EQUIVALENT THERMAL RESISTANCE (ETR) AND PASSIVE COOLING RATIO (PCR) OF GREEN ROOF UNDER TROPICAL CLIMATIC CONDITIONS

Abstract

There is an increasing demand for adopting rooftop greenery within buildings in the recent years. Many generalised studies have shown how thermal performance of green roofs can affect the overall energy consumption of buildings. However, little studies were conducted on the significant factors that will affect the thermal resistance and passive cooling of green roofs under tropical climatic condition. The performance of a building has a correlation to its environment and the sun. U-value is a determinant of the amount of heat loss and thermal resistance through a material. As the U-value of green roofs are not constant, validation is needed in simulating the thermal conductivity and cooling potential of green roofs.

This paper introduces a research methodology in determining the effect of significant factors on the Equivalent Thermal Resistance (ETR) and Passive Cooling Ratio (PCR) of green roofs under the climate of Singapore. This study also proposes a Machine Learning (ML) model to assess the effect and significance of each parameter through Variable Selection based on Linear Regression. Finally, an energy simulation was implemented to predict the cooling energy consumption of a vegetated office conference room.

The results showed that LAI (leaf area index) is the most significant factor and a LAI up to 3 has the most significant impact in the passive cooling of green roof. It is also found that a plant height has a diminishing marginal point of 0.65m and having additional height will result in an increase of cooling load instead. Wind speed has considerable effect on the PCR of green roof but a maximal PCR value of 0.083 is reached regardless the increase in wind speed from 2.0 m/s to 3.5 m/s. These findings will provide a guidance and practically aids in the designing of green roof.