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Thermal energy storage can play an important role to reduce the mismatch between energy demand and supply. This work presents two cascading systems with the aim to increase energy density and storage efficiency. Furthermore, the influence of the system volume on the energy density is depicted compared to only including the volume of the storage material. Both cascading cycles indicate an increase in energy density and storage efficiency on a material level compared to a direct use. When considering also the auxiliary components of the system, the energy density can decrease under the value of the direct use system. Thus, it is very important to gaze at the whole system for the calculation of energy densities.

The main objectives of research on innovative materials (phase change materials, PCM, or thermochemical materials, TCM) for thermal storage are the development of low-loss and compact storage systems with high capacity (sensible water storages being the benchmark). If the storage is to be implemented in an application with the aim to increase its energy efficiency, beside the technical/thermal properties and cost factors, also the environmental impact of the storage production and operation need to be considered during development. Yet up to now, a holistic development approach that considers the primary energy used for the manufacturing, operation and disposal in relationship to the potential energy savings does not exist for innovative storage concepts. Therefore, we are presenting data on the environmental impact of PCM and TCM on material and component level developed within the German project “Speicher LCA” (engl. “Storage Life Cycle Assessment”). The evaluation shows that PCM can be environmentally beneficial compared to water, if they are used in an application with a small useful temperature difference (e.g. cooling). Storing solar thermal heat with solid sorption materials in a closed system does not seem environmentally beneficial. Additional scenarios assuming the possible reuse of undegraded material, configurations with open sorption storage and/or other material classes (such as salt hydrates and liquid sorption) will be studied in the future

An investigation was carried out to determine the extent of relations between various structural properties of zeolite frameworks and their experimental water adsorption capacities. For this aim, average water capacity values were determined for different zeolite frameworks by utilizing water adsorption capacities reported in the literature for related materials. It was observed that the theoretical surface areas and volumes available for water adsorption in zeolites as well as the fractal dimensions of these materials exhibited some correlation with their experimental adsorption capacities. The results might give an indication of the potential for development of different zeolite frameworks, regarding their water adsorption capacities. Analogue materials of known zeolite framework structures, with different chemical compositions, which may allow for relatively high water adsorption capacities, may be prepared for such an improvement. The investigations may also be informative for the development of new zeolite-like adsorbents with relatively high capacities.

The politically endorsed reduction of greenhouse gas emissions entails the transformation of thermal energy systems towards renewable energies, especially in the building sector. This comes along with a demand in energy storage, as there is a time offset between energy availability and demand. As sensible heat storages induce major losses and have limited energy density, current water-based solutions are only partially sufficient to meet these demands. Within the project “Speicher-LCA” the environmental performance of a variety of innovative materials available for energy storage in buildings is assessed. The project provides the first extensive comparison of environmental profiles of various thermal energy storage materials, including phase change, thermochemical and sorption materials. The specific performances in the storage cycle are taken into account. All results will be publically accessible through a spreadsheet tool including a comprehensive set of materials, components as well as their integration into different building types. This paper discusses the methodological framework of the study and presents the environmental assessment results for selected materials. It highlights the main challenges in the assessment of innovative storage materials on different system levels which require specific definition of functional units accordingly. The first assessment results on material level for selected phase change (PCM) and thermo-chemical materials (TCM) allow an environmental characterization regarding their potential application in thermal storages. In addition, ranges of required numbers of storage cycles for amortization have been calculated for the non-renewable primary energy demand. For PCMs amortization cycles range between ∼20 to 150 cycles for salt hydrates and up to ∼280 cycles for paraffins. Regarding TCM, energetic amortization of silica gel and zeolite 13x is reached after ∼60 and ∼260 cycles respectively. Since the realization of storage components and systems which can actually be used in real applications will further increase the cycle number required for amortization, these storage materials may thus not be suitable for applications with a low number of cycles over lifetime, such as seasonal storage.

In this work, methods and processes for the production of hydrophilized and hydrothermally stable activated carbon honeycomb structures based on cost-efficient raw materials for the use in heat storage applications are presented. As a reference, activated carbon (AC) was hydrophilized using nitric acid. In a second step, AC monoliths with a channel substructure were prepared by an extrusion process and consequently oxidized using either nitric acid or ozone gas in order to restore microporosity and create hydrophilic groups on the inner surface of the material. The influence of the shaping and hydrophilization procedures towards substrate chemistry, pore structures, equilibrium water adsorption capacity, thermophysical properties such as heat capacity and conductivity as well as the multi-cycle ad-/desorption stability are comprehensively discussed. The successful hydrophilization by the nitric acid treatment was demonstrated for a powder AC sample. After 4 h of treatment a water adsorption capacity of 0.28 gg−1 at relative pressures p/p0 = 0.4 was observed, which represents a multiplication of capacity by 50 or 70 times compared to the raw material. In case of the AC monoliths, a capacity of 0.12 gg−1 at p/p0 = 0.4 is achieved by nitric acid treatment compared to 0.07 gg−1 for the ozone treatment.

