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Booster heat pumps and central heat pumps in district heating
Abstract
District heating (DH) enables the utilisation and distribution of heating from sources unfeasible for stand-alone applications and combined with cogeneration of heat and power (CHP), has been the cornerstone of Denmark’s realisation of a steady national primary energy supply over the last four decades. However, progressively more energy-efficient houses and a steadily improving heat pump (HP) performance for individual dwellings is straining the competitive advantage of the CHP–DH combination as DH grid losses are growing in relative terms due to decreasing heating demands of buildings and relatively high DH supply temperatures.
... Many publications in the field of innovative heat network concepts assume uniform heating types (e.g., space heating) and low supply temperatures for all buildings, mostly 45 °C [1,2,3,4]. However, existing buildings usually require higher supply temperatures due to the year of construction, as shown by Vivian et al. [5]. ...
... Numerous studies analyze the economical operation of 3GDH, 4GDH, and 5GDHC [1,2,3,4,7,8]. However, to the authors' knowledge there is no study that has considered concepts and operation methods of TFDH. ...
This paper illustrates a new approach for decarbonizing existing district heating networks by introducing Temperature Flexible District Heating Networks (TFDHs) using decentralized booster heat pumps. A rule-based control concept is presented to effectively manage the varying temperatures within the network. Based on an annual simulation, the optimal heat supply for TFDHs is determined and compared with simulated data of 3 rd and 5 th Generation district heating networks using the Levelized Costs Of Heat (LCOH) as a key performance indicator. The results of the calculations reveal a high decarbonization potential in transforming existing heat networks into temperature flexible heat networks, depending on the fuel source. TFDHs get economical, if the investment costs of the decentralized generation technology are reduced by 10 % and the natural gas price increases by 1 €ct/kWh.
... A large amount of studies concerning low-temperature heating networks and BHPs has been performed. Østergaard and Andersen [16] have proven that an ultralow-temperature district heating network (ULTDH) with BHPs ("concept A") consume less energy than a LTDH, without BHPs ("concept B"). Moreover, the COP of the central HP is always higher in "concept A" than in "concept B". ...
... The design temperatures are high, usually 60°C/40°C and higher [31], and the cool load is not taken into account by the CDC. However, for this comparison, only characteristic efficiencies [16] are considered: a boiler efficiency of 95% and the cool demand is covered by decentral compression chiller, with an coefficient of performance (COP) of 4,5. This comparison is given in Table 2. ...
The development and use of more energy-efficient heating and cooling systems is required in order to secure a sustainable energy supply. In this respect, a myriad of concepts are being developed. The combined distribution circuit (CDC) of centralized heating at lower temperatures (ca. 20 to 30°C) or cooling and decentralized booster heat pumps (BHP) for the production of domestic hot water (DHW) is such a concept, notably one of a collective heating and cooling system for apartment buildings. Although certain studies have demonstrated that the use of BHP results in potential energy savings, no energetic evaluation of the BHP in a CDC is available. In order to analyse all concept components a simulation environment in Matlab has been adapted. Therefore, new models are developed. This research compares the concept to a classic CDC with a supply temperature of at least 60°C heated by a central boiler. Moreover, the possible energy recuperations of this concept are quantified. This research has shown that a CDC at lower distribution temperatures with BHP can achieve a total system efficiency of 334% on a yearly basis. Moreover, reducing the CO2-emmisions with 55% is possible in comparison to a classic CDC. Thanks to the configuration of the heat interface unit (HIU), the BHP extracts between 10,2% to 31,5% of the total evaporator heat directly out of the apartment during summer. This study proofs that the concept of a CDC with BHP can contribute to decarbonizing the heat (and cooling) production in apartment buildings, while maintaining the desired comfort. Keywords-Collective heating and cooling, booster heat pump, domestic hot water, energy system simulations
... This implies that shifting from competition between HPs and DH system to ensuring a collaboration between the two may be a promising approach in LTDH. An investigation of two combinations (central HPs only and central HPs plus booster HPs) for supplying space heating (SH) and domestic hot water (DHW), showed that the latter combination enables the DH system running at significantly lower temperatures and reduces operation costs by 39% over the former combination [35]. With the focus on predictions at district scale, the authors used daily average ambient air temperatures instead of hourly values [35]. ...
... An investigation of two combinations (central HPs only and central HPs plus booster HPs) for supplying space heating (SH) and domestic hot water (DHW), showed that the latter combination enables the DH system running at significantly lower temperatures and reduces operation costs by 39% over the former combination [35]. With the focus on predictions at district scale, the authors used daily average ambient air temperatures instead of hourly values [35]. This may not accommodate well for predictions at building scale, where in-depth heating response from atmospheric condition is crucial to be accounted for. ...
In the face of green energy initiatives and progressively increasing shares of more energy-efficient buildings, there is a pressing need to transform district heating towards low-temperature district heating. The substantially lowered supply temperature of low-temperature district heating broadens the opportunities and challenges to integrate distributed renewable energy, which requires enhancement on intelligent heating load prediction. Meanwhile, to fulfill the temperature requirements for domestic hot water and space heating, separate energy conversion units on user-side, such as building-sized boosting heat pumps shall be implemented to upgrade the temperature level of the low-temperature district heating network. This study conducted hybrid heating load prediction methods with long-term and short-term prediction, and the main work consisted of four steps: (1) acquisition and processing of district heating data of 20 district heating supplied nursing homes in the Nordic climate (2016–2019); (2) long-term district heating load prediction through linear regression, energy signature curve in hourly resolution, providing an overall view and boundary conditions for the unit sizing; (3) short-term district heating load prediction through two Artificial Neural Network models, f72 and g120, with different prediction input parameters; (4) evaluation of the predicted load profiles based on the measured data. Although the three prediction models met the quality criteria, it was found that including the historical hourly heating loads as the input to the forecasting model enhanced the prediction quality, especially for the peak load and low-mild heating season. Furthermore, a possible application of the heating load profiles was proposed by integrating two building-sized heat pumps in low-temperature district heating, which may be a promising heat supply method in low-temperature district heating.
... A major challenge in this field lies in transitioning second-and third-generation DH systems to lower operating temperatures, enabling the integration of heat from geothermal and solar plants, industrial and commercial excess heat [8][9][10], and power-to-heat solutions such as heat pumps [11][12][13][14]. Reasonable target temperatures for this transition are values of about 60-70℃ [15]. ...
... The Lorentz efficiency η L accounts for all nonidealities compared to the ideal Lorentz cycle, including HEX losses between the refrigerant and the water in the network and mechanical losses. The Lorentz efficiency η L of the central HP is set at 50% and at 40% for the booster HPs, to reflect the poorer performance of small scale HPs [10]. Part load operation is not taken into account. ...
Low-temperature district heating (LTDH) enables the use of various renewable energy sources, reduces heat losses and increases the energy efficiency of the distribution network. LTDH is especially applicable in energy-efficient buildings as the supply temperature for space heating can be reduced. However, urban areas consist of energetically refurbished and non-refurbished buildings. In these scenarios a LTDH network with a central heat pump (HP) and decentral booster units, such as a booster HP or electrical heater, can be a solution. This study investigates and compares the energetic performance and levelized cost of heat (LCOH) of eight concepts for refurbished and non-refurbished buildings for a district heating network in the city of Ghent, Belgium. The simulations consider supply temperatures ranging from 10 °C to 75 °C. Results show that the primary energy use is lowest when using booster HPs, for both refurbished buildings (402 MWh/year) and non-refurbished buildings (139.6 MWh/year). The LCOH, however, is lowest when booster units are not necessary as the LCOH is mainly driven by the high investment cost of the network and the booster units. This results in a LCOH of 213 €/MWh th for non-refurbished buildings at a network temperature of 75 °C and 297 €/MWh th for refurbished buildings at 55 °C.
