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The integration of large solar heating systems in district heating (DH) networks with large combined heat and power (CHP) plants is rarely considered. This is often due to low costs for heat but also due to subsidies for the elect...
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The integration of large solar heating systems in district heating (DH) networks with large combined heat and power (CHP) plants is rarely considered. This is often due to low costs for heat but also due to subsidies for the electricity by CHP plants. Possible changes in subsidies and requirements in the reduction of fossil fuel based CO2 emissions raise an awareness of improving the operational flexibility of fossil fuelled CHP plants. This paper provides a rather simple but detailed methodology of including large solar heating systems in an existing district heating system, where heat is supplied by a large CHP plant. It uses hourly data of load and temperature patterns as well as radiation data and collector efficiency data to determine collector field size and storage size. The possibility of largely independent operation of sub-networks is analysed, which allows different system temperatures. It is demonstrated that a sub-network can operate without a back-up boiler and that both network parts benefit from the interaction. (C) 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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Environmental awareness increases, with demands for environmental certifications of new communities and buildings as a result. In the district heating industry, enabling of decentralized energy production is one way to meet requir...
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Environmental awareness increases, with demands for environmental certifications of new communities and buildings as a result. In the district heating industry, enabling of decentralized energy production is one way to meet requirements from customers. In this paper the technical impact of small-scale local solar collectors and heat pumps on district heating distribution networks is investigated. Customers that in this way can both produce and consume district heating are in this paper called prosumers. The study has mainly been performed through simulations in the computer programme NetSim. The results show that since the supply temperature from prosumers often is lower than the typical supply temperature, contribution from prosumers may result in lower supply temperature and thus increased velocity. The differential pressure decreases when water from the prosumers is mixed with supply water from the rest of the network and increases in the area where the prosumer creates a new pressure cone. Areas that are not reached by water from prosumers are affected differently depending on how the control of the differential pressure is managed. The results also show that prosumers' lower supply temperature may cause migratory temperature fronts that lead to increased fatigue in the pipes. This was further investigated by the local district heating company and the result showed that migratory temperature fronts generally has little impact on the lifetime of the pipes, since corrosion remains to be the limiting factor. In summary, this paper indicates that introduction of prosumers is possible, but demands management and control. (C) 2014 Elsevier Ltd. All rights reserved.
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Ambitious greenhouse gas emission reduction targets set by EU pose a significant challenge for the member countries. District heating as an efficient solution for heat supply and distribution can play a major part in meeting these...
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Ambitious greenhouse gas emission reduction targets set by EU pose a significant challenge for the member countries. District heating as an efficient solution for heat supply and distribution can play a major part in meeting these targets. One key issue concerning district heating is the integration of renewables. The current study focuses on solar assisted district heating systems.
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Central solar heating plants contribute to the reduction of CO_2-emissions and global warming. The combination of central solar heating plants with seasonal heat storage enables high solar fractions of 50% and more. Several pilot ...
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Central solar heating plants contribute to the reduction of CO_2-emissions and global warming. The combination of central solar heating plants with seasonal heat storage enables high solar fractions of 50% and more. Several pilot central solar heating plants with seasonal heat storage (CSHPSS) built in Germany since 1996 have proven the appropriate operation of these systems and confirmed the high solar fractions.
Four different types of seasonal thermal energy stores have been developed, tested and monitored under realistic operation conditions: Hot-water thermal energy store (e.g. in Friedrichshafen), gravel-water thermal energy store (e.g. in Steinfurt-Borghorst), borehole thermal energy store (in Neckarsulm) and aquifer thermal energy store (in Rostock). In this paper, measured heat balances of several German CSHPSS are presented. The different types of thermal energy stores and the affiliated central solar heating plants and district heating systems are described. Their operational characteristics are compared using measured data gained from an extensive monitoring program. Thus long-term operational experiences such as the influence of net return temperatures are shown.
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The TRNSYS XST-model for the calculation of the thermal behaviour of ground buried hot water heat stores was validated. For the validation procedure measured data of the seasonal hot water heat store in Hannover (Germany) were use...
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The TRNSYS XST-model for the calculation of the thermal behaviour of ground buried hot water heat stores was validated. For the validation procedure measured data of the seasonal hot water heat store in Hannover (Germany) were used. In contrast to previous investigations the temperatures of the surrounding ground were also taken into consideration. The determination of the heat store parameters was carried out using TRNSYS in combination with the parameter identification software DF. The deviation between measured and calculated temperatures is less than ±3%. The measured and calculated heat quantities are also in good agreement (annual deviation less than 2%). The validated XST-model was integrated into a TRNSYS model to calculate the thermal behaviour of the solar assisted district heating system in Hannover in 2002. The deviations between measured and calculated heat quantities do not exceed 5%.
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Solar thermal has contributed little for space heating in China. In 2014, although China shared 75.8% of the total solar collector installations in the world, only less than 0.3% of the solar collectors were used for space heating...
