District Energy Network Research Articles

A Graph Theoretical Approach to Modeling of District Energy Networks

A Graph Theoretical Approach to Modeling of District Energy Networks

Thermoeconomic analysis of a novel topology of a 5th generation district energy network for a commercial user

This research compares an existing 4th generation heating and cooling network with a novel 5th generation heating and cooling network, driven by renewables. The networks are designed to cover the energy demand of a large shopping center. The existing network uses the thermal energy recovered from a trigenerative reciprocating engine coupled with an absorption chiller, to supply the heating and cooling networks. The proposed renewable 5th generation network consists of two neutral rings: the first one is the cold sink for the water-to-water heat pumps, installed in the substations; the second one is the hot sink for the heat pumps installed in the substations. One of the main novelties of the proposed layout consists in the use of a heat exchanger between these two rings. This heat exchanger recovers the heat rejected by the condensers of the heat pumps operating in cooling mode, supplying the evaporators of the heat pumps operating in heating mode. A photovoltaic field equipped with a lithium-ion battery partially matches the electricity demand of the network. The models of the shopping center and the existing and proposed networks are developed in TRNSYS environment. The proposed system achieves promising results: renewable electricity matches roughly 89% of the shopping mall electricity load can be covered by renewable power.

Energetic and exergetic performance analyses of mobile thermochemical energy storage system employing industrial waste heat

With an expanding urban population and increasing energy consumption, the demand for air conditioning is projected to reach 45 % of total energy demand by 2050. Based on projections, there will be a massive demand for air conditioning purposes, and energy consumption for air conditioning will also increase. Mobile thermo-chemical energy storage (MTES) offers an alternative by utilizing waste heat from power plants for heating and cooling via sorption heat storage. MTES proves advantageous due to its portability and phase change material transport capability. This study focuses on an MTES system applied in District Energy Networks (DEN) for cooling application. An analytical model has been developed to evaluate the system performance by considering energy efficiency ratio, round-trip efficiency, coefficient of performance, energetic efficiency, exergy destruction rate, and exergetic coefficient of performance as the performance parameters. Results show that an average round-trip efficiency of 53 %, maximum COP of 1.74, and exergy efficiency of 46.7 % is obtained for the year 2022. Notably, the MTES truck achieves a 50 % exergy efficiency. This study contributes insights into efficient waste heat utilization for sustainable cooling solutions.

A Study on Energy Center under Public Spaces with District Energy Networks

A Study on Energy Center under Public Spaces with District Energy Networks

Solar district heating system in Latvia: A case study

The ever growth of urban population has caused the increase of energy demand. This situation challenges the global public to find a way to produce energy in a secure, environmentally friendly, flexible, renewable and sustainable energy transformation system. One of the most promising technologies that can over-come most of the challenges is the district energy network. This paper focuses on best practice project in Latvia – fully renewable district heating system assisted by solar collector system with thermal storage tank and woodchip boilers. The article demonstrates solar impact to district heating system (DHS) in the framework of the current situation of DHS in Latvia by creating simulation in TRNSYS and validation with real system operation data. Real operational data show that the heat produced by solar collector system with thermal energy storage (TES) per year will cover up to 20% (10933,2 MWh) of the heating demand in under local climate conditions. The TRNSYS simulations concluded that the contribution of this type of solar system integrated into the DHS could be increased up to 50%, if the difference between consumption and heat produced by solar collectors were to be increased during the summer months, this could be achieved, for example, by increasing the solar collector field area.

Evaluation of low temperature waste heat as a low carbon heat resource in the UK

The capture and transport of waste heat represents a great opportunity for the decarbonisation of heat supply in buildings. To date, mostly high temperature waste heat has been reused and reported. However, with the recent advent of low and ambient temperature (4th and 5th generation) district energy networks, there is scope for the recovery and utilisation of heat from a range of novel, low temperature sources. The current study represents one of the first attempts to quantify the size of this opportunity, with particular focus in the UK, and complements the few previous attempts at estimating low temperature waste heat by focussing on a range of novel sources. The approach used was to evaluate a number of low temperature waste heat sources to determine: (a) the annual quantity of waste heat generated; and (b) the temperature(s) of the waste heat, for each heat source. In many cases, this was achieved using methodology and assumptions derived from the authors’ earlier investigations. The relative merits and potential of each heat source are also discussed, with respect to location, proximity to end users, need for upgrade using a heat pump, continuity of supply and distribution options for reuse, for example by using district energy networks with different operating temperatures. The total quantity of waste heat energy identified from the heat sources considered in this study, for England, Wales and Northern Ireland, was estimated to be 572 TWh.a−1, which would represent 132% of the total energy consumption for heat in these countries (432 TWh.a−1). Although this study focused on the UK potential for low temperature waste heat, the estimation methods developed and resulting analysis are generic and could also be applied in the context of other countries.

