Enhancing Energy Efficiency of Built Environment through Daylighting Ir. Yiu-chung WU Senior Building Services Engineer The Government of the Hong Kong SAR Dr. Danny H.W. LI City University of Hong Kong

Enhancing Energy Efficiency of Built Environment through Daylighting  Daylight through Light Transportation System  Daylight through Window

Light Transportation Systems  Sun Pipe System  Hybrid Solar Lighting System

Sun Pipe System Design Concept  Tubular skylight with reflective pipe  Collects daylight on rooftop  Guides daylight down  Diffuses daylight into the building interior

Sun Pipe System Components Dome  consists of clear polycarbonate curved reflector to capture daylight and light intercepting transfer device to redirect daylight  increases the daylight collection and harvest for low sun angles

Sun Pipe System Components Pipe  consists of a very high reflective internal finish with 98% to 99.7% reflectance  straight run or with elbow to convey daylight

Sun Pipe System Components Ceiling diffuser

Sun Pipe System Performance Depends on  location  climate  weather

Sun Pipe System Performance Limitation  in vertical length 530mm – 13m 350mm – 10m 250mm – 6.5m  horizontal run not recommended  one dome supplies one diffuser point only

Sun Pipe System Case Study Electrical and Mechanical Services Department Headquarters  10 nos. 250mm sun pipe  at a corridor on the top floor  artificial lights (CFT) to back up

Sun Pipe System Case Study Diffusers

Sun Pipe System Case Study Domes

Sun Pipe System Case Study Diffuser of sun pipe (right) Artificial light (left)

Sun Pipe System Case Study Results of half months’ measurements in December 2005 TimeIndoor LuxOutdoor LuxWeather Condition 09:00-10: Foggy to sunny 10:00-11: >100000Foggy to sunny 11:00-13: >100000Foggy to sunny 13:00-15: Very foggy to sunny 15:00-17: Foggy to sunny

Sun Pipe System Observation and Discussion  To be installed with artificial lighting with photo sensor  Can direct daylight to more interior areas; and can provide more stable and uniform artificial daylight than skylight  Recommended for obvious energy and environmental benefits  Initial cost is not very attractive and competitive at present; but expected to be lower after further development and advancement of material and equipment

Hybrid Solar Lighting System Design Concept and Case Study Sacramento Municipal Utility District  1200mm diameter roof- mounted solar collector to concentrate daylight into a bundle of optical fibres

Hybrid Solar Lighting System Design Concept and Case Study  Infra-red and ultra- violet filter to filter out unwanted heat to the interior which can further save energy for cooling

Hybrid Solar Lighting System Design Concept and Case Study  Automatic sunlight tracking system to rotate the collector to collect maximum sunlight

Hybrid Solar Lighting System Design Concept and Case Study  The optical fibres are very flexible and configurable, hence require a small penetration through the roof allow light transmitted around and through complex building environment with bents of any angles

Hybrid Solar Lighting System Design Concept and Case Study  A bundle of 127 nos. optical fibres connecting the solar collector to the hybrid lighting fittings with a running length of 20m

Hybrid Solar Lighting System Design Concept and Case Study Hybrid lighting fittings connected  3 nos. fluorescent fitting each with 3 nos. 1200mm T8 tube and 2 nos. emitting rods each connected with 15 nos. of optical fibres  3 nos. 20W halogen spot light and 3 nos. incandescent lamp bulb each connected to 4 nos. of optical fibres

Hybrid Solar Lighting System Design Concept and Case Study  On a sunny day, the system can deliver 50,000 lumens (equivalent to 55 nos. of 60W incandescent lamps)

Daylight through Light Transportation System Conclusion  Various light transportation systems are available in the market which can transmit daylight effectively and efficiently  Two most mature systems are discussed, both of them have their pros and cons  Designers are encouraged to adopt the kind of system that suits their application to best use of daylight to achieve energy saving

Daylight through Window  Daylight is the best light source in the form of renewable energy  Lighting control by photo sensors with dimmers becomes mature  Proper lighting control integrated with daylight can reduce artificial lighting energy effectively  Prediction of indoor daylight illuminance is critical in the design of lighting control to achieve most optimal energy saving

Simplified Daylight Illuminance Prediction Method  Prediction of daylight illuminance is very complicated  Simulation computer software tools available are too sophisticated and time-consuming to run  A simple software tool would be very useful especially during preliminary design stage with different conceptual design schemes are being considered

