regarding day lighting were Dr. ir. G.J. Hordijk and Ir.

Hester Hellinga; Ir. Henk Mihl was the responsible for the integration

between Architecture and Building Technology.

Juan Manuel Dávila Delgado

March 2009

Daylight respondent envelope design

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10

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12

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A+BT or ABT?

Antecedents

Relevance

Structure

Theoretical Framework

Light

Astronomic Fundaments

Daylighting

Dayligth Factor

Approach

Intention


contents

a

b

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Validation

Conclusions

Further Steps

Literature

Design

Appendix A

Design Areas

Base Proporsal

Definitive Design

Daylight Studies

c Problem Definition

d

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Appendix B 42

Desing Redefinement, Validation, Final Results


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contents

e

f

A+BT or ABT

The integration between the architectonic design and the building

technology research is crucial to the graduation project success. The

double graduation program contemplates the sum of both tracks to

come up to a single project which satisfies the requirements of both

parties; however each party has its own concerns and requests, not

always sharing the same objectives.

For this reason, the graduation project was focused not in the sum

but in the intersection of both parties, the project looked for be

within the intersection area, where the most important requirements

of both parties are fulfilled.

Furthermore by adding more specific concerns, the model (figure

a.2) become more detailed and defined. In this specific case the

selected concerns are: urban impact, aesthetics, function, structure,

construction and natural lighting. The graduation project seeks for

the intersection point of all of those concerns, to come up with a

balanced result which responds accordingly to all requirements.

This report will present the research and consequent design which

looked to satisfy the building user’s demands for good quality natural

lighting.

Figure a.2Design Concerns Model

Figure a.1Graduation Project Approach

a

Daylight respondent envelope design 5

Antecedents

Daylight conditions are determined and change depending on the

site location, a successful design which makes efficient use of natural

lighting has to take into account several variables, which will bound

the project possibilities.

The double graduation project started with an urban research of

an underused industrial area in the north part of Amsterdam; the

result was a master plan which will aid to redevelop the region and

to improve the urban qualities in the area; besides a specific project

was proposed to boost the redevelopment and the integration with

the existent city.

The proposed project is a multiuse building, a business complex, the

main function is an office tower; a convention center, auditorium and

media school act as complementary functions.

Figure a.3Project Location

Figure a.4Business Complex

Impression

Figure a.5Typical Tower Floorplan

a


Intention

The intention of this study is to design an office building envelope

(façade/roof) which make use of daylight more efficiently, a design

which performs better according its contextual conditions (location,

climate, function); which functions depending on its specific situation.

The idea is not to come up with the perfect design with an optimum

daylight performance; the plan is simply to consider a number of

conditioning variables (drivers) to make the design function better.

Approach

The proposed way improve the building performance regarding

natural lighting is: first, identify a problem or enhancement areas

in the design; then list a series of requirements and user demands

needed to make the improvement; finally look for the conditioning

variables (drivers) which have influence and determine the user

demands fulfillment. These conditioning variables will drive the design

and set its direction with the only finality of covering the demands

and requirements, and as consequence improving the design in the

identified area.

In this case the chosen area for improvement is daylight illumination.

The need for proper lighting conditions in offices is a major demand.

The final design will have to respond effectively to its location variables

enhancing the natural lighting conditions and providing a comfortable

working space for the users.

A good natural lit office space should provide: good seeing conditions,

support and enhance task performance, create a pleasant and healthy

working atmosphere (demands). These subjective requirements are

determined by measurable variables: illuminance levels, luminance

ratios, light uniformity and glare (drivers); by meeting the requirements

for this variables the design could perform better. (figure a.6)

Figure a.6Research Approach Model

a


Relevance

Providing appropriate daylight conditions in an office building brings

lots of benefits; natural lighting has a direct impact on the user’s well-

being, improving their productivity and their sense of satisfaction.

Several studies have been done regarding the influence of good

quality daylight in work performance and productivity.

According to The Heschong Mahone Group tests: office workers

performed 10 to 25% better on mental function and memory recall

examinations, they worked 6 to 12% faster and were less likely to

report negative health symptoms. The California Energy Commission

determined that higher levels in concentration and better short term

memory recall were consistently related with exposure to daylight,

students in classrooms with the highest daylight factors performed up

to 18% better on standard tests1.

Furthermore an appropriate daylight design will bring energy savings,

not only in the amount of electricity used on artificial lighting, but

could lower the HVAC (Heat, Ventilation & Air Conditioned) costs;

artificial lighting produces lots of heat compared with daylighting.

In residential buildings the energy used for lighting is about the 3,5%

(figure a.7), a very low value compared with the 50% in offices and

commercial buildings; this is mainly caused for the long hours of

daytime occupancy and the high lighting demand per square meter.

Daylight is the most efficient light source, light and heat normally

come together, however the amount of heat produced by different

light sources with the same intensity could notably change. As is

shown in the tables (figure a.8 & a.9) daylight could provide up to

150 lumens (light) per watt (heat energy)2. As the tables shows the

artificial ligth sources will produce more heat while generating the

same amount of light. Figure a.9Light Source Efficacy

Figure a.7Residential vs Comercial Energy Consuption in United States

Figure a.8Light Source Efficacy

1 Data collected from:How Daylighting Can Improve IEQ, Mike Molinski, LEED AP, January 2009

http://www.faci l it iesnet.com/lighting/article/How-Daylighting-Works--10445

2 Data collected from:

Selkowitz Stephen, Richard Johnson, The daylighting solution, Lawrence Berkeley Laboratory, University of California, Berkeley California 94720

Scartezzini Jean-Louis, Innovation and Daylighting in Buildings, Solar Energy and Building Physics Laboratory, Swiss Federal Institute of Technology, Lausanne

http://squ1.org/wiki/Daylight_Sunlight

a


Structure

The research was structured as follows: as a starting point a theoretical

research was made and continued throughout the whole study, this

helped to identify and define the problem.

A series of daylight studies were made to explore the influence of

geometry an opening settings on interior illuminance levels; the result

led to a series of design strategies which were used in the final design

which at the end was validated with daylighting simulation software

(Ecotect, Radiance). The final design was the result of the iteration

between all the steps.

Figure a.10Research Process Structure Model

a


Theoretical Framework

Light

Light or visible light is electromagnetic radiation of a wavelength;

visible light represents a small part of the electromagnetic spectrum,

above the short wave infrareds and below the long wave ultraviolet

(figure b.1). When a ray light reach and object three possible

phenomena could occur with the ray: reflection, refraction and

absorption; the material properties will define which and how will

occur. The object could reflect all the light, in one or more directions;

if has transparent or translucent properties could refract part of the

light in a different direction; or absorbs part of it and diminishes the

intensity of the reflected or refracted light (figure b.2).

