Retrofit

Retrofitting Strategy	Application of multi-skin façade system
	A second façade can be added in front of the external wall or curtain wall on the hottest west façade. The cavity in between the two façades will have an upward passage air to carry away the solar heat absorbed. OTTV can be reduced to 20 W/m². Clear glass could be considered for façade facing highways to help reduce the amount of glare that may affect motorists. It also helps to shield traffic noise from external. A lot of existing buildings are using single glazing. The heat entering the building through solar radiation and conduction can be reduced by installing a second piece of glazing at the internal side of the window. Installation of a second plane of glazing behind the building façade. Energy consumption for the air-conditioning system can be lowered due to the reduction of OTTV.
	Consideration
	Sufficient GFA for the additional space to be checked. Computer simulation checking on heat gain to be made. Load calculation should be carried out to make sure that the window framework can stand the weight of the additional glass. Check if submission to BD is required or can be handled as minor works. Apply it just to windows that are subject to prolonged solar radiation which could have a much shorter payback period despite a smaller energy reduction. The second glazing should have good shading and insulation performance and should have minimal effect on the aesthetic of the window. Other benefits of indoor environment should be considered such as noise reduction and indoor thermal comfort.
	Estimated Saving
	QFACADE = [AgSFSCmin(ESM_FIN, ESM_HANG)]_PRE – [AgSFSCmin(ESM_FIN, ESM_HANG)]_POST+ [AgUgaDT_EQ,V+ AskyUskyaDT_EQ,H]_PRE – [AgUgaDT_EQ,V+ AskyUskyaDT_EQ,H]_POST+ [AskySFSC]_PRE – [AskySFSC]_POST kW_FACADE = 1/COPQFACADEOPHR,yr where Ag = glazing area; Asky = skylight area Ug, Usky = U-value of glazing and skylight SF = solar factor (orientated); SC = shading coefficient a = outer surface absorptivity of façade DT_EQ,V, DT_EQ,H = equivalent temperature different of wall and roof (orientation) ESM_FIN, ESM_HANG = external shading multiplier of fin and overhang Multi-layers affect U-value of glazing by adding insulation, and reducing solar transmission (i.e. SC may change) Please click HERE to view the list of terminology.