1. +
Daylighting Environment in
Hong Kong
By Dr Ernest K W TSANG
Sustainability Consultant, Parsons Brinckerhoff

2. +
2
Agenda
Why Daylight?
Parameters affecting Indoor Daylighting Environment
Daylighting Performances of Commercial Building in Hong Kong
Daylighting Assessment Criteria for Green Buildings

3. +  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
Why Daylight?
“On studying the Causes and Motives
of Nature, the Observer is
Fascinated, above all, by Light.” –
Leonardo da VINCI

4. +
Parameters affecting Indoor
Daylighting Environment
A Snap Shot Study on 35 Buildings from 1960s to mid 2000.
4

5. + 5
Key Parameters
 Building Area and Orientation
 Glass Type
 Window Area
 Shading
 External Obstruction

6. 6
+ Building Area and
Orientation
Effect – Increasing Internal Area reduces the
Daylight Factor (DF)
Building Area varies
No Strong Orientation Effect

7. 7
+
Glass Type
Effect – 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
 Effect Glazing Type WWR
 Amount of Natural Light Clear 36.4%
admits into Building Directly
Tinted 42.0%
Proportional to Window Area
Reflective 44.0%
 Window Area are expressed in Low-E 46.5%
Window to Wall Ratio (WWR)

10. +
Shading were found
for Buildings
completed before
mid-80s and after
late 90s
Shading
Shade Window from Direct Sunlight Penetration
but allows Diffuse Skylight to admit
10

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External Obstruction
 Effect Obstruction Percentage
 Obstructs Part of Sky Angle (θb) (%)
 Reflects Skylight and
Sunlight θb≤30° 25
30° <θb ≤ 60° 45
60°<θb ≤ 80°
 Most of the External Finishing
30
are with Light to Medium Colour

12. Daylighting Performances of
+ Commercial Building in Hong
Kong
A study of Two Commercial Buildings by Simulation
12

13. +  Two Buildings were selected for Detail 13
Analysis
 Daylighting Analysis was Conducted
using RADIANCE
 The CIE Standard Overcast Sky was
selected for Simulation Study
Daylighting
Performances of  The following three performances were
Commercial Building in analysis
Hong Kong  Indoor Illuminance
 Daylight Glare Index
 Annual Lighting Energy Projection
13

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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
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
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

27. + Daylighting Assessment Criteria
for Green Buildings
Different Daylight Assessment Criteria
27

28. Green Buildings
+ 28
Commonly used Assessment Criteria
 PNAP
 LEED
 BEAM Plus

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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 1
Terms 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
Indirect Sun
Component Direct Sky
(145 or 580 Component
sets (aimed ray)
simulation)
Direct Sun Indirect Sky
Component (by Component
neglectable (145 or 580
time for sets
simulation) Overall simulation)
Illuminance
Level

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43
Questions
& Answer
Thank you
28th March 2012