Reflection

When light reach a polished surface is reflected in the same angle of

incidence respect to the normal (reflection law). When light follows

the reflection law is called specular reflection (figure b.3); but in rough

surfaces this law is not met, the light is reflected in all directions due

to the hetereogenity of the surface and is called diffuse reflection

(figure b.4). In reality most materials reflect light in a combination of

both specular and diffuse reflection.

Refraction

Refraction is the electromagnetic wave change in direction when

passes from one medium to another, for example from air (gas) to

glass (solid).

Absorption

Is when energy is taken from a electromagnetic wave by an object,

and its transform in other type of energy, for example: heat.

Figure b.2Light Behaivior: reflection, refraction & absorption

Figure b.3Specular Reflection

Figure b.1Electromagnetic Wave Spectrum

b


Photometrics

Light represents a complex measuring task: its production (Luminous

Intensity in candelas [cd]), transmission (Luminous Flux in Lumens

[lm]), incidence (Illuminance in Lux [lx]) and reflection (Luminance

in candelas per square meter [cd/m2]) could be measure. For this

research Illuminance and Luminance are the important terms.

Illuminance Levels

Measures the amount of light falling on a surface, the incident light;

its units are Lux [lx] defined as one Lumen per square meter [lm/m2].

Illuminance levels measure the amount of light reaching a surface,

which has any significance for the observer, since just perceives

reflected light; but is very important for the designer which allows to

measure the amount of light reaching a space (figure b.5).

Luminance

Measures the surface brightness, the reflected light from a surface; its

units are candela per square meter [cd/m2]. This is what the observer

perceives, the reflected light from each surface; two spaces with the

same geometry could have the same illuminance levels, but different

Luminance; depending on the material properties (figure b.5).

Light Requirements

Visual efficiency increases with higher illumination, is easier to

distinguish more detail with more light; for specific tasks different

illumination levels are needed. There are several publications of

recommended minimum illuminance levels for various tasks (figure

b.6); developed by different institutions all around the world; derived

from visibility test for mid aged persons and medium reflectance

materials. For this research the Neufert Architects Data and the

Commission International de l’Eclairage (CIE) requirements was used.

Figure b.5Illuminance vs Luminanace

Figure b.6Minimun Recommended Illuminance Levels

Figure b.4Diffuse Reflection

b


Astronomic Fundaments

Sun path and position

The apparent sun position in the sky dome changes during the day

and seasonally throughout the year, it’s the same for a particular time

at a particular day of the year, it’s predictable and can be calculated

for a specific date and time. The sun path is the apparent followed

trajectory by the sun every year in a determined location in the earth,

changes depending on the latitude and longitude.

The Earth’s elliptical orbit and its inclination (23.45°) respect its

own axis are the main reasons for seasonal climate changes, these

differences are accentuated in locations far away from the Equator;

specific dates are defined when these seasonal changes occur (figure

b.7).

Summer Solstice

June 21th is the Summer Solstice in the northern hemisphere, the

Earth is located in its orbit more distant point from the sun; the

northern hemisphere is more exposed to radiation from the sun than

the southern hemisphere and reaches it perpendicularly; the sun

appears higher in the sky vault and is visible more hours during the

day (figure b.8).

Winter Solstice

December 21th is the Winter Solstice in the northern hemisphere,

the Earth is still located in its more distant point from the sun, but in

the opposite one; so in this case the southern hemisphere is more

exposed to solar radiation; the sun appears much lower in the sky

dome and during less hours a day (figure b.8).

Figure b.10Azimuth and Altitude anlges

Figure b.9

Noon altitude Sun angles at Solstices and Equinox for

latitude 52° North (Amsterdam)

Figure b.8Solstice and Equinox variations

Figure b.7Elliptical Earth’s orbit around the sun

b


Spring and Autumn Equinox

The Equinox represents the midpoint between the two Earth’s position

extremes, occurs two times a year: March 21th and September 21th

(figure b.8).

Azimuth and Altitude

The sun position is defined by two angles called azimuth and altitude;

the azimuth is the horizontal angle of the sun from the true north,

is always positive and is measured in clockwise direction parting

from the north. The Altitude is the vertical angle from the sun to the

ground plane (figure b.10).

Sun path diagrams

The sun path diagrams are convenient ways of plotting the sun

trajectory during the day throughout the year; the diagram shows

the position of the sun in every day in every hour in a determined

latitude. There are several types of diagrams, depending on the used

coordinates, polar or cartesian. For this research a Stereographic

Diagram was used (figure b.11 & b.12).

Daylighting

Daylighting or natural lighting is the practice that improves the sky

light admittance into interior spaces, its main objective is to provide

sufficient light to perform specific tasks.

Sunlight and Daylight

Sunlight is the light coming directly from the sun, has high intensity

and is unidirectional; changes depending on the sun path throughout

the day and the year (figure b.13). In the other hand daylight is the

diffuse light coming from the sky dome, is not as intense that the

Figure b.11 Stereographic Sun path

diagram

Figure b.13Sunlit space

Figure b.14Daylit space

Figure b.12 3D Stereographic Sun

path diagram

b


sunlight but even in cloudy dark days is a very effective light source

(figure b.14). For calculating the brightness difference in cloudy and

sunny conditions there are mathematical models which represent the

light source behavior.

Mathematical Sky Models

The main light source is the sun, nevertheless due to atmospheric

scattering and reflection, the sky dome also emits light; the light

distribution depends on environmental conditions (figure b.15); as

climate conditions are always changing, average conditions has to be

used. The Commission International de l’Eclairage (CIE) developed a

series of mathematical models which represent ideal scenarios for

different climate conditions: clear sky (sunny) and overcast (cloudy),

intermediate sky and uniform sky. The models describe luminance

levels in the entire sky dome depending on angle from the horizon to

the zenith and the sun position (figure b.16).

CIE Uniform Sky

This mathematical model assumes a constant luminance level in the

entire sky dome.

CIE Overcast Sky

A completely clouded sky where the sun is not visible is the fundament

of this distribution; the radiation passing through the clouds provides

a white light. The distribution is symmetrical along the zenith and

diminishes as approach to the horizon. The luminance levels are three

times higher in the zenith than the horizon. The sky vault itself is the

brightest element; shadows are indistinct and are uncommon totally

overcast conditions (figure b.17).

CIE Overcast Sky distribution formula:

L = sky luminance

Lz = zenith illuminance

a = altitude

Figure b.16Mathematical Illuminance Sky Distributions

Figure b.15Sky types depending on climate conditions

Figure b.17CIE Overcast Sky

Figure b.18CIE Clear Sky

CIE Overcast Sky

CIE Clear Sky

b


CIE Clear Sky

The clear sky distribution assumes that the sun is visible therefore is

the brightest element in the sky dome, close to 10 times more than

in the darkest area, opposite to it; the luminance varies over altitude

and azimuth. The sky vault provides diffuse light; there are sharp

shadows and contrasts (figure b.18).

