Assessment of envelope energy performance in HK-BEAM for residential buildings

The Hong Kong Building Environmental Assessment Method (HK-BEAM) is a voluntary scheme that aims to promote good practices that can minimise the adverse impacts of buildings on the environment. With the new 3/99 version launched in December 1999, HK-BEAM now covers also high-rise residential buildings. The scheme uses the overall thermal transfer value (OTTV) to assess the thermal performance of residential building designs because the cooling load in residential buildings is predominantly "skin-controlled". Due to the largely different frequency and pattern of use of air-conditioning between residential units and commercial or hotel buildings, a new OTTV calculation method has been established. The paper presents the OTTV equation, the method used to generate the data required in the calculation and the correlation of the OTTV with electricity consumption for air-conditioning in residential buildings. Apart from the values of the weather dependent parameters to be used in the calculation, the proposed method differs from the existing one for commercial and hotel buildings in that in the OTTV equation, a corrected absorptivity has been introduced to replace the external surface absorptivity for opaque walls and roofs.Department of Building Services Engineerin