District Heating and Cooling Systems

Under the challenge of global energy transition, coal-fired cogeneration systems are undergoing a technical revolution towards enhanced efficiency, heating capacity, and flexibility. In this paper, four schemes using a steam ejector integrated into a cogeneration system are designed. Considering operational safety, integrated locations are selected at the front and back of high- and medium-pressure turbines. Subsequently, the thermodynamic and operational characteristics under both design and off-design conditions are analyzed based on a model built in EBSILON Professional. Finally, a sensitivity analysis of the heating process is conducted. The results show that the integration of steam ejectors can increase the waste heat recovery ratio of exhaust steam by 18.42–45.61% under design conditions. The largest waste heat recovery ratio is obtained in System 4, resulting in the power generation efficiency (${\eta }_g$) and gross energy utilization efficiency (${\eta }_p$) of 81.95% and 65.53%, respectively. Meanwhile, the steam ejector can expand the power-load regulation range of the cogeneration system, and System 4 has the lowest lower power limit among all the systems. The ${\eta }_p$ values of Systems 1–4 reach extreme values at different mixed steam pressures of the ejector. Increasing the pinch point temperature difference reduces the power load ${\eta }_g$ and ${\eta }_p$ of Systems 1–4. The results provide technical solutions for improving the heating capacity and efficient and flexible operation of cogeneration systems. Full article

Neutral-temperature district heating and cooling (NT-DHC) is a recent concept in the district heating sector. The current literature does not directly address the ability to create comprehensive master plans for NT-DHC systems and reliably model their performance. This research presents a new approach for the evaluation and planning of NT-DHC systems. The methodology involves the use of a knapsack optimization algorithm to perform a comprehensive analysis of the conditions that make the NT-DHC solution competitive against individual heating and cooling technologies. The algorithm determines the optimal combination of potential extensions that maximizes overall economic value. The results of a case study, which was conducted in Italy, show that NT-DHC is more suitable in dense urban areas, while air-to-water heat pumps are better suited for low heat density zones. This methodology aims to reduce the risks associated with energy demand and provide more certainty about which areas a network can expand into to be competitive. It is targeted at energy planners, utilities experts, energy engineers, and district heating experts who require assistance and guidance in the planning and early stages of designing a NT-DHC system. This method might enable pre-feasibility studies and preliminary design to determine the opportunities and limitations of a system of this kind from an economic and technological perspective. Full article

Heat metering is an important measure of China’s heating marketization reform as well as an energy-saving policy implemented in buildings nearly 20 years ago. However, this policy has not achieved the expected results due to various reasons. It is important to note that although northern China is dominated by large apartment buildings, resulting in unique thermal characteristics and user behavior, the measured results of these characteristics are not common. In this study, data from cities in northern China were obtained using household heat meters and field testing. Based on the three levels of station, building, and household, the effects of location, heat outages, and users’ regulation behavior on energy consumption were analyzed. The results show that different locations lead to a considerable difference in heat consumption among users, and an outage leads to a significant increase in consumption by surrounding users. For typical buildings in northern China, it is challenging to realize energy savings with district heating systems based on user behavior, and household metering and charging are not fair and reliable. Adjusting the heat meter unit from the household to the building was suggested. Full article

Despite decades of research and development, digitalization remains a key challenge for the Swedish district heating sector. Business model innovation is believed to be necessary to capitalize on digitalization, yet it is especially challenging for municipal companies. This study aims to identify the potential impact of digitalization on the business models of Swedish district heating companies and to analyze the barriers that exist for digital business model innovation. Through case studies of eight municipal district heating companies, this study demonstrates how the entire business model is potentially impacted by digitalization. This study also identifies the barriers to digital business model innovation that are linked to two conflicting views (restrictive versus comprehensive) on digitalization. The restrictive view diminishes the importance of business model innovation, outsourcing innovation to minimize both costs and risks for the company. In contrast, the comprehensive view embraces digital business model innovation through trial-and-error and opens the innovation process to stakeholder influence. These two perspectives are motivated by different beliefs about the need for digitalization to secure future business opportunities, as well as differences in owners’ risk appetite. The implications for industry outlooks and the design of policy support for the digitalization of district heating are discussed. Full article

