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Daylighting Environment in
Hong Kong
By Dr Ernest K W TSANG
Sustainability Consultant, Parsons Brinckerhoff
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AgendaWhy Daylight?
Parameters affecting Indoor Daylighting Environment
Daylighting Performances of Commercial Building in Hong Kong
Daylighting Assessment Criteria for Green Buildings
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Why Daylight?
Improves Circadian Photobiological
Activation
Prevents Sick Building Syndrome
Enhances the Phase Synchronising
Ability of Light
Has Positive Effects on Sociability and
Hormone Patterns
Provides Energy Saving Opportunities
“On studying the Causes and Motives
of Nature, the Observer is
Fascinated, above all, by Light.” –
Leonardo da VINCI
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+Parameters affecting Indoor
Daylighting EnvironmentA Snap Shot Study on 35 Buildings from 1960s to mid 2000.
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+Key Parameters
Building Area and Orientation
Glass Type
Window Area
Shading
External Obstruction
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+ Building Area and
OrientationEffect – Increasing Internal Area reduces the
Daylight Factor (DF)
Building Area varies
No Strong Orientation Effect
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+ Glass TypeEffect – Visible Transmittance of
Glass affects the DF directly
Major Glazing include Clear, Tinted,
Reflective and Low-e
Trend is observed for the Selection
of Glazing during the Past Five
decades
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+Glass Type
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+Window Area
Glazing Type WWR
Clear 36.4%
Tinted 42.0%
Reflective 44.0%
Low-E 46.5%
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Effect
Amount of Natural Light
admits into Building Directly
Proportional to Window Area
Window Area are expressed in
Window to Wall Ratio (WWR)
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Shading
Shade Window from Direct Sunlight Penetration
but allows Diffuse Skylight to admit
Shading were found for Buildings
completed before mid-80s and after
late 90s
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+External Obstruction
Obstruction
Angle (θb)
Percentage
(%)
θb≤30° 25
30° <θb ≤ 60° 45
60°<θb ≤ 80° 30
Effect
Obstructs Part of Sky
Reflects Skylight and
Sunlight
Most of the External Finishing
are with Light to Medium Colour
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+Daylighting Performances of
Commercial Building in Hong
Kong
A study of Two Commercial Buildings by Simulation
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Daylighting
Performances of
Commercial Building in
Hong Kong
Two Buildings were selected for Detail
Analysis
Daylighting Analysis was Conducted
using RADIANCE
The CIE Standard Overcast Sky was
selected for Simulation Study
The following three performances were
analysis
Indoor Illuminance
Daylight Glare Index
Annual Lighting Energy Projection
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+The CIE Standard Overcast Sky
General Equation of Overcast
sky is shown as below:
The Luminance at Zenith is 3
Times of That for the Horizon
Independent with Solar Position
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+Daylight Glare Index (DGI)
Glare from Windows can arise from Excessive Contrast
between the Luminance of the Visible Sky and the Luminance
of the Internal Surfaces within the Field of View.
Threshold DGI of 22
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+Building A
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Plan of Building Model Details
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+Building A - South-facing
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+Building A - West-facing
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+Building A - North-facing
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+Building A – DGI
Orientation Daylight Glare Index
Lowest Floor Middle Floor Highest Floor
North 14.0 16.3 19.1
South 13.8 18.5 19.0
West 10.9 16.4 17.0
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+Building B
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Plan of Building Model Details
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+Building B - Northeast-facing
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+Building B - Southeast-facing
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+Building B - Southwest-facing
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+Building B - Northwest-facing
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+Building B – DGI
Orientation Daylight Glare Index
Lowest Floor Middle Floor Highest Floor
Northeast 19.6 18.6 19.4
Southeast 16.1 16.7 17.8
Southwest 17.6 15.9 17.5
Northwest 18.4 17.8 19.3
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+ Daylighting Assessment Criteria
for Green Buildings
Different Daylight Assessment Criteria
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+Green Buildings
PNAP
LEED
BEAM Plus
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Commonly used Assessment Criteria
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+PNAP APP-130 Lighting and Ventilation
Requirements – Performance-based
Approach Vertical Daylight factor: 8% for Habitable Room; 4% for Kitchen
Assume the window area is 10% of the usable floor area.
