Heating Network Research Articles

From dumping to circular economy: There is no success like failure.

Waste management has been developing in response to needs. The need to get rid of unwanted materials has always been a motivation but using the resource value of waste has also been a driver from the stone age and forwards. In affluent times not so much. Sanitation became a motivation with the discovery of pathogenic microorganisms in the mid-19th century, and after World War 2 (WW2) a strong focus on environmental protection developed, and in recent times, the resource aspect has received an interest despite material affluence. Legislation has been one of the drivers for recent developments, in the case of Sweden, the environmental protection legislation came in the late 1960s, and a few years later, the municipalities got the exclusive right to collect and manage household waste. Many local and regional waste management companies were established, owned by the municipalities. These organizations became agents of development, due to the increased scope and capacity. Adding to the environmental protection agenda, a renewed interest in waste as a resource was initiated by the oil crises of the 1970s, resulting in new waste incineration plants, with energy recovery, connected to already existing district heating networks. Mistakes, failures and alarms in the 1970s and the 1980s resulted in treatment method improvements and the establishment of source separation as an integral part of waste management. The waste management community stands strong today and is taking a more proactive role than before, which includes a stronger focus on communication with other stakeholders.

Incorporating microbial inoculants to reduce nitrogen loss during sludge composting by suppressing denitrification and promoting ammonia assimilation

To address the challenge of increasing nitrogen retention in compost, this study investigated the effects of microbial communities on denitrification and ammonia assimilation during sludge composting by inoculating microbial inoculants. The results showed that the retention rates of total Kjeldahl nitrogen (TKN) and humic acid (HA) in MIs group (with microbial inoculants) were 4.94 % and 18.52 % higher than those in the control group (CK), respectively. Metagenomic analysis showed that Actinobacteria and Proteobacteria were identified as main microorganisms contributing to denitrification and ammonia assimilation. The addition of microbial agents altered the structure of the microbial community, which in turn stimulated the expression of functional genes. During cooling period, the ammonia assimilation genes glnA, gltB and gltD in MIs were 15.98 %, 24.84 % and 32.88 % higher than those in CK, respectively. Canonical correspondence analysis revealed a positive correlation between the dominant bacterial genera from the cooling stage to the maturity stage and the levels of NO3−-N, NH4+-N, HA, and TKN contents. NH4+-N was positively correlated with HA, indicating NH4+-N might be incorporated into HA. Heat map and network analyses revealed NH4+-N as a key factor affecting functional genes of denitrification and ammonia assimilation, with Nitrospira identified as the core bacteria in the microbial network. Therefore, the addition of microbial agents could increase nitrogen retention and improve compost product quality.

Accuracy improvement of the load forecasting in the district heating system by the informer-based framework with the optimal step size selection

Accurate load forecasting is crucial for effectively regulating regional heat network systems. However, existing forecasting methods often rely on subjective experience to determine the forecasting step, which is limited by the presence of thermal inertia, leading to suboptimal accuracy. To address this limitation, an optimal step size selection method based on the Informer-based framework is proposed to enhance load forecasting accuracy in heat exchange stations. This method leverages the Attention mechanism within the Informer model, enabling the capture of global information in a single step. To verify the effectiveness of the proposed method, real operational data from a typical thermal power plant in North China is utilized to analyze and test the impact of data distribution and prediction step size on the model's prediction capability. The performance is evaluated using Mean Square Error (MSE), Mean Absolute Error (MAE), and Mean Absolute Percentage Error (MAPE). Comparative analysis against Support Vector Regression (SVR) and Long Short-Term Memory (LSTM) models demonstrates that the Informer algorithm with optimal prediction step size achieves the highest prediction accuracy. Notably, the proposed method achieved a minimum reduction of 62.7 %, 46.5 %, and 42.9 % in MSE, MAE, and MAPE, respectively, significantly surpassing the performance of alternative prediction methods.

