Providing a secure, economical and environmentally friendly energy supply in the long term is one of the greatest challenges of the 21st century. This requires the development of new, efficient and environmentally friendly energy conversion technologies.

Heating and cooling are the most important final energies in the civilized world. More than two thirds of final energy consumption in OECD countries is accounted for by the production of these two forms of energy. The thermal conditioning of buildings in particular continues to be heavily influenced by fossil fuels. A comprehensive switch to electricity-powered heat pumps is not possible in the foreseeable future for a number of reasons. For example, the proportion of pumped heat on cold winter days is negligible with electricity-powered heat pumps, meaning that the entire heating energy has to be provided by electricity. In addition, the required heating energy is still so high, even in existing buildings that have undergone energy refurbishment, that the electricity grid would be more than twice as heavily loaded on such days as it is today. It therefore also makes sense in future to use the natural gas grid with its large storage volume and to operate it partly with renewable gas (methane and/or hydrogen). However, a significant improvement in efficiency on the consumer side (heating systems) must be realized at the same time in order to achieve a significant_{reduction in CO2}.

Sorption processes offer a possibility for the technical realization of thermally driven heat pumps, which not only use the heat but also the exergy content of heat flows. This allows heat to be pumped from a low temperature level to a higher one, which opens up new possibilities for generating cold and heat in mobile and stationary applications. Thermally driven refrigeration and air conditioning systems and heat pumps have been known for a long time and are mainly available on the market in large capacity classes, primarily as absorption machines. However, this technology is difficult to scale up cost-effectively to the small output range required for 1-2 family homes and mobile applications. Adsorption heat pumps are more attractive in this respect, as they do not require fast-moving parts and can be operated purely by thermal drive.

The ITFD is working on the development of cost-effective adsorption heat transformers in a series of third-party funded projects. Topics include new adsorber compounds with artificial access pores for rapid material and heat transport, which can significantly increase the power density of the machines and drastically reduce costs. In further projects, modular system concepts are being developed together with industrial partners, with which further cost reductions can be achieved. In addition to the necessary experimental investigations, the focus is on the development of simulation models that are as accurate as possible, which make it possible to optimize materials, geometry and thermodynamic cycles. In the current EXOC-H2 and MODEX projects, the ITFD is developing an exergy-based model-predictive control system for hybrid heating systems and an exergetically optimized demo system for a modular adsorption heat pump.

Contact: Toni Maier, M.Sc., Johannes Thönnissen, M.Sc.

• Kraft, O (2021): Adsorber-Compounds für mobile und stationäre Adsorptionswärmepumpen mit hoher Leistungsdichte. Dissertation, Logos Verlag Berlin, ISBN 978-3-8325-5357-9
• Kraft, O, Stripf, M, and Hesse, U (2019): Heat and mass transfer in activated carbon composites with artificial macro pores for heat pump applications. In: Adsorption, Vol. 25(6), pp 1121–1133, https://doi.org/10.1007/s10450-019-00077-7
• Kraft, O, Stripf, M, and Hesse, U (2018): Determination of Kinetic Parameters of Porous Adsorbents with Artificial Macro-Pores Using a Pressure Jump / Pressure Drop and a Transient Hot Bridge Method. 8th Pacific Basin Conference on Adsorption Science and Technology, 03.09.-06.09.2018, Sapporo, Japan.
• Kraft, O, and Stripf, M (2017): OptiSorp: Entwicklung von Adsorber-Compounds hoher Leistungsdichte für mobile und stationäre Adsorptionswärmepumpen - Experimentelle Untersuchungen und Entwicklung eines Simulationsmodells. Abschlussbericht zum FHprofUnt-Projekt, https://doi.org/10.2314/GBV:1024755177
• Kraft, O, and Stripf, M (2017): OptiSorp: Steigerung der Leistungsdichte von Adsorber Compounds für mobile und stationäre Adsorptionswärmepumpen. In: Forschung aktuell, pp. 47-50.
• Kraft, O, Gaiser, J, Stripf, M, and Hesse, U (2016): Determination of Load Dependent Thermal Conductivity of Porous Adsorbents. In: Proceddings of the COMSOL Conference 2016, 12.-14.10.2016, München.