Daylight Design Formulae and Their Implimentation

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DAYLIGHT DESIGN

FORMULAE AND THEIR

IMPLIMENTATION

“Architecture is the masterly, correct, and

magnificent play of masses

magnificent play of masses brought

brought

together in light. Our eyes are

together in light. Our eyes are made to see

made to see

forms in light; light and shade reveal these

forms."

Le Corbusier Le Corbusier

SUBMITTED BY SUBMITTED BY

SUMITABH CHOWDHURY SUMITABH CHOWDHURY B.ARCH,3

B.ARCH,3RDRD _YEAR,6_YEAR,6 TH TH _SEM_SEM

MITS,GWALIOR MITS,GWALIOR

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Separate evaluation of:

Different conditions regarding

daylight

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Bad daylighting design with

DFs

.Entrance of daylight is from .Entrance of daylight is from rare side

rare side

Because of that the presentation Because of that the presentation board shines thus reflects back board shines thus reflects back to the viewers eyes

to the viewers eyes Due improper daylight Due improper daylight

electricity is used to light the electricity is used to light the room, hence energy

room, hence energy consumption

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Reasons for the success of the

Daylight approach:

••

•If the natural lighting is sufficient on an

•If the natural lighting is sufficient on an overcast day,

overcast day,

it is likely to

it is likely to be more than adequa

be more than adequate when the sun is

te when the sun is

shining.

••

•But ... a daylight factor optimized building admits as

much light as possible, therefore the ideally daylight

building would be fully glazed! This is clearly in

contrast with comfort requirements.

••

•A densely overcast sky looks the same whichever

direction one faces -North, South, East or West.

Therefore the effect of

Therefore the effect of the orientation vanishes from

the orientation vanishes from

the calculation.

••

•But ... the simplification introduced with the use of

the daylight factor does not account for building

location and orientation, season, time of

location and orientation, season, time of day, direct

day, direct

solar penetration, variability of sky conditions. It is not

possible to predict glare.

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Lighting exposure on windows

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Architect’s intentions

••

Let daylight in

••

_{Modulate daylight through}

translucent materials (alabaster,

paper,fibre glass)

••

previously this technique was used in

churches

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Use of daylight using

skylights

••

_{By using skylight we can use the}

sunlight to light the room

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Analysis

•• Shadows cast on a dwelling by eaves and Shadows cast on a dwelling by eaves and treestrees

•• Shadows cast in a stadium from stand and Shadows cast in a stadium from stand and lighting towerslighting towers

•• Reflection study showing reflections from building onto street andReflection study showing reflections from building onto street and adjacent buildings

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Description

For a given mean daylight factor this

method calculates from

1. the reflectance of the room surfaces,

2. the room dimensions,

3. the glazing parameters (transmission,

framing factor, and dirt-on-glazing factor),

4. and the type of rooflight with the

geometric parameters of the light wells

the necessary total rooflight area.

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solar light factor SF2 as function of

distance from the

window and window percentage (of

facade)

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••

_{Properties of}

different

materials which

are used in

buildings

••

_{Their scattering}

property

••

Their thickness

,reflection,perm

eability,absorpt

Properties of materials

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Heating requirement and

sunshine duration

Heating requirement and global radiation are inversely Heating requirement and global radiation are inversely propertional to each other

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approach

•• The DF is the standard recognised daylighting metric in any The DF is the standard recognised daylighting metric in any

place in the World where

place in the World where there is an interest in there is an interest in daylighting.daylighting.

••

_{Reasons for the success of the DF}

_{Reasons for the success of the DF approach:}

_approach:

•• If the natural lighting is sufficient on If the natural lighting is sufficient on an overcast day, it isan overcast day, it is

likely to be more than ade

likely to be more than adequate when the sun is shining.quate when the sun is shining.

•• But ... a daylight factor optimised building admits as muchBut ... a daylight factor optimised building admits as much

light as possible, therefore the ideally daylit building would light as possible, therefore the ideally daylit building would be fully glazed! This is clearly in c

be fully glazed! This is clearly in contrast with comfortontrast with comfort

requirements. requirements.