Least-Cost-Path and Closest Facility Analysis for Generating District Heating Networks on a Communal Level

Due to an urgent need to reduce the fast-progressing climate changes, a rapid, standardized and replicable solution for the infrastructure restructuring of the heat demand coverage of buildings at the district and city levels must be developed. As more and more communities in Europe, especially in Germany, are obligated to have plans for coverage of the heat demand, city planners and energy agencies seek a tool that will help them to design the first drafts of heating network routes, which can supply whole districts and cities with renewable energy. ArcGIS Pro Tools like Least-Cost-Path Analysis (LCPA) and Closest Facility (CF) allow us to find the shortest and “cheapest” way between the heat source and heat consumers in the analyzed areas. Starting from the community level, through the district, county, voivodeship and whole-country levels, the replication of the methods for generating district heating (DH) network infrastructure can be achieved. The proposed LCPA- and CF-based methods help to design the most suitable and efficient DH networks in the analyzed areas. As only a few open-source data inputs, like street networks and building footprints, are needed, the methods can be implemented in all communities in the country of Poland. In this paper, one example of one community in Wroclaw county, called Siechnice, and its surroundings is presented.

Holistic non-linear optimization of the layout, sizing, and operation of a district heating plant

A large fraction of district heating networks in Europe are still operating without thermal energy storage. While offering operational flexibility, the presence of energy storage complicates the problems of optimal sizing and control of the heat production plant. This necessitates a novel approach to system sizing based on non-linear programming in order to capture the system’s thermal response and inertia. Therefore, the present study focuses on such a typical plant in France and describes a holistic approach to optimize the capacities/parameters of system components, positions of the energy sources, as well as hourly flow rates. Such a simultaneous tuning of the system parameters and operating variables is essential to maximize the cost savings over the system's lifetime. The proposed framework here maintains the original non-linear form of the objective function and the constraints for more accuracy while allowing precise modeling of the thermally stratified storage tank by decoupling its calculations at a lower simulation level. Hence, the computation time in MATLAB® R2020A is mostly below 20 min on a typical personal computer. The lowest levelized cost of heat (57.259 EUR/MWh) is achieved when placing the gas boiler on a parallel line between the biomass boiler and the storage tank while sizing the two boilers using fractions of 0.33 and 0.73 of the maximum hourly demand, respectively, as well as a storage volume of 318.9 m3. Such relatively small storage reduces the lifecycle costs by a maximum of 1.34 % while reducing the specific carbon emissions by 17.33 %. Besides, it dampens the fluctuations in supply flow rates, minimizes unnecessary flow recirculation, and ensures a stable heat supply. Overall, thermal storage has a reasonable positive impact from an economic perspective, but a substantial impact on operational flexibility and mitigated carbon emissions.

Model predictive control of bidirectional heat transfer in prosumer-based solar district heating networks

District heating networks with decentralized heat production are ideally suited to include a high share of renewable energy sources for heat production in urban areas with limited space. A new concept is a prosumer-based district heating network in which some or even all buildings are equipped with decentralized building-level heat storages and heat generation plants. To exploit the full potential of the interconnected heating network, buildings with surplus heat are intended to transfer heat to buildings with heating demands to prevent the activation of the central heating plant. This work presents an initial feasibility study on using a model predictive control strategy to manage bidirectional heat transfer between buildings in a district heating network. We formulate this problem as an optimal control problem, incorporating binary decision variables for each potential heat transfer connection. This results in a mixed-integer nonlinear optimization problem that is hard to solve. The problem is solved with a fast gradient-based optimization algorithm in combination with a combinatorial integral approximation strategy. A case study concerning a residential heating network with building-level solar thermal collectors and storage tanks is carried out. The optimized operation is compared to the real operation obtained from one month of measurements. The results show that the optimized strategy with bidirectional heat transfer can exploit the total heat generated in the whole network. The central heating provider is only required when the heat produced or stored by all the buildings is insufficient to meet the total heat demand within the network. In the case study, this leads to a reduction of almost 75% of the required thermal energy from the central heat provider.

