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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

+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

+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

+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

+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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