Distribution grid electrical performance and emission analysis of combined cooling, heating and power (CCHP)-photovoltaic (PV)-based data center and residential customers

As the number of data centers is increasing worldwide, there are concerns about their growing electricity demand on power grids and its impact on the environment. These concerns can be mitigated at the urban scale by utilizing the waste heat generated by data centers and multi-energy hub integration. Using Combined Cooling, Heating, and Power (CCHP) and Photovoltaic (PV) systems within a data center, in combination with district energy network connections, can create energy interactions with residential customers in a multi-energy hub. However, connecting large energy consumers and distributed energy systems to the electrical distribution grid presents challenges due to the conventional design of the power grid with unidirectional electricity flow. There is a lack of understanding about the grid impact of data centers with multi-energy systems regarding electrical performance parameters, energy demand, and emissions. To address these open issues, we developed an hourly energy interaction model that includes a CCHP-PV-based data center and residential customers. In addition, the CCHP-PV-based data center was operated with a cost-optimized energy scheduling. We conducted six case studies to distinguish the specific effects of CCHP, PV, and district energy network connections. The model takes into account hourly outdoor temperatures, energy prices, and varying energy demands to capture the seasonal impact on electrical performance parameters and energy results. From an energy and environmental perspective, CCHP-PV systems can eliminate the data center's electricity demand from the grid, reduce residential energy demand, and decrease carbon dioxide equivalent emissions. This cleaner production and energy exchange further support the United Nations Sustainable Development goals. The experimental results showed a 43% reduction in power loss in the distribution grid and helped the data center's main electrical bus and residential bus against the voltage drop phenomenon. The CCHP-PV-based data center with district heating and cooling connection reduced the peak hour electricity demand on the grid by 39% and annual electricity consumption from the grid by 66%. Furthermore, Greenhouse Gas Protocols (GHG) Scope-2 emissions associated with the data center's grid electricity consumption and only residential electricity consumption were reduced by 77% and 36%, respectively.

Performance of Residential Micro-CHP Operating in a District Energy Network

To resolve the problem of the imbalance between micro-Combined Heat and Power (m-CHP) supply and demand, a district energy network has been established based on residential m-CHP units powered by natural gas-fueled internal combustion engine. The electric and thermal loads of a Harbin residential building in a typical winter heating week are calculated. The performance of the m-CHP systems operating in two operation strategies, i.e., Following the Electric Load (FEL) and Following the Thermal Load (FTL), are analyzed and evaluated from both energy and economic aspects. The result shows that the energy cost of the m-CHP is reduced by 10% when operating in FTL mode, and the income from selling excess energy is 2.7 times more than that in FEL mode, indicating lower operation costs in FEL mode. Moreover, compared with the traditional separate production of electricity and heat, the net cost reduction rate of the system in FEL and FTL mode is 13.68% and 38.83%, respectively. Micro-CHP operating in a district energy network is more profitable than traditional separate electricity and heat production.

Year-round and techno-economic feasibility analyses on integration of absorption based mobile thermochemical energy storage with building cooling system in tropical climate

