A data-based reduced-order model for dynamic simulation and control of district-heating networks

This study concerns the development of a data-based compact model for the prediction of the fluid temperature evolution in district heating (DH) pipeline networks. This so-called “reduced-order model” (ROM) is obtained from reduction of the conservation law for energy for each pipe segment to a semi-analytical input–output relation between the pipe outlet temperature and the pipe inlet and ground temperatures that can be identified from training data. The ROM basically is valid for generic pipe configurations involving 3D unsteady heat transfer and 3D steady flow as long as heat-transfer mechanisms are linearly dependent on the temperature field. Moreover, the training data can be generated by physics-based computational “full-order” models (FOMs) yet also by (calibration) experiments or field measurements. Performance tests using computational training data for a single-pipe configuration demonstrate that the ROM (i) can be successfully identified and (ii) can accurately describe the response of the outlet temperature to arbitrary input profiles for inlet and ground temperatures. Application of the ROM to two case studies, i.e. fast simulation of a small DH network and design of a controller for user-defined temperature regulation of a DH system, demonstrate its predictive ability and efficiency also for realistic systems. Dedicated cost analyses further reveal that the ROM may significantly reduce the computational costs compared to FOMs by (up to) orders of magnitude for higher-dimensional pipe configurations. These findings advance the proposed ROM as a robust and efficient simulation tool for practical DH systems with a far greater predictive ability than existing compact models

Optimal Planning of Future District Heating Systems—A Review

This article provides the state-of-the-art on the optimal planning and design of future district heating (DH) systems. The purpose is to provide practical information of first-step actions for countries with a low DH market share for heating and cooling supply. Previous research showed that for those countries, establishing a heat atlas with accurate geographical data is an essential prerequisite to promote the development of DH systems. In this review, essential techniques for building a high-quality heat atlas are elaborated. This includes a review of methodologies for district thermal energy demand prediction and the status of the integration of sustainable resources in DH systems. In the meanwhile, technical barriers for the implementation of various sustainable heat sources are identified. Furthermore, technologies for the optimal planning of DH systems are discussed. This includes the review of current approaches for the optimal planning of DH systems, discussions on various novel configurations which have been actively investigated recently, and common upgrading measures for existing DH systems

Numerical Analysis of a Residential Energy System that Integrates Hybrid Solar Modules (PVT) with a Heat Pump

Photovoltaic‐thermal (PVT) collectors are hybrid solar collectors that convert solar and ambient energy into thermal and electrical energy. Integrated PVT‐HP, in which PVT collectors are combined with a heat pump, offers an efficient and renewable option to replace conventional fossil fuel‐based energy systems in residential buildings. Currently, system concepts in which the selection, design and control of the components are aligned towards the system performance are lacking. The development of a system model enables the comparison of a variety of system parameters and system designs, informed decision making based on the energetic performance and the market diffusion of PVT‐HP systems. This contribution presents a simulation model of a PVT‐HP system. By means of numerical simulations, with simulation program TRNSYS, the energetic performance of a PVT‐HP system and the system components are investigated. It is shown that the PVT‐HP can cover the annual energy demand of a residential building. The corresponding Seasonal Performance Factor (SPF) is equal to 3.6. Furthermore, the effect of varying weather conditions, occupancy and building orientations on the performance of the reference system is analyzed. The SPF for the investigated scenarios varies between 3.0 and 3.9. Lastly, two system parameters, the PVT collector area, and the PVT collector type are varied as an initial step in the optimization of the system performance. To sum up, the presented PVT‐HP model is suitable for dynamic system simulation and the exploration of the system concepts. The simulation study shows that a PVT‐HP system can cover the annual energy demand of a residential building. Lastly, parametric variations showcase the optimization potential of PVT‐HP systems

Performance analysis of a K2CO3-based thermochemical energy storage system using a honeycomb structured heat exchanger

The application of thermal energy storage using thermochemical heat storage materials is a promising approach to enhance solar energy utilization in the built environment. Potassium carbonate (K2CO3) is one of the potential candidate materials to efficiently store thermal energy due to its high heat storage capacity and cost-effectiveness. In the present study, a 3-dimensional numerical model is developed for the exothermic hydration reaction of K2CO3. The heat produced from the reaction is transferred indirectly from the thermochemical material (TCM) bed through the walls of the honeycomb heat exchanger to a Heat Transfer Fluid (HTF). A parametric study is conducted for varying geometrical parameters of the honeycomb heat exchanger. The obtained results indicate that the reaction rate and heat transport in the TCM bed strongly depends on the geometrical parameters of the heat exchanger. Reducing the cell size of the honeycomb heat exchanger up to a certain level provides better thermal transport as well as improved reaction rate of the TCM bed. The results of this study provide detailed insight into the heat release processes occurring in a fixed bed of K2CO3. The study is useful for designing and optimizing thermo-chemical energy storage modules for the built environment