... The feasibility of using BHPs in the DH has been evaluated by some researchers. Østergaard and Andersen [26] show that BHPs reduce energy use and cost. Averfalk and Werner [27] find that lower operating temperature facilitates the use of low temperature sources such as geothermal heat and industrial excess heat. ...
... which recovers thermal energy through the addition of a heat pump for secondary effluent. According to relevant studies [21], the average thermal recovery rate in the effluent is about 1.18 kWh/m 3 . Assuming a 1.8%/year upgrade rate for this strategy from 2012, the carbon emission intensity will decrease to 0.84 kg CO2e/m 3 by 2030 (Figure 6a). ...
Sewage treatment is an efficient approach to achieving water resource recycling and safeguarding the environment. The municipal sewage treatment plants must not only meet discharge standards, but also incorporate energy-saving and carbon reduction measures during the sewage treatment process under China’s “dual carbon” strategy. This study calculated and analyzed carbon emissions from China’s municipal sewage treatment industry between 2012 and 2021, and forecasted the carbon emission intensity and amount in 2030. The findings revealed that the total carbon emissions increased from 29.33 Mt CO2e to 58.95 Mt CO2e over a decade, with direct and indirect emissions rising by 78.04% and 143%, respectively. Direct and indirect emissions in 2021 comprised 57.37% and 42.63% of the industry’s total carbon emissions, respectively. Sewage treatment plants accounted for the largest unit of carbon emissions, representing an average of 35%. Without effective carbon reduction measures, the industry’s carbon emissions are projected to reach 67.21 Mt CO2e in 2030. Implementing two optimization schemes, the total carbon emissions in 2030 are anticipated to decline to 65.21 Mt CO2e (Optimized 1) or 62.19 Mt CO2e (Optimized 2), corresponding to a 2.98% or 7.46% reduction, respectively, showing a turning point of carbon peaking. These results can provide theoretical and data support for carbon neutralization planning in the sewage treatment industry, and are essential in achieving carbon reduction goals and addressing global warming.
... Thereby, heat loss along the DH system can be decreased [4]. Østergaard and Andersen [5] indicated that applying BHPs enables the DH system to operate at substantially lower temperature levels. Figure 1 presents the results of a bibliometric analysis on the topic of district heating incorporating heat pumps, primarily conducted using the VOS viewer version 1.6.15 ...
... Simplified effectiveness (or COP-coefficient of performance) models of heat-pumps/refrigeration cycles using perfect gases on the compressor and/or equation-fit models have been proposed in many studies. [7] performed models to calculate the COP by using a theoretical Lorentz efficiency multiplied by a constant exergy efficiency (of around 40% for boosters HP and 50% for the centralized HP). [8] gives a review of recent development in variable refrigerant flow (VRF) systems with models ranging from detailed physics-based models to equation-fit models. ...
... Then, during the 1980s, HPs received particular attention-especially in Sweden-due to a national electricity surplus from new nuclear power plants [12,20]. Nowadays, they represent an interesting solution to efficiently use intermittent and unpredictable energy sources, such as photovoltaic and wind power, playing an important role in the conversion to a renewable-based energy system [21,22]. The state-of-the-art of large-scale HPs for DH applications was analyzed by David et al. [23]. ...
Power-to-heat technology represents a promising solution for the decarbonization of the energy sector. The installation of large-scale heat pumps within district heating systems is widely recognized to be a cost-effective and competitive way to provide flexibility to the electric system, enhancing the use of intermittent renewable energy sources. The goal of this paper is to show how the economic and environmental benefits provided by the installation of a large-scale heat pump in existing district heating systems vary according to the installation location in different scenarios. To do that, an integrated methodology is developed. This includes a physical model of the thermo-fluid dynamic of the district heating network and a detailed modeling of the heat pump. To compare the different positions and also the different operating conditions, an approach based on exergy analysis is adopted. Moreover, a specific control strategy of the mass-flow rate is analyzed to further reduce greenhouse gas emissions. The application to a real large-scale district heating network shows that reductions in CO2 emissions of almost 4% can be obtained by installing a single heat pump of about 4 MWe (over a total thermal load of about 305 MWt), while this positive effect can be reduced by up to 63% if placing the heat pump at non-optimal locations.
... На основе математического моделирования авторами [21] исследовалась система теплоснабжения с центральным и вспомогательными тепловыми насосами дополнительно размещёнными в структуре абонентских систем. Предложенная модель, которая учитывала температуру воды в тепловой сети, в системе низкотемпературного отопления и горячего водоснабжения, позволила определить её общую эффективность соответству-ющим коэффициентом преобразования. ...
This work is devoted to determination a generalized indicator for a preliminary assessment of the conditions for increasing the efficiency of modernized systems of centralized and decentralized heat supply using heat pump technologies. This goal is achieved through a critical analysis of the results of the actual state of pipelines and equipment, known approaches to the reconstruction of heat supply systems and the establishment of a generalized indicator of the conditions for increasing the efficiency of using primary fuel energy. This made it possible to formulate a generalized approach to the modernization of heat supply systems with the introduction of heat pump technologies. The most important result of the study is the established generalized dependence of the assessment of the increase in the efficiency of heat supply systems on the initial conditions of regime parameters with the rationale for the feasibility of modernizing district heating systems based on the diverse phased introduction of heat pump technologies at all stages: generation, transportation, distribution, conversion and controlled consumption of heat by subscriber system. The significance of the obtained research results lies in the fact that the proposed approach to the modernization of centralized and decentralized heat supply systems based on heat pump installations with real conversion factors in the range (3--5) with an increase in the available heat potential is to increase the efficiency and expand the use of heat from primary fuel with its savings of 1-2.7 times.
... A heat pump (HP) is a technology that provides heating, cooling, and hot water. There are multiple known applications of heat pumps focused on district heating [20,21]. However, the use of heat pumps for industrial applications is gaining interest due to their potential to aid in the decarbonisation of processes. ...
The present review provides a catalogue of relevant renewable energy (RE) technologies currently available (regarding the 2030 scope) and to be available in the transition towards 2050 for the decarbonisation of Energy Intensive Industries (EIIs). RE solutions have been classified into technologies based on the use of renewable electricity and those used to produce heat for multiple industrial processes. Electrification will be key thanks to the gradual decrease in renewable power prices and the conversion of natural-gas-dependent processes. Industrial processes that are not eligible for electrification will still need a form of renewable heat. Among them, the following have been identified: concentrating solar power, heat pumps, and geothermal energy. These can supply a broad range of needed temperatures. Biomass will be a key element not only in the decarbonisation of conventional combustion systems but also as a biofuel feedstock. Biomethane and green hydrogen are considered essential. Biomethane can allow a straightforward transition from fossil-based natural gas to renewable gas. Green hydrogen production technologies will be required to increase their maturity and availability in Europe (EU). EIIs’ decarbonisation will occur through the progressive use of an energy mix that allows EU industrial sectors to remain competitive on a global scale. Each industrial sector will require specific renewable energy solutions, especially the top greenhouse gas-emitting industries. This analysis has also been conceived as a starting point for discussions with potential decision makers to facilitate a more rapid transition of EIIs to full decarbonisation.
... They suggested that heat pumps integrated into a distributional network (downstream) perform better than those integrated into transmission networks (upstream). Østergaard and Andersen (2016) estimated that district heating with heat pumps could reduce up to 40% of operational costs compared to district heating without heat pumps due to high efficiency and low heat loss. Similarly, Ommen et al. (2014) suggested that with heat pumps at CHP plants to increase the return temperatures, the operational cost of 90/40°C district heating networks could reach as little as 12€/MWh. ...
