Solarenergie Urban - Analysis and evaluation of the economic, energetic and architectural quality of urban solar energy buildings

Status

completed

Summary

Starting point / Motivation

The building sector is one of the major CO2-emittents on the one hand and on the other hand consumes a large share of space. In this context it is reasonable to plan and construct buildings in the most energy-efficient way, in order to keep energy consumption during utilisation as low as possible, and at the same time to use the building shell for energy production in an optimal way.

The investigation of the thermal performance of individual buildings is certainly not new. Solar thermal energy has always been used to heat buildings. The current state of technology makes it possible to cover, even in Central Europe, a high amount of the hot water and heating demand of residential buildings by using solar thermal collectors. But what means efficient use of renewable energy in the urban scale?

Content and objectives

The project tries to answer the following questions: Which amount of the annual demand for heating and hot water supply can be covered by solar thermal systems in the urban area? How big are the effects of urban shading on the solar fraction? How do the energy standards of the buildings effect the solar fraction? What are the energetic, architectural and structural criteria for the implementation of solar thermal systems in multi-storey urban residential buildings?

Methodical approach

Based on four case stories of urban multi-storey residential buildings, the following aspects of solar technical systems have been examined by different professional disciplines:

• Energy analysis of urban conditions (shading analysis, availability of building envelope area, seasonal solar fractions, etc.)
• Analysis and assessment of the architectural aspects
• Constructional analysis and evaluation of usability and integration capabilities
• Dimensioning and simulation of solar thermal systems
• Targeted preparation of planning tools for the early planning phase of urban solar energy buildings focusing on the construction or rehabilitation of large-scale urban residential buildings

The project is based on a strong interdisciplinary collaboration between experts in architecture, construction practices, profitability analysis, the thermal and energy analysis in order to treat the questions in terms of sustainability comprehensively.

Results

The results of the project are documented in form of four case stories by a detailed description of the analysed example buildings and in the conclusions.

• Building physics and engineering requirements of façade-integrated solar thermal collector systems
• Design principles for urban solar energy buildings for the construction or rehabilitation of large-scale residential buildings using four specific case stories (architectonical, energetic, construction, building construction, physics and legislation criteria)

Furthermore a tool for energetic and economic assessment of different solar thermal technologies in the early planning phase was developed.

Conclusions

High-quality green and urban area design in dense living areas with function-mixed ground floor areas, closely tied to public transport, are a precondition of sustainable living. With the use of solar thermal systems in the four selected case stories, a solar fraction of more than 70% can be reached. So it could be shown in the simulations that even in the urban area passive and active solar heat supply of buildings is possible.

However, this high solar fraction can only be achieved if large collector areas and large storage volumes can be integrated into the building structure of highly efficient buildings. From the architectural view, the solar energy gains can be focused on two areas: on the on hand as a normative-generic standard option, which provides elevated panels on – if available – flat roofs, and for this in general small design changes are necessary. On the other hand, the extension of active solar thermal areas in the roof or façade area which intervene directly and profoundly in existing and future appearances.

The use of roof panels can be seen as a first option in the urban environment because little shading of the collector occurs. The integration of facade panels can result in a very low degree of solar coverage in an urban situation. A situation-specific shading analysis of the already existing but also potential shadowing should be evaluated in advance. Furthermore for the achievement of solid designed solutions, for this option the integration into the development process and its iterative decision-making, assessments, comparative studies and visualizations is essential. As the four case stories show, specific design qualities in this approach only can be elaborated with an equally specific project context.

In addition to the guidelines for passive solar energy use, from a design point, the principal incompatibility with historic façade characters can be stated. Design coherent integration of active areas can be realized much better in more sharp-edged, and clearly contoured (contemporary) building cubatures. The multiple motivated use of active elements – for example as a solar thermal collector and also as a parapet - as semitransparent window parapet, as sun protection, as roofing etc.- is very promising and forward-looking.

The development of object and visualization data banks for the active access for the design departments to these existing or potential product and design scopes would be an important step for a wider design discourse by the architecture. Under technical-energetic aspects the identification of additional customers of the produced heat from the thermal collectors has to be seen as one of the challenges of the next years. The larger the solar gains compared to the consumption, the larger is the overproduction of the solar system. Can a business partner for this surplus energy be found even a successful business model can be developed. In any way the technical and economic efficiency of solar thermal systems rises abruptly when the produced amount of solar energy is not limited to the specific demand of the building.

Project context

This project is conducted in close cooperation with the IEA SHC TASK 41 (Solar and Architecture) and the project MPPF (Multifunctional Plug & Play Facade).

Project management

DI Maria Amtmann
Österreichische Energieagentur - Austrian Energy Agency

Project or cooperation partner

• AIT - Austrian Institute of Technology
• Technische Universität Graz - Institut für Wärmetechnik
• Technische Universität Graz - Institut für Gebäudelehre
• Dr. Ronald Mischek ZT GmbH
• Mischek Bauträger Service GmbH

Österreichische Energieagentur - Austrian Energy Agency
DI Maria Amtmann
Mariahilfer Straße 136, A-1150 Wien
Tel.: +43 (1) 5861524-193
Fax: +43 (1) 5861524-340
E-Mail: maria.amtmann@energyagency.at