CIE Intermediate Sky

This distribution is a variant of the CIE Clear Sky; the sun is not as

bright and the luminance changes are not as strong.

Sky Illuminance

The sky illuminance is the amount of light coming from the sky

vault and is mainly determined by the latitude, hence two locations

with the same overcast conditions could have different amount of

incident light. The mathematical models just define the luminance

distribution, but not the amount of light. Sky illuminance levels

are taken from statistical measurements around the world and are

drastically higher close to the Equator. With this data Design Sky

values can be determined from dynamic statistical analysis; they

represent the horizontal illuminance value that is exceeded 85% of

the time between 9:00 hrs to 17:00 hrs throughout the working year,

and represents the worst case scenario (figure b.20).

Clear Skies Frequency

Climate conditions are always changing however specific locations

have repetitive conditions; with statistical measurements climate

conditions could be predicted. This is the case of clear skies conditions,

global illuminance (daylight & sunlight) could be measure and analyzed

to predict the clear skies frequency. The images (figure b.21) show

the global illuminance availability over Europe during working hours

CIE Clear Sky distribution formula:

L = sky luminance

Lz = zenith illuminance

k = angle between the point L and the sun

z = point zenith angle

zs = sun zenith angle

a = 0,91

b = 10,0

c = 0,45

d = 0,32

The angles should be input in

radians; a, b, and d are adjustable

coefficients determined by CIE

(1973). Figure b.20Design Sky illuminance Values for given latitudes

Figure b.21Clear Skies Frequency over Europe

Figure b.19Overcast vs Clear Sky Illuminance homogeneity

b


Daylight Factor

Daylight factor is the illuminance level ratio between a point within a

closed space to the simultaneous unobstructed outdoor illuminance

level under the same sky conditions, expressed as a percentage

(figure b.22); the higher the Daylight Factor, the higher the amount of

natural light is available in the space.

Sky Illuminance levels are always changing, but the daylight factor

of a space will always remain the same, is a characteristic from the

space; provides an objective measure for design comparison, cause

does not depend on the sky conditions. For example the same interior

space will always have a 3%DF no matter if is located in Mexico City

or Amsterdam, the interior illuminance levels will change, but by

knowing the Design Sky value of each location is easy to calculate the

interior Illuminance level.

The interior illuminance level is the sum of three different components:

Sky component (SC), direct illuminance from the sky (if it is visible);

Externally Reflected Component (ERC), illuminance from outdoors

reflections and Reflected Component (RC), illuminance from interior

reflections (figure b.23). The daylight factor is dependent on these

three components.

There is not an international requirement for daylight factors,

the requirements are mainly expressed in illuminance levels, and

openings percentage depending on orientations, however according

to experimental tests a space with daylight factors between 2% and

5% could be considered as day lit. Figure b.23Daylight Factor Components

Figure b.22Daylight Factor Definition

Daylight Factor Components :

DF = Daylight Factor

SC = Sky Component

ERC = Externally Reflected Component

RC = Reflected Component

Illuminace point calculated from Daylight Factors and Design Sky values:

L point= interior illuminance

DFpoint = Daylight factor

L Design Sky= sky illuminance

b

(9:00 to17:00 hrs); this information will help the designer to preview

which condition will be more recurrent and design accordingly. For

The Netherlands: 50% of clear skies in August, 20% in Dicember and

30% throughout the year.


Problem Definition

The objective is to achieve a comfortable and pleasant working

space by providing good natural lighting quality; which will create

good seeing conditions, support task performance, contribute to

appropriate working mood and provide good health conditions.

Criteria

Lighting quality is a perceptive parameter which is determined

not only by physical variables, but by psychological factors, and by

consequence cannot be accurately measured.

However there are series of physical factors that have influence in the

lighting quality perception: brightness, contrast and color rendering;

these physical factors depend on measurable variables: illuminance

levels, light uniformity, luminance ratios, glare, and daylight factors;

then by reaching adequate values for these variables, the design

could fulfill the users demands.

For this research one main variable will be taken in count: Daylight

Factor (DF%), which is determinant at the first stages of natural

lighting design. The objective is to achieve a DF≥ 5% in the 75% of the

workable area; achieving these values a well illuminated space will be

guaranteed.

Several studies have been done regarding the optimum values for

lighting variables, the proposed values are the result of a comparison

between different norms and criterion [3, 8, & 9 in Literature].

c


Daylight Studies

The daylight studies are case explorations made to have a better

understanding of daylight; and the influence of geometry and opening

settings in interior illuminance levels. The results helped to create

design strategies which were applied to the final envelope design.

All the studies were made with specialized computer simulation

software.

Simulation Method

The used method responds to the software requirements to perform

daylight simulations, in the method two different simulation programs

were used: Ecotect and RADIANCE, the image (figure d.1) shows a

basic diagram of the process.

Software

Ecotect was used to model and to define the 3D geometry and

contextual characteristics due to its ease and friendly user interface,

while RADIANCE was use to perform daylight simulations.

Ecotect is a building design and environmental analysis program

that allows performing full range of simulations: thermal, acoustic,

solar, and ventilation analysis; providing an easy user friendly graphic

interface. Ecotect uses a geometrical version of UK Building Research

Establishment’s (BRE) split flux method for performing daylight

calculations, which meet several regulatory norms and is suitable

for most types of conceptual designs; however this method has its

limitations, the main one is that uses a rather simple formula to

calculate internal reflections and cannot consider multiple reflections,

so the method will underestimate the performance of indirect light.

Since the daylight studies were meant to investigate the reflected

diffuse light; RADIANCE, a more precise simulation software, was used

to perform complex and physically accurate daylight simulations.

RADIANCE is a lighting simulation software developed by Lawrence

Berkeley National Laboratories intended to help lighting designers

and architects to predict illuminance levels and appearance of a space

prior to construction. RADIANCE uses a hybrid approach of Monte

Carlo1 and deterministic ray-tracing2 methods to achieve reasonably

accurate results in reasonably time.

The input required to perform daylight simulations in RADIANCE

is: a 3D surface geometry, materials properties and a light source;

for rendering an image: a view point, direction and angles are also

required. For the explorations this data was defined with Ecotect, and

then exported to Radiance to perform the simulations. The results

were post processed in both programs Radiance and Ecotect.

Input

As mention before RADIANCE needs four main sets of data to carry

out the simulations; 3D geometry, materials characteristics, light

source and observer point of view or analysis grid.

