Retrofit

Retrofitting Strategy	Replacement of façade system
	Windows and glazing provide natural light for the health and comfort of the building occupants. However, they are also the major sources of heat gain/loss, visual and thermal discomfort, such that much energy is required to regulate the indoor temperature to a comfortable level. The best glazing selection depends on local climate, orientation of the building, shading and interior space design, in order to achieve low thermal conductivity, low radiant heat transmissivity and high visibility. Solar shading devices can be added based on the sun path, solar angle to determine the type, size for the use and offer better indoor climate environment. The well-designed solar shading devices can reduce building peak cooling load, corresponding energy consumption and enhance daylight utilisation in buildings. Shading devices can also avoid glare by reducing contrast ratios of building interiors, thus improve visual comfort of users. Using advanced computational technology to identify localised shading requirements, the profiles and sizes of the shading fins across each façade were designed according to the extent of solar irradiation received. Combined with high performance glass, this innovative design achieves an OTTV of about 18W/m² – significantly lower than the code requirement of 21 W/m². (2020) The simulation model with shading panels applied on the opaque façades of a Concord type public rental housing building – studied by The Chinese University of Hong Kong 2019, showing the energy saving at westward-facing façade can be up to 8% reduction.
	Consideration
	Review the window-to-wall ratio, shading devices, shading coefficient of glazing, absorptivity of façade 1. Window sizes provision for commercial and residential buildings are regulated by Building Regulations with prescribed area provision to control the lighting and ventilation. 2. However, better energy efficiency for the space can be gained by adjusting window-wall ratio within the requirement of prescribed windows. 3. To investigate the orientation of the buildings, site context, and can provide suitable window-wall ratio with less heat gain 4. Existing building might not comply with the requirement of current Overall Thermal Transfer Value (OTTV). Major retrofitting if involved with Building Submission, the compliance should be made. 5. Building tower, OTTV should not exceed 21 W/m²; Podium should not exceed 50 W/m². 6. The existing building can have actual on site study to figure out the window to wall ratio is appropriate for the building. 7. Computer simulation should be studied to figure out the correct window to wall ratio based on the current use. 8. To have solar simulation for the building envelope, and determine how the solar affecting the building on all façades. 9. Shading of external windows can be provided by natural landscaping such as trees and hills, or by building elements such as overhangs, awnings, fins and trellises. (EMSD, n.d.) 10. To explore different type of solar shading devices together with architectural design incorporation. 11. Loading capacity has to be checked and solar shading devices might extrude out of the site. Relevant building regulations and land requirement have to be advised by authorised person prior to proceeding of design and application. Energy-efficient window and glazing systems can reduce building energy consumption. These high-performance windows feature multiple glazing, specialised transparent coatings, insulating gas in between glass panes and improved frame. All these features reduce heat gain in interior. Comparison for glazing selection can refer to EMSD’s guideline. Loading to be well checked. Building submission on minor works submission may be required.
	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 Please click HERE to view the list of terminology.