Evaluating the appropriateness of adopting a single Overall Thermal Transfer Value and its implication to building energy regulation

Abstract

Control on Overall Thermal Transfer Value (OTTV) in buildings is one of the important building energy regulations that govern the design of energy-efficient building envelope. Currently, there are two distinct strategies for OTTV control: (i) a single OTTV limit applicable to all building types, regardless of their diverse operating hours; and (ii) different OTTV limits for different building types. Through building energy simulations of 40 real building cases in Hong Kong, it is revealed that applying a single OTTV limit to both commercial buildings (primarily operating during daylight hours) and hotel buildings (24-h operation) is problematic when considering both the cooling and heating demands. A 24-hr operating building can be designed to meet an OTTV limit but may have a comparatively poor thermal performance in the heating months when compared to another design option with the same OTTV limit. The literature review reveals that there has been no previous study on this problem. In order to tackle this research gap, a novel method including correlation factors, regression equations and additional OTTV requirement has been developed in this study for assessing the thermal performance of 24-hr operating buildings under the current OTTV regulation in Hong Kong. Based on the result from this study, 24-hr operating buildings can be properly designed under the OTTV regulation to achieve good energy efficiency in both the cooling and heating seasons. Policy makers are advised to incorporate this new OTTV evaluation method into the current OTTV regulation in the next round of OTTV review. The methodology developed in this study can be applied in other cities with OTTV regulation implemented.