3D geometry

This data defines the desired space shape and its location on Earth;

here is where the geometry proportions and openings settings are

defined. The calculations were simulated in Amsterdam: Latitude:

52°2’, Longitude: 4°5’, Altitude: 0.0 m Time Zone: +1, in a suburban

context (figure d.2). The location will have influence on the sun position

and in the sunny days frequency. At first stages a simplification of a

typical floor from the office tower was used to perform the studies,

this helped to identify the influence of each element on illumination

levels, afterwards the model was becoming more complex until

became a precise representation of a typical office floor.

1 Monte Carlo methods are a class of computational algorithms that rely on repeated random sampling to compute their results, are often used when simulating physical and mathematical systems. Monte Carlo methods are useful for modeling phenomena with significant uncertainty in inputs; Monte Carlo simulation methods are especially useful in studying systems with a large number of coupled degrees of freedom, such as fluids, disordered materials and strongly coupled solids.

2 Ray-tracing is a method for producing visual images constructed in 3D computer graphics; it works by tracing a ray from an imaginary eye through each pixel in a virtual screen, and calculating the color of the object visible through it.

d


Materials

Ecotect and RADIANCE allow to define lots of materials properties

which have an important effect on illuminance levels; however the

objective of the studies was to measure the influence of the geometry

and openings and not the materials. The effect of geometry on interior

illumination is helpful for first design stages, the influence of material

properties should be explored further in the design process. For

this reason to perform the simulations, regular plaster was used as

inner material in all surfaces; for the openings regular double glazed

windows with timber frames were used. The images (figure d.3) show

the important materials properties which will have influence in the

calculations.

Light source

This data will define the light source characteristics, as is shown

before there are just around 30% of sunny days in Amsterdam, most

of all the studies were simulated in overcast conditions using the CIE

overcast mathematical model (figure d.4). The model distribution is

based on a completely clouded sky where the sun and its position are

not apparent, providing diffuse light which is three times brighter at

the zenith than in the horizon. Due to the sun position is not consider

in the mathematical model, the date and time will not have influence

in the results when calculating daylight factors, however when

calculating illuminance levels they will affect the calculations due to

the change in sky illuminance levels, this will be further explained in

the next topic “Analysis”.

Observer point of view / analysis grid

RADIANCE uses an eyed based ray tracing method (figure d.5) for its

calculations, this means that light rays are shot from the observer

point of view to the objects in its view area; and trace its behavior

depending on the materials properties and the light sources position.

Plaster

Solar absorption: 0.418

Transparency: 0

Color/Reflectance: 0.57

Specularity: 0

Double glazed window

Solar absorption: 0.81

Transparency: 0.647

Refractive Index: 1.74

Color/Reflectance: 0.57

Specularity: 0

Figure d.1Simulation Process Model

Figure d.2Input: Geometry and Location

Figure d.3Input: Material Properties

Figure d.4Input: Light Source

d


Besides the observer point of view, direction and angles have to be

input to define the view area (rendered image); this is done by placing

a virtual camera which defines these variables.

To measure illuminance levels or daylight factors in specific points

an analysis grid (figure d.6) could be placed within the geometry,

this will help to obtain specific and representative results. In all the

explorations an analysis grid was placed at 750 mm from the floor, a

traditional desk height.

Analysis

Once the input data is defined RADIANCE can perform four different

daylight simulations: Luminance analysis [cd/m2], the amount of

reflected light from each surface exactly as the camera sees it;

Illuminance analysis [Lux], the amount of incident light on each

surface; Daylight Factors [%DF], ratio between sky illuminance level

and interior illuminance levels; Sky Components [%SC], same as

daylight factor except that does not take in count reflections just the

direct light from the sky. For the daylight studies and the final design

validation just Illuminance and Daylight Factors analysis were used

(figure d.7), which are the most useful in the first stages of the design.

Illuminance Analysis [Lux]

This analysis simulates the incident light on each geometry surface

in a specific orientation, date and time (sun position); and it helps to

verify if the required illuminance levels for specific tasks are met. This

analysis could be performed with several light sources: No sky, for night

time and artificially lit spaces; Sunny Sky, which uses the CIE Clear Sky

mathematical model; Intermediate Sky, a mid state between sunny

and overcast conditions; Cloudy Sky, which uses the CIE Overcast Sky

mathematical model; and Uniform Sky which assumes an evenly

distributed light in the whole sky dome (figure d.8). As mentioned

before most of all the analysis were simulated in overcast conditions,

Figure d.5Raytracing Method

Figure d.8Radiance Sky Conditions

Figure d.7Radiance Analysis Types

Figure d.6 Analysis Grid

d


the geometry orientation will not have any influence in the results;

just the date and time, in which the analysis is calculated, will affect

the sky illuminance level; most of all the studies were simulated in the

winter equinox at noon (December 21th, 12:00 hrs).

Daylight Factors Analysis [%DF]

This analysis sets a horizontal sky illuminance level to 100 Lux,

generating an illuminance image at noon in midwinter; the result is

the worst-case scenario. As explained before Daylight Factor is a ratio

between the outside illuminance level and the interior illuminance

levels, so the orientation, date and time (sun position) won’t have any

influence in the simulations; the geometry and the materials will be

the only responsible for any changes in the results, this is very useful

to explore the effects of different geometries and openings settings.

The results of this analysis won’t show if artificial lighting is not

needed or if the required illuminance levels are met. These results

will show which percentage of daylight reached the interior, this ratio

will be the same in any location, date or time; and it’s only influenced

by the geometry and the material properties. These results have to

be complemented with Design Sky values, which are derived from

statistical analysis of dynamic outside sky illuminance levels, to derive

the percentage of daylight use in function to the latitude. (See chapter

e, Validation).

Post processing

The results of all the analysis types could be mainly presented in

two different ways: in a rendered image or in an analysis grid; both

presentation forms have wide range of results display possibilities.

Rendered Image

The result is not like any other render, but a full of information image;

in the base render (figure d.9) illuminance levels can be derived at any

point, and the information can be overlaid en several presentations:

contour lines (figure d.10), contour bands, false colors (figure d.11),

daylight factors and human sensitivity. Throughout the whole research

the false color overlay was the main used type, due to facilitates

illumination levels differentiation and gives a quick visual impression.

Analysis Grid

The analysis grid is a set of points that creates a plane in which the

calculations will be made and displayed, this plane can be place

anywhere within the geometry depending on the needed results, but

should be parallel to one surface. Most of the times the grid is placed

700mm to 800mm parallel to the floor, which is the traditional desk

height; the analysis grid is offset from all other surfaces by 500 mm.