Zeolite A coatings of various thicknesses were directly crystallized on stainless steel plates by using the substrate heating method. The coatings prepared were characterized by X-ray diffraction (XRD), laser microscopy and thermogravimetry (TG). Kinetic measurements were performed to determine the rates of adsorption of these materials, which exhibited rough corrugated surfaces with accessible nature. It was observed that the overall adsorption kinetics slowed down to some extent with the increasing thickness of the coatings. Regarding the power estimated for their use in adsorption heat pumps, the higher mass of the thicker samples could compensate for this limiting effect up to some point. An optimum zeolite A coating thickness, maximizing the power, was determined to exist between 58 μm and 176 μm, representing the thinnest and thickest coatings investigated in this study. For the operating conditions used, the optimum thickness value was around 130–140 μm, which varied to some extent with the amount of normalized loading.

In this work a novel solar driven dehumidification and cooling system is presented. The core components of this combined system are a sorptive dehumidification device based on high performance sorptive coatings and a novel evacuated tube solar air collector providing the driving heat. The essential part of the system is the coated heat exchanger. The chosen adsorbent is attached to the heat exchanger surface by a newly developed coating technique. Besides a brief description of the novel components and the experimental setup, the development of the aluminum heat exchanger, the coating procedure and scale up for geometries comparable to the heat exchanger in the dehumidification setup, as well as a first characterization of a small-sized coated heat exchanger regarding water uptake and dehumidification performance are presented. For estimating an overall system performance, a 2-dimensional thermodynamic model was applied, using the parameters in focus for the development of heat exchanger, coating and demonstration system.

Zeolite A coatings were grown on porous fibrous metal plates by using the substrate heating synthesis method. The coatings prepared were characterized by X-ray diffraction (XRD) and laser microscopy. Kinetic measurements were performed to determine the rates of adsorption of these materials while their adsorption isotherms were obtained by thermogravimetry (TG). The overall adsorption kinetics varied with the different samples investigated. The zeolite A coating grown on a copper fibrous support generally exhibited superior overall adsorption kinetics compared to a zeolite X coating with close mass, prepared previously on a stainless steel flat plate. The coating thickness as well as the support properties affected the performances of the samples. The inclusion of an additional polymer layer exhibited adverse impact on the kinetics especially after relatively high normalized loadings. The adsorption isotherms obtained for the zeolite coatings on fibrous supports were quite typical for zeolite A while the addition of polymer changed the isotherm type.

The performance of thick aluminophosphate molecular sieve layers for heat exchanger applications is evaluated. The aluminophosphate AIPO-18 (AEI structure type code) molecular sieve sorbent is coated on aluminium supports prior the sorption measurements. Two AIPO-18 samples with different morphological appearance, i.e. nano-sized crystals with monomodal size distribution and micron-sized crystals of varying sizes, are used to prepare layers with thickness in the range of 80-750 gm. As a binder component, polyvinyl alcohol (PVOH) was utilized in order to prepare mechanically stable layers, which are mechanically stable over numerous measuring cycles. The sorption measurements are conducted under canonical conditions at 40 C. The AIPO-18 layers showed decreased mass flows with increasing the thickness. Additionally, the layers comprising nanosized crystals showed higher equilibrium loadings and faster kinetics compared to films based on micron-sized crystals. Following the kinetic studies of pressure, temperature and heat flow, it can be concluded that the heat transport is the rate limiting mechanism for thick aluminophosphate layers. Importantly, the diffusion limitation plays a role only for relatively thin microporous aluminophosphate layers (

4th International Conference on Solar Heating and Cooling for Buildings and Industry (SHC) -- DEC 02-04, 2015 -- Istanbul, TURKEY, WOS: 000387506400026, An overview on the recent results on the engineering and characterization of sorption materials, PCMs and TCMs investigated in the working group WG A1 "Engineering and processing of TES materials" of IEA SHC Task 42 / ECES Annex 29 (Task 4229) entitled "Compact Thermal Energy Storage" is presented. (C) 2016 The Authors. Published by Elsevier Ltd.