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Researchers at the TU Berlin present the newly developed absorption chillers, “Bee” and “Bumblebee”.
© TU Berlin
Research projects revisited
19.08.2013

The “Bee” absorption chiller has a 50-kW capacity.
© TU Berlin

Bee and bumblebee begin field tests

As part of a joint project with Vattenfall and ZAE Bayern, scientists from the TU Berlin have developed two new absorption chillers. The 50-kW unit, which the researchers have nicknamed Bee, and the larger 160-kW unit called Bumblebee use heat at a low temperature level for generating cooling energy. The prototypes are smaller, lighter and more powerful than comparable systems on the market. A field test is now starting.

In June 2012, BINE Information Service reported on the research work in a Projektinfo brochure. The optimised absorption cooling technology is now due to be tested at 13 municipal utility companies between Hamburg and Rosenheim and prepared for mass production. Together with partners in the project, the TU scientists now want to determine at which market prices the plants could be ultimately available. The aim is to reduce the costs of such plants to a third of the previous price.

The practical testing is intended to make cogeneration plants more efficient. The research project, which is entitled “EnEff Wärme: Field test on absorption cooling technology for combined heating, cooling and power systems,” was proposed by Professor Felix Ziegler, who heads the Mechanical and Systems Engineering department at the TU Berlin. The German Federal Ministry of Economics and Technology is spending 3.7 million euros on the project over a period of five years.

Structural potential of absorption chillers

In particular structural faults are the reason why conventional absorption chillers do not fulfil their potential for conserving resources and are frequently not profitable for users. “Dead spaces that do not have any function and so-called liquid soups consisting of refrigerants and solvents, which are not even involved in the process, make the plants unnecessarily large and sluggish,” says Stefan Petersen, who as a research assistant in the Mechanical and Systems Engineering department at the TU Berlin has played a leading role in the development. Optimising the heat exchanger and housing as a single unit and no longer designing them as separate entities have enabled dead spaces to be avoided. “With the result that our systems only need half the time to achieve load changes or reach full loading.” Whereas standard absorption chillers have previously required 30 minutes, the new chillers already reach full loading after 15 minutes. “When we began the project, a time reduction of 30 per cent seemed realistic. The fact that we were able to half the time taken means that we have vastly exceeded our expectations,” explains Stefan Petersen. In addition, the improved plants only require around a third of the refrigerant and solvent volumes. The savings with the solvent – a mixture of salt and water – reduce the operating weight as well as the investment and operating costs.

Project partners

In addition to the TU Berlin, Vattenfall Wärme and ZAE Bayern are involved in the development of the absorption chillers. Also involved in the comprehensive field tests are the Arbeitsgemeinschaft für Wärme und Heizkraftwirtschaft (AGFW), the Bundesindustrieverband Technische Gebäudeausrüstung (BTGA) and the TU Dresden.

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