The number of points in the grid will increase de calculation precision

and the calculation time; an optimum has to be found in order to get

reasonable accuracy in reasonable time, 400 points were used for all

the daylight studies.

Once the calculations are done the results could be displayed in

several ways; the most representative is to display the contour lines,

which link points with the same values; these lines help to have a

visual understanding and to deduct light uniformity. The results could

be represented in 3D as well (figure d.12).

d


Figure d.9Radiance Render

Figure d.12Analysis Grid/3D results

Figure d.11False Color Overlay

Figure d.10 Contour Lines Overlay

d


Summer Equinox, June

21th at noon.


21th at noon.

CIE Overcast Sky

CIE Sunny Sky

ease the visualization on illuminance levels variations.

Sky Type

The room was tested in overcast and sunny conditions in the summer

equinox at noon; as is expected with sunny conditions the illuminance

levels are higher, there are sharp shadows and large contrasts (figure

d.14); in the other hand in overcast conditions the illuminance levels

are lower but the illumination is uniform (figure d.15).

Study Cases

First Simplification

In order to easily identify the geometry influence on illumination

levels and to facilitate the geometry modeling and calculations,

a simplification of the typical floor plan was made for the first

simulations. As the image shows (figure d.13) a squared room was

defined with the typical floor basic measurements; an opening of 1/3

of the room height was placed in the top part of the south wall, finally

a wide angle camera was placed to render the images1.

Simulation Verification

These first explorations were made to test the simulation software,

and verify the calculations reliability by testing simple situations, and

checked if the results were the expected. For presenting the results

two images were rendered: a regular image and a false color one to

Figure d.14Sky Type: Clear

Figure d.13 First Simplication

Figure d.15Sky Type: Overcast

d

1Please note that the

measuring scales between

study cases have been changed,

that’s why explorations with

the same conditions in different

study cases (i.e. figure d.15

& d.18) appear distinct. The

change in scales was made for

visualization purposes and to

ease the comparison between

images whitin the same study

case; images from different

study cases should not be

compared.


Spring Solstice, March

21th at noon.

Winter Equinox,

December 21th at

noon.

CIE Overcast Sky

CIE Overcast Sky


21th at noon.

CIE Overcast Sky

Figure d.18Sun Position: Summer

Sun Position

This time the influence of the sun position in overcast condition was

tested, the room was simulated with cloudy sky in the winter equinox,

in the spring solstice and in the summer equinox, all at noon. Even

though the CIE Overcast Sky does not take in count the sun position,

the sky is brighter in summer providing higher illuminance levels as

the pictures show.

Basic Simulations

These first explorations tested the influence of room proportions,

openings settings and light redirecting systems on illuminance levels.

For these studies two different calculations were made: an illuminance

level analysis represented with a false color image, for visualization

purposes, and a Daylight Factor calculation over the analysis grid;

these results were graphed and superposed in a room section. The

graph represents the daylight factors trough the whole depth of the

room; the slope in the curve defines the light uniformity, the larger

the inclination the bigger the contrast.

Room Proportions

The first exploration had the objective to measure the influence

of height proportion on illuminance levels, the simulations were

performed in the winter equinox at noon with overcast conditions.

The results show that by incrementing the height in the room the

illuminance levels increment as well, the slopes in the curves in all the

cases have a similar distribution.

Figure d.16Sun Position: Winter

Figure d.17Sun Position: Spring

d


CIE Overcast Sky

Winter Equinox,

December 21th at

noon.

CIE Overcast Sky

Winter Equinox,

December 21th at

noon.

Figure d.19Room Proportion: low

Figure d.20Room Proportion:

medium

Figure d.21Room Proportion:

high

Figure d.22Opening position:

bottom

Figure d.23Opening position:

medium

Openings Vertical Position

This study explores different openings placements; by positioning

the window in the bottom part of the wall close to the floor (figure

d.22): an uneven illumination is obtained with high levels close to the

window, quickly dropping as moves away. In the second option, with

the opening in the middle part of wall (figure d.23), the illuminance

levels are lower but the uniformity is better. The best option is placing

the opening in the top part of the wall (figure d.24), provides an even

illumination trough the whole room with reasonable illuminance

levels.

d


Roof Openings

This exploration test the effects of having an opening in the roof,

the simulations show that having a small opening in the roof

will dramatically increase the illuminance levels (figure d.26). By

incrementing the openning the illuminace levels increase as well

(figure d.27).

CIE Overcast Sky

Winter Equinox,

December 21th at

noon.Light Shelves

By placing a light redirecting element illuminance levels increase, as

the simulations show tilting the light shelf does not have big effects

on illumination (figure d.30), due to the calculations are made with

overcast conditions; the simulations were performed in the summer

equinox at noon, where a tilted light shelf will be more effective with

clear sky conditions, because the sun inclination in this latitude. Lastly

a simulation with a light shelf and a roof opening combination was

made (figure d.31).

Figure d.24Opening position: top

Figure d.25Roof openings: none

Figure d.26Roof openings: one

Figure d.27Roof opening: double

d


CIE Overcast Sky


21th at noon.

Opening Horizontal Settings

The next set of studies explores different opening settings regarding its

horizontal position; the main objective is to compare light uniformity

and contrasts between cases.

The first analysis is a control simulation (figure d.32) with an entire

wall size single opening; in this case there are high illuminance levels

close to the opening, but quickly drop as go deeper into the room,

generating big illumination contrasts. The second option (figure d.33)

has four floor to ceiling openings, this setting provides a slightly better

uniformity, but big contrasts can be still found close to the openings

creating very bright areas. In the third simulation (figure d.34) the

openings don’t reach the ceiling, the big contrasts are still present

but the illuminance levels are lower. The fourth simulation (figure

d.35) is the opposite approach, the openings don’t get to the floor,

the light uniformity and the illuminance levels are improved. The fifth

exploration (figure d.36) has the openings in the middle part of the

wall; in this case illuminance level is the lowest with an acceptable

light uniformity. The final case (figure d.37) is the best option, with

the openings going al the wall to the ceiling, but retreated from the

floor.

Figure d.28Lightshelf: none

Figure d.29Lightshelf: one

Figure d.30Lightshelf: tilted

Figure d.31Roof opening and

tilted lightshelf

d


Figure d.37 Openings best setting

Figure d.37 Openings placed in the middle

Figure d.36 Openings don’t reach the floor

Figure d.33 Openings from floor to ceiling

Figure d.32 Single whole wall size opening

Figure d.34Openeings don’t reach the ceiling

d


Figure d.39Tilted Light Scope Analysis

Figure d.38 Light Scope Analysis

Light Scopes

In the last studies light scopes were analyzed, the objective was to

look up for the difference in illuminance levels by altering the light

scope geometry; the option with the tilted surface (figure.39) provides

better illumination close to the opening.

