The size of the thermal storage for domestic hot water (DHW) production could be a limiting factor to the wide spread adoption of domestic heat pumps (HPs). To overcome this issue, a latent thermal energy storage (LTES) could represent a good solution, given its compactness and the independence from the cylindrical shape which characterizes sensible storages. Latent storage units are often built as fin-and-tube heat exchangers, with copper tubes and aluminum fins surrounded by a phase change material (PCM). Given that DHW production requires high power, such a heat exchanger (HX) is necessary to compensate for the low conductivity of the PCM, but increases the cost of the LTES. Increasing the thermal conductivity of the latent storage material would allow for the use of smaller and cheaper HX, with large benefits in term of costs, currently the main obstacle to a wider diffusion of this technology. In this work, the impact of a PCM with enhanced thermal conductivity on the HX design and cost is explored. A multi-objective optimization algorithm (TSEMO) is used to identify optimal configurations by varying HX design parameters and simulating the LTES for a complete charge/discharge cycle. The results demonstrate that improved thermal conductivity allows for a reduction in HX size and cost while maintaining performance. The best configurations achieved up to a 28.6

Latent thermal energy storage systems offer a compact solution for domestic hot water applications. However, their adoption is limited by the high heat exchanger cost, mainly due to the copper and aluminium required to compensate for the low thermal conductivity of the phase change material. Reducing the material used while maintaining performance remains a critical challenge. This study presents a novel optimization framework based on a fast numerical model of a fin-and-tube latent thermal energy storage coupled with a genetic algorithm. The framework identifies improved configurations for domestic hot water production by evaluating each geometry through indicators related to practical use, namely the delivered water volume at 40 °C, the occupied volume and the heat exchanger cost. A two-dimensional axisymmetric model with separate charging and discharging circuits is developed, including fin geometry and the supercooling behaviour of the material. The model is validated under representative operating conditions, yielding root mean square deviations of the outlet water temperature below 0.5 °C during charging and 2 °C during discharging. Neglecting supercooling led to an overestimation of the heat transfer rate by up to 30%, showing its importance for accurate discharge prediction. The optimization assessed 580 configurations over complete charge and discharge cycles. The selected configuration reduced the heat exchanger cost by 22.2% and improved the performance-to-cost ratio by 7.6% relative to a reference commercial design. The proposed optimization framework could support storage design for domestic hot water applications.

This study presents a coupled techno-economic and environmental model of hybrid sensible-latent thermal energy storage (TES) systems, integrating phase change material (PCM) macro-capsules to enhance storage capacity and performance. The multi-scale model accounts for stratification in the sensible storage and phase change dynamics in the PCM capsules. This framework is used to perform multi-objective optimization across the full range of thermal self-sufficiency (SSth) levels for a multi-family building. The results show that a 70 % SSth offers the optimal balance between economic feasibility and environmental impact, with a Levelized Cost of Heat (LCOH) of 0.27 CHF/kWh and a Global Warming Potential (GWP) reduction of 76 % compared to fossil fuel alternatives. Systems targeting up to 85 % SSth are technically feasible but come with increased costs (up to 0.33 CHF/kWh), while exceeding 85 % SSth results in exponential increases in both cost and storage volume. Maximizing photovoltaic (PV) and heat pump (HP) power is critical for optimizing system performance. Future advancements in PCM technology and decreasing PV costs could lower the LCOH to 0.23 CHF/kWh and the GWP to 21 % of fossil fuel systems, demonstrating significant potential for long-term cost reductions and sustainability.

We review the literature on analytical models of advanced adiabatic compressed air energy storage plants with isochoric reservoirs, with a focus on the insights that can be extracted from the models.The review indicates that models for plants with adiabatic reservoirs, adiabatic turbomachinery, and without throttling is missing from the literature.We proceed to derive such models, assuming that the plant is operating at the quasi-steady state, that air can be treated as a calorically and thermally perfect gas, and that thermal-energy storage units are free of thermal and pressure losses.The models result in closed-form expressions for key performance indicators like the plant efficiency and volumetric energy density in terms of component efficiencies and pressure ratios.The derivation of these expressions rests on approximating integrals involving simultaneous temporal variations of temperature and pressure.The approximation leads to relative errors with magnitudes smaller than 1%.The models show that the compression and expansion work, the plant efficiency, and the maximum process temperature exhibit minima.The models also show that for a given non-dimensional storage capacity and maximum reservoir pressure, the maximum efficiency of plants that minimize the maximum process temperature is approximately equal to the minimum efficiency of plants that maximize the efficiency.For a two-stage plant with a diabatic cavern and diabatic thermal-energy storage units, our analytical model predicts the volumetric energy density to within 4.76%, indicating that it is accurate enough to be used for initial plant design.

