Pit Ngai Chio

This study aims to determine optimised shading options in order to achieve building energy efficiency in subtropical regions. Energy efficient building retrofit contributes tremendously to the sustainability of the society as buildings consume over 40% of the total energy in most developed countries. In an attempt to mitigate this issue, external shading system was found to be an effective means of energy improvement strategy that could block out undesirable solar heat gains as it reduces the cooling energy demand of a building. Such a solution is especially urged in subtropical regions, where overheating is often a major concern leading to high cooling energy consumption.

In this research, various shading devices were compared in terms of their thermal and daylighting performance, through a case study office building in Macao using IES-VE building simulation software. First, shading device that could provide 100% shade for the facades in different orientations using the Olgyay’s method were determined. The egg crate shading was found to be the most effective strategy in reducing solar heat gain, with a reduction of 77% from the west, 76% from the east, and 73% from the south, as compared to devices without shading. Other shading strategies compared include horizontal louver, vertical louver, overhang, and some resized egg crate shading modules. The results showed that the horizontal louver (600mm wide/350mm spacing) gave the highest average cooling energy saving, with 8-11% from the three orientations. For the performance on useful daylight availability (DA300, UDI300-1000), the horizontal louver and vertical louver function better than the other shading strategies on the east and west side, while the best result of the south side is achieved by the egg crate shading (600mm wide/600mm spacing). Although some shading devices tend to cover most useful daylight hence increase the electric lighting demand, all the shading devices can reduce the UDI>2000 to 0%, implying that the glare level and visual discomfort are reduced to a large extent.

An integrated energy analysis from the cooling and daylighting performance of the shading devices was performed. For office with passive lighting control, the highest energy savings from the east and west side were achieved by the egg crate shading (100% shade design), i.e. 6.8% and 8.9% respectively, while the south side has the highest energy reduction attained by the horizontal louver, with 7.4%. For office with active lighting control, the egg crate (600mm wide/600mm spacing) brings the highest average energy reduction from three orientations, with 17.2% from the west, 7.9% from the east, and 7.5% from the south respectively. Although the horizontal louver provides higher energy reduction than the egg crate (600mm wide/ spacing) on the east side at 9.2%, it achieves around half of the energy saving as the egg crate (600mm wide/ spacing) on the south side, with only 3.8%. It is concluded that, under active lighting control, both horizontal louver and the egg crate (600mm wide/ spacing) provides favorable energy savings on the west and east side. For the south, the egg crates (100% shade design and 600mm wide/ spacing) performed the best compared to the other devices. This study recommends shading devices to be prioritised on the east and west façade for achieving optimal overall energy savings.