A thorough understanding of heat demand is essential for evaluating strategic options to design, plan, and implement future low-carbon heat technologies. Electric heat pumps and decarbonised electricity have been proposed as promising alternatives that could replace gas heating and contribute to the future low-carbon heat mix. District heating has been transformed over several generations to better use renewable sources rather than fossil fuels to meet heat demand. Both technologies are well developed over the past few decades due to a significant amount of scientific research and industrial experience. However, the markets and supply chains for heat pumps and district heating networks are immature in the UK. There are technical, social, and economic factors that present challenges for their deployment. This research offers insights into energy load profiles and peak demand based on data in various types of British dwellings from the largest smart meter field trial. It quantifies energy consumption in dwellings and the aggregated peak demand under cold weather events. This provides an empirical basis for evaluating potential low-carbon heat technologies to replace the existing prevalent gas-fired domestic heating systems. This research investigates the role of heat pumps and district heating by assessing the topological configurations of heat pumps and district heating networks at different scales through techno-economic modelling, in order to explore their comparative advantages from different perspectives, including technical performance, carbon emissions, and cost-competitiveness. This study demonstrates the economies of scales of heat pumps and district heating, and it highlights the advantages of using heat pumps and district heating to reduce carbon emissions via utilising low-carbon electricity and heat sources that would otherwise be wasted.
... Papers in a similar area of research have already been published in SDEWES SI. In (Østergaard and Andersen 2016), the role of booster heat pumps (BHP) and central heat pumps in the district heating sector is examined and concluded that BHP is important for the integration of low-temperature heat and enables the reduction of the temperature regime in the network. Another SDEWES SI study is (Nielsen and Möller 2012) where the production of waste heat from netzero energy buildings (NZEB) was investigated. ...
This paper presents an overview for the Special Issue (SI) of Clean Technology and Environmental Policy journal (CTEP), and it includes accepted papers from 16th Conferences on Sustainable Development of Energy, Water and Environment Systems (SDEWES) held from October 10–15, 2021, in Dubrovnik, Croatia. Considering CTEPs policy of high-quality research papers, guest editors have invited 35 research articles, presented at the SDEWES 2021 conference. After a vigorous review process, 12 papers have been accepted for publication in this special issue. All 12 accepted papers are briefly presented in this overview together with a wider view that presents research efforts within the SDEWES community published through previous SDEWES special issues.
... Booster HPs are able to decouple the supply temperature required by the building from the DH temperature [5] allowing to operate the DH network with a lower temperature reducing distribution losses. In addition, HPs could contribute to increase the PV self-consumption potentially offering an economic advantage from the user's point of view. ...
Booster Heat Pumps (HPs) are integrated into the District Heating (DH) networks aiming at increasing the PV-self consumption. In this work, a dynamic model of a booster HP for the preparation of the Domestic Hot Water (DHW) in a typical Austrian multi-family house is developed. A series of dynamic simulations considering different controls, DHW profiles, storage quality, demand for the appliances and common areas, PV and battery sizes are performed to analyse the influence of this technology on the PV self-consumption, electricity demand and thermal energy demand from the DH network. The results show that when appliances are included in the balance, the PV yield available for the booster HP is limited. A non-optimal control logic of the booster HP could lead to an increase in electricity demand from the grid. The application of battery to increase the PV self consumption for the common areas is not beneficial as the available PV peak power per flat is limited and it would be anyway self used for appliances and HP. Batteries contribute to a slight reduction in electricity demand from the grid when the PV yield cannot be used to cover the appliances. Moreover, the operation of the booster HP influences the energy demand from the DH and makes the CO2 emission of the building dependent on the energy mix of both DH and electricity grid.
... Those systems will only be economically competitive if the heat generation cost savings, which is enabled by unlocking more sustainable and low quality heat sources, outbalance the extra substation costs (including the installation capital cost, power consumption cost and the maintenance cost). Compared with traditional DH systems, a lower distribution temperature in future DH systems will also lead to lower heat loss cost [37]. Another potential saving term could be from the distribution capital cost in 5GDHC systems, where the close to ground operation temperature does not require insulated pipes anymore. ...
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.
... EnergyPlan [63,66] and EnergyPRO [48] have the default High -Extensively linked with other tools using both soft and hard linking methods time step of 1 h and EnergyPRO can also run models at higher resolutions than hourly. On the other hand, OSeMOSYS [51][52][53][54][55][56][57][58][59][60], TIMES [95], EnergyPRO [101] and Balmorel [98][99][100][101][102][103][104][105][106] can analyse models over longer periods, while EnergyPlan is used generally to simulate/optimise models only over one year. Oemof [137] and Calliope [147] have been used to simulate models both at higher time resolution and over larger periods. ...
Recovery and use of industrial excess heat and cold are expected to play a huge role in the decarbonisation of heating and cooling systems in Europe. From the perspective of the industry, it could also promote a coupling between the sectors and help offset emissions, leading to a sustainable industry. However, there exists a gap in knowledge regarding the planning of infrastructure for utilization of excess heat, specifically for industries. This study aims at reviewing energy system optimisation tools that can be used by industrial stakeholders to plan energy investments for recovery and utilization of excess heat and cold. Through a study of existing energy systems models, seven tools are found suitable for analysing industrial excess heat and cold recovery. A detailed review of these tools is conducted and they are compared. The capability of the models to represent and analyse industrial excess heat and cold recovery options are critically discussed. The main requirements of such an analysis are used to establish criteria for comparison. The results of the comparison are used as a knowledge base to form a simple decision support tool to help industrial stakeholders choose the most suitable energy system model. The results from the review, comparison and decision support tool indicate that none of the models is capable of fulfilling all needs in every case. They also highlight that the choice of the tool depends especially on the required temporal and spatial resolution and its interoperability.
... When the central heat producer is a CHP and decentral BHPs are used, the total system efficiency reduces by 20% compared to a low temperature DH grid (70°C supply) heated by a central HP. Furthermore, the studies of Köfinger et al. (2016) and Østergaard and Andersen (2016) confirm the energetical efficiency of a BHP when producing domestic hot water (DHW) in ultralow temperature district heating (ULTDH) and stored in a thermal energy storage (TES). Thirdly, a shift in the relative heat and cold demand is taking place in the building stock in Europe. ...
A combined distribution circuit (CDC) is a collective two-pipe heating and cooling system for apartment buildings. Previous research has demonstrated the advantages of implementing a booster heat pump (BHP) in district heating. However, no detailed study is available on the influence of the BHP’s sizing and low design temperatures (e.g. 40°C/33°C). Our research aims to gain more insight into the sizing of a CDC with a central ground-source HP and decentral BHPs for DHW production. This was achieved by using a dynamic simulation environment in Matlab to study the impact of various design choices. The results show that the performance of the central HP is decisive for the total system efficiency (334%) and that the sizing of the BHPs affects their performances.
... In conclusion, this paper designs a community energy system to manage an electrified community delivered through 100% utilisation of EVs and electrified heating supply. The system is elaborated by three mapping studies; an electrified heating network, an electrified community, and the deployment of PV generation coupled with storage units, and demonstrated on a commercial software energyPRO [25]. These models utilise the conditions in the UK for demonstration, such as energy demands, the distribution network, etc. ...