Results

All the simulations were compared and analyzed, these are the found

outs:

- By increasing the room height by 25%, the illuminance levels increase

10%

- The best light uniformity is achieved by placing a single opening in

the top part of the room; however openings for outside interaction

should be also consider, cause are an important factor on the user

comfort perception.

- By placing an opening in the roof illuminance levels are increased by

35%, by doubling the opening area the increment is just 20% more.

The openings in the roof are very effective cause take advantage of

the brightest part of the sky dome, at the zenit; which is three times

more brighter than the horizon.

- Placing a light shelf will have minor effects in overcast conditions;

a tilted light shelf will have negligible effects; however they could

represent large benefits with clear sky conditions

- The best results are obtained by mixing roof openings and light

shelves.

CIE Overcast Sky

Winter Equinox,

December 21th at

noon.d


Design

This chapter will review the followed design process which led to the

envelope final design; it will describe the approach and the strategies

used to maximize natural lighting efficacy in overcast conditions.

Design Areas

The typical floor plan was divided in different areas for its analysis,

depending on user requirements and orientations; in this way the

design will respond to the specific needs of each area. Even though

when dealing with overcast conditions openings orientations don’t

affect illuminance levels, they do play an important role for thermal

comfort and on illumination with clear sky conditions.

The first division was made in the north–south axis, dividing the floor

plan in two symmetrical parts; the envelope was designed assuming

that both areas will have the same lighting conditions; even though

one section will face west and the other east, for illumination and

shading analysis, will not represent big changes; nevertheless will

make big difference in a thermal comfort analysis. The typical floor plan

was then divided into three design areas depending on orientations,

functions and requirements.

Design Area 01

This area is south-east oriented, shares the biggest part of the

workable area; the minimum required illuminance level is 500 Lux.

A rotating light shelf and a perimetrical roof opening are proposed;

the light shelf will divide the envelope in two parts, the top one for

daylighting and the bottom one for having a view to the exterior.

The light shelf rotation will represent more benefits in clear sky

conditions, an optimum inclination could be found depending on the

sun path and sunny days frequency per season. The daylighting part Figure e.2

Typical tower floorplan divided according orientations

Figure e.1Typical tower floorplan ploted in a 3D stereographic sun

path diagram, for latitude 52° North (Netherlands)e


will consist of a totally glazed surface going all around the building,

meanwhile the viewing part will consist of openings and closed areas

to avoid excessive heat loss or gain; a 60-70% of openings and shading

systems are proposed.

Design Area 02

Regarding illumination in overcast conditions this area has the same

requirements as “Area 01” consequently the same strategies are

considered; however for clear sky conditions sunlight incidence will

noticeably change, specific shading systems should be proposed;

concerning thermal comfort a maximum of 50% viewing openings are

proposed.

Design Area 03

This area is north-east oriented, is where the lavatories are located,

therefore the illuminance requirements are low, a minimum of 100

Lux has to be achieved. No shading system is considered, glare will

not be cause of discomfort; sunlight incidence will be only present

in summer days early hours or close to the sunset time (figure

e.1). Heat loss and gain could represent a problem thus just 20% of

openings is proposed. Due to in overcast conditions daylight has the

same brightness in all orientations, at the same altitude; this part

of the envelope was used to bring in natural light, by retreating the

restrooms ceiling from the top floor creating a lighting tunnel, with

high reflectance finishing to improve its efficacy.

The last part is where the lifts, stairs and service shafts are located, a

total closed façade is proposed.

Figure e.3 Design Area 1

500 lux minimun rotating lightshelf

roof openings shading system

60-70%openings


500 lux minimun rotating lightshelf

roof openings shading system

max. 50% openings


100 lux minimun no shading system

20% openings light tunnel

e


Figure e.9Results Matrix

Figure e.7Floorplan Simplication

with Analysis Grid

Figure e.6Basic Section

Figure e.8 Simplified 3D Model

Base Proposal

The next step was to propose an envelope profile based on the Daylight

Studies, a base section was created (figure e.6); this section contains

three main elements which could be altered to improve illuminance

levels: the room height, the light shelf position and the set back are

parameters which can be altered and measure its influence.

With this section a 3D model (figure e.8) closest to the typical floor

plan was created and further analyzed with the simulation software.

The results were more accurate and representative, but still were a

design simplification.

A set of simulations was performed exploring all the different

possibilities and configurations by altering these parameters; a total

of sixteen possibilities were simulated and analyzed to measure its

influence on illumination. The best configurations were highlighted in

a result matrix (figure e.9).

As is expected the configurations with higher ceilings and more set

backs are the ones with higher illuminance levels; by increasing the

area for lighting the illumination increases dramatically. In overcast

conditions will not be any problems with high contrasts next to the

openings if they start from the floor (see: Daylight Studies/Study

Cases/Openings Horizontal Settings). The round shape (figure e.7)

allows a uniform illumination cause the light penetrates with the

same intensity in all directions. (For the complete set of simulations

results refer to Appendix A).

e


Figure e.13Set back Graph

Figure e.12Light Shelf Position Graph

Figure e.11Height Proportion Graph

Comparison

With these results a comparison was made to measure which

parameters have more influence for better illumination. The three

variables were analyzed separately to see the influence of each one,

and which brings more benefit. A set of graphs were plotted, relating

daylight factors with the room depth as is shown in the image (figure

e.10).

The first comparison is the height of the room, the graph (figure

e.11) shows an increment in daylight factors trough the whole room.

Nevertheless this increment is not very effective; the room height was

doubled, but the daylight factors wasn´t.

The second graph (figure e.12) relates the light shelf position in the

wall, which indirectly sets the area percentage for daylighting and

for viewing. The graph shows how by having slightly more area for

daylighting the daylight factors increases even more than doubling

the room height.

The third graph (figure e.13) shows the difference of doubling the

setback, as expected the daylight factors are noticeably higher close

to the opening, and become almost the same as moves deep into the

room.

Figure e.10Daylight Factors Graph underlaid in the proposed section

e


Figure e.15Schematic 3D impession

Figure e.14Schematic Section

Definitive Design

The final design is divided in two main areas, one for daylighting

and one for viewing, and has a setback in relation with the top floor.

This setback has to be defined with the overall tower shape and

illumination requirements.

The part for viewing was minimized as possible, is two meters high,

just above human sight to avoid glare; the openings for interaction

with the exterior represent 50% of the whole area for viewing; after

a sun shading and a thermal analysis this percentage could change,

depending on orientations. A one meter wide light shelf is integrated

in this part of the façade, a shading system is considered in the

openings.

