Vertical Green and its impact on the building energy and CO₂ balance

Climate change endangers urban populations by intensifying heat stress and heat-related health risks, amplified by the Urban Heat Island effect. Vertical green systems provide in-door cooling and thereby contribute to climate change adaptation. A vertical green system can be acknowledged as climate mitigation when air conditioning demand is reduced and bioenergy or biobased raw materials are derived from their biomass. The amortization timespan in which vertical green systems reach carbon dioxide equivalent (CO2-eq) break-even points and climate positivity depends on their annual CO2-eq savings and the amount of CO2-eq emissions, which arise from installation and maintenance. Among vertical green systems, green façades have lower CO2-eq emissions than living walls, while providing simi-lar CO2-eq savings. However, only a few species-specific studies have addressed the rele-vance of biomass production and indoor cooling for CO2-eq savings with green façades. Therefore, this dissertation addresses the following open research questions: How much biomass and bioenergy do green façade plants produce? What is the role of plant species, wall type, and plant parameters in the indoor cooling potential of green façades? What is the relationship between solar radiation and the indoor cooling potential of green façades, and which façades should be prioritized for indoor cooling with green fa-çades? Over the course of three scientific articles, these research questions were examined for five plant species: Fallopia baldschuanica, Hedera helix, Phaseolus coccineus, Par-thenocissus tricuspidata, and Humulus lupulus. In the first article, green façade biomass production rates were measured over multi-ple years. Biomass production differed significantly between plant species. Green façades produced similar biomass to that of other vertical green systems (living walls) in the vertical plane and exceeded agricultural and silvicultural biomass production rates in the horizontal plane. In the second article, indoor cooling potentials of green façades were simulated with a validated process-based heat and mass transfer model that considered the vertical leaf area index, transmittivity, crop thickness, and leaf inclination. Indoor cooling potentials differed significantly between plant species. The contribution of evapotranspiration to the total in-door cooling (between 2.8 and 25.6 %) decreased as indoor cooling potential increased. The transmittivity, which describes the plants’ shading potential, showed the strongest correlation with indoor cooling (R2 = 0.99). Therefore, the transmittivity of the three most abundant green façade plants in Berlin was measured and applied to solar radiation inversion models in a subsequent research note. In the third article, measured long-term solar radiation data from cities in different latitudes of the northern hemisphere were applied to different orientations and urban mor-phologies. Given the demonstrated strong linear relationships between solar radiation input and indoor cooling potential of green façades, the radiation data can be used to identify fa-çades that should be prioritized for greening as a heat stress reduction measure. In the synthesis chapter, CO2-eq break-even points were calculated. The following green façade properties influence the timespan until CO2-eq break-even is reached (in the order of relevance): vertical greening system type, plant species (transmittivity and biomass production), received solar radiation on the wall surface, coefficient of performance of the air conditioning unit, bioenergy conversion efficiency, and wall type. This results in the following planning recommendations: Priority should be given to (i) green façade systems with low CO2-eq emissions, (ii) high-performing species such as F. baldschuanica, which achieved the highest indoor cooling and biomass production potential, and (iii) façades with high solar exposure on buildings with high energy demand. Depending on these properties, CO2-eq break-even of green façades ranged from 0.5 to 350 years, underscoring the im-portance of careful planning. To conclude, these results help to maximize green façades’ CO2-eq savings and to es-tablish them as a standard urban and building climate mitigation and adaptation measure. In general, targeted application of urban green infrastructure can maximize its multifunctionali-ty and its ecosystem service provision. This contributes to vital and livable cities responding to urbanization, technological change, and climate change impacts.

Author dc:creator

• Dahm, Yannick Luca

Advisor dc:contributor.advisor

• Churkina, Galina

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Identifier URI

https://doi.org/10.14279/depositonce-26303

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/27467