To improve the performance of conventional double-effect absorption refrigeration systems (DEARS), new series parallel (SP) and reverse parallel (RP) configurations using LiCl-H₂O and LiBr-H₂O as working fluids, combined with two vapor compressors (VC), are proposed and thermodynamically evaluated. The effects of the distribution ratio (D) and compression ratio (CR) on the system performance are discussed. The results reveal that both configurations can extend the operation ranges of DEARS effectively at a higher distribution ratio, and the performance for low-grade heat source utilization is improved substantially by the use of VC. The compressor positioned between the evaporator and absorber is superior to that between the high-pressure generator and low-pressure generator because of the better performance improvement and larger operating ranges. In all the examined cases, LiCl-H₂O systems perform better than LiBr-H₂O systems in terms of the coefficient of performance (COP) and exergetic efficiency. At the higher CR of approximately 2, the compression-assisted DEARS can be driven by heat sources below 100 °C with high levels of COPs above 1.16 for the LiBr-H₂O working pair and 1.29 for the LiCl-H₂O working pair. The system can operate at the optimum condition by adjusting the CR values according to the characteristics of the heat sources. Full article

Under the dual carbon strategy, with the frequent occurrence of extreme weather and the further increase in uncertainty of multi-user behavior, it is urgent to improve the stability of the heating systems and reduce heating energy consumption. Aiming at the problem of fault-disturbance control of the multi-user heating network in an integrated energy system, this paper proposes a novel analysis method of resistance–capacitance reactance based on the circuit principle to construct a dynamic thermal-power-flow model of the whole link of the multi-user heating network and analyze the fault-disturbance propagation characteristics of the heating network by this model. It shows that the difference in disturbance characteristics of different users in a multi-user heating network mainly depends on the characteristics of the heating pipeline between the heat user and the heat source, which provides a necessary basis for formulating intelligent control strategies against fault disturbance. Finally, taking a typical daily outdoor temperature in Beijing in winter as an example, this paper compares two different heating strategies and the blocker installation methods of the multi-user heating network to obtain a better heating strategy under actual conditions. Considering the heating fault disturbance, this paper proposes a novel intelligent heating strategy whose heating temperature will decrease during the fault-disturbance time, with an energy saving of about 16.5% compared with the heating strategy under actual conditions during the same period. Full article

In this study, a novel fifth-generation district heating (DH) model was proposed that implements the energy-prosumer concept of bilateral heat trading (BHT) process between the DH network and the building. The newly proposed BHT model can be characterized by the feature of using the low temperature of DH return pipe’s water. The technical feasibility of the proposed BHT model was evaluated through operation simulation analysis based on the actual operation data of the hybrid pilot system combined with the fuel cell and heat pump and the annual hourly temperature profile of the existing DH return pipe. The main objective of this study is to examine the technical feasibility of the interconnection operation model with the existing DHN as an alternative to overcome the limitations of the current fuel cell cogeneration model, which suffers from the low production volume caused by the high initial investment cost. From the simulation results, it was confirmed that considerable operational benefit, more than 30% in terms of primary energy savings, can be achieved with the proposed model, and compared to the stand-alone model of the fuel cell cogeneration system for the building, it can provide a more flexible technical environment to improve the system utilization rate by about 40%. Full article

This article provides the state-of-the-art on the optimal planning and design of future district heating (DH) systems. The purpose is to provide practical information of first-step actions for countries with a low DH market share for heating and cooling supply. Previous research showed that for those countries, establishing a heat atlas with accurate geographical data is an essential prerequisite to promote the development of DH systems. In this review, essential techniques for building a high-quality heat atlas are elaborated. This includes a review of methodologies for district thermal energy demand prediction and the status of the integration of sustainable resources in DH systems. In the meanwhile, technical barriers for the implementation of various sustainable heat sources are identified. Furthermore, technologies for the optimal planning of DH systems are discussed. This includes the review of current approaches for the optimal planning of DH systems, discussions on various novel configurations which have been actively investigated recently, and common upgrading measures for existing DH systems. Full article

