Smart District Heating: Distributed Generation Systems' Effects on the Network☆

Abstract The European strategy 20-20-20 – providing for energy efficiency increase, pollutant emissions reduction and fossil fuel consumption reduction – leads to an increasing attention on the concept of smart cities. In this scenario, it is important to consider a possible integration between networks and distributed generation systems – i.e. to realize a bidirectional energy flux at the utilities, giving rise to the so-called smart grid – not only for the electrical sector, but also for the thermal energy field. Therefore, the concept of smart grid could be extended to the heat sector in relation to District Heating Networks (DHNs) and considering thermal energy distributed generation systems, such as solar thermal panels or micro-Combined Heat and Power (micro-CHP) generators. In this study several different layouts for the utilities substations in smart DHNs will be presented and discussed. These layouts have been developed in order to allow the bidirectional exchange of thermal energy at the utilities, optimizing the thermal exchange as function of network design temperatures (for both the supply and the return), of utilities' thermal power requirement and depending on the characteristics of the production system. Further, in this paper the results obtained from the simulations, carried out with the software Intelligent Heat Energy Network Analysis (I.H.E.N.A.) considering the implementation of the elaborated layouts, will be analyzed

Optimum sizing of cogeneration plants by means of a genetic algorithm optimization: A case study

In the context of increasing energy consumption, multi-generation systems such as combined heat and power generation (CHP) are attractive to meet the increasingly stringent requirements regarding energy saving in buildings. Hospitals are great consumers of energy, both electrical and thermal: the use of heating and cooling equipment for maintaining satisfactory comfort and indoor air quality for the patients as well as the adoption of several electrical health equipment result in the highest energy consumption per unit floor area of the entire building sector. In the present study, co/tri-generation systems\u2019 optimal set-up, size and operation are investigated for small/medium size hospital facilities. More specifically, after the presentation of the energy consumption profiles for a medium size hospital with 600 beds, set as reference case for this study, a parametric analysis has been carried out varying the peak loads of the user. For each of the proposed scenarios, the optimal plant configuration (sizing of all the energy production systems) has been outlined by means of a numerical code (Trigen 3.0) in-house developed. Afterwards, in order to optimize the load distribution in a smart grid characterized by electrical, thermal, cooling and fuel energy fluxes, an ulterior numerical investigation has been performed. The software, named EGO (Energy Grids Optimizer) consists of a genetic algorithm procedure: it defines the optimal load distribution of a number of energy systems operating into a smart grid based on the minimization of an objective function which expresses the total cost of energy production. Finally, an economic analysis has been carried out in order to evaluate the profitability of the proposed CHP-heat pump scenario

Thermodynamic Evaluation of Repowering Options for a Small-size Combined Cycle with Concentrating Solar Power Technology☆

Abstract The increasing penetration of low-carbon technologies and enhancements in fossil-fuelled power plants efficiency are some of the most important and up to date research topics. Renewable energy, in particular solar, has the potential of meeting the world energy needs while addressing environmental concerns, but technological advances in renewable energy electricity production are necessary to become competitive with conventional technologies. New opportunities to increase the penetration of renewables energies, smoothing out renewables variability and intermittency problems, come out from the hybridization concept. Hybrid renewable-fossil fuel systems join the advantages of both renewable energies and programmable devices. Among all the renewable technologies available for hybridization, Concentrating Solar Power (CSP) with parabolic trough is the most diffused because of its relatively conventional technology and ease of scale-up. CSP hybrids are well established worldwide, predominantly with natural gas: the hybridization options for CSP ranging from feed water heating, reheat steam, live steam to steam superheating. Based on a detailed thermodynamic cycle model of a reference small-size one pressure level Combined Cycle (CC) plant, the impact of CSP addition is thoroughly evaluated. Different hybrid schemes are evaluated and compared considering CC off-design operation. The goal of this study is to evaluate, from a thermodynamic point of view, three repowering options of a small-size CC with a CSP system in a hybrid system configuration and to quantify their potential benefits in terms of system's performance increase. In particular, the optimal size of CSP plant is shown for each investigated hybrid repowering options. The changes in CC steam cycle operating parameters are presented together with CC performance increase. It is shown that solar hybridization into an existing CC plant may give rise to a substantial benefit from a thermodynamic point of view

Low-temperature district heating networks for complete energy needs fulfillment

In order to reduce fossil fuels consumption and pollutant emissions, high contribution is given by district heating. In particular, the integration with renewable energy may lead to a significant increase in energy conversion efficiency and energy saving. Further benefits can be achieved with low temperature networks, reducing the heat dissipations and promoting the exploitation of low enthalpy heat sources. The aim of the paper is the analysis of the potential related to the conversion of existing district heating networks, to increase the exploitation of renewables and eliminate pollutant emissions in the city area. Further aim, in this context, is the optimization \u2013 from both energy production and operation management viewpoints \u2013 of a low temperature district heating network for the fulfillment of the connected users\u2019 energy needs. To this respect, a traditional network with a fossil fuel driven thermal production plant has been considered and compared with a low temperature district heating scenario, including geothermal heat pumps, photovoltaic panels and absorption chillers. These scenarios have been analyzed and optimized with a developed software, demonstrating the reduction of primary energy consumption and CO2 pollutant emissions achievable with low temperature networks. In addition, a preliminary economic comparative evaluation on the variable costs has been carried out. Future studies will investigate the economic aspect also from the investment costs viewpoint