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Solar thermal has contributed little for space heating in China. In 2014, although China shared 75.8% of the total solar collector installations in the world, only less than 0.3% of the solar collectors were used for space heating. To promote solar district heating (SDH) in China, based on Danish experiences and Chinese clean heating transformation practices, a PEST (policy, economics, social, and technology) analysis and a SWOT (strengths, weaknesses, opportunities, and threats) analysis on SDH development in China were conducted. An extensive survey and on-site investigation were carried out to identify the applicability of SDH in rural areas. SDH development strategies, roadmap, and decision-making process for a SDH project are summarized. SDH has a broad application prospect in China with abundant solar resources and favorable policies. The solar heated floor area can achieve 756 million m(2) with an assumption of 3% coverage of the total heat demand of buildings. Particular areas with low population density, scarce resources, and strict environmental requirements, e.g., Tibet, should be given a high priority for SDH. Rural villages and small towns with better infrastructure, e.g., district heating networks, are the best target market for SDH in the next five years. With the development of seasonal heat storage technologies and the accumulation of practical experience, SDH can be expanded to industrial parks, large residential communities in sparsely populated northwest China. Integration of solar heat with existing heating networks in big cities with central heating will be challenging in the long run.
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The prosumer, already widespread in the electrical sector, is still uncommon in the district heating (DH) sector. Nevertheless, this figure can potentially provide a relevant contribution to increase the renewable fraction of heat...
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The prosumer, already widespread in the electrical sector, is still uncommon in the district heating (DH) sector. Nevertheless, this figure can potentially provide a relevant contribution to increase the renewable fraction of heat and to decrease the fossil fuel consumption, hence enhancing sustainable and efficient district heating. Moreover, prosumers are more informed and responsible towards energy production and energy savings. In order to enable the two-way heat exchange, the thermal substation at the interface between the prosumer and the DH network must be properly upgraded.The present paper aims at providing a comprehensive contribution to the design and testing of an innovative bidirectional substation for active district heating, focusing on the hydraulic configuration and on the control strategies. The realized substation primarily fulfils the prosumer's heat demand and supplies the excess heat to the DH network only if it is available at the temperature contractually defined with the DH operator, while it uses the network as a source if the local production is not sufficient to cover the user's heat demand. The prototype, with a technology readiness level TRL 4, can be connected to a generic micro-generation system, e.g. solar thermal or heat recovery units. An extensive test campaign has been carried out in order to evaluate its dynamic behavior both from energetic and hydraulic points of view. Test confirmed the reliable operation of the substation, which is able to handle simultaneous heat exchanges with the user's heating system and the DH network at pressure loss lower than 0.2 bar and at temperatures within +/- 0.6 degrees C of the prescribed setpoint after transients shorter than 5 min, even with +/- 10 degrees C step changes in the inlet fluid temperatures. (C) 2021 Elsevier Ltd. All rights reserved.
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In the paper a multi-objective optimization model for distributed energy supply systems optimization is presented. The superstructure of the system comprehends a district heating network that connects the users to each other, smal...
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In the paper a multi-objective optimization model for distributed energy supply systems optimization is presented. The superstructure of the system comprehends a district heating network that connects the users to each other, smalt-scale CHP systems, large centralized solar plant and a thermal storage. The optimization has to determine the optimal structure of the system, the size of each component inside the optimal solution and the optimal operation strategy. The multi-objective optimization is based on a MILP (Mixed Integer Linear Programming) model and takes into account as objective function a linear combination of the annual cost for owning, maintaining and operating the whole system and the CO_2 emissions associated to the system operation. The model allows to obtain different optimal solutions by varying the relative weight of the economic and the environmental objectives. In this way the Pareto Front is identified and the possible improvements in both economic and environmental terms can be highlighted. The model has been applied to a specific case study and it has been optimized for different superstructure configurations and for two different values of the electricity carbon intensity. The obtained results show that the solar plant, coupled with the optimal thermal storage, allows reaching both environmental and economic goals.
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To better facilitate renewable energy systems, the district heating sector is currently changing towards lower temperatures and increased cross-sectoral integration. Seasonal thermal energy storage systems alongside heat pumps hav...
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To better facilitate renewable energy systems, the district heating sector is currently changing towards lower temperatures and increased cross-sectoral integration. Seasonal thermal energy storage systems alongside heat pumps have received an increasing attention. However, the operation of a seasonal thermal energy storage system alongside a heat pump is more complex than a short-term thermal energy storage system, and as such, several complex simulation models have been developed. These models have shown to be usable for simulating the operation, but due to their complexity are difficult to implement in simulation models that focus on overall energy system analyses. Based on the operation of an existing seasonal thermal energy storage system, this paper provides a simulation method for a seasonal thermal energy storage system with a heat pump that can be utilized in overall energy system simulation models. The simulation method is based on the proven different operational situations of the seasonal thermal energy storage system. The method is shown to be able to approximate the actual operation on an hourly basis and the yearly thermal losses. (C) 2018 Elsevier Ltd. All rights reserved.
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Solar energy use in Nordic countries suffers from a high seasonal mismatch of generation and demand. However, given a large enough community, seasonal thermal storage could be utilized to store summertime heat gains for use in win...
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Solar energy use in Nordic countries suffers from a high seasonal mismatch of generation and demand. However, given a large enough community, seasonal thermal storage could be utilized to store summertime heat gains for use in winter. This simulation study examined a Finnish case of fully electric solar heating, where heat pumps (HP) powered by photovoltaic (PV) panels were used for generating heat for both immediate use and for seasonal storage through a borehole thermal energy storage (BTES) system.
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