Electrification in energy supply-demand plays a critical role in domestic heating and road transport, delivering an electrified community to reduce carbon emissions. This solution, however, places a significant power demand increase on the distribution networks. To ensure the security of electricity supply, an efficient energy system and energy demand reduction are essential. In this paper, a multi-vector community energy system, applying an electrified heating network, electric vehicle smart charging, community-scale peak shaving and photovoltaic (PV) generation, is demonstrated in three models to manage an electrified community. Firstly, a heating network model, comprising a central ground source heat pump, low-temperature district heating system, electric heaters and thermal storage, is established to measure the optimum distribution temperature. Next, an electrified community model illustrates hourly electricity demands and performances of a community energy system, which is then used to identify the required degree of housing thermal efficiency improvement (i.e., heating demand reduction). The third model evaluates decentralised PV/storage units to maintain the power demand below a targeted power. Modelling results show that the demand ratio of domestic hot water to space heating determines the distribution temperature, which indicates the temperature is increasing with growing housing thermal efficiency. Moreover, the electrification of a community could increase the peak power demand on the highest demand day by over five times, converting heating demands into electricity directly. This significant peak demand can be possibly reduced to only a 33% increase by employing a community energy system. The model of PV/storage units is validated through a 12-week assessment. Ultimately, a modelling tool is developed by assembling the mentioned models, providing four pathways to attain electri-fication. Users can adjust specific parameters and database to align with the local conditions. The results indicate the requirements of building a community energy system and electricity demands in the highest consumption period. Ó 2022 Published by Elsevier B.V.
... When modelling energy systems, simplified approaches to representing HPs are frequently used, assuming either a constant COP [59][60][61][62] or a constant Lorenz efficiency, which results in various COPs throughout the year depending on the temperature of the heat source and heat sink [63,64]. However, studies have shown that if the operating conditions deviate significantly from the design settings of the HP, this can still lead to considerable discrepancies in COP exceeding 20% for water-based heat sources [65]. ...
The current state of power-to-heat integration into the heat supply in the Baltics is examined. In the socio-economic analysis, three scenarios for prospective district heating electrification development in the Baltic countries until 2050 were investigated and compared: Baseline scenario, Grid Tariff scenario, and Investment Support scenario. Large-scale HPs were analysed as key future technologies. Furthermore, the results are focused on excess heat and renewable thermal energy sources used for heat supply, as well as expanding the representation of DH areas. In 2050, large-scale HPs will generate more than half of the heat for the Baltic states in the Baseline scenario, while biomass plants will generate one-third. One of the dominating fossil fuels in heat supply (natural gas) consumption should gradually decrease from 7.9 TWh in 2020 to 1.4 TWh in the same period. Large HPs generated the lowest quantity of heat in the Grid Tariff scenario. The current network tariffs in each of the Baltic countries, it may be inferred, are an impediment to the introduction of HPs. In 2050, only up to 1/4 of thermal energy will be produced by large-scale HPs. Investments in large-scale HPs are half-subsidised in the Investment Support scenario, which greatly affects the introduction of HPs, and, according to this scenario, in 2050, up to 68% of heat will be produced via HPs in the Baltic states. Detailed results are presented for Estonia, Latvia, and Lithuania.
... Examples of low temperature thermal grids coupled to borehole thermal energy storage with decentralized solar supply have been reported in a few projects such as the well-known Solar Drake Landing Community in Canada and the Suurstoffi district in Switzerland [11]. In Østergaard and Andersen [12], the performance of ULTDH is significantly better, compared to LTDH, in terms of both costs and primary energy demand for a theoretical case representing a typical small Danish DH network. An innovative low-temperature heating and cooling network, the district "Suurstoffi", in Central Switzerland, was monitored by Vetterli et al. [13]. ...
Towards the development of highly integrated and energy efficient heating and cooling systems, with an energy community perspective, the present paper proposes a novel technical solution for the provision of air-conditioning, domestic hot water and electricity to a small residential district in heating-dominant regions. Three reference climates have been considered: Helsinki, Berlin and Strasbourg. Detailed dynamic models have been created using TRNSYS and NeMo, and long term operations of the energy system, including a new-generation ultra-low temperature district heating and cooling network have been performed. The core of the energy system is the network supplied by a high-efficiency ground source heat pump and used as the source and sink by booster heat pumps installed in the substations. Rooftop photovoltaic thermal panels partially meet the electrical demand of the district, as well as the thermal load for domestic hot water production. Moreover, the panels are cooled by the network, obtaining a reduction in the thermal unbalance to the ground and enhancing their electrical efficiency. This solution allows obtaining high coefficient of performance for the heat pumps in the substations and supply stations, reaching values of 5.4 and 4.0, respectively, for heating provision in the coldest locality. The proposed multi-energy district reaches an electrical self-consumption of 71% in the coldest locality and efficiently combines different renewable energy sources at district level in cold climates.
... The efficiency of HP was analyzed depending on a number of factors: the type of power system, the type and characteristics of the fuel oil source, the technical characteristics of HP, the properties of the cooling medium [10][11][12][13]. The researchers evaluated the efficiency of the use of HP in district heating systems in the energy markets of various countries (for example, [14][15][16][17]). ...
The variety of possible solutions for the integration of heat pumps (HP) into the circuits of generation facilities dictates the need for preliminary selection of the most promising options. Determining the maximally economically efficient HP capacity may be the key limiting factor for the potential range of solutions. The purpose of the study is to analyze the influence of the type of power equipment of a thermal power plant (TPP) on the choice of HP capacity. In the course of the study, we identified factors that can influence the choice of HP capacity. The correlation between the limitation of the maximum capacity of HP (from the point of view of break-even operation in the electricity market) from the electric capacity and the efficiency of the TPP equipment was established. The ranges of HP capacity for the most common types of TPP power equipment in the Russian Federation were determined. The maximum HP capacity for TPPs based on a steam turbine unit (STU) of type K-300-170- 1P was determined. The method proposed in the paper allows limiting the number of circuits options, as well as TPPs and external conditions suitable for the use of HP. Firstly, under the conditions of a given power system and fuel prices, it is possible to determine the type of power equipment of a TPP in combination with which HP can be used. Secondly, under the conditions of a given power system and type of equipment, the maximum fuel price at which HP can be used at thermal power plants can be determined. Thirdly, under the conditions of a given type of equipment and fuel price, it is possible to select an energy system (region) in which it is possible to build a TPP with HP. It was found that increasing the efficiency of thermal power plant equipment contributes to increasing the HP power capacity and expanding the range of external conditions under which the use of HP becomes rational. It was verified that for TPP equipment of a given type, the use of HP is more rational when operating in cogeneration mode. It was found that, all other conditions being equal, an essential factor determining the range of HP capacity is the electric capacity of TPPs.
... Investigating typical cases, they conclude that HP can play a pivotal role in the energy infrastructure due to the ability to balance heat and electricity demand, thereby providing flexibility in the district power system. A deep investigation has been already carried out by [9], clarifying the effects of booster HP (decentralised) and central HP in DHS. They conclude that applying booster HP enables the DHS to operate at substantially lower temperature levels, improving the performance of central HP, while simultaneously lowering the heat losses significantly along the thermal network. ...
The manuscript analyses the management of low and ultra-low-temperature district heating systems (DHS) coupled with centralised and decentralised heat pumps. Operative conditions are defined in order to satisfy the heating needs without overloading the electric grid. The results are achieved by dynamic simulations, based on a real DHS located in southern Switzerland. At the building level, the heating needs are estimated considering real data and simultaneous energy simulations. Two DHS configurations, alternatives to the existing one, are simulated and suitable parameters for the management of the DHS are selected. The global performance of the two DHS is evaluated by KPIs also including the flexibility and the impact on the electric peak due to heat pumps. The achieved results are discussed providing suggestions for the stakeholders involved in DHS management for an optimal matching of the electric grid and thermal networks towards a reduction of the peak power. The rule-based control strategies defined allow the expected electric peak shaving and load levelling, conversely, the yearly energy consumptions are lightly increased and have to be further investigated. The outcomes demonstrate a global better performance of the ultra-low temperature DHS in terms of response to the applied control strategies and of energy savings.