The area for daylighting is 1,20 meters high, special glazing with high

light transmittance should be considered for optimum results; a

translucent shading system is proposed, a system which avoids direct

sunlight but allows diffuse daylight (figure e.14).

e


Figure e.17Schematic Cross Section

Figure e.18Schematic Front view

The north-east and north- west parts of the façade have light tunnels

above the lavatories areas (figure e.16); high reflectance finishing has

to be considered for optimum results.

Figure e.16Light Tunnels

e


Validation

The final design was analyzed with RADIANCE using the same

methodology for the Daylight Studies; the calculations were made

in the winter equinox at noon, in overcast conditions, with regular

plaster finishing in all surfaces, and traditional double glazing windows

for the openings. A more complex and accurate 3D model was made

with the definitive dimensions (figure e.19).

An analysis grid at 750 mm was superposed in the typical floor plan

covering all the workable area; a wide angle camera was set for

rendering the images (figure e.20). As is expected the lower daylight

factors are deep into the room close to the lifts shafts. With this

configuration a 5 %DF is achieved in the 57% of the area (figure e.21),

and by adding the 29% with 2.5%DF an 86% of the workable area

could be considered as day lit1.

In the two images (figure e.22) daylight factors and illuminance levels

are overlaid.

Using the daylight usage graph in relation with the latitude, the

percentage of office hours throughout the year of needed artificial

light can be determined. Using the daylight factor formula is possible

to determine the needed outside illuminance, depending on the

required interior illuminance and the daylight factor obtained.

For example: taking the 5%DF obtained with the proposed design,

and considering that the required illuminance level for offices is 500

Lux, the needed outside illuminance level is 10 000 Lux2. This value

and the latitude (52°) can be plotted in the graph to find out the

percentage of office hours throughout the year that this illuminance

level (10 000 Lux) is available. For this case around 70% of the office

time will be possible to achieve at least 500 Lux with natural lighting

(figure e.23).

Figure e.19Definitive 3D model

Figure e.20Daylight Factors Analysis

e

1The division of the areas in

figure e.21 are determined by

joning the sections with similar

day light factors; to make this

division, the plotted isolines

(lines that join points with the

same day light factor) were

used. Three main areas where

defined: 5%DF; 2,5%DF and

1,5%DF.


Figure e.23Natural Lighting Usage Percentage

Figure e.22Daylight Factors and Illuminace Levels

Comparison with a Traditional Office Façade

A common office tower floor was modeled with the same geometry

and dimensions as the definitive design (figure e.24); but with a

traditional curtain glass façade, to compare the results and verify the

proposed design efficacy.

The first comparison (figure e.25) relates the proposed design

without setback, just the façade divisions and the light shelf, with

the traditional façade. The graph shows that daylight factors and

uniformity are similar along the whole room; just close to the

openings the traditional approach has more light intensity. However

the traditional façade has 30% more glass area than the proposed

one; having the same illumination with fewer openings will help to

the building thermal behavior.

Figure e.21Daylight Factors Distribution

2

Ext. illuminance = Int. illuminance/DF

DF= 0.05

Required int. illuminance = 500 Lux

Needed ext. illuminance = 10 000Lux

e


Figure e.28Summary Graph

Figure e.27High Reflectance Graph

Figure e.26Setback Graph

Figure e.25Lightshelf Graph

Figure e.24Traditional Office Facade

The second graph (figure e.26) compares the traditional façade with

the proposed design, in this case with a setback, is evident that

daylight factors are dramatically increase close to the openings, the

light uniformity is also improved.

The proposed design proved to be effective and better than the

traditional approach; however the improvement is not significant. All

the simulations were calculated assuming a standard material in all

surfaces, by assigning high reflectance properties to the light shelf

and the ceiling, the proposed design maximize its benefits, as the

third graph shows (figure e.27).

The last graph (figure e.28) is a summary of all the comparisons, is

evident that the setback and the high reflectance property represent

the most benefit for illumination. e


Conclusions

Daylight is the most efficient light source, its usage should be

maximize, even in overcast conditions and with low sky illuminance

levels the benefits of taking advantage of it are large; good quality

lighting depends on daylight improving the work performance and

the user comfort perception. The savings on energy by using natural

lighting are considerable especially in commercial buildings.

There is a big difference between overcast and clear sky conditions,

the designer should be aware of it and approach the problem

accordingly. Knowing the sun path is not sufficient for accomplishing

a successful daylight design; the sky illuminance levels distributions

in both cases have to be considered. The clear skies frequency

is an important data as well, will define which situation is more

predominant and consequently how to approach the design problem.

A complete daylight design should consider both sky types and

respond accordingly.

The research confirmed that light shelves are more efficient during

clear sky conditions; however still represent a solution for the overall

design. Dividing the façade in two different areas, one for lighting and

the other for viewing brings lots of benefits, and helps to deal with

them in different ways depending on the requirements. Openings

in the roof are the best illumination option in overcast conditions;

even for an office tower; mixing these openings with redirecting light

elements gives good results.

Reflectance is a very important material property that should be take

in count in all daylighting designs, adequate geometry is not sufficient

for achieving successful results, for a good design: geometry, material

properties and light sources should be taken in count.

Recommended Further Steps

The next research stage should be an analysis with clear sky conditions;

this will help to define if the light shelf inclination is needed, the

advantages of rotating light shelves and its influence in illuminance

levels. This analysis will also help to design the sun shading systems

for both parts of the façade (day lighting & viewing), and to determine

the optimum openings percentage for the viewing part; off curse

should be complemented with a thermal comfort analysis.

A luminance analysis should be performed as well, as is shown the

material reflectance is a determinant characteristic for improving

illumination. High reflectance materials for the light shelves and the

ceiling should be considered; all the material should be defined and

simulations performed. With these results a glare analysis should be

performed as well. The façade setback should be defined according

the whole tower profile.

Energy savings and artificial lighting integration analysis should be

performed to maximize the design benefits. In the search for a good

quality lighting design, this research is just the first step; further studies

have to be performed in relation with the user comfort perception.

