Energy performance assessment method for residential buildings in Hong Kong

Abstract

This thesis describes the development of a new energy performance assessment method for envelope designs of high-rise residential buildings in Hong Kong, which formed a key part of the development and updating work for the Hong Kong Building Environment Assessment Method (HK-BEAM). In the early phase of this study, an assessment method that is based on the overall thermal transfer value (OTTV) of the building envelope was developed and incorporated into the 1999 version of the HK-BEAM scheme. At the same time, a comprehensive energy end-use data survey and a survey of residential building characteristics were conducted. The detailed evaluation of the heat transfer performance of residential building designs, and of the appropriateness of using OTTV as an index of performance of envelope designs, conducted in the later phase of this study, were based on the data collected in these surveys. From the collected data, and data found from the open literature, patterns of occupancy and of utilisation of lighting, domestic appliances and air-conditioning equipment in residential units were compiled, which are, thus far, the most detailed, reliable and up-to-data data about the energy characteristics of dwellings in residential buildings in Hong Kong. A comprehensive review has been conducted of the evolution of building energy standards that are based on OTTV of buildings. Comparison of the OTTV calculation methods adopted in the standards of various countries and the analytical methods for heat transfer modellling unveiled that there are fundamental fallacies in the OTTV calculation methods. The use of pre-calculated parameters for OTTV calculation could lead to large discrepancies in the OTTV of envelope elements, as the heat gain from an element could be significantly influenced by the building configuration, which has been illustrated by detailed simulation predictions in relevant case studies. Consequently, OTTV was abandoned for use as the index of thermal performance of building envelope designs. Instead, the proposal is made to base the assessment on the predicted annual cooling load (ACL) of the buildings. In the proposed assessment method, a building will be assessed with reference to a reference building of standardised envelope element construction characteristics. The assessed parameter will be the factor of reduction in the ACL of the assessed building compared to that of the reference building. It was found that an envelope design that was incorporated with all the considered energy enhancement features could have an ACL of about 65% of that of the reference building. Simulation results also showed that inserting an insulation layer into external walls would be an effective measure for reducing ACL notwithstanding that this is seldom used in Hong Kong. The assessment scale were set taking into consideration the economical benefit-cost ratios of incorporating more and more energy enhancement features into the building design such that the number of credits to be awarded would be proportional to the total investment made into these features. This assessment feature is intended to provide incentives to developers to aspire to higher performance levels and to provide a reflection of the standard achieved for the information of potential homebuyers. The latter is considered a key role that a voluntary assessment scheme like HK-BEAM could play. The new proposed assessment method, which will replace the existing method in the next update of HK-BEAM, represents a novel way of assessing the energy performance of residential building envelope designs.