... When modelling energy systems, simplified approaches to representing HPs are frequently used, assuming either a constant COP [59][60][61][62] or a constant Lorenz efficiency, which results in various COPs throughout the year depending on the temperature of the heat source and heat sink [63,64]. However, studies have shown that if the operating conditions deviate significantly from the design settings of the HP, this can still lead to considerable discrepancies in COP exceeding 20% for water-based heat sources [65]. ...
The water-heated humidification–dehumidification desalination system was incorporated with a vapor compression refrigeration cycle, where the condenser was used to heat the seawater, and the evaporator was used to recover the carried heat from the discharged brine. Mathematical models based on mass and energy equilibrium were developed considering the integration mechanisms between the desalination and refrigeration units. The outcomes accurately illustrated how well the integrated system performs under design parameters, considering gained output ratio and water production. Additionally, the simulation and analysis of the essential effects of the critical parameters that have been prescribed on the desalination system's performance are performed.
Heating and cooling systems account for approximately 50% of global energy consumption and contribute 40% of carbon dioxide emissions. District-heating systems offer enhanced energy efficiency, diversification, independence from energy sources, and the utilization of waste and renewable energy sources. One key energy-efficiency measure in district heating is reducing the supply and return temperatures. Fourth-generation district-heating systems operate with supply temperatures of 50 to 60 °C, enabling better utilization of renewable and waste heat. Fifth-generation district-heating systems further lower the supply/return temperatures, requiring additional heat sources, such as boosters, to heat domestic hot water. Heat pumps, specifically vapor-compression heat pumps, are the most energy-efficient devices for converting fuels or electricity into heat for space and water heating. However, vapor-compression technology faces challenges related to environmentally friendly refrigerants, noise, vibration, compactness, and energy efficiency, especially for small units. In this study, we introduce a novel design of thermoelectric-based heat-pump booster. Despite its lower exergy efficiency, this technology offers advantages such as compactness, silent operation without vibration, easy power control, and longevity. We demonstrate that these thermoelectric heat-pump boosters can increase the supply-water temperature of district-heating systems from around 32 °C to 42 °C, with a heating coefficient of performance equal to 2.4 and an exergy efficiency of 9.9 %.
Fifth Generation District Heating and Cooling (5GDHC) networks, also called bidirectional low-temperature district energy systems, is a promising strategy that is more efficient for districts with simultaneous cooling and heating demands. This study presents an economic life cycle assessment of bidirectional low-temperature district systems with varying shares of different energy sources. Solar thermal energy and waste heat from the cooling demand in summer can be transferred to the geothermal energy storage to be reused by heat pumps during winter. The capital investment of the heat pumps, geothermal boreholes and photovoltaic/thermal (PVT) systems can be paid back at the end of the lifetime of the project. Additionally, geothermal systems can increase the recovery of the waste heat and solar energy.KeywordsLow-temperature district heating networksBidirectional low-temperature district energy systemsLife-cycle assessmentHybrid thermal-photovoltaic systems
This study introduces a novel, ambient-temperature district energy system topology that enables bi-directional mass flow to booster heat pumps and includes distributed solar-thermal generation. The ambient system topology is described and a detailed model is developed in MATLAB-Simulink. An equivalent model is developed for a conventional, supply-return district system utilizing hot (75 °C) and chilled (15 °C) water, allowing for the direct comparison with the proposed system—with and without solar-thermal integration—in technical, environmental, and economic analyses. Annual simulations are conducted for the case study: an existing network in Ottawa, Canada with 12 commercial buildings. The ambient system achieves a system coefficient of performance of 1.40 without solar assistance and 1.43 with solar assistance. The conventional system achieves coefficients of performance of 1.26 and 1.28, respectively. The solar fractions of the ambient and conventional systems are 5.5 and 4.0% for heating and 9.3 and 10.0% for cooling, respectively. The ambient system without solar decreased annual carbon emissions by 32.16% relative to the conventional system, a significant improvement. While the ambient system's levelized cost of energy is higher both without solar (8.1 vs. 6.0¢/kWh) and with solar (11.0 vs. 9.2¢/kWh), the ambient system is less expensive if carbon pricing is considered.
Climate change mitigation and transformation strategies with expansion targets for renewable energy sources are defined at the national level. Due to the decentralised character of these sources, local energy system planning plays an important role. However, local communities often lack the capacity to develop energy concepts and thus exploit local renewable potentials consistently. This study develops a highly transferable methodology for deriving local energy system transformation scenarios in line with national greenhouse gas reduction strategies. Thus, an energy system optimisation model is substantially extended to collectively optimise the transformation of final energy demand in the residential, industry, tertiary and transport sectors, as well as established and niche greenhouse gas reduction technologies. Here, a focus is set on the building stock transformation, and a stochastic model is presented to better grasp and represent the dynamic developments and heterogeneity of the local building stock. Based on superordinate parameters such as retrofit rates and heating technology diffusion, the stochastic model generates informative building stock scenarios that are used as input for the developed energy system optimisation model. Exemplarily, the model is applied to the central European city of Karlsruhe. The results show that an increase of the retrofit rate to 2 %/a and strong electrification of the heat supply in the building sector is economically and environmentally beneficial. Furthermore, an accelerated expansion of photovoltaics compared to the national expansion rate can save costs and CO2 emissions. Building on the methodology presented, transferable infrastructure models for the electricity, gas and district heating network should be developed that can be used to assess the feasibility of the transformation paths determined by the methodology presented.
THE PURPOSE. Improving the energy efficiency of a hydroelectric power plant (HPP). Determination of the volume of lost thermal energy from HPP equipment. Development of options for the beneficial use of low-grade heat. Economic evaluation of the proposed options. Selection of the most appropriate waste heat utilization option. METHODS. The methods of the theory of heat and mass transfer, thermodynamic analysis, technical and economic calculations in the energy sector are used in the work. RESULTS. The article determined the temperatures of heat carriers in the cooling system of the hydroelectric generator of the Bratsk HPP. Calculated heat losses in the amount of 92,52 MW. 3 variants of heat supply for the facilities of the Bratsk HPP have been laid. An optimized scheme of heat generation using a heat pump installation (HPI) has been developed. A feasibility study of the proposed options for heat supply has been carried out. An analysis of the Russian HPI market was carried out. A cost-effective heat supply option with 2 Viesmann Vitocal 350-G Pro HPI was selected for implementation with a capital investment 34,46 million of RUB and a payback period of 7,3 years. CONCLUSION. The results of technical and economic calculations show the feasibility of introducing a HPI into the heat generation system of the Bratsk HPP.
Energy systems analyses are integrated elements in planning the transition towards renewable energy-based energy systems. This is due to a growing complexity arising from the wider exploitation of variable renewable energy sources (VRES) and an increasing reliance on sector integration as an enabler of temporal energy system integration, but it calls for consideration to the validity of modelling tools. This article synthesises EnergyPLAN applications through an analysis of its use both from a bibliometric and a case-geographical point of view and through a review of the evolution in the issues addressed and the results obtained using EnergyPLAN. This synthesis is provided with a view to addressing the validity and contribution of EnergyPLAN-based research. As of July 1st, 2022, EnergyPLAN has been applied in 315 peer-reviewed articles, and we see the very high application as an inferred internal validation. In addition, the review shows how the complexity of energy systems analyses has increased over time with early studies focusing on the role of wind power and the cogeneration of heat and power and later studies addressing contemporarily novel issues like the sector integration offered by using power-to-x in fully integrated renewable energy systems. Important findings developed through the application of EnergyPLAN includes the value of district heating in energy systems, the value of district heating for integration of VRES and more generally the importance of sector integration for resource-efficient renewable energy-based energy systems. The wide application across systems and development stages is interpreted as inferred validation through distributed stepwise replication.