In recent years, growth in urbanization resulted in increased global energy demand. It is projected that by 2050, 45% of overall energy demand is through air conditioning/building space cooling applications. To meet the above-mentioned energy demand, there is a need for thermal energy management of the cooling system by utilizing waste heat from the industries. Thus, mobile/portable thermochemical energy storage (MTES) came into existence to utilize waste heat for building space cooling applications. In the present investigation, a case study on year-round and techno-economic feasibility of MTES system in district energy network, by extracting waste heat from Rourkela Steel Plant and transporting it to the NIT Rourkela academic building space cooling system is analyzed by developing a thermal model. For this case study, the capacity of the cooling system, the distance between the steel plant to the admin building, steam temperature through which thermal energy is generated and mass flow rate of steam are chosen as 1055 kW (300 Ton of Refrigeration), 7.4 km, 500 °C, and 25 tons/hr., respectively. Lithium Chloride is taken as molecular/thermochemical energy storage material or liquid desiccant. The required quantity of absorption material for each trip, no. of trips between the plant and building per day, device storage capacity, amount of heat dissipated to the surroundings for each trip, and location of the waste heat utilization unit in the steel plant are taken as techno-economic evaluation parameters. Then, MTES system performance and techno-economic feasibility studies for the year 2020 is carried out in accordance with the tropical climatic conditions of Rourkela, India. From this analysis, it is observed that during peak sunny day, heat dissipation from charging station to discharging station is about 927.24 MJ whereas from discharging station to charging station is about 145.76 MJ. The energy and round-trip efficiencies ratio which are the ratio of useful cooling output to the waste heat input and the ratio of heat dissipated to the surroundings during transit from charging station to discharging station to the waste heat provided at the charging station are observed to be 4.51 and 52%, respectively. Moreover, to make the system more economic and dependent upon renewable sources, the efficacy and profit incurred by diesel trucks, solar-powered trucks, and hybrid trucks are also assessed and compared in detail.

Resilient cooling through geothermal district energy system

Decarbonization and resilience to heat waves have recently become high priorities for building and district energy systems. Geothermal coupled district heating and cooling systems that operate a water loop near ground temperature gain increasing adoption to support decarbonization. In these systems, vapor-compression machines, distributed in the energy transfer stations, lift the temperature up or down to the needs of the particular building. In principle, these systems can provide low-power, free cooling from the geothermal bore field during heat waves when electricity is often scarce. However, the performance of such a resilience operation mode and its implication on the energy system configuration and the sizing of the bore field and HVAC equipment is not yet understood. Consequently, we are assessing their resilience, power use and design implications under a scenario of a heat wave on five working days during which chillers are switched off to reduce electrical consumption. Our analysis is based on high-fidelity, coupled dynamic models of district energy, building-side HVAC and actual control logic, with whole building energy simulation used to assess thermal conditions in a 2004 vintage multi-zone office building in Chicago, IL. The results show that relying only on waterside economizer cooling, the indoor thermal conditions can be maintained in a tolerable range for the majority of the building zones with half the electrical energy compared to standard chiller operation. Thermal comfort in the hottest zones can be further improved by oversizing the cooling coil. However, the waterside economizer has significant implications on the system configuration and sizing: The geothermal bore field needs to be sized about 30% larger than the upper limit of the range observed for conventional geothermal systems. Nevertheless, if a central chiller plant is added, the bore field can be downsized to the typical design range. The latter configuration still allows compressor-less cooling during the heat wave with peak power reduced by 60% compared to the standard design and chiller operation. • Geothermal coupled energy systems improve resilience of buildings during heat waves. • Demonstrated acceptable thermal comfort in typical office building during heat wave. • Integrated waterside economizer in ETS of ambient loop district energy network. • Used model-based HVAC and controls co-design for economic and reliable operation.

Incentivising multi-stakeholders’ proactivity and market vitality for spatiotemporal microgrids in Guangzhou-Shenzhen-Hong Kong Bay Area