•• A densely overcast sky looks the same whA densely overcast sky looks the same whichever directionichever direction

one faces -North, South, East or West. Therefore the effect one faces -North, South, East or West. Therefore the effect of the orientation vanishes from the calculation.

of the orientation vanishes from the calculation.

•• But ... the simplification introduced with the use But ... the simplification introduced with the use of theof the

daylight factor does not account for building location and daylight factor does not account for building location and orientation, season, time of day, direct solar penetration, orientation, season, time of day, direct solar penetration,

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lighting simulation

•• Input: 1) weather data, 2) Input: 1) weather data, 2) 3D model, 3) sensor points3D model, 3) sensor points

•• Pre-process: calculation of daylight coefficients to savePre-process: calculation of daylight coefficients to save

time. If dynamic daylighting systems are used, such as time. If dynamic daylighting systems are used, such as movable blinds, sun tracking systems, electrochromic movable blinds, sun tracking systems, electrochromic

glazing, etc., different sets of daylight coefficients need to glazing, etc., different sets of daylight coefficients need to be calculated.

be calculated.

•• Simulation: coupling of daylight coefficients with climateSimulation: coupling of daylight coefficients with climate

data over the chosen time

data over the chosen time basis and occupancy profile. Forbasis and occupancy profile. For

dynamic systems, a control algorithm triggers the use of dynamic systems, a control algorithm triggers the use of the different set of daylight coefficients.

the different set of daylight coefficients.

•• Results: time series of Results: time series of illuminance and/or luminanceilluminance and/or luminance

(annual, seasonal, daily, etc ...) (annual, seasonal, daily, etc ...)

•• Post-process: time series can be plotted, and otherPost-process: time series can be plotted, and other

indicators can be calculated

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Windows options

S

Sttaattiic c ddiiffffuussiinng g ffaabbrriic c bblliinnddss SSeeaassoonnaalllly y aaddjjuusstteed d bblliinnddss,, manual control

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Automatic open/close roller Automatic open/close roller blinds

blinds Automatic venetian blindsAutomatic venetian blinds

Light level control -three luxlevel control that allows the Light level control -three luxlevel control that allows the slats to adjust to

slats to adjust to maintain light levels within a selectedmaintain light levels within a selected band width.

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Fixed interstitial louvres Fixed interstitial louvres

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Average Daylight Factor

•• The average daylight factor is the ratio between the mean illuminance in a The average daylight factor is the ratio between the mean illuminance in a space and that from an unobstructed sky externally expressed as a

space and that from an unobstructed sky externally expressed as a

percentage. In calculation terms the sky is generally assumed to be the CIE percentage. In calculation terms the sky is generally assumed to be the CIE overcast sky. It is measured or predicted on the working plane that for

overcast sky. It is measured or predicted on the working plane that for domestic buildings is assumed at 0.85m. There are two formulae that give domestic buildings is assumed at 0.85m. There are two formulae that give an average daylight factor, Sumpner’s and the BRE

an average daylight factor, Sumpner’s and the BRE average daylight factoraverage daylight factor formulae. Both are based on a ratio of the window area

formulae. Both are based on a ratio of the window area to the surface areato the surface area of the room, with corrections for

of the room, with corrections for any obstructions, glass transmission andany obstructions, glass transmission and room reflectance.

room reflectance.

•• BRE formula : DF = θTW/A ( BRE formula : DF = θTW/A ( 1-R2)1-R2)

•• Sumpner’s formula: DF = θTW/2A(1-R)Sumpner’s formula: DF = θTW/2A(1-R)

θ is the angle of obstruction measured from the mid-point of the window θ is the angle of obstruction measured from the mid-point of the window T is the light transmission of glazing

T is the light transmission of glazing W is the window area

W is the window area A is the area of all

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••

Alternatively the average daylight factor can be

calculated using a

calculated using a variety of computer programs

variety of computer programs

which determine the daylight factor on

predefined grid and take the average. It is clear

that the latter method will give a more accurate

result, but the former is particularly useful at an

early design stage.