The transition towards carbon-neutral energy systems requires the identification of solutions that are optimal at a societal level, however, market actors operate under a different logic where each individual investment option is required to show business-economic feasibility. Thus, while there are energy system analysis modelling tools that can help identify optimal transition paths for a given society in general through the minimisation of national or regional energy system costs, there is also a need for modelling tools that take a closer focus on how energy system actors and their investment considerations perceive and are affected by the economic and technical environment. The modelling tool energyPRO is of the latter type developed and evolved over the last decades to assist in the assessment of the feasibility of different energy units in the energy systems, but which can also model larger complex systems. This article presents energyPRO with a focus on its system understanding and general model characteristics and a thorough view into its two optimisation approaches based on analytical programming or mixed integer linear programming. Finally, a comparison with other models as well as a review of its characterisation and application in the academic literature is supplied.
The use of heat pumps in buildings is one of the best and often the only option for the decarbonization of the building stock. District heating seems a promising solution in urban areas and in existing buildings when the use of heat pumps is restricted and also technically and economically challenging (source exploitation, space restrictions, sound emissions, etc.). Heat pumps can be integrated in various ways in buildings and district heating systems: large central high-temperature heat pumps in district heating, medium-size heat pumps block- or building-wise or small heat pumps decentral apartment-wise. The best option depends on the individual district heating CO2 emissions and the electricity mix as well as on the perspective of the building owner versus that one of the district heating system and its future development. Austrian examples of district heating systems and different variants of integrating heat pumps are investigated in a comprehensive way by means of an energetic and environmental simulation-based analysis. This assessment includes a detailed investigation of the capabilities of the booster heat pump to increase the PV own-consumption and is also expanded to include various scenarios for the development of the electricity mix and the decarbonisation of district heating.
THE PURPOSE. Determination of the permissible power of the heat pump (HP) used in the cooling system of the steam turbine condenser for a thermal power plant (TPP) based on double-circuit combined-cycle gas turbine (CCGT).
METHODS. Mathematical modeling of the operating modes of a heating CCGT with a HP in the cooling system was used as a research method. The research was conducted using statistical data on technical parameters and economic indicators of CCGT-450, for climatic and market conditions of St. Petersburg. The research of the most characteristic modes of operation of the main power equipment, in the annual context, was carried out. The maximum permissible capacity of the HP, from the point of view of the organization of stable heat supply to the consumer, available low-potential resources and breakeven operation of TPP in the electricity market was determined.
RESULTS. It was found that lowpotential energy resources in the cooling system of the steam turbine condenser are formed in significant volumes and the thermal power of the consumer is consistently high, including in summer. Therefore, market restrictions related to the break-even operation of TPP in the wholesale electricity market are the most essential condition determining the permissible level of HP power. It was found that for the object of study, with an average annual electrical capacity of 650 MW, the maximum power of the HP is 160 MW.
CONCLUSION. The main factors limiting the permissible level of HP power were analyzed using the example of a real power facility. A direct connection between the maximum capacity of the HP and external economic conditions, as well as the level of energy efficiency of the TPP equipment was established. This approach can be used to select and justify the HP capacity regardless of the location region, the type of power system, the cost of energy resources, market conditions, as well as the type and characteristics of the equipment used.
The use of solar radiation data models is widespread in energy system analysis, however a gap exists when assessing their impact in modelling large-scale solar thermal systems integrated in district heating (DH) systems. Therefore, this study presents an analysis of how using satellite-based radiation data models (SARAH), reanalysis models (CFSR, ERA and MERRA2) and other data models (Danish Reference Year) affect the modelling of these systems. Taking three DH plants in Denmark as study cases, the measured radiation between 2016 and 2019 are utilized.
Using energyPRO-based mathematical models of the systems, heat outputs are calculated and compared with measured data. Moreover, the yearly DH plant operational cost is calculated to observe the economic impact of using inaccurate models. It is found that heat production assessments based on the SARAH model show a better agreement with measured data than the reanalysis-based ERA5, MERRA2 and CFSR models. The empirically-based DRY shows low errors when observing its yearly values but has a higher inaccuracy on the hourly level, providing inaccurate operation profiles of the plant.
Additionally, the satellite-based solar data model SARAH is further analysed to identify patterns of its inaccuracy. After comparing it with 18 locations in Denmark using month-hourly profiles, no error trend can be identified, supporting the robustness of the model.
Local governments play dual roles in developing renewable energy projects. They are the targets of many goals concerning energy and climate, set by national and international actors, and they are important actors in energy planning, regulation setting, and the development of infrastructure and residential areas. In this paper, I study how local governments’ technology policies affect the actual outcome of project development based on experiences from 14 local governments. Technology policies are studied from the perspective of Sørensen’s [1] four areas of concern: direct support of innovation, infrastructure, regulation (protection and standards) and public engagement. I find that local governments use policy instruments within all four areas, and that the way local governments involves in the process of bioenergy development are surprisingly similar despite differences in location and size of both the local government and the project.
This paper outlines how an existing energy system can be transformed into a 100% renewable energy system. The transition is divided into a number of key stages which reflect key radical technological changes on the supply side of the energy system. Ireland is used as a case study,but in reality this reflects many typical energy systems today which use power plants for electricity, individual boilers for heat, and oil for transport. The seven stages analysed are 1) reference, 2) introduction of district heating, 3) installation of small and large-scale heat pumps,4) reducing grid regulation requirements, 5) adding flexible electricity demands and electric vehicles, 6) producing synthetic methanol/DME for transport, and finally 7) using synthetic gas to replace the remaining fossil fuels. For each stage, the technical and economic performance of the energy system is calculated. The results indicate that a 100% renewable energy system can provide the same end-user energy demands as today’s energy system and at the same price. Electricity will be the backbone of the energy system, but the flexibility in today’s electricity sector will be transferred from the supply side of the demand side in the future. Similarly, due to changes in the type of spending required in a 100% renewable energy system, this scenario will result in the creation of 100,000 additional jobs in Ireland compared to an energy system like today’s. These results are significant since they indicate that the transition to a 100% renewable energy system can begin today, without increasing the cost of energy in the short- or long-term, if the costs currently forecasted for 2050 become a reality.
In this work, we develop a model to forecast world electricity production up to 2100. We analyze historical data for electricity production, population and GDP per Capita for the period 1900–2008. We show that electricity production follows general trends. First, there is an electricity intensity target of 0.20-0.25 kWh per unit of GDP (US$2012) as economies mature, except in countries traditionally relying heavily on renewable electricity (hydroelectricity), for whom this target ranges between 0.50 to 0.80 kWh per unit GDP. Also, countries that belong to the same region tend to follow the evolution of electricity production and GDP/Capita of a regional “modelcountry”. Equations that describe the behavior of these model countries are used to forecast electricity production per capita up to 2100 under a low and a high scenario for the evolution of GDP per Capita. For electricity production two main scenarios were set: “Current Energy MixScenario” and “Electricity as Main Energy Source Scenario”, with two additional sub scenarios considering slightly different electric intensities. Forecasts up to 2100 yield a demand forelectricity production 3.5 to 5 times higher than the current production for the “Current EnergyMix Scenario” and about 9 to 14 times for the “Electricity as Main Energy Source Scenario”. Forecasts for the “Current Energy Mix Scenario” matched well with forecasts from IEA/EIA (International Energy Agency/ Energy Information Administration) while the forecasts for the“Electricity as the Main Energy Source Scenario” are much higher than current predictions.
