1,721,048 research outputs found
Leave 2nd generation behind: cost effective solutions for small-to-large scale DH networks
No full textDemand response and other demand side management techniques for district heating: A review
Full text linkIf demand side management in electricity grid is a well known concept, the application to district heating systems (i.e. modifying the thermal demand in order to make it more compliant with the heat production) is significantly less widespread. Various attempts can be found in the literature concerning thermal demand modification in district heating, despite often researchers working on this topic are not fully aware of the other research activities also because various names are used to identify similar techniques. This paper represents the first survey on the use demand side application in district heating networks. The review clarifies the terminology and the stages for implementing demand side management to district heating network. Simulations and real applications are both considered in the review, including direct and indirect demand side management (demand response). Demand side management is found to be a great technique for district heating management. Various works show that the following benefits can be achieved: peak shaving up to 30%, doubled load factor, reduction of primary energy needs up to 5%, emission and cost reduction up to 10%. This clearly leads to significant cost and emission reduction, contributing to the decarbonization of urban areas
Thermal energy storage in district heating and cooling systems: A review
No full textThermal storage facilities ensure a heat reservoir for optimally tackling dynamic characteristics of district heating systems: heat and electricity demand evolution, changes of energy prices, intermittent nature of renewable sources, extreme wheatear conditions, malfunctions in the systems. The present review paper explores the implementation of thermal energy storage in district heating and cooling systems. Both short-term and long-term storages are considered highlighting their potential in combination with district heating. Connections of sensible, latent (phase change material) and chemical heat storage are analyzed taking into account the research maturity of each type technology. The transition of current energy systems towards next generation district heating, and sustainable multi energy networks is considered. Performance assessment by using proper thermodynamic indicators and costs are investigated. Further addressed topics include the use of heat capacity of the network and the buildings connected to the system to store energy. The main issues currently limiting the diffusion of daily and seasonal thermal storage and the main research paths are discussed
Optimization of the Thermal Load Profile in District Heating Networks through "virtual Storage" at Building Level
Full text linkThermal storage is of extreme importance in modern district heating networks in order to increase the share of waste heat and heat produced through renewable sources and cogeneration. Nevertheless, installation of large storage volumes is not always feasible, especially in dense urban areas. A possible option consists in virtual storage, which is obtained through variation of the thermal request profiles of some of the connected buildings with the goal of producing an effect similar to that obtained using storage. To perform such approach there are three crucial elements: 1) an advanced ICT solution able provide real time information about the thermal request of the buildings and the thermodynamic conditions at the thermal substations; 2) a detailed thermo fluid-dynamic model of the district heating network able to simulate the temperature evolution along the network as the function of time; 3) a compact model of the buildings in the district able to check the acceptability of the internal temperatures following the modified strategies. The model produces changes in the start-up time of the buildings connected with the network as well as possible pauses during the day. These changes in the request profiles usually involve a slightly larger heat load. Nevertheless, peak shaving is accompanied by a reduction in heat generation of boilers and an increase in the thermal production of efficient systems, such as cogeneration units. This results in a significant reduction in the primary energy consumption. An application to the Turin district heating network, which is the largest network in Italy, is presented. In particular, a subnetwork connecting the main transport network to about 100 buildings located in the central area of the town is considered. The analysis if performed in selected days where the optimization was conducted the day before on the basis of weather forecasts and then applied to the network. Despite the changes in the request profiles could be applied only to a limited number of buildings, the analysis show that the peak request can be reduced. Simulations performed considering the application of changes to a larger number of buildings show that reduction in the primary energy consumptions of the order of 5% can be obtained
Second law analysis of wildfire evolution under wind and slope effect
Full text linkhis paper aims at investigating possible relations between the fire main driving forces of forest fires,
particularly wind speed and ground slope, and the corresponding entropy generated. Second law
analysis is applied to an uncontrolled fire event in a g
rassy area (grassfire). The system is first
studied through a full physical numerical model, with the aim of collecting local data in the same way
that would be achieve through pervasive sensors. Simulations are conducted considering separate
contributions
of different wind speeds and terrain slopes. Three terms that contribute to the entropy
generation are separately calculated and analyzed in the parametric simulations: mass transfer term,
heat transfer term (heat losses) and transient term. The first ter
m is globally large, especially when
large wind velocities and terrain slopes are considered. This contribution is highly variable during the
fire evolution, with oscillations of about ± 120% with respect to the mean value. The second term is
also large an
d becomes dominant in the case of lower driving forces. Its behavior is more regular,