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VARIOUS TEST ROOMS

••

Not only numerical but also visual information is

included. This gives a fast understanding of the

visual perception of daylight in rooms. A powerful

simulation tool has been used to show the strong

impact of simple modifications of basic

daylighting design parameters like window size

and placement. The study is not suited for

thorough numerical analysis; it should rather be

understood as design guide for architects and

building designers in the early conception of a

building. The study has

building. The study has been performed for Swiss

been performed for Swiss

conditions, thus some of the

conditions, thus some of the provided information

provided information

is restriced to Swiss latitudes, climates, and

regulations.

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Application Example

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Daylight performance at the lower floors of high-rise

residential development was very poor. VDF of

approximately 6% to 8% were recorded. The room

average

daylight factor for habitable rooms was typically in

the

order of 0.2%, whilst kitchens located at the rear

end of a

deep re-entrant recorded close to 0.0% - ha

deep re-entrant recorded close to 0.0% - hardly any

rdly any

light at all. (F

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•• Daylight performance of Daylight performance of a typical residential unit a typical residential unit in high density sites in in high density sites in Hong Kong. Daylight Hong Kong. Daylight

Factor at the rear of the Factor at the rear of the space is about 0.2%

space is about 0.2%

•• (Right), the window(Right), the window

facing into a narrow facing into a narrow space and obstructed space and obstructed by an opposing building by an opposing building is allowed by the is allowed by the building regulations. building regulations. (Left), the window (Left), the window facing directly a high facing directly a high block but with an open block but with an open aspect on its left is not aspect on its left is not permitted.

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Some key problem areas were identified. Whilst satisfying the building Some key problem areas were identified. Whilst satisfying the building

regulations, these windows do not provide adequate daylight to regulations, these windows do not provide adequate daylight to their respective interior spaces.

their respective interior spaces.

(A) Windows placed inside deep re-entrant (local term for (A) Windows placed inside deep re-entrant (local term for

deep recesses from the main façade). deep recesses from the main façade).

(B) Windows facing into narrow streets where no height (B) Windows facing into narrow streets where no height

restriction in force. restriction in force.

(C) Windows placed in the ‘large’ light well formed by (C) Windows placed in the ‘large’ light well formed by

surrounding building blocks. surrounding building blocks. (D)

(D) The misuse The misuse of of the regulatory the regulatory Rectangular HorizontalRectangular Horizontal Plane (RHP). This results in tight spaces being formed Plane (RHP). This results in tight spaces being formed between building blocks.

between building blocks.

(E) Windows not properly positioned in the space. (E) Windows not properly positioned in the space.

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..

simulated daylight

performance

•• At the same time, daylightAt the same time, daylight

performances of around 6000 performances of around 6000 windows of the 12 housing windows of the 12 housing estates were computed using estates were computed using simulated results (Figure 5). simulated results (Figure 5). Lightscape was used as it has Lightscape was used as it has been noted previously that it been noted previously that it could cope with high-density could cope with high-density

conditions reasonably well. From conditions reasonably well. From the computed results, daylight the computed results, daylight availability of the windows of availability of the windows of each of the residential unit that each of the residential unit that were user surveyed was

were user surveyed was

identified and coded into the identified and coded into the survey forms. The performance survey forms. The performance data of each of the space and data of each of the space and the associated user responses the associated user responses

User satisfaction vs. User satisfaction vs. simulated daylight simulated daylight performance performance

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TOWARDS A NEW DESIGN AND REGULATORY

METHOD

•• How to formulate a simple method fHow to formulate a simple method for daylight design andor daylight design and

building regulations is the next task. It is important to strike building regulations is the next task. It is important to strike for “simplicity” and “reasonable accuracy” at the

for “simplicity” and “reasonable accuracy” at the samesame

time. time.