Utilities Substations in Smart District Heating Networks

Abstract In the last decades the concept of distributed generation – i.e. the installation of (electrical and/or thermal) energy production systems at the final users – was born and found gradually increasing diffusion. For what concerns the electrical production, the distributed generation systems are directly connected to the National Electricity Transmission Grid, allowing a bidirectional energy flux at the utilities and giving rise to the so-called smart grid. In this scenario and considering that, even thanks to the direction taken by European regulations, in the European territory there is already a large number of thermal power generation's distributed systems (e.g. solar thermal panels), in the near future the concept of smart grid could be extended to the heat sector, especially in relation to District Heating Networks (DHNs). As a consequence, with the aim of analyzing the penetration of this type of networks, several possible layouts for the exchange utilities' substation have been developed and will be presented in this study. Such layouts allow to optimize thermal exchange, as a function of network design temperatures (for both the supply and the return), of utilities' thermal power requirement and depending on the characteristics of the production system

combined heat and power generation systems design for residential houses

Abstract Nowadays cogeneration is recognized as one of the most effective techniques to meet the increasingly stringent requirements regarding energy efficiency increase and energy saving in buildings. In this context, the aim of this study is the definition of reference parameters for the optimal energy systems design in residential applications. To this purpose, a generation scenario with cogeneration units, heat pumps, auxiliary boilers and chillers (both compression and absorption machines) has been set for the fulfillment of residential users' needs (in terms of electrical, thermal and cooling loads). For a given number of involved households, commercial cogeneration units have been selected, sized on the basis of the electrical peak need, and the generation scenario has been optimized by an in-house developed software, obtaining the optimal energy systems design and operation. Then, a parametric analysis has been carried out varying the number of considered households in order to define the optimal range of the energy systems size. In particular, specific values in terms of installed power for household and installed power for unitary peak load have been determined. For completeness, an economic analysis has been finally carried out for the evaluation of the return on investment and of the differential net present value – with respect to a standard generation scenario (only natural gas boilers for thermal needs fulfillment and electricity purchase from the grid for electrical and cooling needs) – considering a time horizon of ten years

Renewable Energy Storage System Based on a Power-to-Gas Conversion Process

Abstract The increasing penetration of renewable energy generation in the electric energy market is currently posing new critical issues, related to the generation prediction and scheduling, due to the mismatch between power production and utilization. In order to cope with these issues, the implementation of new large scale storage units on the electric network is foreseen as a key mitigation strategy. Among large scale technologies for the electric energy storage, the Power-to-Gas solution can be regarded as a long-term viable option, provided that the conversion efficiency is improved and aligned with other more conventional storage alternatives. In this study, a Power-to-Gas storage system is investigated, including as main components a high-temperature electrolyzer for hydrogen generation and a Sabatier reactor for methane production. The high-temperature Solide Oxide Electrolyser Cell (SOEC) technology, currently under development, is considered as a promising solution for hydrogen generation, due to the expected higher efficiency values, in comparison with conventional low-temperature electrolysis technologies. In order to evaluate the performance of the system and the energy efficiency, in this study a numerical model of the SOEC integrated with the Sabatier reactor has been implemented, including also the necessary additional auxiliaries, which can significantly affect the energy conversion performance. The whole energy conversion and storage system has been analyzed, taking into account different layout variants, by means of Aspen HysysTM numerical tool, based on a lumped modelling approach. The various Power-to-Gas storage configurations have been compared, with the aim to optimize both the system's efficiency and the composition of the produced gas stream

A Micro-ORC Energy System: Preliminary Performance and Test Bench Development

Abstract A large market potential for small electricity and heat generators can be identified in the domestic sector. Among the under development micro-scale power generation technologies the ORC (Organic Rankine Cycle) concept is a promising solution, already proven in the MW-range of power. There is still a prospective for smaller units for domestic users, with low temperature thermal demand. A test bench for a micro-CHP unit, currently run with a prototypal prime mover, is under development at University of Bologna. In particular, the system in study in the test facility is a micro-ORC system, rated for up to 3 kW. The ORC input heat is provided from an external source, which can be an external combustion system (a 46 kW biomass boiler will be connected to the thermal cycle) or an electric heater. The heat source delivers hot water to the bottoming ORC, currently operated with R134a as working fluid, which evolves in a recuperated cycle, with a 3-piston reciprocating expander, producing mechanical/electric power. The residual low-value heat is discharged to the environment with a water cooled condenser. The hot and cold water circuits have been realized in the lab to test the ORC performance. The micro-ORC internal layout and the external hot and cold water lines have been instrumented, implementing an acquisition and control software by means of LabVIEW software. A preliminary test campaign has been performed on the micro-ORC system, obtaining information on the actual thermodynamic cycle and the real performance under different operating conditions

Trends of European research and development in district heating technologies

There is a considerable diversity of district heating (DH) technologies, components and interaction in EU countries. The trends and developments of DH are investigated in this paper. Research of four areas related to DH systems and their interaction with: fossil fuels, renewable energy (RE) sources, energy efficiency of the systems and the impact on the environment and the human health are described in the following content. The key conclusion obtained from this review is that the DH development requires more flexible energy systems with building automations, more significant contribution of RE sources, more dynamic prosumers׳ participation, and integration with mix fuel energy systems, as part of smart energy sustainable systems in smart cities. These are the main issues that Europe has to address in order to establish sustainable DH systems across its countries.This research was conducted in collaboration between Wrocław University of Technology (Poland) and Brunel University London (UK). The support for the Polish team was by the Ministry of Science and HigherEducationunderGrantno.50532