Thermal-energy storage systems consisting of multiple tanks allow the implementation of thermocline-control methods, which can reduce the drop in the outflow temperature during discharging and increase the volumetric storage density and utilization factor. Multi-tank systems based on the extraction and mixing thermocline-control methods were assessed using simulations assuming fluvial rocks as storage material and compressed air as heat-transfer fluid. For adiabatic conditions, the simulations showed improved performance for all multi-tank systems, with diminishing improvements as the number of tanks increases. The mixing method performed better than the extraction method. The mixing method delivered an outflow temperature drop of 5.1% using two tanks whose total volume was 2.15 times smaller than that of the single-tank system. For diabatic conditions, more than three tanks were not beneficial. With two tanks, the mixing method attained a temperature drop of 5.8% with a volume that is 2.5 times smaller than that of the single-tank system. The exergy efficiency of the two-tank system was 91.3% compared to 98.1% of the single-tank system. The specific material costs of the two-tank system were 1.5 times lower than those of the single-tank system.

This work reports on the development of a transient heat transfer model of a solar receiver–reactor designed for thermochemical redox cycling by temperature and pressure swing of pure cerium dioxide in the form of a reticulated porous ceramic (RPC). In the first, endothermal step, the cerium dioxide RPC is directly heated with concentrated solar radiation to 1500 °C while under vacuum pressure of less than 10 mbar, thereby releasing oxygen from its crystal lattice. In the subsequent, exothermic step, the reactor is repressurized with carbon dioxide as it cools, and at temperatures below 1000 °C, the partially reduced cerium dioxide is re-oxidized with a flow of carbon dioxide. To analyze the performance of the solar reactor and to gain insight into improved design and operational conditions, a transient heat transfer model of the solar reactor for a solar radiative input power of 50 kW during the reduction step was developed and implemented in ANSYS cfx. The numerical model couples the incoming concentrated solar radiation using Monte Carlo ray tracing, incorporates the reduction chemistry by assuming thermodynamic equilibrium, and accounts for internal radiation heat transfer inside the porous ceria by applying effective heat transfer properties. The model was experimentally validated using data acquired in a high-flux solar simulator (HFSS), where temperature evolution and oxygen production results from model and experiment agreed well. The numerical results indicate the prominent influence of solar radiative input power, where increasing it substantially reduces reduction time of the cerium dioxide structure. Consequently, the model predicts a solar-to-fuel energy conversion efficiency of >6% at a solar radiative power input of 50 kW; efficiency >10% can be obtained provided the RPC macroporosity is substantially increased, and better volumetric absorption and uniform heating is achieved. Managing the ceria surface temperature during reduction to avoid sublimation is a critical design consideration for direct absorption solar receiver–reactors.

In der hier vorliegenden Arbeit soll das Verhaltnis der Begriffe: Bewegung und Gedanke in drei Primartexten untersucht werden. Ziel ist es dabei, nicht nur das Verhaltnis der genannten Begriffe in ein Verhaltnis zueinander zu bringen, sondern es soll vielmehr auch in Augenschein genommen werden, wie sich diese Begrifflichkeiten zu dem speziellen Schreiben der Autoren der Primartexte verhalten, beziehungsweise gelesen werden konnen. Die drei Primartexte umfassen die Nationalliteraturen dreier Lander, von England, der Schweiz und Deutschland. Als Primartexte werden in dieser Arbeit Ausschnitte aus: „To the Lighthouse“ von Virginia Woolf aus dem Jahr 1927, „Bin oder Die Reise nach Peking“ von Max Frisch aus dem Jahr 1945, und „Das Gesprach der drei Gehenden“ von Peter Weiss aus dem Jahr 1963 behandelt. Der erste thematische Teil der Arbeit widmet sich der Frage, warum fur diese Untersuchung die vorliegenden Primartexte gewahlt worden sind. Dieses ergibt sich durch die Konzentration auf die Begriffe die mit Bewegung und Gedanke in Zusammenhang gebracht werden konnen. Fur den Text von Virginia Woolf ist der Begriff des stream-of-consciousness von vordringlicher Bedeutung. Fur Max Frisch sind es die Begrifflichkeiten der Kontemplation, sowie der Erkundung des Subjekts. Der vordringliche Begriff im Falle von Peter Weiss ist der des Surrealismus. Im Folgenden gilt die Aufmerksamkeit einem Close Reading. Es werden dazu die drei Textstellen aus den Primartexten zur genaueren Klarung des Sachverhalts analysiert. Erst in einem Close Reading erscheint es also moglich die Besonderheit der Texte fur den Diskurs von Bewegung und Gedanke herauszuarbeiten. An eine genaue Lekture der gewahlten Textstellen schliest dann eine abschliesende Schlussanalyse an, die die erarbeiteten Ergebnisse und Erkenntnisse aus dem Close Reading der drei Texte zusammentragt und zu klaren versucht in welchem Sinne sich eine thematische Verbindung zwischen ihnen, immer in Bezug zu den Begriffen Bewegung und Gedanke, entdecken lasst.