•• A method based on a tA method based on a two-dimensionawo-dimensional “the visible areal “the visible area

/volume in front of the window” was first speculated – on a /volume in front of the window” was first speculated – on a napkin during a dinner session! It was considered very

napkin during a dinner session! It was considered very similar in spirit to the existing regulatory Rectangular similar in spirit to the existing regulatory Rectangular

Horizontal Plan (RHP) requirements. The method was based Horizontal Plan (RHP) requirements. The method was based on modifications a more accurate three-dimensional sky

on modifications a more accurate three-dimensional sky component overlay method developed by Tregenza.

component overlay method developed by Tregenza.

•• The new method, dubbed the The new method, dubbed the Unobstructed Vision AreaUnobstructed Vision Area

Method (UVA) is a simple method suitable for h

Method (UVA) is a simple method suitable for high-rise,igh-rise,

high-density development. The method is not high-density development. The method is not fundamentally new. R G

fundamentally new. R G Hopkinson proposed similarHopkinson proposed similar

offering before. The Unobstructed Vision Area (A) is offering before. The Unobstructed Vision Area (A) is

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••

[Take a cone of light φL+φ

[Take a cone of light φL+φR=100° from the

R=100° from the

window, given a vertical obstruction angle of

θL=71°, the mathematical formula relating the

horizontal area in front of the window (A) and the

Height of the building (H) can be given here, k is

a constant relating A with H2. ]

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Ray-Tracing Techniques

•• The ray-tracing technique determines the visibility of The ray-tracing technique determines the visibility of

surfaces by tracing imaginary rays of light from a viewer’s surfaces by tracing imaginary rays of light from a viewer’s eye to the objects of a rendered scene. A centre of

eye to the objects of a rendered scene. A centre of projection (the viewer’s eye) and an

projection (the viewer’s eye) and an arbitrary view planearbitrary view plane

are selected to render the scene on a picture plane. Thanks are selected to render the scene on a picture plane. Thanks to the power of

to the power of novel computer algorithms and processors,novel computer algorithms and processors,

millions of light rays can be traced to

millions of light rays can be traced to achieve a high-achieve a

high-resolution rendered picture. resolution rendered picture.

•• Originally developed for imaging purposes, some Originally developed for imaging purposes, some ray-

ray-tracing programmes (e.g., RADIANCE, GENELUX, and tracing programmes (e.g., RADIANCE, GENELUX, and

PASSPORT) were adapted and optimised for calculation of PASSPORT) were adapted and optimised for calculation of daylighting within building spaces [Ward and Rubinstein daylighting within building spaces [Ward and Rubinstein 1988]. In this case, light rays are t

1988]. In this case, light rays are traced until they reach theraced until they reach the

main daylight source, which is usually the sun position main daylight source, which is usually the sun position (clear and intermediate skies) or the

(clear and intermediate skies) or the sky vault (cloudysky vault (cloudy

skies). Figure 6-3 illustrates the principle of ray tracing, skies). Figure 6-3 illustrates the principle of ray tracing,

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•• Most daylighting and electric lighting calculationMost daylighting and electric lighting calculation programmes currently use this backward

programmes currently use this backward ray-tracingray-tracing

technique (from the viewpoint to the

technique (from the viewpoint to the source). A slightlysource). A slightly

different technique is used by

different technique is used by some software to improvesome software to improve

daylighting calculations, especially for clear sky

daylighting calculations, especially for clear sky conditionsconditions

(with sun). A forward rather than backward

(with sun). A forward rather than backward ray-tracingray-tracing

technique is used by the GENELUX programme to

technique is used by the GENELUX programme to followfollow

rays from the light source to a scene. rays from the light source to a scene. The principal features of the

The principal features of the ray-tracing technique for all typesray-tracing technique for all types

of light calculations are the following: of light calculations are the following: • the method accounts for

• the method accounts for every optical phenomenon that canevery optical phenomenon that can

be analytically expressed by physical e

be analytically expressed by physical equations;quations;

• the method can

• the method can consider specular materials, like windowconsider specular materials, like window

panes and glossy surfaces; panes and glossy surfaces;

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Sky Simulators

View of the EPFL View of the EPFL scanning sky scanning sky simulator simulator the BRE the BRE mirror sky mirror sky (UK), (UK),