Evaluation of the shape plan, orientation, and ceiling height on daylight performance of tall office buildings in Tehran, Iran

Research Problem: 

Optimum use of daylight, as one of the main effective factors in improving the quality of office spaces, plays an important role in reducing electric energy consumption and improving the performance and health of employees. In high-rise buildings, usable space with the potential to benefit from sufficient daylight is often placed between the outer wall and the core of the building, which we call "useful space" here. The floor height, the floor area, the geometric shape of the plan, and the orientation of the building are the most important physical components affecting the ratio between the useful space and the entire floor space. By simple decision in the initial stages of design, while increasing the ratio of useful space to the entire floor space, future conflicts between different design components can be avoided to optimize the natural lighting of the building. The importance of this issue in the design of tall office buildings is more visible due to the importance of using natural lighting, scale, and correlation of design components

Research Question:

 how is the correlation between floor height, plan shape, and the orientation of the building with the spatial daylight autonomy (SDA), as an index to measure the amount of useful floor space with the potential of using natural lighting in the interior space?

This paper applies spatial daylight autonomy (SDA) to assess the impact of geometrical parameters on daylight performance by dynamic simulation in typical plan shapes of tall open office buildings in Tehran’s climatic conditions. The research involves three steps: First, 100 high-rise office buildings built before 2022 are investigated to find tall office buildings' most common geometrical aspects. Each geometry is parametrically modeled in the Grasshopper plugin in the second stage. For this step, initial data such as floor area core to floor area are entered as inputs of daylight simulation. The Honeybee parametric plugin inputs include data such as material reflection, glass Visual Transmission (VT), geographic location, activity period, and office layout. In the last part, simulation results for each case are compared and optimized.

The results indicate that among the evaluated geometrical factors, the orientation of the building is less important than the plan shape and ceiling height on the SDA. Among the studied plan shapes, the triangle shape had the best daylight performance concerning the SDA index, followed by the rectangle and ellipse plan shapes. Results show that a slight change in the geometry can improve SDA by more than 10%. A comparison of the results of the orientation study on the amount of natural light in the indoor environment based on the SDA index in each of the studied geometric shapes shows that the change of orientation of the building relative to the south improves to about 4.5% in the geometry of the triangle. This effect is up to 3% in rectangular geometry, about 2% in the ellipse, and about 1% in the square. Results can be used as a simplified method for architects in the early design stages to assess the impact of the geometrical characteristics on the daylight performance of tall office buildings in Tehran city.