Energy-efficient retrofitting of existing buildingsis a huge contribution to sustainability of the society since building energy consumes more than one fourth of total energy consumption. The application of external shading system could block out unwanted radiant heat gain, thus reduces the indoor space cooling load. Life cycle assessment could be an important reference during the decision-making period of a retrofitting project. In this paper, a case study involving an overhang system design and payback period analysis in a university campus in HongKong is presented.Result shows that due to the requirements of structural strength under typhoon situation, although introducing overhang shading system could reduce almost half of the cooling load in the related area, the energy and CO2 emission payback periodsof the project are still unrealistically long.
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