Study of Residential Thermal Transfer Values (RTTV) and Vertical Daylight Factor (VDF) for Hong Kong

In Hong Kong, over one-quarter of the total electricity use was consumed by residential buildings. Recently, the Hong Kong Government issued a practice note namely Design and Construction Requirements for Energy Efficiency of Residential Buildings. This practice note set out the Residential Thermal Transfer Values (RTTV) of building envelopes. To enhance energy efficiency of residential buildings, the RTTV of wall (RTTV_wall) and roof (RTTV_roof) should not exceed 14 and 4 W/m², respectively. Being one of the most densely populated cities in the world, most of building developments in Hong Kong are high-rise blocks located in densely built zones. The shading effects due to surrounding buildings could substantially restrict the diffuse light coming from the sky. In 2003, a practice note on lighting and ventilation requirements was issued. Referring to the performance-based approach, the note adopted the vertical daylight factor (VDF) to specify the daylighting performance of the building. The VDF should not be less than 8% for habitable rooms and 4% for domestic kitchens. This paper presents the energy performance of recently designed building fulfills the RTTV requirements. It found that VDF is a good indicator to shows the lighting elecricty consumption in buildings. For most of the bedroom, about 40% of air conditioning and 3 % lighting energy can be saved.