District Energy Network Research Articles

Thermoeconomic modeling and exergy analysis of a decentralized liquefied natural gas-fueled combined-cooling–heating-and-power plant

A small-scale combined-cooling–heating-and-power (CCHP) plant is proposed as a possible alternative to large-scale, centralized, electricity-only power plants. The proposed system is based on a non-ideal gas turbine (Brayton) cycle, integrated with a cooling plant and a district energy network. The study analyzes whether the proposed system could be an ideal candidate for distributed generation applications, especially in locations which are distant from centralized power plants. Therefore apart from reducing transmission and distribution losses, waste heat could be recovered effectively to generate heating, or cooling (via a cooling plant based on absorption refrigeration technology). The system considers fueling with liquefied natural gas (LNG), which is a safe and transportable fuel option. The cooling energy in the LNG is recovered in a useful manner since LNG regasification is coupled to the ambient air feed to the air compressor. The study includes a basic thermodynamic analysis, followed by an exergy analysis and a cost analysis. The simulation results signify a potential for further investigation of the proposed system, since its performance results in significant thermodynamic and environmental improvements, when compared to an equivalent conventional system. The system operates in two modes: (a) winter operation, where recovered heat is distributed to the district energy network, (b) summer operation, where recovered heat is used to drive an absorption chiller cooling plant to generate cooling, which is also distributed to the district energy network. The average primary energy ratio of the proposed system is 0.91, while the net electrical efficiency is 0.356 and 0.365, for summer and winter operation, respectively. The average exergetic efficiency is 0.419, which is a 25% improvement when compared to the conventional system. The cost analysis shows that the payback period is within a reasonable time frame (approximately 4 years), for a total initial cost of 17.1 million €.

Exergy performance analysis of the conceptual district energy network system with heat pump

To increase the efficiency of a district heating system, we propose a district energy network concept which combines several heating resources with additional electric heat pump and thermal energy storage. With help of thermal energy storage, a heat pump can be operated at maximum efficiency at all the time. Electricity generated with less CO2 emission makes the proposed system much more environmentally friendly. Even though the proposed concept can be applied to any given situation, a specific target area was chosen to show the effectiveness of the newly proposed energy network concept more clearly. Several constraints were applied for the selection process and a simplified model used for quantitative comparison between the existing and the developed concept. Exergy analysis showed the increased performance of proposed energy network system. The result showed that the newly proposed concept generates less CO2 emission by 46% at maximum compared to the existing system. By using additional renewable energy sources, we can reduce CO2 emission even further.

The potential benefits of widespread combined heat and power based district energy networks in the province of Ontario

In this work, an assessment is conducted of the potential primary energy savings and CO2 reductions associated with converting a conventional energy system comprising high thermal power plant penetration to one of two configurations. The first configuration consists of widespread DE (District Energy) grids equipped with CHP (Combined Heat and Power) plants, and the second includes wind energy. A model is constructed and five scenarios are evaluated with the EnergyPLAN software taking the province of Ontario, Canada as the case study. Scenario optimization results show that reductions in fuel utilization and CO2 emissions of up to 8.5% and 32%, respectively, are possible when switching to an energy system comprising widespread CHP based DE grids. A sensitivity analysis reveals that widespread CHP based DE systems have lower fuel utilization and CO2 emissions than large-scale wind systems for relative installed capacities below approximately 25% of the total generation mix. Differences in fuel utilization and CO2 emissions of up to 6.4% and 10%, respectively, are observed when comparing outputs from energy systems made up of two distinct CHP technologies, demonstrating the importance of accounting for heat to power ratio in large-scale energy planning studies that incorporate CHP generation.

Waste heat usage

This paper presents an overview of heat transfer issues arising from the current national situation regarding energy sustainability and global warming. An important concern addressed is the inefficiency of present fuel usage in the UK – namely large-scale, fossil-fuelled power stations and energy-from-waste plants that discharge huge quantities of low-grade heat to the atmosphere. Other countries recover this thermal energy and use it to supply heating and hot water to nearby domestic, commercial and industrial buildings. Such district heating schemes can provide cost-effective and low-carbon energy to local populations. Although the amount of district heating in the UK is small, Sheffield currently has an award-winning city-wide district energy network that incorporates a combined-heat-and-power energy-from-waste facility, providing electricity and district heating; this scheme is explored herein, with the purpose of identifying potential expansions through heat mapping. Heat transfer will clearly need to play a major part in one or more of the various power generation technologies proposed to meet the demands of the developing energy situation – these comprise high-efficiency systems using high-temperature regenerators or high-pressure combustion and energy storage utilising supercritical steam accumulators, which are all considered in this paper.

