Daylight Simulation: Skylight Designs for Large Retail Mall
We are the sustainability consultant for a new large retail mall in the new financial hub of Kuala Lumpur. The design intent of the mall has a huge roof park that provides open space and an outdoor nature connection to the occupants.
While the principal purpose of the roof is to provide an outdoor green space for the mall occupants, the client also intended to incorporate some skylight elements into the corridors of the retail mall to allow entry of natural light and give a visual connection to the outdoors from inside the mall.
Since the site is surrounded by tall buildings the main issue to address would be how the skylight design could enhance the daylighting levels within the mall, while maintaining views between the interior and exterior and keeping direct sun/glare at a minimum.
An iterative process was used to evaluate the skylight options and to develop new design options, which could meet the requirement.
1. By using SketchUp and IES-VE, we modelled the whole new retail mall with the surrounding buildings in order to accurately determine the quantity and quality of daylight entry through the skylight design across the day.
Fig: IES-VE modelling of the retail mall and the surrounding buildings forming an "urban canyon" around the mall
2. IES-VE SunCast and Radiance were used to determine how the surrounding buildings will affect the quantity and quality of daylight for the design of the skylight that has been proposed by the architect.
Fig: IES-VE modelling of the retail mall and the surrounding buildings
We also created a video showing the perspective from the sun (imagine that you are the sun!).
Video: View from the sun on Equinox (21 September)
3. With the current design (base case) modelled in IES VE, various options for the skylight design were studied to increase the overall daylighting levels on the ground floor, level one and level two.
4. During the detailed design phases, issues of direct sun and radiation were addressed in multiple simulations using IES VE and Ladybug Tools for Rhino/Grasshopper.
OUR FINDINGS & RECOMMENDATIONS
As we can see from the model and video above, the retail mall is surrounded by high rise buildings, the initial design of the skylight is designed as vertical type skylights.
From the daylight simulation results, the quantity of daylight in the mall is not encouraging, the average indoor lux level at the top level of the atrium (L2) is only 85 lux and drops to 0 lux at the bottom two atrium levels. For comparison, the Malaysian Standard MS1525 recommends at least 100 lux level for the corridor.
Even though the direct sunlight has been reduced substantially, however, the design doesn’t match the stated design intent of the skylights, which is to allow as much daylight into spaces, reduce the artificial lighting and increase the outdoor connection for the shoppers.
In an effort to improve the daylight performance of the mall skylight design, we recommended to change to horizontal type skylight since the surrounding high rise buildings have blocked most of the low angle daylight from near the horizon.
From our IES-VE Radiance simulations, the average indoor lux level (L2) of the final design is 684 lux, which is 8 times higher than the original design!
Fig: Chronological of the design of the mall skylights
Fig: Daylighting results from all the skylight designs with light levels (lux) for each level of the mall atrium. The daylight levels are based on overcast conditions using the simulated daylight factor (D.F.) values.
Fig: Initial/new skylights - daylighting results from IES Radiance, maximum 214 lux at level 2
Fig: Final skylights - daylighting results from IES Radiance, maximum 684 lux at level 2
Fig: Comparison of daylight factor area of the original design (Aug 2018) and final design
Also keeping glare issues and thermal comfort in mind, the design of the skylights has been optimized in such a way to control the glare. The angle of the internal ceiling and surface has been modelled to optimise both daylight and glare. Our original design proposal was a horizontal skylight with vertical walls (see Case 1 below), as this would reduce excessive daylight and potential glare issues for the top-most corridor level of the shopping mall. Adhering to the original architectural design intent of sloped atrium ceilings, the final skylight design (Case 2) was agreed upon that keeps the daylight and glare levels at the top-most corridor level manageable.
Fig: Raytrace study to ensure direct sunlight and glare are manageable
The selection of glazing for the skylights is vital in ensuring thermal and visual comfort for the shoppers. In the tropical climate with lots of overhead sun, a laminated double glazing unit with a low-emissivity (Low-E) coating was selected for the skylights. This spectrally selective performance glazing allowed visible light to enter through the skylight limiting the heat.
Fig: Glazing performance of the skylights
As shown in the glazing performance, the visible light transmission (VLT) of the glazing is at 64%, this is usually too high and will have the possibility of glare and discomfort to the occupants, in order to further reduce potential glare to the shoppers, a fritted layers are introduced in the glazing unit, glazing actual sample as below:
However, the final test result of VLT of the skylight glazing is yet received from the manufacturer, stay tuned for the update and future post where we will discuss the effectiveness of fritted layer on the glazing...
The retail mall has yet been completed, however, from the construction photos below (no artificial lighting installed yet), the result of the daylighting is very encouraging with the daylighting level very close to the simulation result. Direct sunlight can also give a sense of connection for the shoppers to the outdoors. The direct sunlight will move according to the sun's direction and will not stay in the same place for too long. Besides, the direct sunlight only hits the corridor areas, which are transitory spaces for shoppers to pass through, hence, any momentary glare is not an issue.
Fig: Skylights under construction (1)
Fig: Skylights under construction (2)
Fig: Skylights under construction (3)
Once the shopping mall completes and is taken into operation, we will perform a post-occupancy evaluation to get feedback from the shopping mall users as well as undertake measurements of the light levels inside the mall atrium.