The increasing use of high shares of renewable energy sources (RESs) in the current electricity network introduces challenges to the design and management of the electricity network due to the variation and uncertainty nature of the RESs. Some existing energy infrastructures, such as heat, gas, and transport, all have some level of inbuilt storage capacity and demand response (DR) potentials that can be exploited in an energy system integration to give the electricity network some level of flexibility and promote an efficient transition to a low-carbon, resilient, and robust energy system. The process of integrating different energy infrastructure is known as multi-vector energy systems (MESs). This paper reviews different studies on the planning of MESs using the energy hubs (EHs) approach. The EHs model used in this paper links different energy vectors such as gas, electricity, and heat energy vectors in its planning model, as opposed to planning each energy vector independently, in order to provide more flexibility in the system, minimise total planning cost, and encourage high penetration of renewable energy source for future energy demands. In addition, different uncertainty modelling and optimization methods that have been used in past studies in planning of EH are classified and reviewed to ascertain the appropriate techniques for addressing RESs uncertainty when planning future EH. Numerical results show 12% reduction in the planning cost in the case of integrated planning with other energy vectors compared to independent planning. Full article

One challenge in today’s district heating systems is the relatively high distribution heat loss. Lowering distribution temperatures is one way to reduce operational costs resulting from high heat losses, while changing the distribution system from steel pipes to plastic pipes and changing the heat distribution concept can reduce investment costs. The result is that the overall life cycle cost of the district heating system is reduced, leading to the improved cost competitiveness of district heating versus individual heating options. The main aim of this study was to determine the most cost-efficient distribution system for a theoretical solar district heating system, by comparing the marginal life cycle cost of two different distribution systems. A secondary aim was to determine the influence of the employed pipe type and insulation level on the marginal life cycle cost by comparing detailed economic calculations, including differences in pipe installation costs and construction costs, among others. A small solar-assisted district heating system has been modeled in TRNSYS based on a real system, and this “hybrid” model is used as a basis for a second model where a novel distribution system is employed and the heating network operating temperature is changed. Results indicate that a novel distribution concept with lower network temperatures and central domestic hot water preparation is most efficient both from an energy and cost perspective. The total life cycle costs vary less than 2% for a given distribution concept when using different pipe types and insulation classes, indicating that the investment costs are more significant than operational costs in reducing life cycle costs. The largest difference in life cycle cost is observed by changing the distribution concept, the novel concept having approximately 24% lower marginal life cycle cost than the “hybrid” system. Full article

In this work, the optimal design of a hybrid energy complex, including wind turbines, an internal combustion engine, and an adiabatic compressed air energy storage system is investigated. A novel bi-level optimization strategy is proposed for optimizing the capacity and operational power of each component of the system based on techno-economic considerations. The article presents information and discussions about the impacts of the partial-load operation of the energy storage system components on the optimal rated power and working strategies. The off-design characteristics are proven to have a huge negative impact on the efficiency and economy of the hybrid system. The efficiency reduction of the compressed air energy storage system is about 21% in summer and 8.9% in winter, when the system is operating in partial-load conditions. The operation cost of the system is reduced significantly when carrying out the proposed bi-level optimization strategy. Full article

To solve the problem of low heat dissipation efficiency for the conventional S-type runner water-cooling plate of the fan converter IGBT module, two new water-cooling plates were designed with rectangular and elliptical column structures in the S-shaped runner of the water-cooling plate. The heat dissipation performance, the fluidity of cooling water, and pressure drop of different spoiler column structures were compared using Fluent software for the simulation and experiment. The comparative results show, compared with the water-cooling plate without a spoiler column in the flow channel of the control group, that the spoiler column structure in the flow channel significantly improved the heat dissipation performance of the water-cooling plate. When the inlet velocity of the water-cooling plate was 2 m/s, the highest temperature inside the water-cooling plate with a rectangular spoiler column structure was 12.25 °C, lower than the control water-cooling plate. The highest temperature inside the water-cooled plate with an elliptical structure was 12.40 °C, lower than the control water-cooled plate. The obstructive effect of the elliptical spoiler column structure on water flow was smaller than in the rectangular spoiler column structure. The fluidity of the cooling water inside the elliptical spoiler column structure water-cooling plate was better. When the inlet velocity of the water-cooling plate was 2 m/s, the cooling water flowing through the former was 282 L more than the latter in half an hour. Compared to the pressure drop, we found that in the design group, the pressure drop of the water-cooled plate with a rectangular spoiler column structure was 40,988.3 Pa. The pressure drop of the water-cooled plate with an elliptical spoiler column structure was 25,576.6 Pa. The difference between the two was 15,411.7 Pa, which proves that the energy loss inside the latter is smaller. To further explore the relationship between the heat dissipation and energy consumption of the two types of water-cooled plates, the comprehensive evaluation index η was calculated, η_b = 26.2, η_c = 31.6; therefore, η_b was significantly smaller than η_c. The overall performance of the water-cooled plate with an elliptical spoiler column structure was superior. Full article