Developments to an existing city-wide district energy network: Part II – Analysis of environmental and economic impacts

District heating can provide cost-effective and low-carbon energy to local populations. Although this is rare in the UK, Sheffield already has an award-winning district energy network. It has been previously determined that this could be expanded to incorporate new heat sources and sinks. This paper determines the environmental and socio-economic impacts, focussing on various fuels. Combined-heat-and-power generation in Sheffield coupled with sustainable/renewable fuels, like waste, offer high efficiencies (>77%) and consistently lower carbon emission factors (0.04–0.14kg/MJ) than conventional energy generation using fossil fuels, since up to 80% of the fuel-carbon is biogenic (CO2-neutral). Processing municipal waste into a refuse-derived fuel prior to combustion or lowering the return-water temperature by 35°C in the district heating network could further improve efficiencies (81–93%) and reduce CO2 emission rates by 4t/h for the Sheffield plant, increasing avoided emissions from 69,000t/a to 80,000–91,000t/a. Moreover, ways in which the energy supply could be further decarbonised were identified, as well as methods to minimise the impacts of responding to changes in demand. Though initial costs of such schemes are high, they can be economically-viable for the investor/operator and consequently offer competitive rates for customers. Financial support is also available through government-backed schemes.

Developments to an existing city-wide district energy network – Part I: Identification of potential expansions using heat mapping

District heating can provide cost-effective and low-carbon energy to local populations, such as space heating in winter and year-round hot/cold water; this is also associated with electricity generation in combined-heat-and-power systems. Although this is currently rare in the UK, many legislative policies, including the Renewable Heat Incentive, aim to increase the amount of energy from such sources; including new installations, as well as extending/upgrading existing distributed energy schemes. Sheffield already has an award-winning district energy network, incorporating city-wide heat distribution. This paper aimed to demonstrate the opportunities for expansions to this through geographical information systems software modelling for an in-depth analysis of the heat demands in the city. ‘Heat maps’ were produced, locating existing and emerging heat sources and sinks. Heat loads (industrial, commercial, educational, health care, council and leisure facilities/complex) total 53MW, with existing residential areas accounting for ∼1500MW and new housing developments potentially adding a further 35MW in the future. A number of current and emerging heat sources were also discovered – potential suppliers of thermal energy to the above-defined heat sinks. From these, six ‘heat zones’ where an expansion to the existing network could be possible were identified and the infrastructure planned for each development.

Modelling and mapping sustainable heating for cities

Decentralised energy in the UK is rare. Cities in the north of England however lead the UK in terms of sustainable, low-carbon, local/district heating, through the implementation of combined-heat-and-power (CHP) facilities; substantial schemes are installed in several cities, including Barnsley and Sheffield. This paper presents the results from extensive experimental and theoretical feasibility studies, in which the merits of these were explored. Barnsley has a number of biomass-fuelled community energy generators, where pollutant monitoring and mathematical modelling were conducted to assess combustion characteristics and overall system performance. Measured pollutant levels were within the relative emission limits, though emission concentrations (CO, CO2, NO and particles) in the flue gas from the coal boiler were higher than the wood pellet boiler. Sheffield already has a citywide district energy network, centred around a sustainably-sourced waste-to-energy facility; an expansion of this scheme was investigated here. This focuses mainly on the link to a 30 MW wood-fired CHP plant, which could be a significant provider of additional thermal capacity (low-grade heat) to an expanded network. Through identifying heat sources and sinks – potential suppliers and end-users – key areas were identified where a connection to the heat network would be feasible.

Sheffield energy recovery facility and district energy network

This paper provides output data for the first year of operation of the new Sheffield energy recovery facility. It should be of interest to the energy provision community as a whole, but particularly to those promoting, planning, designing, constructing or operating a renewable electricity and heat energy facility utilising non-recyclable, kerbside-collected, municipal solid waste as fuel. An overview of the location of the facility and the extent of the associated district energy network is provided. Details of the fuel, energy output, emissions and operating data are given.