A Parametric approach to optimize solar access for energy efficiency in high-rise residential buildings in dense urban tropics

Abstract

Solar access in buildings is a topic predominantly investigated in the urban contexts at higher latitudes and to a much lesser extent in the tropics. Existing research focuses on ensuring unobstructed solar access, whereas, in the tropics, unobstructed solar access is avoided in buildings due to external heat gain. In addition, most regulations for high-rise residential buildings in the tropics are inadequate to ensure sunlight exposure for residents. Four research objectives were formulated in this study to investigate the definition, typology, planning and architectural issues of solar access in high-rise residential buildings in dense urban tropics. This study investigated the shading effect of the urban context on solar access in terms of energy savings and daylight in high-rise residential buildings in the tropical city of Colombo, Sri Lanka. The methodology consisted of three phases. In Phase I, three simulation models of 11, 21 and 31 floors (SM1, SM2, and SM3) were developed based on the archetypal highrise residential building characteristics in Sri Lanka.

In Phase II, the study demonstrated a parametric urban context for the simulation models utilizing simulation software Rhino3D and the Grasshopper interface. Archsim and DIVA4 plugins were used to simulate the effects of the urban context on spatial daylight autonomy (sDA), annual energy use for cooling, and annual day-time lighting energy use. A multiobjective

optimization process applying the Pareto-front identified the thresholds for optimum solar access. Phase III of the study investigated the daylight and energy performance of external shading scenarios of a high-rise residential building in a dense urban context. This study defined the optimum solar access for a perimeter zone in a high-rise residential building that achieves 75 sDA with corresponding annual energy savings of 28%- 36% in the east-west and 8%-12% in the north-south directions. The prescribed building setback curves for ensuring optimum solar access were validated with three calibrated case studies located in Colombo, Sri Lanka. All case studies demonstrated 50% of interior spaces (living rooms and bedrooms) with 55 sDA (300lx|50) and annual energy savings of 26-31% in east-west and 8%-15% in the north-south direction. The Floor area ratios (FAR) calculated for optimum building density for SM1, SM2, and SM3 were 4.2, 6.5, and 8.4, respectively. (300lx/50) The best performance external shading scenario in the vertical façade of the 11-floor Simulation model 2 (vertical and horizontal shading on the nineteenth floor, horizontal shading only for the eleventh floor, and no shading for the second floor) satisfied 75 sDA at all floors with corresponding energy savings of 16%-20%. The best performance scenario was applied to a 17-floor case study building located in Colombo, Sri Lanka. The simulation results indicated that 58% of the spaces had over 75 sDA for both Baseline and Best performance scenarios, while an increase in energy savings of 1%-3% was found in the Best performance scenario compared to the Baseline scenario of the case study. (300lx|50) This research study redefined solar access for the tropics, prescribed building setbacks for optimum solar access and informed optimum building density for the high-rise residential building typology. The study also identified the best performance external shading scenario for a high-rise residential building façade in the urban context. The research outcomes established in this study provide a much-needed platform to initiate the dialogue on solar rights in dense urban tropics.