Calculation of overall thermal transfer value (OTTV) for commercial buildings constructed with naturally ventilated double skin façade in subtropical Hong Kong

Abstract

Overall thermal transfer value (OTTV) regulation, developed in a performance-based approach, is used to govern the design of a building envelope with an aim to reduce the electricity demand of air-conditioning system and thus the emission of greenhouse gas. Since the current OTTV calculation method including the OTTV equations and coefficients was originally developed for buildings with traditional single skin façade, building professionals have difficulty to compute the OTTV for buildings constructed with sophisticated designs such as double skin façade. The aim of this study is to derive a set of correction factors for OTTV calculation of air-conditioned commercial buildings constructed with naturally ventilated double skin façade. A generic commercial building was modeled using a validated building energy simulation program EnergyPlus. Through a series of computer simulation, a correlation between the OTTV of a traditional single skin façade of a commercial building and the sum of heat gain through the façade area over the cooling season was established. With this correlation, a dataset of correction factors was derived which can be used by architects and building engineers to calculate the OTTV of air-conditioned commercial buildings constructed with double skin façade. The details of methodology and findings are reported in this paper.