Energy and carbon emission payback analysis for energy-efficient retrofitting in buildings—Overhang shading option

Energy-efficient retrofitting of existing building is a huge contribution to the sustainability of the society since building energy consumption takes more than one fourth of total energy consumption. The application of external shading system could block out unwanted radiant heat gain, thus reduces the cooling load of the air-conditioning system. During the assessment of energy-efficient retrofitting projects, apart from annual saving figures and economic payback time, energy and CO2 emission payback periods should also be taken as indispensable references. In this paper, a methodology is described for analyzing the energy and CO2 emission payback periods of external overhang shading in a university campus in Hong Kong. Result shows that due to 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 periods of the project are still unrealistically long. This case study presents an example of multi-disciplinary approach being not only important to the energy-efficient retrofitting but also necessary for policy making in different climatic and geographic regions.

► A life cycle analysis for an overhang shading system in Hong Kong is performed.
► Methodology to analysis energy and CO2 emission payback periods is presented.
► East and west facing overhang shading could cut radiant heat gain by half.
► Energy and CO2 emission payback periods are too long due to structural requirements.
► Life cycle analysis is an important reference to energy-efficient retrofitting works.