Sustainability transformation calls for renovation and reformation on traditional energy systems. E-mobility and electrification in building sectors provide a promising alternative for cleaner power sharing in cross-boundary regions. Meanwhile, the renewable and sustainable transition requires multi-stakeholders’ collaboration from techno-economic-environmental perspectives. In this study, spatiotemporal energy sharing mechanisms were investigated for an E-mobility-based cross-boundary energy network in Guangdong-Hong Kong-Macao Greater Bay Area. In according to the energy boundary within the district energy network, diversity in energy pricing policies for external power trading (e.g., buildings and vehicles with power grid) was integrated for cost-optimal energy interaction modes (e.g., Vehicle-to-Building (V2B) and Vehicle-to-Grid (V2G) interaction). Furthermore, dynamic energy pricing strategies in internal power trading were explored based on supply-to-demand ratio, to promote multi-stakeholders’ participation. Through the parametrical and comparative analysis, trade-off strategies on V2G price and integrated wind turbine capacity have been proposed, to comprehensively balance battery depreciation cost, internal and external trading costs. Results show that roles of hotel and commercial building transit from economic payers to income earner along with the increase in integrated capacity of renewable systems, while commercial building always acts as an income earner, and residential buildings always act as economic payers. Moreover, the annual battery depreciation cost in the V2B interaction accounts for 6.5% of the vehicle cost (0.934 × 105 RMB), and the V2G interaction can reduce the vehicle cost from 1.33 × 106 to 1.15 × 106 RMB. By adopting the dynamic energy pricing in internal power trading, the roles of vehicles will transit from economic payer (1.01 × 106 RMB in Policy 2) to income earner (0.70 × 106 RMB in Policy 5), offsetting the battery degradation cost and economically incentivising participation willingness of vehicle owners. Furthermore, to compromise battery depreciation cost, internal and external trading cost and ensure the economic benefits of vehicle owners, V2G price is identified as 2.4 RMB/kWh and 2.3 RMB/kWh for scenarios with integrated wind turbine capacity at 1 and 2 MW. Research results can provide frontier guidelines on system designers and planners, pricing policy-makers, and energy managers to collaboratively develop a smart Greater Bay Area for sustainability transformation.

Optimal cost management of the CCHP based data center with district heating and district cooling integration in the presence of different energy tariffs

Data centers are expected to be one of the major prosumers in energy networks because of their high electricity demands as well as being a possible source of waste heat energy utilization. A combined cooling, heat, and power (CCHP) system can be a perfect match with a data center for supplying the data center's less fluctuated, uninterrupted power and cooling demand. Moreover, CCHP based data center integration with regional district heating and cooling system can gain data center's excess heat, improve the efficiency of the primary energy sources, and give flexibility to district energy operators. This paper aims to offer a comprehensive energy cost management for a CCHP based data center that considers power, heating, cooling, and data center's excess heat utilization in the presence of hourly energy prices and varying outdoor temperatures. Mixed Integer Linear Programming (MILP) is used to determine a cost-optimized operational strategy for the overall system. The result shows that CCHP and regional energy integration to the data center decrease the overall energy cost of the operation while providing more flexibility to the data center and district energy network operators. Optimized operation of the CCHP system with the data center's excess heat recovery, district heating, and cooling integration can cut its annual electricity costs by 40.3% compared to the local operation of the CCHP based data center. Return of investment (ROI) is estimated to be in 6.6 years for additional required systems for the conventional data center.

Iterative sizing of solar-assisted mixed district heating network and local electrical grid integrating demand-side management

Demand-side management and load-shifting strategies can reduce peak loads as well as temporal production/consumption mismatch, two classic issues in district energy networks that integrate solar sources. Nevertheless, the classic current sizing methods for such networks only consider the total demand, and not the possible loads after use of such techniques. The present paper aim is so to ascertain the connection between the possible demand reductions and the capacity design of generation sources. The study proposes an iterative sizing method with demand-side management as the central pillar. It retro-fits production units by assessing the network's overall performance through several criteria, both energetic and economical and with operational considerations. Exergy, which accounts for the quality of energy and is especially useful for multi-energy networks, is also considered. The method is illustrated on a mixed grid coupling a standalone heating network with a local electrical grid. Thousands of residential dwellings, with haphazard demands covered by solar-assisted technologies and a heat-pump are used in a series of ten scenarios with various management strategies, pricing policies and types of end-user contracts. In summary, the iterative method reduced the number of installed solar thermal collectors and photovoltaic panels by 13–38 % and 8–30 %, respectively. Furthermore, the method is stable: results converged after 2 iterations, in all scenarios. We also discuss the influence of low or high demand-side management penetration rate, and the final sizing selection by the decision-maker.

