EVALUATION OF SINGAPORE'S ETTV FORMULA

Abstract

The regulation of Envelope Thermal Transfer Value (ETTV) is one of the efforts made by Singapore to achieve energy efficiency in buildings. The ETTV is a measure of thermal performance of a building envelope and has also been used as a criterion for award of the prestigious Building and Construction Authority (BCA) Green Mark Award. However, can ETTV be applied to every air-conditioned commercial building in Singapore?

This study has reviewed and compared the ETTV (and its equivalent) standards in various Asian countries and found that the formulae are fundamentally same. The review of literatures has identified two gaps in researches that evaluated the standards in different countries. Firstly, there is a lack of researches into the relationship between ETTV and non façade-related properties of a building. Secondly, while many studies have found a relationship between ETTV and shading coefficient of a fenestration system, the influence of external shading devices on ETTV is unknown.

This study aims to bridge the above gaps in knowledge and evaluate how accurately ETTV models the thermal performance of a building. Four hypotheses have been developed to test the validity of ETTV in buildings in which there is 1) non-air-conditioned zone along the perimeter, and 2) overhang external shading devices. Computer simulations and statistical analysis have been used to test and validate these hypotheses. Thirty-four building test cases were simulated using EnergyPlus software and the solar heat gains were compared with the ETTV values.

This study has concluded that ETTV does not accurately model the thermal performance of buildings in which there is a non-air-conditioned zone along the perimeter. In such cases, an inverse relationship have been observed between the thermal load and ETTV indicating that the ETTV does not accurately model the thermal performance of such buildings. That is, while the ETTV shows high values, the heat transmitted by the façade is low. Thus, the use of ETTV as part of the regulatory control on such buildings may be unfair and the method to compute the ETTV needs to be reviewed.