Energy Efficient Processes

The increase in efficiency makes a significant contribution to the development of our future energy structure. In addition to reducing heat consumption in buildings, the efficient conversion of heat in energy supply systems and industrial processes is a central element. The efficiency of thermal processes for power, heat and cooling must be improved by the targeted reduction of exergy losses.

Industrial processes have a high optimisation potential, e.g. through the consistent use of waste heat. In addition, the sensible use of renewable energy sources such as biomass, solar and geothermal energy contributes to the reduction of fossil fuels and CO2 emissions. For example, processes for thermal biomass utilisation, conversion of solar radiation or electricity generation at a low temperature level must be optimised and integrated into comprehensive overall energy concepts.

Sustainable energy use in the industrial sector, based on waste heat utilisation, depends on efficient technologies for heat transformation and energy storage.

Fields of Research

Geothermal Energy

ZAE Bayern undertakes research in the fields of near-surface geothermal energy and deep geothermal energy, two fundamentally different technologies.

In near-surface geothermal energy, the focus is on component development and quality assurance methods. Component development covers material issues such as backfill materials for geothermal probes and new probe designs such as the two-phase thermosiphon as geothermal probe. The Thermal Response Test can be cited as a practical example of quality control. This is a method with which the thermal underground properties can be measured in situ at a specific location. For this purpose, ZAE Bayern has developed a mobile measuring device and suitable methods for evaluating and simulating heat transport in the subsurface. In addition, ZAE Bayern is working on the use of geothermal probe storage facilities, e.g. as seasonal storage facilities for heat or for heating and cooling.

When it comes to the use of deep geothermal energy, ZAE Bayern is currently active in the field of consulting for building owners and operators (mostly municipalities), especially in the development, optimisation and evaluation of system concepts with low system temperatures. The focus here is on the special requirements for the thermal water circuit, the technology in the energy centre with and without power generation, the design of the heating network, the house transfer and the associated building technology.

In the field of near-surface geothermal energy, ZAE Bayern employees also work in the VDI committee "Thermal Use of the Underground" and manage Annex 27 "Quality Management in Design, Construction and Operation of Borehole Systems" of the IEA Implementing Agreement ECES.


Dipl.-Phys. Lars Staudacher
+49 89 329442-41

Dr. Jens M. Kuckelkorn
+49 89 329442-17

Thermal Transformation

Since the foundation of the institute, the development of thermally driven heat pumps and cooling machines has been a core component of the activities of ZAE Bayern. The work ranges from basic theoretical and experimental investigations to component development and the design and optimization of complex energy supply systems.

In the area of the basics, cycle concepts and variants for process control are developed and thermodynamically modelled. Experimental work deals with the investigation of new material combinations and the mechanisms of heat and mass transfer. Based on these basic research, heat exchanger configurations and complete heat pump systems are developed. The system engineering work is concerned with the use of sorption heat pumps and chillers for solar cooling, combined heat and power generation and cooling from district heating, as well as building heating and waste heat utilisation in industry and commerce.

The application-related work significantly exceeds the current state of the art and resulted in several patents in the area of process engineering implementation and system integration.

The scientific work in the field of thermal heat pumps has gained international recognition. ZAE is also active in the scientific advisory board of international conferences. The results of the research work will be integrated at international level in working groups of the International Energy Agency (IEA).


Dipl.-Ing. Manuel Riepl, M.Sc.
+49 89 329442-43

Solar Thermal Energy

Current research focuses at ZAE Bayern are on collector developments for the low and medium temperature range (temperature range up to 200 °C), as well as the short- and long-term storage of solar heat. The integration of solar thermal energy into solar-assisted heating and cooling systems is complex due to the dynamics of solar radiation, the mutual interaction of components and buildings and therefore requires a dynamic system simulation for the design. For larger plants with and without long-term heat accumulators, the complete solar local heating systems must be simulated. In particular, the solarisation of existing buildings or existing quarters with new buildings requires R&D efforts and new approaches in the area of adaptive and anticipatory regulations. In order to achieve and secure the high level of acceptance among users, intensive quality control is required for the planning, construction and operation of solar thermal systems. This takes place through scientific monitoring and qualified monitoring of innovative plants. The goals of the optimization are to increase the solar coverage and to improve the efficiency of the systems.

Solar thermal systems in all temperature ranges require suitable heat accumulators to adapt the supply to the demand. Depending on the application, this ranges from buffer or short-term storage to seasonal heat storage.

ZAE Bayern is currently working on projects in the areas of collector development, solar-assisted local heating systems, seasonal storage of solar heat, solar air conditioning and solar process heat supply. In addition, work is also underway to improve the integration of solar-active exterior wall elements into the building envelope. Solar-active wall elements create synergies and reduce costs. With its solar local heating concepts, ZAE Bayern is a national and international leader and is one of the few institutes that independently develops process heat collectors for the medium temperature range.

