solSPONGEhigh - High solar fraction by thermally activated components in an urban environment

Within this project the intensive use of thermally activated building elements (TABs) as an additional thermal storage in different buildings, with solar technologies (thermal, PV) preferred for energy supply, was investigated. The aim was to activate and use the thermal storage potential that is immanent in the building elements and thereby achieve solar coverage of the building's heat demand of nearly 100 %.

Short Description




Starting point / motivation

Thermally activated building elements (TABs) have been employed in the building sector for years, whereby floor heating as near-surface activation combined with a low-temperature heating system is the most common variant in residential buildings. Also for office buildings, the advantages of TABs have been discovered, whereby there, cooling via the ceiling is the most common application.

The achievement of high solar fraction in the heating supply of buildings is usually realized with using large-volume, water-filled buffers. In such concepts it is to be expected disadvantages as high investment costs, large space requirements and high thermal losses. This implies the question of alternative and especially cost-effective, simple and quick realisable potential of heat storage in buildings. For this question the attention is directed to thermally inert or heavy building.

Following the approach of the objective research project, the solar heat in such buildings should directly storage into the building's components. The ability to use the components of such buildings for the purpose of heating or cooling, is created when these components are thermally activated.

Contents and goals

In general, thermal activation of building elements is feasible for all surfaces in a room (floor, ceiling, walls). With this technology, construction elements that are existent in the building anyway, are employed as thermal storages. Thereby, a high fraction of the building energy demand can be covered by solar technologies (thermal and PV) without the need of an unusually big water storage.

On the other hand - in comparison to a conventional heat emitting system with radiators - the thermal inertia of the system is significantly increased, leading to growing challenges for the control strategies - for reaching specific thermal conditions in the room, well planned conditioning in advance is inevitable. At the same time it has to be kept in mind that a set condition can only slowly be changed. These facts have to be considered in the development of control strategies, whereby approaches incorporating predictive elements are functional.

The research project is based on two exemplary solSPONGE concepts, whereby one concept primarily use solar thermal and the other use mainly photovoltaic for the energy supplies. On basis of these system concepts, based on thermal building and system simulation, the execution of the TABs as a building immanent energy storage will be analysed.

The main goal of this project was:

Analysis of system concepts with a high as possible solar fraction (solar thermal and / or photovoltaic) and high user comfort in combination with thermally activated component storage mass for new residential buildings, commercial buildings as well as a group of buildings. It intends to show under which conditions a nearby 100 % coverage of energy demand can be achieved. In addition to the energy view an analyses for the system costs is carried out.


System concepts with nearly 100 % solar fraction (solSPONGE-concepts) for energy supply for space heating and domestic hot water preparation in various building types are evaluated in simulation studies with respect to the issues named before. For some concepts (especially those with a PV-system and a heat pump in combination), cooling is also studied. The development of control strategies is performed in close cooperation with the industrial partners and is an essential part in the evaluation of the simulation studies.

In a first step detailed searches on the state of the art and the state of science in all its aspects of the project will be taken. This research forms a document with a conclusion in which the opportunities and possibilities of TABs in connection with solar technologies are summarised, which is used as a basis for the following work.

In close cooperation with the project partners and based on the expertise of the research, consistent and feasible solSPONGE-concepts should be defined with high solar fraction and evaluated with the use of detailed thermal building and system simulation. To evaluate the solSPONGE-concepts, in addition to an energy rating also ecological and economic analysis shall be carried out.

With the dissemination of the project results, also a large-scale transfer event will be held on the project topic besides the usual dissemination activities.

Epected results

The expected results included new insights and findings about the interactions between TABs, solar technologies, heat pumps and the urban energy system are the key to optimized system concepts and control strategies for SOLsponge-systems with high solar fraction.

Project Partners

Contact Address

Graz University of Technology
Institute of Thermal Engineering
Working Group Energy-efficient Buildings
Dr. Richard Heimrath
Inffeldgasse 25 b
A-8010 Graz
Tel.: +43 (316) 873 7317
Fax: +43 (316) 873 7305