Modeling thermochemical reactions in thermal energy storage systems

In this chapter on simulation techniques for thermochemical reactions in thermal energy storage systems the focus is mainly on molecular modeling techniques for the hydration and dehydration (sorption and desorption) processes occurring in salt hydrates at the nanoscale. Modeling techniques such as density function theory, molecular dynamics, and Monte Carlo are briefly introduced. Some attention is also given to micro- and macroscale modeling techniques used at larger length scales, such as Mampel’s model and the continuum approach. Before introducing all the length (and time) scales involved when modeling a heat storage system, a qualitative description is given of the hydration and dehydration processes on the nano/microscale

Thermochemical storage for long‐term low‐temperature applications: Performance estimation of ideal systems

Thermochemical heat storage has the potential to store a large amount of thermal energy from renewables and to cope with the seasonal mismatch of energy demand and supply, ideally without energy losses typical of sensible heat storage. However, in order to have a commercially attractive system, research at material, reactor, and ultimately at system level is still required. The aim of this work is to investigate the current state-of-the-art research at prototype- and system-scale, and to estimate the performance of ideal long-term low-temperature thermochemical storage systems in terms of energy densities and storage capacity costs. First, a review on existing systems based on solid/gas reactions is carried out. Especially for open systems, the choice of adsorbents rather than salt hydrates as active materials is prominent due to their enhanced stability. However, high material costs and desorption temperatures, coupled with lower energy densities, decrease their commercial attractiveness. Then, the performance of ideal open thermochemical heat storage systems based on solid/gas reactions are estimated for different active materials among which salt hydrates, an adsorbent, and an ideal composite. The common reference scenario assumes that the seasonal space heating energy of a passive house has to be stored. The results show that the open system based on a composite material, can represent a valid compromise between hydrothermal stability and storage capacity costs. However, it results in a very large system for the assumed reference scenario conditions. The performances of open systems are then compared with the ideal performance of closed solid sorption systems. The results show that closed systems are in general more expensive and less compact for the assumed reactor layouts. Finally, liquid sorption systems from the literature are compared with the open and closed solid sorption systems. The results show that most of the liquid systems are not able to achieve the minimum temperature required by the consumer in the reference scenario. However, a liquid sorption system based on NaOH-H2O can in principle satisfy the consumer needs and result more compact and less expensive than solid sorption systems based on pure adsorbents and certain salt hydrates. Beside research at material- and reactor-scale, integration of thermochemical storage at grid level has to be investigated to assess its techno-economic feasibility based on their performance and interactions with production and consumption technologies

Proteoglycans in health and disease: novel regulatory signaling mechanisms evoked by the small leucine-rich proteoglycans.

The small leucine-rich proteoglycans (SLRPs) are involved in many aspects of mammalian biology, both in health and disease. They are now being recognized as key signaling molecules with an expanding repertoire of molecular interactions affecting not only growth factors, but also various receptors involved in controlling cell growth, morphogenesis and immunity. The complexity of SLRP signaling and the multitude of affected signaling pathways can be reconciled with a hierarchical affinity-based interaction of various SLRPs in a cell- and tissue-specific context. Here, we review this interacting network, describe new relationships of the SLRPs with tyrosine kinase and Toll-like receptors and critically assess their roles in cancer and innate immunity

Techno-economic optimization of an energy system with sorption thermal energy storage in different energy markets

Sorption thermal energy storage (STES) has the potential to have higher energy densities and lower thermal losses compared to conventional thermal storage technologies, and it can contribute to increase the energy grid flexibility and the penetration of intermittent and distributed energy sources. However, STES is a technology still under research, and system-scale investigations are necessary to determine its potential in future energy systems. In this regard, the objective of this work is to investigate the STES potential in a reference energy system interacting with different energy markets. The system consists of a geothermal doublet supplying thermal energy to an organic Rankine cycle (ORC) and to a district heating network that satisfies the thermal energy demand of a residential neighborhood. A techno-economic optimization of the energy system is carried out using mixed integer linear programming. The optimization aims at finding the optimal STES size and system operational behavior that maximizes the yearly profits from selling the ORC energy to the energy markets. Among the main results, it is found that the STES integration increased the overall system profits by 41% in the scenario where the ORC interacted with the UK day ahead market (2017 data), and with two UK balancing services: the capacity market, and the short term operating reserve. In conclusion, this work highlights how a thermal storage technology still under research could become an asset under specific market conditions. Future policy mechanisms can benefit from similar analyses and foster the integration of new technologies into the energy grid