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National energy models provide decarbonization strategies. Most national energy models focus on costs and greenhouse gas emissions only. However, this focus carries the risk that burdens shift to other environmental impacts. Energy models have therefore been extended by life-cycle assessment (LCA). Furthermore, deep decarbonization is only possible by targeting all high-emission sectors. Thus, we present a holistic national energy model that includes high-emission sectors and LCA. The model provides detailed environmental impacts for electricity, heat, and transport processes in Germany for meeting the climate targets up to 2050. Our results show that renewable energies and storage are key technologies for decarbonized energy systems. Furthermore, sector coupling is crucial and doubles electricity demand. Our LCA shows that environmental impacts shift from operation to infrastructure highlighting the importance of an impact assessment over the full life cycle. Decarbonization leads to many environmental cobenefits; however, it also increases freshwater ecotoxicity and depletion of metal and mineral resources. Thus, holistic planning of decarbonization strategies should also consider other environmental impacts., Frontiers in Energy Research, 9, ISSN:2296-598X

Hundreds of sorption working pair equilibrium measurements have been reported in the literature, and many experimental results have been fitted to equilibrium equations. However, an open database does not exist for the equilibrium equations. Therefore, this work compiled 438 published equilibrium equations of sorption working pairs into an open-source database called SorpPropLib. SorpPropLib is accessible from six programming environments commonly used in sorption cycle simulation (C++, Excel®, Python®, Matlab®, Modelica® and Lab-VIEW™). Plotting capabilities allow fast cycle visualization in each programming environment. Thereby, the open-source database SorpPropLib aims to enable and encourage easy data sharing to advance sorption research., ISHPC 2021 Proceedings: Online Pre-Conference 2020

Water is often used as refrigerant in adsorption chillers due to its high enthalpy of vaporization and environmental friendliness. However, water as refrigerant limits the minimal cooling temperature of adsorption chillers to the freezing-point of water. To provide cooling below the freezing-point of water, we propose to use ethanol as antifreezing agent. Experiments with a water-ethanol refrigerant mixture as refrigerant show that the adsorption chiller process works at cooling temperatures of -5 °C., ISHPC 2021 Proceedings: Online Pre-Conference 2020

To account for volatile renewable energy supply, energy systems optimization problems require high temporal resolution. Many models use time-series clustering to find representative periods to reduce the amount of time-series input data and make the optimization problem computationally tractable. However, clustering methods remove peaks and other extreme events, which are important to achieve robust system designs. This work addresses the challenge of including extreme events. We present a general decision framework to include extreme events in a set of representative periods. We introduce a method to find extreme periods based on the slack variables of the optimization problem itself. Our method is evaluated and benchmarked with other extreme period inclusion methods from the literature for a design and operations optimization problem: a residential energy supply system. Our method ensures feasibility over the full input data of the residential energy supply system although the design optimization is performed on the reduced data set.We show that using extreme periods as part of representative periods improves the accuracy of the optimization results by 3% to more than 75% depending on system constraints compared to results with clustering only, and thus reduces system cost and enhances system reliability.

Industry requires mainly heat above 100 °C, but waste heat is mostly available at temperatures below 100 °C. To close this temperature gap, Adsorption Heat Transformers (AdHTs) are particularly promising and, therefore, recently discussed in the literature. However, an experimental feasibility study of closed AdHTs is currently lacking for temperatures around 100 °C. Therefore, we present an experimental setup for a lab-scale cyclic operating prototype of a closed AdHT in one-bed configuration that uses TiAPSO-34 & H2O as working pair. For the AdHT prototype, we demonstrate that heat transformation from 90 °C to 110 °C is experimentally feasible, while achieving a Coefficient Of Performance (COP) of 0.136 and a Specific Heating Power (SHP) of 32.4 W/kg. Moreover, we identify main challenges of the AdHT cycle that limit the AdHT performance and need to be resolved., ISHPC 2021 Proceedings: Online Pre-Conference 2020

The metal-organic frameworks (MOFs) Al-fumarate and aluminum-isophthalate CAU-10 (CAU = Christian Albrechts University Kiel) are considered for water-based adsorption chillers because of their excellent cyclic stability and high water uptake. However, water uptake captures only the equilibrium behavior, while process performance depends strongly on kinetics. In this work, we, therefore, determine characteristic time constants for water ad- and desorption on Al-fumarate and CAU-10. The MOF coatings are studied by small-scale Infrared Large-Temperature-Jump (IR-LTJ) experiments. Commercially available granular silica gels serve as benchmark. We show that the performance expected from the characteristic time constants depends strongly on the chosen characteristic time as well as the chosen reference in the heat exchanger: For area-specific mean power, silica gel performs best for small time constants, CAU-10 and silica gel both perform best for intermediate time constants, and Al-fumarate performs best for large time constants for the temperature triple 10/30/80 °C. For volume-specific mean powers, silica gels are outperformed by both MOF-coatings with the best results for CAU-10 at intermediate time constants. The results highlight the potential of MOF coatings for adsorption chillers, ISHPC 2021 Proceedings: Online Pre-Conference 2020

Capillary-assisted thin-film evaporation has attracted increased attention recently to efficiently evaporate the natural refrigerant water at low pressures. Although capillary-assisted evaporators have been studied in many publications, it remained unclear if published results can be compared. Respective measurements are often conducted under different conditions in terms of setup, procedure and evaluation, and potentially important factors are not specified or disregarded. In this work, we compare experimental setups and procedures. Experiments with finned copper tubes are conducted at RWTH Aachen and Fraunhofer ISE. A set of requirements is identified to ensure good agreement of the overall heat transfer coefficients. Major requirements are the specification of the heat exchanger’s surface properties, analysis of measurement uncertainty, well-specified input conditions, and control of non-condensable gases (NCG). Furthermore, dynamic experiments with continuously decreasing filling levels prove to be well-suited to quickly assess the heat transfer at all filling levels in a single experiment. Thus, this work identifies approaches for fast, reproducible and comparable characterization of capillary-assisted evaporation., ISHPC 2021 Proceedings: Online Pre-Conference 2020

A potential way to reduce the global greenhouse gas emissions for cooling and heating are thermally-driven cooling and heating technologies, such as sorption chillers. However, sorption chillers often suffer from high electricity consumption due to sub-optimal system integration. To optimize system integration, model-based approaches are very promising, but require valid models. For efficient model validation, we present a method based on the Optimal Experimental Design (OED) and apply the method to a dynamic adsorption chiller model. For this purpose, we plan an experiment with OED, execute it and estimate the unknown model parameters. To improve parameter accuracy and thus a valid model, we repeat the procedure iteratively. The results show that the presented method leads to a valid adsorption chiller model with only three optimally planned experiments. Furthermore, we show that the experimental effort decreases by up to 83 % compared to randomly planned experiments., ISHPC 2021 Proceedings: Online Pre-Conference 2020