Investigation on how daylight simulation should be used to characterize daylight-related issues for buildings in Hong Kong

Abstract

Given the popularity of climate-based daylight modelling (CBDM) that derives various photometric quantities using space geometries and typical meteorological year (TMY) data in recent years, great efforts have been made to characterize daylight quantity and quality in different building environments. Though most of buildings in Hong Kong are expected to have sufficient daylight due to its geographical location, serious problems, such as low energy efficiency of electric lighting systems and occupants' low satisfaction with indoor and outdoor luminous environments, still exist. In this dissertation, three studies related to CBDM calculations were conducted, aiming to characterize the daylight-related issues for the buildings in Hong Kong. The first study was carried out to quantify the difference between predicted and actual daylight quantity and quality and the performance of a closed-loop daylight-responsive dimming system in a real classroom. The predictions were made using the TMY data, while the actual performance was characterized using a real weather data. It was found that the daylight illuminance levels derived using the actual weather data were around 30% higher than those derived using the TMY data. The system was suggested to perform the calibration at the time that had similar weather conditions as the selected calibration hours in the TMY data. Otherwise, the system achieved lower energy savings and had a more frequent occurrence of over-dimming conditions, with the differences being as high as 15% and 86% respectively. A supplementary study was conducted to investigate the effect of a prismatic film on the performance of a daylight-responsive dimming system using the actual weather data. The prismatic film was found to cause the over-dimming conditions to happen more frequently in a south-facing space regardless of the calibration hours. To characterize an acceptable daylight quality for residential buildings, the second study was conducted to correlate residents' long-term subjective evaluations on the daylight quality to the objective measures characterizing the daylight quantity and quality in their flats during a same period of time. The flats with the average sDA300/50% above 66% and the maximum average daylight illuminance above 5624 lx were considered to provide an acceptable daylight quality. The final study was carried out to compare how different daylight simulation methods can be used to characterize the reflected sunlight from a curtain wall. It was found that the simulation results were significantly affected by the material specification and the luminance characterization of the sun, the ambient calculation, and the resolutions of the bidirectional scattering distribution function (BSDF) and sky patches. The forward ray-tracing method was recommended to identify the locations and directions introducing and receiving the reflected sunlight, with the backward ray-tracing method being followed to quantify the reflected sunlight illuminance. All the three studies further our understanding about how to use daylight simulation software to characterize the daylighting performance in Hong Kong. The dissertation not only provides useful guidance to designers and engineers to better design buildings for enhancing the daylighting performance, but also allows policy makers to better evaluate the daylighting performance in buildings in Hong Kong.