With the increasing need for cooling and the concerns for pollution due to fossil fuel-based energy use, renewable energy is considered an add-on to cooling technologies. The climatic condition in the Middle East, analyzed in this paper, provides the potential to integrate solar energy with the cooling system. Due to the availability of various solar energy and cooling technologies, multiple configurations of solar-cooling systems can be considered to satisfy the cooling demand. The research presented in this paper aims to assess and compare these configurations by considering the energy prices and the installation area. The proposed model is formulated in Mixed-Integer Linear Programming and optimizes the holistic system design and operation. The economic, renewable energy use, and environmental performances of the optimal solution for each configuration are analyzed and compared to the base grid-DCS configuration. Results show that the electricity tariff and the available installation area impact the economic competitiveness of the solar energy integration. When electricity tariff is subsided (low), the conventional grid-based DCS is the most competitive. The PV-DCS configuration is economically competitive among the solar assisted cooling systems, and it can contribute to reducing the environmental impact by 58.3%. The PVT-DCS configuration has the lowest operation cost and the highest environmental performance by decreasing the global warming potential by 89.5%. The T-DCS configuration becomes economically competitive only at high electricity tariffs. Full article

Outer edge bending is already used on the axial fan blades of air conditioners, reducing the leakage flow loss at the blade tip and suppressing the tip vortex development, thereby improving fan aerodynamic and acoustic performance. However, there are few studies on the multi-parameter design and optimization of this complicated structure, and most studies only focus on the overall sound pressure level rather than the sound quality when evaluating the fan noise. This study investigated the effects of outer edge bending structure on the aerodynamic performance and sound quality of air conditioners’ axial fans by experiments and numerical methods. Based on the orthogonal design method, the effects of three bending parameters, the circumferential starting angle, radial relative position, and the bending degree effects on the performance of the axial flow fan blade were analyzed, and the best efficiency scheme was selected. A comparative analysis of the preferred and the original bending schemes shows that the bending towards the blade suction surface successfully inhibits the development of tip leakage vortex at the blade tip, thereby achieving efficiency enhancement and noise reduction. The experimental results show that the preferred bending scheme with a 10° circumferential starting angle, 90% radial relative position, and 8% bending degree can effectively reduce the fan’s broadband noise within 200~1000 Hz by 0.54~2.68 dB (A) at different operating conditions. Additionally, the preferred bending blade with reasonably designed bending effectively reduced the loudness and roughness of the fan noise in the rated conditions, and the sound quality of the studied fan was correspondingly improved. Full article

With the gradual depletion of shallow resources, the process of resource exploitation is being transferred to greater depths. The temperature of the surrounding rock increases gradually in the process of deep mining, and the temperature of the underground substation chambers often exceeds the normal working temperature in summer. In this paper, the equipment layout and ventilation conditions of the deep substation chamber of the Jiangxi Qujiang Mining Company were selected as the research subjects, and numerical simulation software was used to study the temperature distribution within the chamber under different conditions by changing the combinations of the wind velocity and air temperature of the inlet air of the chamber. The study showed that, under the conditions of the current equipment layout and air door size, the equipment temperature was prone to being too high in the summer. Therefore, the layout of the equipment was optimized based on the simulation results. The transformer equipment was changed from the original serial mode to the juxtaposed mode, and the size of the air door was increased, which effectively reduced the disturbance of the air flow and the length of the air flow path in the chamber. This meant that the high temperature area of the chamber was at the end of the chamber, which efficiently reduced the area of the high temperature zone and ensured that the equipment was in a lower temperature environment. This method can be used as a reference for temperature distribution, layout, and temperature control measures within buildings. Full article

District heating systems are almost always located in densely populated urban areas where various heat sources are available, such as cooling and refrigeration systems in supermarkets, shopping malls, and power transformers. These urban sources often have a large share of waste heat, which is usually emitted into the environment. This waste heat could be used to partially cover the thermal load in district heating systems. The biggest challenge for their integration is the spatial distribution of urban heat sources in relation to the existing heat network and the temporal distribution of the availability of waste heat energy throughout the year. In this paper, we have developed an economic assessment model for the integration of urban heat sources into existing district heating systems. By the hourly merit order of waste heat utilization technologies based on pinch analysis, we have defined the most suitable integration of urban heat sources into existing district heating systems. Different temperature regimes of the urban source and the existing heat network have been considered. Finally, the method was tested on the case study of a supermarket and power substation located in Zagreb, while the sensitivity analysis was carried out with a focus on various technical and economic boundary conditions. Full article

