Thermal Study on Extensive Green Roof Integrated Irrigation in Northwestern Arid Regions of China

Abstract

Selection of xerophils and drought tolerant plants is highly crucial in green roof techniques in the drought prone regions of Northwest China. In this study, the thermal performance under the natural conventional climate in summer was analyzed using a self-made simulation experimental platform through comparison of the internal surface temperature with and without green roofs. The distribution frequency of internal surface temperature was investigated by dividing internal surface temperature into several ranges. Statistical analysis showed that the frequency of internal surface temperature lower than 33 • C for green roofs was 91.8%, about 1.09 times higher than that for non-green roofs, and that the sum of internal surface temperature exceeding 35 • C was about one third of that for non-green roofs. The results proved that green roofs have a significant insulation effect. Moreover, the thermal insulation property of green roofs had a strong positive relation with outside temperature. The thermal insulation characteristic was improved as the outdoor temperature increased, additionally, it had a better insulation effect within two hours after irrigation.

Evaluation of Different Roof Materials for the Mitigation of Urban Warming in a Subtropical Monsoon Climate

“…Latent heat losses through green roofs are associated with the evapotranspiration from plants and soil (Cascone et al, 2019), which largely depends on the water content of the roof (Santamouris, 2014). Previous studies suggested that the water content of green roofs largely influences their thermal performance; further, irrigation can improve the thermal performance of green roofs in dry regions (Feng et al, 2010;Sun et al, 2014;Wang et al, 2017). However, an experimental study conducted in Hong Kong (Jim & Peng, 2012) found that soil moisture had only a limited effect on the thermal performance of green roofs as evapotranspiration was predominately controlled by energy availability and not by water availability at their site, which was located in a humid region.…”

“…Long-term monitoring in New York City showed that white roofs could effectively maintain their temperature control effect for several years (Gaffin et al, 2012). Meanwhile, the cooling effects and energy saving potential of green roofs were shown through experiments and model simulations in cities, such as in Southern Italy (Brunetti et al, 2018), Chicago (Sharma et al, 2018), Toronto (Berardi, 2016), Hong Kong (Chan & Chow, 2013;Jim, 2014), and northwestern China (Wang et al, 2017). However, the answer to the question of which roof material has the best performance for mitigating the urban heat remains unclear, as relatively few studies have monitored and compared the temperature effects of different roof materials together.…”

“…Meanwhile, simulations in European cities showed that white roofs perform better in warm climates and green roofs perform better in cold climates (Ascione et al, 2013). These divergences appear because the thermal performance and energy-saving capacity of white and green roofs are strongly affected by the background climate and hydrological characteristics (Gao et al, 2017;Santamouris, 2014;Wang et al, 2017;Yu et al, 2018), as the background climate is important in the surface energy balance (Berardi et al, 2014;Heusinger et al, 2018). The regional climate simulation over the United States showed the tradeoffs among white and green roofs and suggested the need to find geographically appropriate strategies instead of a one-size-fits-all solution (Georgescu et al, 2014).…”

“…Under the dry climate, the green roofs were mainly constructed using drought tolerant plant species, which limit the green roof cooling potential due to stomatal closure (Coutts et al, 2013). Hence, previous studies suggested that the thermal performances of green roofs were largely influenced by water content in the dry regions, which further, can be improved by irrigation (Feng et al, 2010;Heusinger et al, 2018;Sun et al, 2014;Wang et al, 2017). However, an experimental study conducted in Hong Kong (Jim & Peng, 2012) found that soil moisture had only a limited effect on the thermal performance of green roofs as evapotranspiration was predominately controlled by energy availability and not by water availability at their site, which was located in a humid region.…”

Simulation Modeling of a Photovoltaic-Green Roof System for Energy Cost Reduction of a Building: Texas Case Study

“…Another critical component is an irrigation system to manage the water supply to a green roof [38]. The irrigation system used for an extensive green roof consists of a reservoir (or a water tank), irrigation pipe, and water supply pump [39]. If the system tends to reuse the water, additional drainage pump and water collecting pipe is required.…”