Vacuum-insulated facade elements made from textile concrete
Text: Frank Hülsmeier, Alexander Kahnt
Slimmer facade cross-sections with a higher insulation effect and an improved environmental impact for concrete construction – this is what the four-man team from HTWK Leipzig aims to achieve with the vakutex facade elements. Key to their performance are two materials: the fibre concrete coating and an insulating core as well as vacuum isolation panels. In this article, Frank Hülsmeier and Alexander Kahnt describe the functionality and advantages of their new development.
The environmental and energy-related demands made on building envelopes will continue to rise over the next few years. If we continue to use existing materials, this means a continual strengthening of the exterior walls. To counteract this effect, new solutions are being found with constructions made from micro- to nano-structured materials. Thanks to thermal conductivity reduction as well as improvements in stability, heat capacity and quality, slimmer buildings are now possible.
The research group energiedesign, from the Leipzig University of Applied Sciences, has been investigating these problems since March 2010, after their research proposal was approved by the Federal Ministry of Transport, Building and Urban Development.
The aim of the research is to develop and extremely light and energy-efficient building envelope that looks like concrete. With the combination of newly developed materials such as textile concrete, vacuum insulation panels (VIPs) latent heat storage material (PCM) and glass-fibre strengthened plastic, construction components of 11cm are possible, which can fulfil every demand placed on facades of the future.
Less weight, better eco-balance
New assessment tools with the relevant material operating balances allow a holistic analysis of the environmental effects a construction has. This analysis forms a key focus of the research area and various types of construction were compared to the planned vakutex elements. The assessed construction elements all have the same heat transfer coefficient of 0,15 W/m²K, which reaches the passive house standard. For the analysis, one square metre is examined per facade type. The four constructions represent brick, timber, reinforced concrete and the newly developed vakutex. The brick facade is the only supporting construction – all the others are self-supporting. These self-supporting constructions depending on the balance square metre will be stressed by a supporting construction. With the timber facade a timber-frame construction made up of a supporting construction will be taken onboard, with the concrete facade, a steel frame construction for a two-storey building
The ecological potential of vakutex lies in the fact that it reduces construction element weight to just a fifth of that of a similar reinforced concrete construction. This leads to shorter assembly times, less heavy equipment, less strain on the supporting system and also savings in transportation.
The greenhouse gas emissions of the vakutex elements can are half those of a similar steel concrete structure. The greenhouse gas emission savings generated over a lifecycle of 50 years can be reached though a lower raw materials usage as well as recyclable building materials. An important characteristic in creating the balance sheet is the calculation of renewable raw materials. An exemplary demonstration of this is the balanced passive house timber construction. It can demonstrate a negative greenhouse gas potential within a defined period since the tree used CO2 during its growth phase. The lifecycle of the construction material is expanded around the growth period of the tree, therefore as one changes out the timber pieces the greenhouse gas balance becomes better. In consideration of the enormous population increase one could question if land-intensive timber can continue to be a competitor to the food industry and if a sustainable forestry can handle the rise of resource reduction for construction and heating needs. The future ecological alternatives to timber that are being researched prove to have a higher and competition-free raw materials occurrence.
The primary energy that is used to manufacture, maintain and dispose of the vakutex elements is half of that needed for a reinforced concrete element; the lower volume means the transport costs are lower.
Vakutex elements can already contribute to future environmental political goals like energy and raw materials productivity. The positive characteristics of vacuum insulation panels meet the current heat transfer coefficient with its 3cm thickness on outside walls according to EnEV 2009. The balanced 6cm thick vacuum insulation panels half the heat transfer and meet the requirements of future regulations.
The research group team from eneriedesign is made up of the project leader and three employees. The leader of the young team, Prof. Dipl.-Ing. (FH) Architect Frank Hülsmeier teaches building services engineering, building physics and energy concepts at the Leipzig University of Applied Science (HTWK). Dipl.-Ing. (FH) Alexander Kahnt gives the research group motivation with his doctorate in highly insulated, thin and light prefabricated section facades from textile concrete. Dipl.-Ing. (FH) Stefan Huth handles constructive and creative challenges, Dipl.-Wirtsch.-Ing. (FH) Matthias Tietze organises the project management and looks at the energy efficiency aspects. When putting the team together the project made sure that it was a young, motivated and interdisciplinary team. The team leads the main ideas behind application-oriented research at HTWK Leipzig.
The research group deals with the current situation of the technology behind building envelopes and develops hypothetical solutions, two of which have been already implemented as models. The next working steps shall be to research specific variations with sound, fire, thermal bridges, etc. Next to these structural properties simulations, ecological and economical comparisons will be done. Chosen solution scenarios will be implemented as demonstrational construction parts and practical sampling such as a controlled fire or a dynamic structural properties measurement will be conducted in the newly created HTWK Leipzig climate testing bed for building envelopes.
Next to HTWK Leipzig, the partner companies that are part of the project bring with them their own know-how into the project. For example, the company Variotec GmbH, from Neumarkt, delivers competence in vacuum insulated panels (VIP). As a partner in the field of latent heat storage material (PCM), CTS GmbH from Geesthact is also participating. HFB Engineering GmbH, from Leipzig, has many years of experience in fibreglass and textile concrete.
On top of the implemented and tested demo construction pieces from the research projects, the practical feasibility will also be proven in the experimental construction. With the architectural development of the building, an improvised student project has been started in May 2010 with the task to develop a parasite that will be placed on the HTWK Leipzig campus. This means that the experimental building can show the advantages of light and sustainable construction to students, users and visitors. The project partners of the research project vakutex support the implementation by providing the necessary facade elements. The focus of the experimental building is on the reduction and integration of building and technical components in order to combine a sustainable product with a comprehensive energy concept.
With the vacuum-insulated facade elements from textile concrete, an essential ecological and economical contribution towards sustainable concrete architecture is created.