Abstract
Three experimental green roofs in Melbourne with depth of 100, 150 and 300 mm have been assessed to quantify their thermal performance. To evaluate the benefit of substrate depth, temperature was recorded every 50 mm along a vertical profile. Green roofs consisted of scoria substrate and a mix of three species of plants: Lomandra longifolia, Dianella admixta and Stypandra glauca. Statistical analyses applying the hierarchical partitioning technique showed that solar radiation is the main driver affecting the green roof surface temperature, air temperature has strong correlations with the variations of the temperatures recorded below the surface, while moisture content has the least influence. Temperature profiles of the green roof show that the first 50 mm do reduce the heat flowing through the green roof substrate regardless the total green roof substrate depth. Differences in thermal performance arise at deeper points, where thicker green roofs are able to delay the change of substrate temperatures. Similar effects were found for the heat fluxes measured at the interface between the green roof and building roof. These results confirmed that green roofs may be used as a sustainable passive technology to reduce building energy consumptions for South-East Australia climate.
Highlights
The number of green roofs - engineered structures that enable plants to grow on top of buildings - has been increasing in towns and cities as they seek to reduce their environmental impact
Statistical analyses applying the hierarchical partitioning technique showed that solar radiation is the main driver affecting the green roof surface temperature, air temperature has strong correlations with the variations of the temperatures recorded below the surface, while moisture content has the least influence
There are two reasons for this: the experimental green roofs are fully exposed to solar radiation and had relatively sparse vegetation cover than the green roof modules so solar radiation more directly affected the green roof substrate
Summary
The number of green roofs - engineered structures that enable plants to grow on top of buildings - has been increasing in towns and cities as they seek to reduce their environmental impact. While there is strong evidence for tropical [10, 11] and temperate [12] climates, this is not the case yet for other climates, such as hot and dry climate This is mainly due to contrasting results in different regions and across the seasons, likely due to specific selection of plants for green roofs and to changeable vegetation layer over the years. It was reported that in a tropical climate, a 100 mm thick green roof substrate is sufficient to reduce heat penetration into the building [11]; in a cold temperate climate, intensive green roofs (i.e. substrate thicker than 300 mm) offer an enhanced thermal performance and insulation effects [13]. This chapter investigates the effect of substrate thickness and vegetation cover on the green roof thermal performance and recommends the appropriate thickness of green roofs in South-East Australia to reduce heating and cooling loads
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