Significant reductions of heat demand, low-carbon and renewable energy sources, and district heating are key elements in 100% renewable energy systems. Appraisal of district heating along with energy efficient buildings and individual heat supply requires a geographical representation of heat demand, energy efficiency and energy supply. The present paper describes a Heat Atlas built around a spatial database using geographical information systems (GIS). The present atlas allows for per-building calculations of potentials and costs of energy savings, connectivity to existing district heat, and current heat supply and demand. For the entire building mass a conclusive link is established between the built environment and its heat supply. The expansion of district heating; the interconnection of distributed district heating systems; or the question whether to invest in ultra-efficient buildings with individual supply, or in collective heating using renewable energy for heating the current building stock, can be based on improved data.
The district heating (DH) system of Greece, mainly supported from lignite fired stations, is facing lately significant challenges. Stricter emission limits, decreased efficiency due to old age and increased costs are major challenges of the lignite sector and are expected to result in the decommissioning of several lignite-fired units in the coming years. As a result, managers of DH networks are currently investigating alternative scenarios for the substitution of thermal power that it is expected to be lost, through the integration of Renewable Energy Sources (RES) into the system. In this paper, the DH systems of Kozani and Ptolemaida are examined regarding possible introduction of RES. The first study examines district heating of Kozani and alternative future options for covering a part of city’s thermal load whereas the second study refers to a biomass CHP plant (ORC technology, 1MWe, 5MWth) to be powered from a biomass mixture (wood chips and straw).
The simulation model created in the environment of EnergyPro software is used to evaluate the influence of an accumulator tank used with 215 MW power unit in the Balti Power Plant, which can operate in cogeneration mode. The plant supplies heat to the city district heating system. Production of heat reduces the electricity generation in the power unit and the highest electricity capacity can be reached without heat being produced. The electricity sale prices are variable, changing hourly. After installation of the heat accumulator tank, the power unit can operate in cogeneration mode with charging the accumulator tank when electricity prices are lower and delivering district heat during the period when the unit operates in condensation mode (electricity only). The real input data on the operation of district heating system; heat and electricity generation and ambient temperature have been used for simulation.
Rising energy costs, anthropogenic climate change, and fossil fuel depletion calls for a concerted effort within energy planning to ensure a sustainable energy future. This article presents an overview of global energy trends focusing on energy costs, energy use and carbon dioxide emissions. Secondly, a review of contemporary work is presented focusing on national energy pathways with cases from Ireland, Denmark and Jordan, spatial issues within sustainable energyplanning and policy means to advance a sustainable energy future.
Full text: http://dx.doi.org/10.5278/ijsepm.2014.1.1
Background
Human induced pluripotent stem cell-derived mesenchymal stem cells (hiPSC-MSCs) have emerged as a promising alternative for stem cell transplantation therapy. Exosomes derived from mesenchymal stem cells (MSC-Exos) can play important roles in repairing injured tissues. However, to date, no reports have demonstrated the use of hiPSC-MSC-Exos in cutaneous wound healing, and little is known regarding their underlying mechanisms in tissue repair.MethodshiPSC-MSC-Exos were injected subcutaneously around wound sites in a rat model and the efficacy of hiPSC-MSC-Exos was assessed by measuring wound closure areas, by histological and immunofluorescence examinations. We also evaluated the in vitro effects of hiPSC-MSC-Exos on both the proliferation and migration of human dermal fibroblasts and human umbilical vein endothelial cells (HUVECs) by cell-counting and scratch assays, respectively. The effects of exosomes on fibroblast collagen and elastin secretion were studied in enzyme-linked immunosorbent assays and quantitative reverse-transcriptase¿polymerase chain reaction (qRT-PCR). In vitro capillary network formation was determined in tube-formation assays.ResultsTransplanting hiPSC-MSC-Exos to wound sites resulted in accelerated re-epithelialization, reduced scar widths, and the promotion of collagen maturity. Moreover, hiPSC-MSC-Exos not only promoted the generation of newly formed vessels, but also accelerated their maturation in wound sites. We found that hiPSC-MSC-Exos stimulated the proliferation and migration of human dermal fibroblasts and HUVECs in a dose-dependent manner in vitro. Similarly, Type I, III collagen and elastin secretion and mRNA expression by fibroblasts and tube formation by HUVECs were also increased with increasing hiPSC-MSC-Exos concentrations.Conclusions
Our findings suggest that hiPSC-MSC-Exos can facilitate cutaneous wound healing by promoting collagen synthesis and angiogenesis. These data provide the first evidence for the potential of hiPSC-MSC-Exos in treating cutaneous wounds.
The purpose of this paper is to offer a methodology for the evaluation
of large district heating networks. The methodology includes an analysis
of heat generation and distribution based on the models created in the
TERMIS and EnergyPro software Data from the large-scale Tallinn district
heating system was used for the approbation of the proposed methodology
as a basis of the case study. The effective operation of the district
heating system, both at the stage of heat generation and heat
distribution, can reduce the cost of heat supplied to the consumers. It
can become an important factor for increasing the number of district
heating consumers and demand for the heat load, which in turn will allow
installing new cogeneration plants, using renewable energy sources and
heat pump technologies
Within five years from now, Lithuania is going to close down Ignalina, the only nuclear-power plant in the country. Since Ignalina generates more than 75% of the Lithuanian electricity production, new generation capacities are needed. Traditional steam-turbines, fuelled with fossil fuels, would mean further imports of fuel as well as a rise in CO2 emissions. At the same time, several small district-heating companies one suffering from high heating-prices. Typically, the price in small towns is 20-50% higher than the price in large urban areas. Consequently, alternative strategies should be considered. This article analyses the conditions for one such strategy, namely the replacement of boilers in the existing district-heating supplies with combined heat-and-power production (CHP). Compared with new power stations, fuel can be saved and CO2-emissions reduced. Also this strategy can be used to level the difference between low heating prices in the large urban areas and high prices in small towns and villages.
China accounts for half of the world's annual coal consumption. Coal is the primary energy source for heating in urban areas, particularly in northern China. This causes significant challenges for urban air quality problems in China and greenhouse gases emissions. Urban district heating (DH) systems penetration is very high in northern China. It supplies space heating to more than 80% of urban buildings in the area. Unlike the electricity and transportation sectors, the heating sector has received little attention from policy makers and researchers in China, DH systems are an enabling infrastructure which facilitates energy efficiency improvements and the use of renewable energy sources. This study explores the dynamics and possibility to expand alternative energy sources (natural gas, biomass, direct geothermal heat, ground-source heat pump, municipal waste heat, industrial waste heat) for DH in China. We apply an analytical framework largely based on the multi-level perspective in socio-technical transitions theory, in which transitions are interpreted as the result of the functioning of niche, regime and landscape elements, and interactions between them. The study provides an integrated picture of the socio-technical structure and functioning of DH in China. The results show that an energy transition in Chinese DH systems has barely started. The system is characterised by stability of the coal-based DH regime, while a number of alternative niches are struggling to emerge. Among these, natural gas is the most successful example. However, at local level different niches present opportunities in terms of physical availability, economic viability and technical capacity to address changes in landscape pressures. A sustainable heat roadmap based on integrated energy planning and policy attention at the national level could be developed as one mechanism for instigating a much needed energy transition in DH in China.
Increasing amounts of intermittent renewable energy sources (RES) are being integrated into energy systems worldwide. Due to the nature of these sources, they are found to increase the importance of mechanisms for balancing the electricity system. Small-scale combined heat and power (CHP) plants based on gas have proven their ability to participate in the electricity system balancing, and can hence be used to facilitate an integration of intermittent RES into electricity systems. Within the EU electricity system, balancing reserves have to be procured on a market basis. This paper investigates the ability and challenges of a small-scale CHP plant based on natural gas to participate in the German balancing reserve for secondary control. It is found that CHP plants have to account for more potential losses than traditional power plants. However, it is also found that the effect of these losses can be reduced by increasing the flexibility of the CHP unit.
