A Review of Daylight Design for Sustainable Building

1. A Review of Daylight Design for Sustainable Building WU, Bin 1155022517 2012.12.15

2. Introduction Fig.1 Sky light with large splayed distribution surfaces at Mt. Angel Abbey Library in St. Benedict, Oregon.

3. Historical review Ancient Egypt RomanEmpire Preindustrial architecture Innovations to free the building form Daylight was replaced by artificial light Industrial architecture energy crisis– return to make use of daylight Innovative technologies and materials of daylighting Postindustrial architecture Fig. 2 Conventional Greek and Roman atrium yards served as safe spaces and work spaces Fig. 3 Seagram Building designed by Mies van der Rohe with Philip Johnson

4. Daylight metrics & design guidelines The Daylight Factor（DF） Climate-based metrics：Daylight Autonomy（DA），Useful Daylight Illuminance（UDI）

5. The Daylight Factor（DF） Daylight Factor is defined as a ratio of interior illuminance at a point in a building to the external horizontal illuminance under the CIE (International Commission on Illumination) overcast sky. Daylight Factor indicates the efficiency of the building daylight system in harvesting the daylight from exterior environment. Limitations: disregard the direct sunlight, building orientation and the climate condition. Criteria and requirements of Daylight Factor can be found in codes or rating systems in many countries and areas.

6. Daylight Autonomy（DA） Daylight Autonomyis defined as the proportion of occupied time of a building when a minimum illuminance is maintained completely by daylight. Continuous Daylight Autonomy (DAcon) and Maximum Daylight Autonomy (DAmax) Objective: 1 credit for 40%< DAcon <60%, 2 credits for 60%< DAcon<80%, 3 credits for DAcon>80%. When using Max DA as a method, it is required that no more than 5% of the space having a DAmax>1%.

7. Useful Daylight Illuminance（UDI） UDI divides annual occurrence daylight illuminance into four defined ranges: 0-100 lux for fell-short UDI, 100-500 lux for supplementary UDI, 500-2000 lux for autonomous UDI, and over 2000 lux for exceeded UDI. The range of 100-2000 lux is for Useful Daylight Illuminance. Currently, there are no official recommedations or rating systems for the object of climate-based metrics.Whereas it is admittedly deemed that the quantified UDI is reasonable that occupants usually are more satisfied in rooms with interior illuminancein the range of 100-2000lux.

8. Discussion: factors influencing the interior Daylight illumination. Environment: location, sun path，cloudiness，the microclimate. Architectural Factors: orientation, building form. Daylight apertures: sidelight, rooflight, atria. Shading devices. Innovative daylight technologies: prismatic glazing, light pipes, light shelves.

9. Environment The relative position of the sun and the building Determine the shading devices because of the different solar latitude Sun path Sunny climates Cloudy climates The placement and size of daylight apertures shall have a sensible respond to sky condition Cloudiness Local condition: air pollution, obstructions, etc. The Microclimate

10. Architectural Factors—Orientation Usually implies the direction that main façade or facades face Benefits more from the main facades facing south and north, rather than east and west Different building in different climate zones have the different orientation to provide a better interior environment. Fig. 3 plan of Jacbos House IIwith large glazing area facing to the south. Fig. 4 plan of TheuerHouse with large glazing area facing to the north.

11. Architectural Factors—Building form the width of the building form is sufficiently narrow the orientation is important Toplighting is needed when depth is relatively large Linear forms have an internal core commonly design strategies are utilization of atria, lightwells, or courtyard to reduce the depth toplighting is unavoidable Centric forms more beneficial to harvest daylightingcomparing with centric form The large building envelope areas of clustered forms enable architects to organize the sidelighting and toplighting Clustered forms

12. Daylight apertures Uses apertures located in the wall planes Provide the visual connection of exterior and interior The depth of a room and the window heightare two essential parameters to the interior illumination. Sidelighting Uses apertures located at the roof plane No restriction with depth More effective for cloudy climate Control the potentia problem of glare and overheated Rooflight For the building with large depth The shape and form of atria The structure of the atrium roof can reduce its transparency by between 20 and 50 percent. The surface parameters : colourand reflectivity Atria

13. Shading devices to avoid direct sunlight coming into the building through the apertures because: i) the illumination of direct sunlight is usually not needed to provide useful daylight illuminance in most climates at most time; ii) direct sunlight always brings unwanted heat gain; iii) direct sunlight is deemed as greatly increasing of potential problem of glare window is most common part to install shading devices, and sometimes the roofs and walls variable types

14. Innovative daylight technologies To refract and redistribute the incoming light to produce a more diffuse distribution Prismatic glazing use lenses or mirrors to concentrated daylight and then transmitted the light to a lower level in building by “pipes” heavily reliant on the availability of sunlight and has to work with the artificial light Light pipes provide shade and reflected sunlightand relatively inexpensive work most effectively under the condition of sunlight sky rather than cloudy sky Light shelves

15. conclusion • The outline of simple steps for daylight design strategies • If a building has intelligently daylit design then it is able to reduce the use of energy for artificial light that may take a considerate proportion of total energy consumption particularly in some commercial buildings. • A comprehensive daylight system shall not forget the occupants’ comfort, productivity and health. • It shall be noticed that every aspect of the sustainable design strategies work integrated. When design the daylight system, it is at the point that the needs of other disciplines shall be take into consideration, such as ventilation, heating, cooling, sound attenuation and energy conversion.