Optimal scheduling of electric-gas-heat system considering dual virtual energy storage of gas network management and heat network storage

Aiming at the problem of wind curtailment caused by the lack of system flexibility, an optimal scheduling strategy for improving the flexibility of the electricity-gas-heat interconnection system by the coordinated operation of the gas network management and storage characteristics and the heat storage characteristics of the heat network is proposed. Firstly, the influence of gas network storage and heat network storage on improving flexibility is analyzed respectively. Then, an electricity-gas-heat interconnected system scheduling model considering the dynamic characteristics of gas network management and t the delay characteristics of heat storage in heat network, which greatly improves the imbalance between supply and demand of flexibility in space and time brought by the anti-peak regulation characteristics of wind power to the system. Finally, the IEEE-24 nodes power system, Belgium’s 20-node natural gas network and 6-node thermal network are used, for example, analysis. The results show that the proposed scheduling scheme improves the flexibility of the system while its operating cost and wind curtailment cost are the lowest, which promotes the consumption of wind power.

Performance analysis of solar desalination using crushed granite stone as an energy storage material and the integration of solar district heating

ABSTRACT This study explores the feasibility of solar desalination using black powder coated crushed granite stone, evaluating their energetic, exergetic, and economic aspects, wherein the stone bed preheats water for the solar still. In addition, the system integrates with a district heating network to meet desalination needs during off-solar or high-demand hours in which water from the powder-stone grid’s outlet flows through a heat exchanger, powered by district heating’s return flow. Desalination pipe absorbs heat and cools district heating line. The outcomes illustrated that cumulative distilled water for a water depth of 1 cm was 13.1% and 28.2% higher than cumulative distilled water for water depths of 2 cm and 3 cm, respectively. The energy efficiency was improved by 9.5% and 15.7% and the exergy efficiency was enhanced to 13.6% and 27.2% at 1 cm water depth compared to 2 and 3 cm water depths. The integration of the system with the district heating network could lead to a great improvement in the productivity; summer’s low district heating demand allows surplus heat to boost water production and lower outlet water temperature, benefiting both desalination and cooling process. The cumulative productivity will not be sensitive to the water depth anymore, increasing up to 105%, 135%, and 182% for 1, 2, and 3 cm water depths, respectively. This integration has a fascinating effect on the reduction in temperature of the district heating return flow (about 3°C), improving the cooling potential of the flow.

Real-time outdoor experiment and performance analysis of dual-coil heat exchanger integrated thermal energy storage

Integrating a thermal energy storage system into a solar water heater enables a continuous heat supply to ensure hot water is available for household uses throughout the day. This research emphasizes integrating TES units into solar water heating systems. The overall performance of flat plate solar water heaters for a regular (conventional) solar water heating system and a solar water heating system integrated with TES using phase change material (PCM) are analyzed. This innovative design ensures efficient heat capture from the sun, storing it in the phase change material for later use, guaranteeing a sustainable and cost-effective solution for hot water needs. A split PCM tank is integrated within the solar water heating network for the second scenario and is made of a 25 L filled with a phase change material that acts as the thermal storage medium. The PCM tank has a dual-coiled heat exchanger to aid the heat transfer process with paraffin wax as the phase change material. The parameters that are looked into from the conventional and TES-integrated solar water heating systems include the water temperature profiles throughout the entire solar water heating networks and the PCM's temperature distribution throughout the day. A customized water draw schedule is adapted to represent the average hot water usage of a typical household in Kuala Lumpur. Findings reveal that the TES-integrated solar water heating system can be 21 % more efficient than the conventional system due to the lesser heat losses and prolonged hot water supply. The maximum efficiency obtained is about 82 %, and energy can be saved about 50 % from the electric heater. The maximum energy storage is at the 50 °C temperature controller's setting and is feasible for the existing conventional solar water heaters.

Construction of a cold island network for the urban heat island effect mitigation