Identification of key performance indicators and complimentary load profiles for 5th generation district energy networks

Mass adoption of renewable heating is essential for achieving Net Zero 2050 emission targets. Rapid decarbonisation of heating could be delivered by 5th generation district heating networks, which share heating and cooling and offer energy, cost and carbon savings. We present an assessment framework for determining the economic, operational, and carbon benefits of heat pump driven energy sharing networks for an urban centre. Our analysis of complementary heating and cooling loads enabled novel identification of the building types which are best suited to thermal energy sharing. An urban street was modelled using Integrated Energy System Virtual Environment software, which produced heating, cooling, and hot water loads. These were implemented into a linear programming cost and carbon optimisation problem, producing operating curves for a pool of de-localised heat pumps under either cost or emission minimalization scenarios. Results show that energy sharing networks may reduce the Levelised Cost of Energy by 69% and carbon emissions by 13% when compared to an electrified non-shared energy system. Based on these findings, a load matrix was constructed to identify which energy loads from different building types can be suitably used for energy sharing. Despite promising cost-savings results, we conclude that low temperature district heating networks have much greater financial benefit when utilising appropriately sized thermal storage and time of use tariffs, rather than energy sharing. However, carbon savings can be made over alternatives, such as natural gas boilers. For developers undertaking a heat network project, the primary goal should be clearly defined as either carbon saving or money-making objective, as these are difficult to achieve synergistically.

Integrating Mobile Thermal Energy Storage (M-TES) in the City of Surrey’s District Energy Network: A Techno-Economic Analysis

The City of Surrey in British Columbia, Canada has recently launched a district energy network (DEN) to supply residential and commercial buildings in the Surrey Centre area with hot water for space and domestic hot water heating. The network runs on natural gas boilers and geothermal exchange. However, the City plans to transition to low-carbon energy sources and envisions the DEN as a key development in reaching its greenhouse gas emissions (GHG) reduction targets in the building sector. Harvesting and utilizing waste heat from industrial sites using a mobile thermal energy storage (M-TES) is one of the attractive alternative energy sources that Surrey is considering. In this study, a techno-economic analysis (TEA) was conducted to determine the energy storage density (ESD) of the proposed M-TES technology, costs, and the emission reduction potential of integrating waste heat into Surrey’s DEN. Three transportation methods were considered to determine the most cost-effective and low-carbon option(s) to transfer heat from industrial waste heat locations at various distances (15 km, 30 km, 45 km) to district energy networks, including: (i) a diesel truck; (ii) a renewable natural gas-powered (RNG) truck, and (iii) an electric truck. To evaluate the effectiveness of M-TES, the cost of emission reduction ($/tCO2e avoided) is compared with business as usual (BAU), which is using a natural gas boiler only. Another comparison was made with other low carbon energy sources that the city is considering, such as RNG/biomass boiler, sewer heat recovery, electric boiler, and solar thermal. The minimum system-level ESD required to makes M-TES competitive when compared to other low carbon energy sources was 0.4 MJ/kg.

Description and analysis of typical adjustment scenarios of regional energy system from the perspective of energy network theory

The district energy system has realized the effective consumption of new energy and the cascade utilization of energy, and has been widely used in the continuous and in-depth advancement of China's urbanization process. The district energy system is an organic combination of source-grid-load, and in practical applications, its components are usually in a dynamic change process, which has a certain impact on the matching of supply and demand of the district energy system. This article first puts forward the concept of district energy network, and then describes the typical adjustment scenarios of its energy supply nodes, energy consumption nodes and energy pipe network side respectively, and allocates energy resources of the district energy network according to various typical adjustment scenarios of the district energy network. The impact of the strategy is analysed to provide a reference for the economic construction of the regional energy system and the rational and efficient use of energy.

Data-driven modelling of operational district energy networks

There has been a resurgence of interest in district energy networks due to the cost, energy and emission reductions they can deliver. The prohibitively large computational cost of estimating thermal energy demand based on district- and urban-scale energy simulations is a major barrier to the wide-scale use of modeling in design and operation of district energy networks and in feasibility studies of technologies such as thermal energy storage. In this paper, a simple, computationally efficient modelling approach is proposed where operational data from the district energy network is used to construct temporal load profiles and thereby eliminate the need for building energy simulations. The proposed model is validated against data from a newly developed natural-gas powered district energy network in British Columbia, Canada. The utility of this data-driven approach is demonstrated through case studies on the feasibility and effectiveness of hourly thermal energy storage. It is shown that hourly thermal energy storage in a water tank can reduce the daily peak loads on the boilers by as much as 20%. Furthermore, using thermal energy storage, the highly fluctuating demand can be met with a constant-power supply, which would facilitate the use of biomass as an alternative energy source.