In addition to purely technical development opportunities, ZAE Bayern has extensive expertise in organising scientific conferences (participation in conference advisory boards, etc.), regional and national potential assessments and systemic considerations (municipal and regional energy concepts). This expertise can also be used for technology assessment and risk analysis for policy advice.


Dipl.-Phys. Lars Staudacher
+49 89 329442-41

Dipl.-Phys. Markus Pröll
+49 89 329442-81


Industrial waste heat utilisation through thermal energy storage

Photo industrial waste heat utilisation

Foundries are among the most energy-intensive industrial companies. Most of the energy used is needed to heat the melting furnaces with the metals in them, in order to liquefy the metals so that they can then be cast into the desired moulds.

Melting furnaces supply waste heat during their operation as well as in the cooling down phases, which is often released unused into the environment - also at the Heunisch foundry in Bad Windsheim. The Heunisch foundry therefore wondered whether this waste heat could be used economically - as process heat, for heating or even for generating cold. The use of waste heat is also made more difficult by the fact that it is generated at times that are not identical with the phases in which heat is required.

An answer to this question was found in a cooperation between ZAE Bayern, the Heunisch foundry and the plant manufacturer Küttner:
The developed solution focuses on an energy storage system that stores the waste heat from the melting furnace (cupole furnace) so that it can be used to provide process heat and thermal energy as well as process cooling during the stoppages of the furnace. This is achieved through the use of innovative technologies in the field of heat storage and heat transformation as well as through an energy management system that efficiently links heat sources and sinks.

A number of problems have to be solved on the way to this end: For example, systems for storing large quantities of heat at temperatures up to 300 °C are not yet available on the market, so that these high-temperature storage tanks must first be developed. Equally new is the combination of such storage tanks with absorption heat pumps, which can also provide the cooling required by the foundry.

The high-temperature heat storage tank currently under development is a so-called two-substance storage tank. It contains a solid bulk material that is directly surrounded by a heat transfer fluid. No high pressures are required for its operation. This concept has considerable advantages over alternative storage concepts (e. g. pressurized water storage tanks or thermal oil storage tanks). Among other things, relatively low production costs can be achieved by using cost-effective solid bulk material - e. g. rock.

For the development of the thermal storage tank, a test stand will be set up at ZAE Bayern, which will be used to identify suitable solid fillings as storage filling material and to investigate their chemical resistance and cycle stability. This test stand is used in particular to analyse the effects of different types of bulk material, bulk sizes and forms, bulk densities and bulk surfaces on the performance of the storage tank, and a suitable storage filling material is determined on the basis of the results.

Another focal point of work is the required heat pump. Whereas with conventional absorption heat pumps, the drive heat is supplied by hot water, steam or flue gas, an absorption heat pump is required for the planned heat recycling system, which uses thermal oil as the heat transfer medium. Therefore, both the concept of heat transfer in the absorption heat pump and the dimensioning of the required heat exchanger must be adapted. In addition, it is necessary to adapt the absorption heat pump to the required temperature levels when providing refrigeration (approx. 5 °C, recooling at approx. 40 °C) and heat (approx. 85 °C, low temperature source at approx. 30 °C).

The stored waste heat can thus be used in a variety of ways to provide process cooling, drive the heat pump, for heating and for domestic hot water preparation.

After the initial operation of the energy storage system, testing under real operating conditions begins. During this phase a continuous, intensive technical and scientific support of the plant takes place. Based on monitoring, the energy storage system is analysed under technical, economic and ecological aspects. The data obtained will be used to identify further optimization potentials and to develop them for the installed plant as well as for other systems to be implemented in the future.

The plant for waste heat recycling at the Heunisch foundry is expected to save about 3000 MWh of primary energy and 600 t CO2 per year. This corresponds to the heating requirements of around 300 low-energy houses or the CO2 emissions of 300 vehicles with a mileage of 10,000 km per year.



Dipl.-Ing Richard Gurtner
+49 89 329442-14

Heat exchanger development for compact absorption chillers

Photo heat exchanger

The aim of the project is to advance and test a compact absorption refrigeration system with highly efficient plate heat exchangers as its main component. With regard to the provision of refrigeration for the air-conditioning of domestic rooms or offices at temperatures above 0°C, the two-substance mixture of water/aqueous lithium bromide solution is used as the working medium, with water as the refrigerant and aqueous lithium bromide as the absorbent. The drive heat is provided at a low temperature level, such as solar heat, district heating or combined heat and power plant (CHP) waste heat.

The use of environmentally friendly absorption chillers enables a significant reduction of primary energy consumption and the associated CO2 emissions in the provision of refrigeration compared to conventional compression chillers, which are primarily driven by electrical energy. The availability of efficient heat exchangers makes a decisive contribution to making this energy-saving technology available cost-effectively and reliably at the same time.

Within the scope of a project funded by the BMWI under the number 0327875A, compact plate heat exchangers are being developed for the application in absorption chillers and following this a compact chiller. The innovative heat exchanger concept promises advantages over conventional tube bundle technology in terms of dimensions and manufacturing costs, especially for small capacities. Detailed knowledge of heat and mass transfer is required for this purpose, which is why extensive investigations are carried out in this context.

