Sorption heat storage

Thermal energy storage for use in connection with solar heating systems is described, concentrating on storage employing sorption heat energy

Flat-plate PV-Thermal collectors and systems : a review

Over the last 30 years, a large amount of research on PV-Thermal (PVT) collectors has been carried out. An overview of this research is presented, both in terms of an historic overview of research projects and in the form of a thematic overview, addressing the different research issues for PVT

Performance and costs of a roof-sized PV/thermal array combined with a ground coupled heat pump

A photovoltaic/thermal (PVT) panel is a combination of photovoltaic cells with a solar thermal collector, generating solar electricity and solar heat simultaneously. Hence, PVT panels are an alternative for a combination of separate PV panels and solar thermal collectors. A promising system concept, consisting of 25 m2 of PVT panels and a ground coupled heat pump, has been simulated in TRNSYS. It has been found that this system is able to cover 100% of the total heat demand for a typical newly-built Dutch one-family dwelling, while covering nearly all of its own electricity use and keeping the long-term average ground temperature constant. The cost of such a system has been compared to the cost of a reference system, where the PVT panels have been replaced with separate PV panels (26 m2) and solar thermal collectors (7 m2), but which is otherwise identical. The electrical and thermal yield of this reference system is equal to that of the PVT system. It has been found that both systems require a nearly identical initial investment. Finally, a view on future PVT markets is given. In general, the residential market is by far the most promising market. The system discussed in this paper is expected to be most successful in newly-built low-energy housing concepts

Shrinking core model for the reaction-diffusion problem in thermo-chemical heat storage

In this work, we develop a kinetic model to study the dehydration reaction of Li2SO4.H2O single particles involving interaction between the intrinsic chemical reaction and the bulk diffusion. The mathematical framework of the model is based on the shrinking core model. A variable-grid, finite-difference method with fully implicit formulation is used for solving the model. It is found that the Damkӧhler number 0 0 (k r ) / (D c ) Da r e plays an important role in determining the nature of the diffusion/reaction dynamics. A very small Da value means that the overall reaction is controlled by the intrinsic chemical reaction at the interface, while a very large Da value means that the overall reaction is controlled by the diffusion of water through the product phase. Moreover, the numerical results of fractional conversion calculated in the model are in good agreement with the theoretical analysis under extreme cases in which either diffusion (large Da) or reaction (small Da) dominates the dehydration process. With consideration of numerical solutions at various Da values, it is concluded that both intrinsic reaction and mass diffusion are important in determining the reaction kinetics within a range of Da values between 0.1 and 10

Kinetic study of LI\u3csub\u3e2\u3c/sub\u3eSO\u3csub\u3e4\u3c/sub\u3e·H\u3csub\u3e2\u3c/sub\u3eO dehydration using microscopy and modeling

\u3cp\u3eA phenomena-based method is presented to study the kinetics of the dehydration reaction of Li\u3csub\u3e2\u3c/sub\u3eSO\u3csub\u3e4\u3c/sub\u3e·H\u3csub\u3e2\u3c/sub\u3eO single crystals. The reaction proceeds by nucleation and growth processes, which are recorded photographically using a camera system. Based on a series of pictures of surface observations under isothermal conditions, an areic nucleation rate and growth rate were estimated. Since only surface information was obtained so far, an experimental study about the speed of growth into the crystal was carried out to quantify the growth rate in-depth. Together with the surface information, a nucleation and growth model was developed and employed to predict the reaction kinetics. The fractional conversion of the dehydration reaction was calculated and compared with experimental results from TGA (thermogravimetric analysis) measurements. A satisfactory prediction was achieved as a function of sample medium and experimental environment.\u3c/p\u3

Seasonal sorption heat storage - research on thermochemical materials and storage performances

Advantages of thermochemical heat storage over conventional heat storage are a higher energy density and loss-free storage of the heat after charging, since the heat is stored in chemical form. At ECN, a thermochemical heat storage is developed for seasonal heat storage applications. This paper shows results of materials testing, experiments with a lab scale reactor and first modeling results. The required output temperature of 60°C was realise

Performance analysis of industrial PCM heat storage lab prototype

\u3cp\u3eA 140 l lab scale shell-and-tube PCM heat storage was built and tested, and the experimental results were compared to a numerical model. Natural convection in the PCM was found to significantly influence the local temperature distribution in the storage vessel, which could not be predicted well by the model, since the model assumes only conductive heat transport in the PCM. Nevertheless, the overall thermal power output of the storage could be predicted fairly well, if a correction term was used in the model to compensate for the enhanced heat transfer in the molten PCM. Experimentally, a horizontal orientation was found to be beneficial due to increased heat exchange during charging (melting). Comparing the two PCMs used in the testing (RT70 and MgCl\u3csub\u3e2\u3c/sub\u3e·6H\u3csub\u3e2\u3c/sub\u3eO), it was found that the RT70 had stable performance while the salt hydrate showed a reduced melting enthalpy which was ascribed to phase separation. For the RT70, a thermal power of 5 kW is obtained during phase change in the charging phase, and 3.5–2 kW during phase change in the discharging phase, while for MgCl\u3csub\u3e2\u3c/sub\u3e·6H\u3csub\u3e2\u3c/sub\u3eO this was 3.5 kW and 3–2 kW respectively.\u3c/p\u3

In situ observation of the dehydration of Li2SO4.H2O monocrystals

In this study the dehydration reaction of Li2SO4.H2O crystals is investigated at different temperatures with the help of optical microscopy. The nucleation and nuclei growth processes during the reaction were recorded photographically using a camera system. Based on a series of pictures the propagation of the reaction front on the crystal surface was captured and an effective speed of growth (in μm/min) was estimated. It is demonstrated, using this in situ measurement technique, that the effective speed at certain temperature and water vapor pressure is a constant for different nuclei. From the surface observations it appeared that the mode of growth of nuclei is non-isotropic with a preferential direction along the [010] axis. In order to measure the growth rate in-depth, measurements on encapsulated crystals were also carried out. It is observed that the propagation of the interface in the crystal is linear and cracks have a remarkable influence on this propagation speed because of a higher mass diffusivity in the cracks