The urban heat island (UHI) effect seriously challenges sustainable urban development strategies and livability. Numerous studies have explored the UHI problem from the perspective of isolated blue and green patches, ignoring the overall function of cold island networks. This study aims to explore the construction method of cold island network by integrating scattered cold island resources, rationally guiding urban planning and construction, and providing effective ideas and methods for improving the urban thermal environment. Taking the central city of Fuzhou as an example, the identification of the cold island core source (CICS) was optimized by applying relative land surface temperature (LST), morphological spatial pattern analysis, and landscape connectivity analysis. The combined resistance surface was constructed based on a spatial principal component analysis. Subsequently, the cold island network was constructed by applying circuit theory and identifying the key nodes. The results showed that the central and eastern parts of the study area experienced the most significant UHI effects and there was a tendency for them to cluster. Overall, 48 core sources, 104 corridors, 89 cooling nodes, and 34 heating nodes were identified. The average LST of the CICSs was 28.43 °C, significantly lower than the average LST of the entire study area (31.50 °C), and the 104 cold corridors were classified into three categories according to their importance. Different targeting measures should be adopted for the cooling and heating nodes to maintain the stability of the cold island network and prevent the formation of a heat network. Finally, we suggest a model for urban cold island network construction and explore methods for mitigating issues with UHI to achieve proactive and organized adaptation and mitigation of thermal environmental risks in urban areas, as well as to encourage sustainable urban development.

The bidirectional substation for district heating users: experimental performance assessment with operational profiles of prosumer loads and distributed generation

The regulatory European and national policies outline the role of efficient district heating in achieving mid and long-term decarbonization targets. Prosumers could be equipped with bidirectional exchange substations to increase the local production contribution. The present paper evaluates the contribution of a bidirectional substation in maximizing the use of thermal energy produced locally by renewable sources or waste heat in a densely populated area, considering the limitation due to the non-contemporaneity of production and consumption and possibilities to overcome them. The substation prototype and the control system were tested in operational conditions, assuming the district heating network operating at two temperature levels (80 °C/50 °C and 60 °C/30 °C for supply and return) and applying the hardware-in-the-loop technique for coupling the substation in real-time with data-driven thermal loads (multi-family residential building) and production (solar panels and waste heat) profiles. The various energy flows in the substation are presented for representative days, resulting in a district heating contribution to the user’s load ranging between 99.8 % (winter day) and 21.8 % (summer day). The net-metering mechanism was considered, and the assessment extended to the entire year. The local production contribution to the user’s load ranges between 24 % and 100 %, depending on the system configuration considered.

Методичні аспекти ціноутворення на ринках теплової енергії за аукціонного підходу

The development of competition in the heat energy markets with main heating networks is possible on the basis of the organization of unilateral heat auctions between heat producers. A prerequisite for opening competition in the heat energy markets is the separation of heat generation and heat networks, as well as the provision of regulated access to heat networks for independent producers. In terms of time segmentation, it is advisable to introduce: annual auctions, where basic heat needs are being contracted; monthly auctions – for peak needs, and daily auctions – for hourly imbalances. The article proposes organizational and technological regulations for conducting annual heat auctions, which should cover 80–90% of heat needs. Heat auctions should function according to the declared pricing method, where the producers who are the auction winners receive income for the contracted volumes of heat generation at a given price, while consumers pay a single weighted average price. Heat auctions operate under centralized dispatching, which provides for the coordination of physical and commercial heat energy flows, taking into account the technical specifics of heat networks. The article substantiates variants of economic and mathematical models of auction pricing in the heat energy market with different configurations of heat networks. As such a configuration, are considered heating networks with: 1) unlimited flow connections; 2) insulated heat producers; 3) system restrictions on throughput capacities within the heating area; 4) one-way and 5) two-way flows between adjacent heating areas. Establishment of a fair price for heat energy is reduced to solving the function of minimizing the weighted average price of heat energy for consumers under the following conditions: a) full satisfaction of consumer demand for thermal energy; b) technical capabilities of heat generation; c) connections and throughput capacities of heating networks within the heating area; d) directions of flows and capacity between adjacent heating areas. Each heat network represents a unique configuration of these conditions, therefore, the solution of the economic and mathematical problem of setting the auction price for heat energy will be different in each local heat market. Approbation of the proposed approach proves that with a large number of regulatory and systemic restrictions within the heating area, the price of thermal energy will increase, while bilateral flows of thermal energy between adjacent heating areas lead to a decrease in the price of thermal energy. The proposed methodological aspects of auction pricing for thermal energy should be introduced in large and medium-sized settlements with trunk networks, which will allow independent heat producers who work on renewable energy sources or have excess and waste heat to integrate into the market, contributing to the decarbonization of the city and the country as a whole.