The hot exhaust gas generated by a downhole combustion heater directly heats the formation, which can avoid the heat loss caused by the injection of high-temperature fluid on the ground. However, if the temperature of the exhaust gas is too high, it may lead to the carbonization of organic matter in the formation, which is not conducive to oil production. This paper proposes the use of low-temperature catalytic combustion of a mixture of methane and air to produce a suitable exhaust gas temperature. The simulation studies the influence of different parameters on the catalytic combustion characteristics of methane and the influence of downhole high-pressure conditions. The results show that under high-pressure conditions, using a smaller concentration of methane (4%) for catalytic combustion can obtain a higher conversion efficiency (88.75%), and the exhaust temperature is 1097 K. It is found that the high-pressure conditions in the well can promote the catalytic combustion process of the heater, which proves the feasibility of the downhole combustion heater for in situ heating of unconventional oil and gas reservoirs. Full article

One of the most crucial factors for energy transition and the incorporation of renewable energy sources into the existing energy map is citizen engagement. Local energy communities (LECs), which are cooperative-based coalitions aimed at reducing the carbon footprint of the residential building sector, have received increasing attention in the past decade. This is because residential buildings account for almost half of the total energy consumed worldwide. A resounding 75% of it is used for thermal energy consumption, heating and cooling, cooking and bathing. However, the main focus of the literature worldwide is explicitly on electrical LECs, despite the fact that the significant increase in natural gas and oil prices, creates instability in the heating and cooling prices. The scope of this study is to provide an overview of the research field regarding Thermal LECs, using both a thorough literature review as well as bibliometric analysis (VOSviewer software), in order to validate the findings of the review. The results indicate a collective scarcity of literature in the field of thermal/cooling energy communities, despite their proven value to the energy transition. A significant lack of directives, research background and state initiatives in the context of LECs incorporating thermal/cooling energy production, storage and distribution systems, was also observed. Case studies and the applications of such systems are scarce in the available literature, while published studies need further feasibility assessments. Full article

A pumped two-phase thermosyphon loop is broadly utilized to intensify the cooling duties of electronic chipsets/systems and the effectiveness for harvesting thermal energy. The configuration of a condenser not only affects the heat transfer in the condenser, but also has an effect on the saturation pressures during the boiling and condensation processes to alter the hydrothermal performance of a pumped thermosyphon loop. The influence of the condenser configuration on the hydrothermal performance of a pumped thermosyphon loop is rarely studied. The present study comparatively examined the thermal performances of two pumped thermosyphon loops with a conventional tube-fin condenser and the expansion-tank condenser. The thermodynamic cycles in pressure-temperature and pressure-enthalpy diagrams, Nusselt numbers of evaporator and condenser, thermal resistances and various performance indexes evaluated at constant pumping powers at the controlled through-flow Reynolds numbers, boiling numbers and condenser thermal resistances were measured. At the similar thermal loads, flow rates, and fluid entry temperatures of condenser, the operating pressure of the thermosyphon loop with expansion tank condenser was considerably reduced from that with tube fin condenser, leading to the lower saturation temperature for reducing the thermal resistance and the lesser pressure drop across the loop with a noticeable hydrothermal performance improvement. At the parametric conditions tested, the ratio of dimensionless overall thermal resistances between the loops with expansion tank condenser and tube fin condenser fell in the range of 0.81–0.99. When the loop performance was compared at a constant cooling airflow rate without considering the more pumping power consumption for the loop with tube fin condenser, the ranges of thermal resistance for the loops with expansion tank condenser and tube fin condenser were 0.13–0.21 (KW⁻¹) and 0.15–0.23 (KW⁻¹). The merit indices evaluating the comparative hydrothermal performances of evaporator, condenser and loop between the two looped thermosyphons highlighted the significance of condenser design and affirmed the performance improvement by changing tube fin condenser into expansion tank condenser. The empirical correlations of evaporator Nusselt number, condenser Nusselt number, and overall thermal resistance using Reynolds number, boiling number, and condenser thermal resistance as the controlling parameters were generated for relevant applications. Full article