RELATIONSHIP BETWEEN RETV AND INDOOR AIR TEMPERATURE

Abstract

Residential Envelope Transmittance Value (RETV) was introduced by Building and Construction Authority (BCA) in 2008 as an indicator for the envelope thermal performance of residential buildings in Singapore. RETV takes into consideration the three basic components of building envelope heat gain — the heat conduction through walls, heat conduction through windows, and solar radiation through windows. RETV is also a prerequisite criterion in the BCA Green Mark Scheme. RETV is an important index to evaluate the façade design of residential buildings in Singapore. However, few studies have been done to explore the relationship between RETV and indoor air temperature, which is one of the most concerned indoor environmental parameters for building occupants.

This project aims to study the relationship between RETV and indoor air temperature. Field measurement was first conducted on an East Coast Road public residential housing block to investigate the impact of external shading corridor and shading device on indoor air temperature.

Secondly, simulation models in EnergyPlus were validated using the field measurement data. Satisfactory agreements were obtained between the measured and simulated air temperatures. After validation, parametric studies were conducted to study the impacts of WWR, orientation, length of external shading device on the RETV and indoor air temperature under local climatic data. Based on the simulation results, the correlation between indoor air temperature and the RETV of residential façades with different WWRs and lengths of shading devices were investigated. The simulation results show that east and west facing facades have a relatively higher indoor air temperature in general, among the eight orientations. Besides, external shading device helps to reduce heat penetration effectively. With the same WWR of 0.4, the increase in the length of overhang could bring quite a significant reduction in indoor air temperature and RETV.

Furthermore, linear regression models were proposed to predict the relationship between RETV and indoor air temperatures, including annual average, daily maximum, daily average, and daily minimum temperatures. Based on the proposed models, optimal WWRs from 0.3 to 0.4 for facades of different orientations are recommended to achieve thermal and visual comfort in residential buildings, according to BCA Green Mark Scheme.

In summary, this project analysed the impacts of common façade features (WWR, orientation, and shading device) on the thermal performance of residential buildings in Singapore. Moreover, correlation models were proposed to predict the relationship between air temperature and RETV. The models can be easily used by architects and building engineers to evaluate their design and fulfil the BCA requirements. Future studies should be undertaken to study more types of shading devices with different lengths, shapes and position angles.