Carbon sequestration and thermal performance of vertical greening

• Other Authors: Pan, Lan (author.)
• Format: Others
• Language: English; Chinese
• Published: 2016
• Subjects: Carbon sequestration; Wall plants; SD387.C37 P36 2016
• Online Access: http://repository.lib.cuhk.edu.hk/en/item/cuhk-1291557

Vertical greenery systems (VGSs) on building walls in cities develop rapidly worldwide in recent years, which is a potentially effective way to mitigate urban heat island (UHI) effect mainly through evapotranspiration and shading. Benefits of using vertical greening applications are of social and environmental origins, such as CO₂ emission reduction, energy saving, air quality improvements and enhanced aesthetic. However, little is known about C sequestration and CO₂ flux of vertical greening, and less attention has been paid on the C balance of vertical greening. In addition, many factors have great influence on C sequestration of vertical greening, including plant species, orientations and fertilizer application. However, limited studies report their impacts on C cycling, mitigation of UHI effect and improvement of urban microclimate of vertical greening. === Firstly, C sequestration of seven common plant species and that of Peperomia claviformis under six fertilizer treatments were studied. The results showed that plant species and fertilizer application had significant effects on shoot and root biomass. In contrast, we investigated C sequestration of Schefflera octophylla in four orientations, and showed that orientation had no significant influence. C sequestration of the seven species in VGSs ranged from 61 to 523 g C m⁻² y⁻¹. Meanwhile, the total C footprint of their maintenance ranged from 196 to 434 g Ce m⁻² y⁻¹, including the C footprint of fertilizer, pesticide and electricity consumption for irrigation. Newly established VGSs with these seven species could become C source from C sinks with large amount of C emissions from the maintenance practices between 2.7 and 43.6 years. === Secondly, the CO₂ fluxes of VGSs were determined by chamber-based measurement. Plant species and photosynthetically active radiation (PAR) played a dominant role in CO₂ fluxes. Fertilizer also significantly contributed to CO₂ fluxes of VGSs. Net ecosystem exchange (NEE) of CO₂ and respiration rates of VGSs varied with plant species, and most species in VGSs were higher in summer than other seasons. === Thirdly, VGS in the west-facing wall had the best capacity in terms of daily maximum wall temperature on sunny days. In addition, VGSs decreased the indoor air temperature of the thermal test room with VGSs. Solar radiation, total bright sunshine and relative humidity had the greatest significant correlations and relatively stronger coefficients with thermal indicators. === Finally, we compared the electricity consumption for cooling in flats with and without a VGS (8.22m²) in a pubic housing estate, and quantified the environmental benefits and burdens of a commercially available VGS. The daily electricity saving by the VGS in the flats with and without a VGS (8.22m²) in sunny, cloudy and rainy days in summer was 1.30, 0.84 and 0.71 kWh, respectively. A life cycle assessment (LCA) was conducted to analyze the environmental burdens of the VGS in its material, transportation, use and end-of-life stages. A comparison of the environmental burdens and benefits gained from cooling showed that the environmental burden of the VGS in regard to abiotic depletion of fossil fuels could be paid back in 20 years. === Overall, vertical greeneries installed on building walls did not only play a significant role on alleviation the problems of global warming and climate change through C sequestration and energy saving, but alse contribute to mitigating the UHI effects and improving urban microclimate due to the thermal performance. === 近年來城市中垂直綠化快速發展，主要通過植物蒸騰和遮陰效應而成為一種減緩城市熱島效應的有途徑。垂直綠化的應用由於其多種社會和環境效益，比如降低二氧化碳排放、節能、提高空氣品質和提升審美效果。然而，我们對於垂直绿化的碳匯和二氧化碳通量所知甚少，并且很少有研究關注垂直绿化的碳收支。並且，許多因素影響垂直綠化的碳匯，包括植物品種、朝向和施肥。但是在垂直綠化的碳循環、減緩城市熱島效應和提升城市微氣候方面研究卻很少。 === 首先，我们研究了七種常见的垂直绿化植物的碳汇和黑叶椒草在六种不同施肥处理下的碳匯。结果显示，植物品種和施肥對茎部和根部生物量有顯著促進作用。相比之下，我們還研究了鵝掌柴在四個朝向的碳匯，結果顯示，朝向對其並沒有顯著影響。七種垂直綠化植物的碳匯範圍為每年每平方米61到253克碳。同時，這些植物的維護包括施肥、噴藥和灌溉用電，造成了每年每平方米196到434克碳排放。因此，由於維護所造成的大量碳排放。所以這七種植物垂直綠化系統在2.7年到43.6年之內將從碳源變成碳匯。 === 第二，我們用二氧化碳分析儀測定了垂直綠化的碳通量。植物品種和光合有效輻射在碳通量上起主導作用。施肥也同樣顯著影響垂直綠化的碳通量。淨生態系統碳交換量和呼吸速率隨植物品種而變化，並且在夏天高於其他季節。 === 第三，在晴天最大牆面溫度上，西向的垂直綠化有佳的植物降效應。並且，垂直綠化降低了測試房間的室內空氣溫度。太陽輻射、總日照和相對濕與熱能指標有最多的顯著關係，並且有更高的相關係數。 === 最後，我們比較了在公共住宅的有垂直綠化(8.22平方米)和無垂直綠化的房間用於降溫的電量消耗，並評估了一個商業化垂直綠化系統的環境效益和環境負荷。在對比已安裝和未安裝垂直綠化的兩個房間後，在晴天、陰天和雨天每日省電量分別為1.30, 0.84 and 0.71千瓦時。我們用生命週期評價來對垂直綠化在材料、運輸、使用和最終階段的環境負荷進行了分析。對比了垂直綠化的環境效益和環境負荷後可知，化石燃料的不可再生資源消耗能夠在20年內償還。 === 總之，建築物外牆的垂直綠化不僅通过其碳匯和节能作用能夠對溫室效應和氣候變化有顯著作用，而且由于其熱性能還能緩解城市熱島效應和提升微氣候。 === Pan, Lan. === Thesis Ph.D. Chinese University of Hong Kong 2016. === Includes bibliographical references (leaves 217-246). === Abstracts also in Chinese. === Title from PDF title page (viewed on 24, October, 2016). === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only.