On the opportunity to integrate absorption heat pumps in substations of district energy networks

This article aims to study the opportunity to integrate absorption heat pumps (AHP) in substations of district heating networks (DHN). Three different operating modes of the AHP are proposed to match the varying building needs throughout the year from the heat provided by the DHN. The upgrade mode allows to increase locally the temperature of the DHN to cover high temperature needs with low temperature DHN. The cooling mode allows to cool down buildings from DHN heat in summer. And the heating mode allows to improve the heat transfer from the DHN to the building. To compare the performance reached with several absorbent/refrigerant couples, a steady state model was developed to simulate the AHP in DHN substations in typical operating conditions for the three operating modes considered. The results of the simulations confirm the thermodynamic opportunity to use AHP in DHN substations and the opportunity to switch between the operating modes during the day or the year to improve the profitability of the system. However, this study showed that attention should be paid to crystallization risks. Regarding the performance and the crystallization occurrence, couples using ammonia as refrigerant should be preferred to ones using water.

Feasibility limits of using low-grade industrial waste heat in symbiotic district heating and cooling networks

Low-grade waste heat is an underutilized resource in process industries, which may consider investing in urban symbiosis projects that provide heating and cooling to proximal urban areas through district energy networks. A long distance between industrial areas and residential users is a barrier to the feasibility of such projects, given the high capital intensity of infrastructure, and alternative uses of waste heat, such as power generation, may be more profitable, in spite of limited efficiency. This paper introduces a parametric approach to explore the economic feasibility limits of waste heat-based district heating and cooling (DHC) of remote residential buildings depending on network extension. A parametric model for the comparative water–energy–carbon nexus analysis of waste heat-based DHC and Organic Rankine Cycles is also introduced, and applied to an Italian and to an Austrian setting. The results show that, for a generic 4 MW industrial waste heat flow steadily available at 95 °C, district heating and cooling is the best option from an energy–carbon perspective in both countries. Power generation is the best option in terms of water footprint in most scenarios, and is economically preferable to DHC in Italy. Maximum DHC feasibility threshold distances are in line with literature, and may reach up to 30 km for waste heat flows of 30 MW in Austria. However, preferability threshold distances, above which waste heat-to-power outperforms DHC from an economic viewpoint, are shorter, in the order of 20 km in Austria and 10 km in Italy for 30 MW waste heat flows.

Heuristic battery-protective strategy for energy management of an interactive renewables–buildings–vehicles energy sharing network with high energy flexibility

Interactive energy sharing networks with centralised coordinated energy management between buildings and vehicles can increase eco-economics viability, while tracking battery degradations is critical to the assessment of techno-economic performance and energy flexibility. In this study, a mathematical model was developed to characterise the cycling aging of electrochemical battery storage in multidirectional interactions within interactive renewables–buildings–vehicles energy sharing networks, with classification of the cycle life into two groups (slow degradation zone and acceleration zone). An advanced battery-protective energy control strategy was developed that fully utilises inherent battery depreciation characteristics for flexible energy management. Multi-criteria were investigated, including equivalent CO2 emissions, import cost, energy flexibility, and the equivalent relative capacity of battery storage. With respect to the advanced battery-protective energy control strategy, the grid-battery charging process can decrease the depth of discharge and thus slow down the battery depreciation rate, but it will also lead to an increase in the number of cycles along with cycling aging. The research results show that, in terms of cycling aging, the single-variable mathematical fitting method with piecewise fitting curves (correlation coefficient of 0.9807) is more accurate than the bivariate mathematical fitting method (correlation coefficient of 0.9206). In addition, the proposed battery-protective control strategy can contribute to multi-criteria improvement. Furthermore, robust solutions for relative capacity improvement have been proposed with a lower limitation of fractional state of charge at 0.7. This study formulated a synergistic interactive energy framework for flexible district energy management, involving complementary solar-wind renewable systems, static and mobile battery storage, diversified energy demands in district buildings, and an advanced battery-protective energy management strategy, which can provide technical guidance to designers, operators, and stakeholders in terms of flexible participation in smart and resilient district energy networks.