Best practice case study: More than just a phase

As the name implies, the Futurium exhibition and event building is a pioneering development, as it complies with the standard required for a nearly zero-energy building and is supplied exclusively by renewable energy. (Copyright: Schnepp Renou)

In Berlin, the Futurium’s latent heat accumulator provides a glimpse of the energy future

The Futurium is a place where representatives from politics, science, business, the arts and wider society can meet to discuss the future. The building uses solar energy for heating and electricity supply, with an innovative paraffin-based latent heat accumulator at the center of this system for highly efficient low temperature storage.

The future has found its home right on the banks of the Spree river in Berlin between the Reichstag and central train station. The name Futurium says it all – the building is to act as a stage, museum, laboratory and forum of the future. It came to be through an initiative started by the German government in collaboration with leading German research organizations, foundations and business enterprises. The Futurium is designed to be an independent hub for dialogue and networking between representatives of the state, science, business and wider society.

The exhibition and event building, set to open officially in September, is dedicated to the question of how we want to live in the future. In line with its focus, the building itself is also innovative, as it complies with the standard required for a nearly zero-energy building and is supplied exclusively by renewable energy. To this end, the roof surface is almost entirely covered with collector panels for photovoltaic and solar thermal systems.

A special storage system for a special building

Discussing the building’s requirements, architect Jan Musikowski, who co-designed the Futurium with Christoph Richter, says, “The Futurium project was not only about architecture, but also about a sustainable and efficient technical concept. Buffering heating and cooling energy in the building, energy which had previously been generated by solar collectors and a combined heat and power unit, was one part of the project.” The search for a suitable storage system manufacturer was not easy, he says. Ultimately, Axiotherm from Eisenberg, Germany, proved daring enough to break new ground and was chosen as their partner. “Our cooperation brought about a latent heat storage system which uses the phase change material paraffin for highly efficient heat and cold storage. It achieves many times the capacity of conventional water tanks.”

Axiotherm’s Dirk Büttner describes the challenges faced: “We installed a paraffin latent heat storage system based on our HeatSel technology which is still quite a novelty in the construction industry and is unique in its dimensions – five storage tanks with a total volume of 50,000 liters.” The storage capacity is over 1 MWh. The use of five smaller storage devices instead of one large tank is due to the building’s multi-level architectural design. Thermal cooling energy that cannot be used directly is held in the five PCM storage units until it can be used later for the air conditioning – for instance when events are taking place – thereby balancing peak loads. This enables a smaller chiller which can charge up the storage device at times when electricity prices are low.

It is true that large cold storage systems are already being deployed in some buildings, says Büttner, but these are ice storage systems. He explains that this is a major disadvantage from an energy standpoint, because the generation of temperatures well below 0 °C greatly reduces the efficiency of the chillers and lots of energy is wasted. The system installed at the Futurium is the first large-scale PCM-based storage system which is calibrated with the absorption chiller to maintain a constant charging and discharging temperature of 12 °C. “This allows for highly efficient operation even with small temperature differences between cooling generation and energy consumption. With such small temperature differences, water storage systems are incapable of achieving any useful capacity.”

Stacked high and then filled

The five storage tanks, each with a volume of approximately 10,000 l, are located centrally in the building, stacked one on top of the other 20 m high on a sort of heavy-duty high rack. Due to their weight, they had to be lifted by a construction crane and stacked empty before the roof of the building was closed, which required careful planning. “Since each storage tank was followed by the floor for the level above, coordination with subsequent work was important. The macro-encapsulated PCM was therefore inserted in five ‘sessions,’” Büttner explains. “This was done using manholes in the floor and the dome areas of the tanks. Special care had to be taken to ensure that there was sufficient space between the storage dome and the floor above it.”

The tanks are filled with over 55,000 Axiotherm HeatSels. These are patented high-performance macro encapsulations made of customized synthetic material. The design combines a large surface area with PCM layers sufficiently thin for the entire PCM module to run through the phase change process. This in turn leads to highly efficient heat transfer, even with very small temperature differences. The storage system is optimized by using the HeatSels within a heat-transfer medium – in this case, water.

Cold in glass

Together with Axiotherm, EM-Power exhibitor 2018 and 2019, the architects were able to fulfill special aesthetic requests, too. “Our original intention was to set up a ‘glass’ storage facility in the center of the building so that visitors could see the phase change process,” Richter explains, “but we quickly learned that  the storage system of course must be insulated to work efficiently. Still, we kept looking for possibilities that would make this phase change process visible. Eventually, we talked Axiotherm into experimenting with inserting the paraffin between two glass panels. This proved tricky for several reasons, but the result was captivating.” After several more series of tests – in which even the TU Dresden was later involved – they finally succeeded in developing the glass paraffin façade which now houses the storage system and from time to time provides a behind-the-scenes look at its inner workings.

The architects also took other steps to aesthetically present this energy technology, and thus raise public awareness of it – for instance with the accessible roof. The skywalk provides both a view of the solar sea made up of an array of collectors for photovoltaics and solar thermal technology, and a unique view of the Chancellery and the Spreebogen – the district surrounding the banks of the river in the city center. Its shape means that the roof also collects all rainfall in a catch basin. The water is channeled to the lowest point, collected in a cistern and used for the building’s cooling system. Thanks to the sleek, sustainable energy concept, the planning team has succeeded in winning the building gold status under the German federal rating system for sustainable construction, the BNB. The Futurium’s modernity has certainly impressed its first visitors.


This contribution is largely based on a detailed interview which initially appeared online in Messe München’s BAU Magazin.


More information: Axiotherm

Axiotherm is an exhibitor at EM-Power 2019, booth C4.272