Abstract
Green roofs are consistently being used to reduce some of the negative environmental impacts of cities. The increasing interest in extensive green roofs requires refined studies on their design and operation, and on the effects of their relevant parameters on green roof thermal performance. The effects of two design parameters, substrate thickness (ST) and conductivity of dry soil (CDS), and four operating parameters, leaf area index (LAI), leaf reflectivity (LR), stomatal resistance (SR), and moisture content (MC), were investigated using the green roof computer model developed by Sailor in 2008. The computer simulations showed that among the operating parameters, LAI has the largest effects on thermal performance while CDS is a more influential design parameter than ST. Experimental investigations of non-vegetated and sparsely vegetated green roofs in Melbourne were principally used to understand the effect of the substrate and enable better understanding of dominant heat transfer mechanisms involved. Investigated green roofs had three substrate thicknesses (100, 150 and 200 mm), and their performance was compared to a bare conventional roof. In contrast to the computer simulations, the experimental results for summer and winter showed the importance of MC and ST in reducing the substrate temperature and heat flux through the green roof.
Highlights
As part of efforts to reduce air pollutants, greenhouse gases and their carbon footprint [1,2], cities and towns have introduced new technologies and techniques to mitigate some of negative impact of cities on the environment and make cities greener and more sustainable [3,4,5]
In the first part of this study, we investigate the effect of two design parameters and four operating parameters using the green roof computer model developed by Sailor [28]
Measured substrate temperatures and heat fluxes from non-vegetated and sparsely vegetated green roofs were collected to compare the effect of those parameters between experimental results and simulations
Summary
As part of efforts to reduce air pollutants, greenhouse gases and their carbon footprint [1,2], cities and towns have introduced new technologies and techniques to mitigate some of negative impact of cities on the environment and make cities greener and more sustainable [3,4,5]. For hot and dry climates, appropriate plant selection is essential because green roofs need to be drought tolerant [27] Because of these wide ranging results, it is not possible to specify one “optimum” green roof build-up (drainage layer, substrate or growing medium and plants) that will maximise green roof thermal benefits in all countries or climate zones. Parametric, called sensitivity, analyses using existing green roof thermal models can help understand which parameters are most effective in enhancing green roof thermal benefits, and maximise green roof thermal performance in different locations This is not sufficient, unless the results of the parametric analysis are validated with field measurements and a comprehensive evaluation. We discuss the results from computer simulations and experimental green roofs
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