Initial situation: Particularly for distributed microgrids (for example smaller heat distribution systems of settlements or companies), is a novel necessary approach on new low-temperature technologies for distribution, consumption, storage and also for the provision of heat energy with a special focus on the exergy optimization. The development of this approach or these technologies with a special focus on solar-coupled near-surface geothermal heat pump systems and thermal storage mass activation with respect to microgrids is the starting point of Low-ex Microgrid.
Problem: It is a holistic and integral consideration for an exergy optimization the entire system both in terms of plant design, so also the operation necessary, whereby the degree of complexity due to many degrees of freedom increases significantly: The dimensioning of the individual plant components in microgrids is done so far separately and usually under stationary conditions. The thermal storage potentials of component activation, decentralized hot water boiler and a potential geothermal heat storage in the application are not systematically used. Intelligent control technology approaches for the energy-efficient use of thermally activated components are only available to a limited extent or do not take into account the overall system. In addition, there are no communication models between the buildings and the heating network operator. In actively operated heat distribution networks (network of generation, consumption, distribution and storage) are greater optimization potentials that have not been exhausted yet. Geothermal systems in micronetworks haven‘t been studied, especially for near-surface applications (mainly for probes deeper than 50 m). The injection of excess heat into the solar coupled heat exchanger is a new approach, which requires further investigation. The influence of the groundwater flow and the moisture content of the earth strata on the exergy optimization have not been taken into R & D projects so far (dehydration of the soil and the associated reduction of the heat conduction properties due to the formation of cavities). The transient behavior of thermally activated components under realistic conditions requires modifications via the implementation of new control and plant engineering approaches, taking into account the weather and user-dependent boundary conditions. In particular, relevant approaches to extend the compressor run time of the heat pump systems are missing.

Objectives: Based on the following sub-topics, the exergy optimization potential for thermal (micro) networks for heat (and cold) is to be identified and also metrologically evaluated, with a special emphasis on multiplicable and practical suitability:

1. Heat supply and feed-in: Active use of the distribution network as busbars for the multiple heat supply for decentralized (waste) heat with particular emphasis on solar-coupled near-surface geothermal heat exchangers, taking into account the influence of the groundwater flow and the moisture content of the earth layers.
2. Use of exergy-optimized components: Optimized / coordinated low-temperature technologies for the exergetic optimization of energy conversion processes.
3. Optimized active building-wide storage applications to achieve an energy self-sufficiency: Optimization of active and systematic storage operation via geothermal storage, earth collector, network buffering and thermal component activation, decentralized hot water boiler module.
4. Create compatible interfaces between all actors, subsystems and components.
5. Optimized operating modes as well as overall system optimization: Innovative strategy development of the active heating and cooling supply via the existing distribution grids, consideration of the exergy influencing factors, load shifting, in particular inert storage masses.
   The aim is to achieve an exergy optimization between 15 and 20% compared to the current state of the art, which requires 40% less primary energy.

Methodology: (1) Assessment and analysis of the framework conditions, (2) Use of numerical methods for model development, (3) Parameter studies based on 2 concrete network integration concepts (housing and operational use), (4) Hardware-in-the-box validation -loop environment, (5) evaluation and benchmarking, (6) deriving recommendations for action for exergy-optimized microgrids;

Results: (1) Identification of different optimization potentials by exploiting the exergetic advantages of microgrid networks, (2) Development of different approaches to the realization of an integrated dimensioning and control strategy of exergy optimized thermal networks (adapted heat supply, components optimized for each other, active multi-building Memory applications, compatible interfaces between all actors, subsystems and components). (3) Innovation leap: 15 - 20% improvement in exergy in micro grids compared to the current state of the art. (4) Metrologically evaluated results from laboratory use. (5) Barriers / Success factors / Conclusions.