with oscillations of the order of ± 40% with respect to the mean value. The third term, instead, gives
an almost negligible contribution. Results also show that the total
entropy generated during the fire
propagation increases with increasing slope or wind speed, which also means with increasing fire
propagation velocity. In the range of data considered in this analysis, entropy generated is well
approximated by a logarithmic evolution as the function of propagation velocity, with a mean error of
about 5
Exergoeconomic analysis for the design improvement of supercritical CO2 cycle in concentrated solar plant
Full text linkIn this work, an exergoeconomic analysis is applied to the power cycle of a concentrated solar plant for its design improvement. A supercritical CO2 cycle connected with the exothermic reactor of a thermochemical storage unit is considered. The analysis is conducted with the goal of highlighting the advantages of exergoeconomic analysis while suggesting changes to both the design parameters and the system configuration. Starting from the plant configuration which guarantees the maximum efficiency, the exergoeconomic analysis is iteratively applied with the goal of reducing the unit cost of electricity. The analysis is conducted in a way that cost functions of the components can be substituted with the cost analysis of specific designs. This is a big advantage of this procedure, which is suitable for applications in which economic analysis requires a detailed knowledge of the system characteristics. The procedure is then validated comparing the results with those obtained through mathematical optimization
Automatic fouling detection in district heating substations: Methodology and tests
Full text linkDiagnosis of anomalies in heat exchangers of district heating substations is an essential point to assure high comfort level in buildings, as well as to exploit energy sources efficiently. The aim of this paper is to propose a methodology for automatically detecting fouling in the heat exchangers located in the substations of a district heating system. The methodology is tailored for large district heating networks, where a large number of buildings should be examined with reasonable availability of data. Fouling is analysed using only the data collected by the meters installed in the substations: the mass flow rate on the primary side and the temperatures on both sides of the heat exchanger. Evaluation is difficult due to the rawness of the data gathered and the variable operating conditions, which are adjusted on the basis of the external temperatures and set-points. The software created to implement the proposed methodology receives rough data as the input and it is able to manage data gap and lack of data. Furthermore, it provides a graphical output, which can be used for assisting the operators who manage the network and plan the cleaning schedules. The software has been tested considering space heating substations in six distribution networks of the Turin district heating system, for a total amount of 325 heat exchangers. A regular application of the approach and the cleaning of the heat exchangers presenting fouling is expected to lead to an average annual decrease of about 1.6% of the primary energy consumption in the entire network
Utilizzo di un modello ibrido 1d/zone per lo studio di logiche di ventilazione per lunghe gallerie in caso di incendio
No full textOvercoming bottlenecks due to supply temperature reductions in existing district heating
No full textIn the past decades, across the world and the Europe, several district heating networks have been built in the urban areas using the design criteria of that time. The criteria include the adoption of high design supply temperature (often larger than 100 °C) in order to reduce the size of the pipelines installed. This is the criteria that has been also used for the networks installed in major cities, which are characterized by several thousands of pipelines and a multitude of substations. These networks are often still operated using their design supply temperature, despite this is no more suitable to the smart exploitation of the energy resources (e.g. renewable, waste heat and in general low exergy heat). The work aims at the analysis of actions that allow to quantify which supply temperature reduction can be achieve by overcoming the issues due to the water congestion in the district heating pipelines. In fact, reduction of the supply temperature leads to the problem of the increase of the mass-flow rates circulating in the pipelines; this could set significant limitations on temperature reduction in fully-loaded infrastructures. This issue is analyzed by using a fluid-dynamic model of the thermal network. The work is applied to a real case, i.e. a district heating network still fed with overheated water
Multi-objective optimization of district energy systems with demand response
Full text linkIn district energy applications, implementation of management strategies is crucial to achieve reductions in primary energy consumption and carbon dioxide emissions. The development of optimization tools to upgrade the operation of smart energy systems should take into account all the relevant elements of these complex infrastructures. In this paper, a global optimization approach, applied to district heating, cooling and electricity networks interconnected to each other, is proposed. The suggested approach combines the optimization of the production side, useful to understand how it is convenient to produce heat, cold and electricity, with demand-side management for district heating customers. This is reached by using a bi-level optimization structure, exploiting the genetic algorithm and linear programming. A physical model of the district heating network is included in the procedure to accurately reproduce the effects of demand-side management. The tool can be applied to different objective functions. In this paper, a multi-objective optimization is carried out with two different objective functions: the operation cost and the carbon dioxide emissions. Results show that, by choosing an intermediate trade-off among the two goals, it would be possible to have a 12% reduction in the emissions at the expense of a 25% increase in the operating cost
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