The system development concentrates on a cooling capacity of 3 to 5 kW, so that it can be coupled to existing solar combi-systems, which are used for domestic hot water heating and heating support. This means that there is considerable potential for the market entry of such a development.


Dipl.-Phys. Lars Staudacher
+49 89 329442-30

Dipl.-Phys. Markus Pröll
+49 89 329442-81

Solar air conditioning system for existing buildings

foto Solar air conditioning system for buildings

The focus is on the development of an integrated system that can be used all year round for heating and cooling in conjunction with panel heating and cooling systems. The core component is an absorption refrigeration system powered by solar heat, which can be additionally fossil-heated to cover load peaks or in times of insufficient solar radiation. In heating operation during the winter months, the same system is used as a thermally driven heat pump. In this operating mode, the collector system serves as a heat source for feeding low-temperature heat into the evaporator of the heat pump. This achieves the highest possible solar yield of the collector system during the cold season. In order to achieve high energy efficiency in operation with additional fossil fuel firing, a combined single- and two-stage absorption heat pump circuit is used, which enables flexible coupling and decoupling of low-temperature heat - for solar drive of the refrigeration machine and simultaneous heating and cooling.

The complete system for solar building air conditioning is particularly suitable for systems with a higher cooling capacity and is also suitable for retrofitting in existing buildings.

In the research project funded by the Bavarian Research Foundation, a pilot installation was realised in Arnstorf together with Lindner AG and put into continuous operation. Comprehensive metrological recording of all relevant variables enables detailed energy analysis, which is carried out over several heating and cooling periods.


Dipl.-Ing. Manuel Riepl, M.Sc.
+49 89 329442-43

Annual efficiency and annual emissions of wood pellet small-scale combustion plants

photo pellet boiler

In a research project, the influence of different parameters on the annual efficiency and the emission behaviour of modern wood pellet small-scale combustion plants was investigated on a laboratory test bench. Two typical hydraulic circuit variants (with and without buffer storage tank) were examined on two different real wood pellet small combustion plants (underfeed firing and chute firing).

Load profiles of selected characteristic type days (VDI 4655) were based on a dynamic building simulation for a non-insulated existing single-family house with an average specific total heat requirement of about 240 kWh/m2a. The energy flows and emissions were continuously measured for the respective type days and from this data, type utilisation ratios were determined, which were then extrapolated to the annual utilisation factor with a weighting over the heat requirement of the respective type day and its frequency in the reference year. In addition, tests were also carried out to assess the influence of the boiler design (dimensioning) on the annual utilisation factor.

The tests also measured gaseous emissions, in particular carbon monoxide and dust emissions. For dust measurements, the measurement method was modified in accordance with the guideline VDI 2066 - 1 in such a way that a 24-hour dust balancing could be carried out. By determining the average dust emission of each type day, the total annual emissions were extrapolated.

The project was largely financed by the funding programme "Optimisation of the use of biomass for energy production" with funds from the Federal Environment Ministry.

Further information can be found here , FKZ 03KB026


Dipl.-Ing. Robert Kunde
+49 89 329442-26

Geothermal switch heating

photo rails point heating

For safety reasons, railway switches are heated in winter to ensure proper operation even in snow and ice. Electric resistance heaters or gas burners are generally used for this purpose. In Germany alone, the total energy consumption of the plants, including local transport and railways not belonging to DB AG, averages around 200 GWh per season. The electricity required is a seasonal load, the majority of which consists of peak loads. In Germany, approximately 900 MW of installed capacity must be available for these plants.

The research project " Environmental Inert and Emission-free Low-Temperature Point Heating" aims to develop a new type of switch heating system for the use of near-surface geothermal energy in order to replace conventional systems. For this purpose, heat is extracted from the substrate with a CO2 thermosiphon consisting of a CO2 geothermal probe and a condenser mounted on the switch.

In order to be able to implement the system economically, a very small temperature difference of only a few kelvin must suffice for heat transfer from the ground to the switch. Based on the heating surface, this requires a specific output of up to 1000 W/m2. This is the main challenge of the completely regenerative heating system.

The development of the overall system and its design tools, which are necessary for the planning, took place as part of the already completed project "Environmental Inert and Emission-free Low-Temperature Point Heating". The first geothermal point heating system with CO2 as heat transfer medium was planned for 2010 and built in January 2011. If the overall operating experience is positive, the system still has room for improvement. The aim of the next project phase is to improve the capacitors, construct several pilot plants and support them with metrological measurements.


Dipl.-Phys. Lars Staudacher
+49 89 329442-41

ZAE Bayern

We work at the interface between knowledge-based basic research and applied industrial research. Under the motto "Excellent Energy Research - Excellent Implementation", we realize complete innovation packages that build on synergies between generation, storage and efficiency measures.

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