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Technische Universität Berlin (2018)

Quantification of cooling effects and water demand of urban facade greenings

Hölscher, Marie-Therese

Titre : Quantification of cooling effects and water demand of urban facade greenings

Quantifizierung von Kühlungseffekten und Wasserbedarf urbaner Fassadenbegrünungen

Auteur : Hölscher, Marie-Therese

Université de soutenance : Technische Universität Berlin

Grade : Doktor der Naturwissenschaften -Dr. rer. nat. 2018

Higher air temperatures in cities lead to increased heat stress for the urban population, especially during the night in hot summer periods. Facade greening is often discussed as a promising mitigation strategy as it can be applied on building surfaces where the heat stress is mainly caused. It reduces the stored energy in the building mass through shading and transpirative cooling and additionally influences the heat distribution within the street canyon. In previous studies, it was hardly differentiated between shading and transpiration effects because no studies are available on transpiration rates and water demand of climbing plants. This thesis quantifies water demand and cooling effects of facade greenings for the building and the urban street canyon. Therefore, methods for the quantification of transpiration rates are extended and adjusted to urban facade greening settings. Several experiments were conducted in summer on three building facades in the city centre of Berlin, Germany. Transpiration rates (xylem sap flow, lysimeter) were determined for three typical facade greening species : Parthenocissus tricuspidata, Hedera helix and Fallopia baldschuanica. Furthermore, surface temperatures of greened walls, bare walls and plant leaves as well as different meteorological parameters were measured. Finally, facade greenings were evaluated concerning their hazard reduction potential and compared with other countermeasures. Only minor cooling effects were detectable for the urban street canyon. In contrast, the effect for the building was clearly measurable : surface temperatures of the exterior and the interior building walls were decreased by up to 15.5 K and 1.7 K, respectively. A risk analysis shows that already a mean Tair reduction of 0.8 K can reduce the number of heat-related deaths. Thus, facade greening has up to medium potential to reduce indoor heat-stress hazards and is generally more effective to cool buildings than other vegetation, such as parks, street trees or green roofs. Provided cooling effects on hot summer days mainly depended on shading, while only a lower proportion was due to transpiration. Nevertheless, facade greening must be sufficiently irrigated with up to 3.0 L d-1 m-2 per wall area in order to realise its maximum cooling performance.


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Page publiée le 19 janvier 2019