Motivation

Building integrated greening measures such as roof and facade greening make an important contribution to energy efficient and sustainable building and urban planning. Evaporative cooling, shading, insulation, and an improved microclimate allow the energy optimization potential to be expanded beyond purely structural and technical building measures. Especially in view of higher outdoor temperatures caused by advancing climate change it is crucial to use all available options for cooling and increasing resilience. Currently however planning participants and building owners lack the possibility to reliably quantify and objectively compare the specific influence of greening measures on a building for example by using the energy performance certificate.

Objectives and Innovative Content

The goal of MARGRET was to define procedures for measuring the impact effects of building greening and to propose specific adaptations in calculation models and standards. To this end greening was metrologically investigated on a facade test box and at special roof greening test stands under natural weather conditions. The investigations focused primarily on the comparison between greened and non greened reference objects based on contemporary building standards. A  significant innovative aspect lay in the development and testing of standardized test procedures that enable the derivation of suitable characteristic values for implementation in the relevant standards.

Methodological Approach

The methodological approach was divided into the development of specialized measuring procedures and their practical application in field trials. For the vertical greening the AEE INTEC facade test box was used which has two thermally decoupled rooms with identical facade sizes. A technical innovation was the use of a pyroscanner for high resolution recording of the shading performance. In parallel test setups for roof greening were established to evaluate the difference between an intensively reduced green roof and a conventional gravel roof. Data recording and monitoring were realized via a digital twin. The technical measurement was flanked by accompanying plant monitoring. To ensure practical feasibility transdisciplinary stakeholder involvement was carried out  through technical discussions and workshops.

Results and Conclusions

In the course of the project standardized measuring and testing procedures for building greening were successfully developed and validated. Measurements on the opaque highly insulated facade clarified that the remaining heat flows in contemporary building standards are already largely  minimized which means that the decisive energy lever lies primarily in the area of transparent  components.

The investigations into facade greening also provided important insights into the dynamics of bioshading. It was shown that the shielding of solar radiation only increases significantly as the day progresses and is hardly pronounced in the morning. A central conclusion is the partial compensation of the shading effect by additional diffuse radiation via the foliage. A methodological challenge remained the dynamic character of the plant as a building component since the biomass growth at the exposed location fell behind expectations despite early cultivation and professional care. Significant potential was identified for green roofs for which a substantial savings potential for conventional insulation materials on roof surfaces was calculated. Furthermore their high water retention capacity and the associated evaporative cooling provide a passive contribution to summer overheating protection and simultaneously relieve the sewer system during heavy rain events. Based on these data proposals for determining relevant characteristic values were developed which form the basis for the further development of calculation models.

Outlook

A central area for future research lies in the deeper analysis of bioshading particularly with regard to the dynamics of radiation shielding in transparent components. In order to map these effects reliably for planning it is recommended to create tabular characteristic values for the seasonally fluctuating total energy transmittance of the combined system of glazing and vegetation. A further focus lies on the methodological simplification of the evaluation of green roofs. It is recommended to replace the multitude of complex individual parameters with a validated equivalent thermal insulation value. Such a flat rate characteristic value would summarize the energetic performance of the entire setup in a standardizable size and significantly facilitate integration into energy performance certificates. These further aspects will be considered in detail in the follow up project MARGRET Bioshade.

Project management

IBO - Austrian Institute for Building and Ecology GmbH

Project or cooperation partners

• AEE - Institute for Sustainable Technologies
• GRÜNSTATTGRAU Forschungs- und Innovations- GmbH
• Consulting (third party): BOKU Institute of Soil Bioengineering and Landscape Construction (IBLB)

IBO - Österreichisches Institut für Bauen und Ökologie GmbH
Alserbachstraße 5/8
1090 Wien
Tel.: + 43 (1) 319 20 05
E-Mail: ibo@ibo.at
Web: www.ibo.at