Fast and Generic Energy Flow Analysis of the Integrated Electric Power and Heating Networks

Energy flow analysis is a fundamental tool to determine the network states of the integrated energy systems (IES). For the widely deployed IES with coupled power grids (PG) and heating networks (HN), we still lack a generic tool that can be easily employed to calculate the quasi-dynamic energy flows of it. In this paper, we have developed a generic code package (named as MATHN) for energy flow analysis of the quality-regulated HN. After that, a generic solution framework that leverages MATPOWER and MATHN to realize decomposed energy flow calculation of PG and HN is proposed. Behind the MATHN tool, a model reformulation technique is proposed to eliminate the massive indirect variables of the basic HN model discretized by finite difference, which finally derives a compact matrix formulation (similar to the network equation of power grid: I=YU) for generic description of any HN and also slashes the original model scale by around 20 times. Moreover, the solution strategy behind the MATHN tool further converts this matrix formulation into a standard system of non-homogeneous linear equations, with which some existing well-recognized algorithms can be directly applied for efficient and accurate solution. Case studies on three different scales of test systems demonstrate the generality, efficiency and accuracy of our methods. All the codes and input data are packaged into the MATHN tool and are made open-source for non-commercial use.

Upgrading utility infrastructure systems in the Russian Federation: Concession mechanisms

In the Amur region (Russian Federation), the extent of wear and tear of engineering heating networks was 21 percent as of the year-end 2022, which was an average value for this region. In some cities of the region under study wear and tear reaches 72 percent. The current wear and tear of utility infrastructure systems substantially degrades the quality of utility services provided to the population and boosts the percentage of heat losses and accidents in heat networks. The goal of the research project is to devise an action plan to reduce the rate of accidents and the wear and tear of heat networks in the Amur region of the Russian Federation by developing a concession mechanism focused on upgrading utility infrastructure systems. Logical analysis of the regulatory legal framework, as well as analysis of qualitative and quantitative values of utility infrastructure systems (heat networks in the Amur region). The need for the mechanism of concession agreements was substantiated as a means of upgrading utility infrastructure systems. Actions are proposed to boost the funding of repair and replacement of utility infrastructure systems in the Russian Federation.

District Heating: Time To Heat Up? More Investment in Heat Networks Would Contribute to the Race to Net Zero <br>

District Heating: Time To Heat Up? More Investment in Heat Networks Would Contribute to the Race to Net Zero <br>

Preventing scale formation on heat transfer surfaces

The article considers the problem of scaling in power equipment on the example of Thermal Power Plants in the Republic of Kazakhstan. The most optimal solution is proposed – replacement of the traditional preparation of the feed water in the heat network by an ion exchange method for a more effective method using complex-forming reagents. The influence of inhibitor of mineral salts concentration (IMSC), trisodium phosphate, and Zinc Complex 1-hydroxyethylendiphosphonic acid (Zn-OEDF), as well as the heat carrier temperature on scaling intensity, has been studied to prevent the equipment from scale formation and corrosion. The technological parameters of feed water in the presence and absence of complex formers have been determined. The corrosion resistance of steel No. 3 samples in the presence of said reagents has been studied. The most optimal complexone has been chosen to prepare feed water for the TPP heating network.

FIELD EXPERIMENTAL INVESTIGATION OF THE INSULATION DETERIORATION CHARACTERISTICS OF OVERHEAD PIPELINE FOR STEAM HEATING NETWORK

The thermal insulation performance of pipeline is significant for the safety and economical operation of vapor steam network. In order to investigate the long-time insulation performance of pipeline, a field test was carried out in pipelines of 12 different heating networks with the operating time ranging from 1 to 11 years. Two different types of insulation coating layer were included. The total heat flux and surface heat flux in a pipeline were measured to obtain the equivalent thermal conductivity of the insulation coating layer, and a deterioration coefficient was applied to analyze the insulation deterioration characteristics. The results show that the one-dimensional thermal conduction method is feasible to calculate the heat flux of the pre-manufactured pipeline with hard insulation materials, and an error less than 2% for pipeline 1 was obtained. Further, a proper size of slip in the insulation coating layer has improved the insulation performance by 13.6% in pipeline 2. For the soft type insulation coating, the structure has been changed under the long-term effect of gravity. Accordingly, a single thermal conductivity cannot accurately characterize the heat transfer process within the insulation layer. The surface heat flux accounts for less than 30% of the total heat loss. The insulation deterioration trend with operating time cannot exactly be obtained by the surface heat flux. In addition to the thickness reduction at the top and hollow at the bottom, the convection heat leakage from the gaps should also be a concern for long time operation.

