Comment on the overall thermal transfer value (OTTV) for building energy control

Overall thermal transfer value (OTTV) is taken as a parameter for controlling the building energy use in many places such as the Hong Kong Special Administrative Region (HKSAR, formerly Hong Kong) and Singapore. However, there are several approaches in determining the OTTV, and the results are therefore different. Four different methods of OTTV calculation are reviewed with the concept clarified in this paper - the direct simulation; empirical formulas; ASHRAE Standard 90A; and the Code of Practice at the HKSAR. The OTTV of building envelopes was analyzed by studying the building energy use in single compartments by energy simulation programs TRACE 600 and BLAST 3.0. Three types of rectangular single compartments of volumes varying from 4,000 m3to 40,000 m3were considered. Finally, results on OTTV calculated from these four methods were compared. A clear picture on the advantages and limitations for each method was listed for use by the building designers.