Importance of Daylighting  Daylighting is an effective approach to have a more flexible building façade design strategy  Enhance a more energy-efficient building design (always an energy saver)  Provide visual comfort  Greener building development  People desire good natural lighting in their living and working environments

Estimation of daylight illuminance  A key step in evaluating daylighting performance  Once the daylight illuminance obtained, it is quite straightforward to compute the lighting energy savings  The presentation mainly for the indoor daylight illuminance estimation

Prediction method  Traditional daylight factor approach Based on CIE standard overcast sky only Simple Not flexible :Cannot cater for the dynamic variation of daylight illuminance for different solar positions under non-overcast sky conditions

The CIE Standard Skies  In 2003, the International Commission on Illumination (CIE) has adopted 15 standard skies  Containing 5 clear, 5 partly cloudy and 5 overcast skies  Covering the whole spectrum of usual skies found in nature

The CIE standard skies  The relative luminance distribution, l v, for a standard sky combining gradation function  (Z) and indicatrix function f(  )

The CIE standard skies  gradation function  (Z)  indicatrix function f(  )

 Classify the CIE standard skies for Hong Kong  Measured sky luminance were compared with modeled standard sky models to determine the root-mean-square error (RMSE):  The standard skies classified with the lowest RMSE The CIE Standard Skies

The CIE standard skies  Standard sky numbers 1 (overcast) and 13 (clear) are of the highest frequency of occurrence

Methodology  For daylight prediction, three components are involved Sky component (SC) Externally reflected component (ERC) Internally reflected component (IRC)  Only SC and IRC are considered in this program : For buildings facing small sky obstructions such as top floors in high-rise blocks or buildings located in low density business areas

Methodology  Internal daylight illuminance depends on the outdoor illuminance and exact sky luminance distribution at that time  The approach: relates the luminance distribution of the sky to the illuminance at a point in a room

Sky Component  is the sum of the sine function of the elevation for each the sky element that is seen by the reference point times solid angle times angle between the sky element and the line normal to the window facade  For those sky element which can be “seen” by reference point, it can expressed as:

Internally reflected component Lighting coming directly from the sky C 1 Reflected lighting coming from below the horizon C 2

A = the total area of all the interior surfaces R = the average reflectance of all the interior surfaces R cw = the average reflectance of the ceiling and upper walls above the mid-height of the window R fw = the average reflectance of the floor and lower walls below the mid-height of the window τ = the overall transmittance of the window W = the window area (i.e. they are building parameters) Internally reflected component

Internally Reflected component C 1 is the ratio of illuminance received by vertical window to the horizontal diffuse illuminance, E vd : C 2 : For overcast sky: For non-overcast sky: (For 0≤θ<π/2, -π/2<Φ-Φn<π/2; =0 otherwise)

Calculation Sequence Devise a set of factors for sky and Internally Reflected components Calculate a sky luminance distribution pattern Calculate hourly daylight level of a typical day of each month Predict lighting power consumption

Input and output of software Building Geometry Surface Reflectance Lighting Properties Illuminance Database Software Tool Indoor Illuminance level Lighting Power Consumption Lighting Energy Saving

User Interface Lighting Inputs Building Geometry Surface reflectance

A Case Study External Conditions Sky number1 (overcast) and 13 (cloudless polluted) Building height3m Building width along the window façadeinfinite Ground Reflectance20% ObstructionNone Room Parameters Room Length6m Room Depth6m””” Room Height3m Sill Height0.75m Window dimensions1.8m x 4.8m Ceiling Reflectance70% Wall Reflectance50% Floor Reflectance20% Glazing TypeClear, 85% transmittance External conditions and room parameters for validation:

Validation  For sky type 1, the estimated value by the software is 4.89% while RADIANCE is 4.32, the discrepancy is less than 0.6%.  The prediction by the software is slightly smaller than the prediction by RADIANCE.  The peak different between the software prediction method and RADIANCE is only 2.7% (for clear sky 13).  Using traditional CIE overcast sky pattern only would considerably underestimate the interior daylight illuminance.

Conclusions  The software can be used to estimate the indoor daylight illuminance and hence the likely electric lighting energy savings under CIE standard skies 1 and 13.  The software is convenient for architect and building engineers during initial design stage when different schemes and concepts are being considered

Enhancing Energy Efficiency of Built Environment through Daylighting Thank You