Numerical simulation of thermal performance based on cogeneration low carbon heating unit manufacturing

The renewable energy complementary cogeneration system has broad application prospects in the field of regional comprehensive energy utilization. The author proposes a trough solar assisted biomass cogeneration system, which uses medium and low temperature trough solar energy to heat conduction oil, drives absorption heat pump to preheat water in the heating network, saves heating steam extraction and increases power output under the condition that biomass fuel and heat supply remain constant. The EBSILON professional software was used to model and simulate the case unit and integrated system, and based on this, thermodynamic characteristics such as system energy flow and energy loss were analyzed. The results indicate that: under the design condition, 1.78 MWh of solar power can be generated, the photoelectric efficiency is 20.06%, and the photoelectric conversion efficiency can reach 21.60%. Hourly simulation analysis of the whole heating season shows that the total solar power generation generated in five months of the heating period is 1124.30 MWh, and the average photoelectric efficiency is 16.49%.

PROBLEMS OF RELIABLE HEAT SUPPLY PROVIDING IN THE CONDITIONS OF NON-GUARANTEED ELECTRICITY SUPPLY TO HEAT-GENERATING ENTERPRISES

The paper analyzes the current state of centralized heat supply systems. Considered problems that arise when the power supply is turned off for a longer period of time. For example, due to natural disasters or the destruction of power stations, substations and networks. An analysis of the consequences of long-term shutdowns of centralized heat supply sources in the winter period at extremely low temperatures, which leads to the failure of the main and auxiliary equipment, heat networks and domestic heating systems, was carried out. Considered several real options for reservation or full self-sufficiency of boiler room heat supply needs in power supply for the most common types of boiler room. Namely, with water heating boilers and direct connection to the heating network and with steam boilers and steam water boilers. It is proposed to introduce elements of own power generation on a permanent basis, as part of the technological process of the heat supply system or a separate boiler house of medium and large capacity, which, with their rational combination, can lead to a significant economic effect. It is shown that the most promising is the redundancy due to the built-in heat generation scheme, the electricity generation system, i.e. full or partial cogeneration. It was found that when gas turbines are used in the cogeneration system of heat and electricity, it is advisable to use units with a low temperature of up to 800°C and a gas pressure before the turbine of up to 0.8 MPa, which are characterized by high reliability, low cost and provide the greatest release of utilized heat. Keywords: centralized heat supply systems, reliability of power equipment, power supply of boiler houses

Analysis of heating load distribution and operation optimization for 350MW high back pressure double extraction series units

Large-scale high backpressure cogeneration units can make full use of the waste heat of the spent steam to reduce the unit's cold-end losses, improve the fiel utilization rate, and heating efficiency, the energy saving effect is remarkable. The 2?350MW cogeneration unit of a power plant is modeled as an example. The boundary conditions of the heat network are calculated according to the ambient temperature, and the thermal economy and exergy efficiency of the condensing unit and the high backpressure unit are analyzed during the heating period, to obtain the advantages of the high backpressure unit during the heating period. In turn, the study presents the high backpressure unit extracts steam distribution method is adjusted to optimize the operation strategy during the heating period. The results indicate that: after adopting high back pressure operation during the heating period, the average power generation increased by 24.5MW compared to the condensing unit, The average reduction in coal consumption for power generation is 97.5g?(kW?h)-1, exergy efficiency increased by an average of 9.4%, exergy efficiency of the unit?s heating network has increased by an average of 19.2%. After the unit adopts optimized allocation of extraction load, the average coal consumption for power generation is reduced by 0.69 g?(kW?h)-1on the basis of high back pressure heating operation. The average efficiency improvement of steam-water exergic is 0.44%, while the efficiency average improvement of heating networks is 0.6%, with a maximum increase of 1.4MW of exergy energy.