Figure f.1Luminance Levels Render


f

Literature

1. Moore Fuller, Concepts and Practice of Architectural Daylighting,

Van Nostrand Reinhold, New York, 1991

2. Ruck Nancy, Daylight in Buildings, Internacional Energy Agency,

New York 2000

3. Ernst and Peter Neufert, Neufert Architects data, Blackwell

Science

4. Selkowitz Stephen, Richard Johnson, The daylighting solution,

Lawrence Berkeley Laboratory, University of California, Berkeley

California 94720

5. Loveland Joel, Dayligth by design, BetterBricks Daylighting Lab,

Seatle

6. Scartezzini Jean-Louis, Innovation and Daylighting in Buildings,

Solar Energy and Building Physics Laboratory, Swiss Federal Institute

of Technology, Lausanne

7. Sethi Amarpreet, A Study of Daylighting Techniques and their

Energy Implications using a Designer Friendly Simulation Software,

College of Architecture and Environmental Design, Arizona State

University

8. Assaf Leonardo, Glare and Illuminance Uniformity as Components

of Innovative Glazing Performance, Institiuto de Luminotecnia,

Universidad de Tucuman, Argentina

9. LEED for New Constructiion & Major Renovations, U.S. Green

Building Council, October 2005

10. Sethi Amarpreet, Study of daylighting techniques and their energy

implications using a designer friendly simulation software, College

of Architecture and Environmental Design, Arizona State University

Internet

- Daylighting Design, School of Architecture, University of Hawaii, www.arch.

hawwaii.edu/site/calss/arch316

- Lighting Design, Autodesk Ecotect, http://squ1.org/wiki/Lighting_Design

- The sun, Autodesk Ecotect, http://squ1.org/wiki/The_Sun

- Confortable Low Energy Architecture (CLEAR), http://www.learn.londonmet.

ac.uk/packages/clear/index.html

- CLEAR Comfortable Low Energy Architecture, http://www.learn.londonmet.

ac.uk/packages/clear/index.html

- How Daylighting Can Improve IEQ, Mike Molinski, LEED AP, January

2009http://www.facilitiesnet.com/lighting/article/How-Daylighting-Works--

10445

g


Appendix A

These sets of images correspond to the simulations made for analyzing

the base proposal; these results were the base for the matrix results

(figure e.9). They represent different configurations by altering the

room height, the light shelf position and facade the setback.

g


Appendix B

Design Redefinement

After finishing this research, the design of the whole business complex

continued, the office tower was redefined in its interior setting: the

floor plan was subdivided into modular offices, instead of an open

floor plan; to fulfill the existing commercial trend requirements. No

structural elements were used to create the subdivision allowing

choosing between an open floor plan, a subdivided one, or a mix or

both (figure g.2).

To optimize the office modules area the columns were replaced by

a central structural core, freeing all the floor plan and easing the

internal subdivision. The floors are supported by stainless steel

tension rods which hang from a steel space frame matrix at the top of

the tower. The space frame matrix distributes the loads two the two

structural cores which take the loads to the fundation (figure g.1).

The new central core serves as a natural ventilation and daylighting

device running trough the whole height of the tower. The office cabins

g

Figure g.1Project Longituninal Section

Figure g.3Office Module Section

Figure g.2Office Tower Floor Plan & Office Module


g

are distrubuted along the outside perimeter of the tower, while in

the central part next to the core, the meeting rooms and auxiliary

functions are located.

Natural ventilated atriums were placed every four floors in the

bottom part of the tower and every three floors in the top part. All

the atriums face South and aid with the building thermal behaivor

and bring daylight to the deepest areas of the tower.

In essence the façade design remained the same; the final dimensions

were defeined and a basic interior arrangement of the office cabin was

proposed; one module of 22m2 will house two users (figure g.2). The

section of the façade for viewing is 2,4m high, with thermal double

glazing openable window; and the section for lighting is 0,8m high

with high light transmittance glazing; this part is the most exposed to

solar heat gain, for that reason this area of the façade is composed

by three different layers: the exterior layer is a double glazing fixed

panel, then a 400 mm cavity which serves as air exhaust as well, and

a single glazing openable panel in the interior (figure g.3). Both parts

of the façade have tension textile sunshading systems. The exterior

elements which serve as a lightshelf and as a sunshading device are

white coloured GFRC panels (figure g.4).

Figure g.7Office Module Daylight Factors

Figure g.4Facade Module 3D Model

Figure g.6Office Module Interrior Impression

Figure g.5Office Module 3D Model


g

Validation

An office module then was modeled and analysed with the same

previous metodology (figure g.5-g.7), first the Illuminance levels

for the worst case escenario were simulated, and then the Daylight

Factors were also calculated.

Illuminance Levels

The simulation was performed in the Winter Solstice with Overcast

Sky, the worst case escenario. The results show (figure g.8) that 300

Lux is the maximun level reached in the surface of the desk, near the

façade; the lowest value is araound 130 Lux in the deepest part of the

room. The minimun requirement for an office task is 500 lux; there is

Figure g.10Illuminace Levels in Winter Solstice, Ovecast Conditions. False Color Overlay

Figure g.9Illuminace Levels in Winter Solstice, ovecast conditions

Figure g.8Illuminace Levels overlaid in office module floor plan

Figure g.11Illuminace Levels in Winter Solstice, Ovecast Conditions. Line Color Overlay


g

still 200 Lux deficit that have to be completed with artificial lighting.

Daylight Factors

These calculations were also made in the Winter Solstice with Overcast

Sky. As expected the higher Daylight Factors are located in the area

close to the façade; 6,4%DF is the maximun value reached in the desk

surface, in the deepest part of the room a 2.9%DF is achieved (figure

g.12).

Final Results

Using the 6.4%DF is possible to deduct which is the needed outside

Illuminace level to achieve at least 500 Lux. By dividing the Daylight

Figure g.12Daylight Factors Overlaid in Office Module Floor Plan

Figure g.14Daylight Factors in Winter Solstice, Ovecast Conditions. False Color Overlay

Figure g.13Daylight Factors in Winter Solstice, ovecast conditions

Figure g.15Daylight Factors in Winter Solstice, Ovecast Conditions. Line Color Overlay


Factor between the required Illuminance Level: 7.800Lux are needed

in the outside to achieve a 500Lux in the interior 1.

Translating this data to the Daylight Usage Graph, is deducted that

75% of the office time troughout the year a minimun of 500 Lux will

be reached. In other words 75% of the time artificial lighting won’t

be needed, in the other 25% of the time artificial lighting will be

required to fulfill the minimun requirements, the use of dimming and

swtiching systems in concordance with daylight availabilty should be

consider to minimize the energy usage for lighting. In the worst case

scenario dayligthing contributes with 300 Lux and the lasting 200 Lux

have to be provided with artificial lighting.

The other main benefit of this façade is that compared to a tradicional

glass curtain façade, has 30% less glazing area; in rough numbers this

façade will have 30% less heat gain, improving its thermal behavoir.

gFigure g.18

Luminace Impression, Winter Solstice, Clear Sky Conditions

Figure g.17Luminace Impression, Winter Solstice, Overcast Conditions

Figure g.16Daylight Usage Graph

1

Ext. illuminance = Int. illuminance/DF

DF= 0,064

Required int. illuminance = 500 Lux

Needed ext. illuminance = 7 800Lux


Daylight Respondent Envelope Design

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