Under the standard CIE Overcast sky condition
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+BEAM Plus
1 Credit where at least 80% of Floor Area in all Normally
Occupied Spaces is adequately lit with an Average Daylight
Factor of 2% or more.
1 Credit where provision of Suitable Daylight Glare Control and
Maintaining the Average Daylight Factor of 2%.
-> the CIE standard Overcast Sky
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+LEED 2.2
Option 1 – Glazing factor Calculation
Achieve a min Glazing Factor of 2% in a minimum of 75% of all
Regularly Occupied Areas.
Option 2 – Daylight Simulation Model
Min Daylight Illuminance level of 25fc achieved in a min 75 %of all
Regularly Occupied Areas.
The CIE Standard Clear Sky in noon of Equinox
Option 3 – Daylight Measurement
Option 4 - Prescriptive
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+LEED 2009
Option 1 – Simulation
75% or more regularly Occupied Space achieve daylight illuminance
levels of a min. of 25 fc and a max 500fc in a clear sky condition on
21 September 9:00 and 15:00
Option 2 – Prescriptive
Option 3 – Measurement
Option 4 – Combination
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+LEED 2012 (based on draft 3)
Provide manual or automatic glare devices for all regularly occupied spaces
Option 1 – through Annual Computer Simulations, achieve Daylight Autonomy value of 55% (2 points) or 75% (3 points) regularly occupied spaces.
Option 2 – Using a model, achieve required illuminance levels for 75% (1 point) or 90% (2 points) regularly occupied spaces
Option 3 – Using direct measurements, achieve required illuminance levels for 75% (1 point) regularly occupied spaces
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+ Are We Ready for the New Version?Parsons Brinckerhoff’s Approach
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+Which Option are we
recommended?
Option 2 is recommended.
Only two different sets ofSimulation
Similar to LEED 2009 Option 1 with followingRefinements:
1. Standardise outdoor illuminance levels from Typical
Meteorological Year (TMY)
The AVERAGE of the Two Time Slots
Reflectance (Ceiling 0.8; Floor 0.2; Wall 0.5)
No Furniture layout is required
What are still unclear?
How to calculate Illuminance for Sun and Sky Components?
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Option 1Terms and Criteria
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+Spatial Daylight Autonomy
“The % of Aggregate Floor Area of Regularly Occupied Spaces
which achieves a minimum highly Illuminance value of 300 lux
at task level for at least 50% of the hours between 8am to 6pm,
Local Clock Time, after accounting for Typical Weather
Conditions, Exterior Obstructions, Attached Furniture
Systems and after Blinds have been operated hourly to block
direct sun predicted to enter the space that would fall on more
than 2% of the calculation grid.”
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+Criteria
achieve Daylight Autonomy value of 55% (2 points) or 75% (3
points) regularly occupied spaces.
No more than 10% of any qualifying daylight space could
receive direct sunlight for more than 250 hours per year at task
level before operable blinds or shades are deployed and after
accounting for exterior obstruction, typical weather, and
attached furniture system
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+Problems Ahead
Weather Data
TMY does not include any Illuminance Information
No Sky Distribution Pattern is Defined
Simulation Time
Over 3,650 sets Simulation
How to predict Direct Sun/Shadowing?
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+Weather Data
Sun and Sky Illuminance values
Illuminance Data would be calculated from Irradiance Data of TMY
Sky Luminance Distribution Data
Based on ASRC-CIE Model/Perez’s sky Model
Based on the latest the CIE Standard Skies
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+Daylight Coefficient Approach
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+Simulation method
Overall Illuminance
Level
Direct Sun Component (by
neglectabletime for
simulation)
Indirect Sun Component (145 or 580
sets simulation)
Direct Sky Component (aimed ray)
Indirect Sky Component (145 or 580
sets simulation)
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Thank you
28th March 2012
Questions
& Answer
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