The reduction of energy use in existing buildings through energy renovations is required to reach the energy efficiency goals in Denmark. To facilitate the adoption of technologies for extensive energy renovations, there is a need to understand how these take place and what influences the process. In this paper, we open the 'black box' of what actually happens when actors engage in the adoption of energy renovation technologies and the necessity of trust between the actors. In the case study of an energy renovation project of hotel facilities, we analyse the journey from having the intention to implement extensive energy renovation measures to actually implementing a solution. For extensive energy renovations, the process is not associated with a radical technological development. It is complex owing to the number of actors involved and the complexity in the socio-technical interactions between them.
The ambitious policy in Denmark on having a 100% renewable energy supply in 2050 requires radical changes to the energy systems to avoid an extensive and unsustainable use of biomass resources. Currently, wind power is being expanded and the increasing supply of electricity is slowly pushing the CHP (combined heat and power) plants out of operation, reducing the energy efficiency of the DH (district heating) supply. Here, large heat pumps for district heating is a frequently mentioned solution as a flexible demand for electricity and an energy efficient heat producer. The idea is to make heat pump use a low temperature waste or ambient heat source, but it has so far been very unclear which heat sources are actually available for this purpose.
In this study eight categories of heat sources are analysed for the case of Denmark and included in a detailed spatial analysis where the identified heat sources are put in relation to the district heating areas and the corresponding demands. The analysis shows that potential heat sources are present near almost all district heating areas and that sea water most likely will have to play a substantial role as a heat source in future energy systems in Denmark.
Feasibility of district heating networks for areas with low heat demand of passive and low energy houses implies the development of innovative concepts for the production, storage, distribution and supply of thermal energy. Low supply temperatures enables the use of heat from renewable and alternative sources, currently been neglected due to the usually high supply temperatures used in conventional district heating systems. Further on, low network temperatures are supporting the reduction of operational and investment costs.
This paper investigates to which extent heat should be saved rather than produced and to which extent district heating infrastructures, rather than individual heating solutions, should be used in future sustainable smart energy systems. Based on a concrete proposal to implement the Danish governmental 2050 fossil-free vision, this paper identifies marginal heat production costs and compares these to marginal heat savings costs for two different levels of district heating. A suitable least-cost heating strategy seems to be to invest in an approximately 50% decrease in net heat demands in new buildings and buildings that are being renovated anyway, while the implementation of heat savings in buildings that are not being renovated hardly pays. Moreover, the analysis points in the direction that a least-cost strategy will be to provide approximately 2/3 of the heat demand from district heating and the rest from individual heat pumps.
CHP (Combined heat and power) production in connection with DH (district heating) systems has previously demonstrated a significant reduction in primary energy consumption. With extended installation of intermittent sustainable sources, such as eg. wind turbines rather than thermal units, the changed distribution of generation technologies may suggest a reconsideration of optimum for DH network temperatures, in order to achieve low cost and minimize carbon emissions. A mixed integer linear optimisation model was used to investigate the changed operation based on changed network characteristics. Utility plants and demand curves corresponded to the current and future scenarios for the DH system of Greater Copenhagen. Performance curves from typical CHP-plant technologies were used to represent the changed operation of power and heat production for changed DH temperatures. The results show that primary fuel consumption is reduced approximately 5-7% at DH design temperatures of 60-70 °C. Further reduction in DH temperatures resulted in opposing tendencies, as hot tap water requires electricity to reach the required temperatures. The results are network-specific, as they represent the given network and production units, but similar trends can be expected for other large networks.
District heating may supply many consumers efficiently, but the heat loss from the pipes to the ground is a challenge. The heat loss may be lowered by decreasing the network temperatures for which reason low temperature networks are proposed for future district heating. The heating demand of the consumers involves both domestic hot water and space heating. Space heating may be provided at low temperature in low energy buildings. Domestic hot water, however, needs sufficient temperatures to avoid growth of legionella. If the network temperature is below the demand temperature, supplementary heating is required by the consumer. We study conventional district heating at different temperatures and compare the energy and exergetic efficiency and annual heating cost to solutions that utilize electricity for supplementary heating of domestic hot water in low temperature district heating. This includes direct electric heating and three heat pump solutions applying R134a and R744. The results show that conventional solutions at lowest possible temperature have the highest exergetic efficiency of 28% and lowest annual cost of € 690 for a 159m2 house. The best low temperature system is an R134a heat pump with hot water storage on the district heating side, which reaches 25% exergetic efficiency.
We present a comprehensive review of modelling approaches and associated software tools that address district-level energy systems. Buildings play an important role in urban energy systems regarding both the demand and supply of energy. It is no longer sufficient to simulate building energy use assuming isolation from the microclimate and energy system in which they operate, or to model an urban energy system without consideration of the buildings that it serves. This review complements previous studies by focussing on models that address district-level interactions in energy systems, and by assessing the capabilities of the software tools available alongside the theory of the modelling approaches used.
New models and tools that address these district-level interactions are reviewed and their competences assessed. These are divided into the following sections: district energy systems (including heat networks, multi-energy systems and low-temperature networks), renewable energy generation (including solar, bioenergy, wind and the related topic of seasonal storage), and the urban microclimate as it relates to energy demands. The scope and detail covered by twenty cross-disciplinary tools is summarised in a matrix; many other tools that focus on specific areas are also discussed. We end by summarising the current state of district-scale urban energy modelling as it relates to the built environment, along with our perspective on future challenges and research directions.
In the transition towards a 100% renewable energy system, energy savings are essential. The possibility of energy savings through conservation or efficiency increases can be identified in, for instance, the heating and electricity sectors, in industry, and in transport. Several studies point to various optimal levels of savings in the different sectors of the energy system. However, these studies do not investigate the idea of energy savings being system dependent. This paper argues that such system dependency is critical to understand, as it does not make sense to analyse an energy saving without taking into account the actual benefit of the saving in relation to the energy system. The study therefore identifies a need to understand how saving methods may interact with each other and the system in which they are conducted. By using energy system analysis to do hourly simulation of the current Danish energy system, the combination of reductions in heat and electricity demands is analysed within the Danish district heating sector to show the benefits of coordinating savings in the electricity and district heating sectors.
Energy systems with high degrees of renewable energy integration require on the one hand energy scenario making and energy system analyses for the optimal design of systems and pathways and on the other hand well-established criteria for decision-making and for characterisation of energy system suitability. This article has a threefold objective, it reviews the application of a given energy system simulation model - EnergyPLAN - analysing its application on geographic level as well as the types of simulations or scenario analyses performed on the model. Secondly, it reviews the types of performance indicators applied in said energy systems simulations and thirdly it reviews and details existing advanced energy system performance indicators and proposed additional indicators.
Denmark is aiming for a fossil-free heating sector for buildings by 2035. Judging by the national heating plan, this will be achieved mainly by a further spread of DH (district heating) based on the renewable heat sources. To make the most cost-effective use of these sources, the DH supply temperature should be as low as possible. We used IDA-ICE software to simulate a typical Danish single-family house from the 1970s connected to DH at three different stages of envelope and space heating system refurbishment. We wanted to investigate how low the DH supply temperature can be without reducing the current high level of thermal comfort for occupants or the good efficiency of the DH network. Our results show that, for a typical single-family house from the 1970s, even a small refurbishment measure such as replacing the windows allows the reduction of the maximum DH supply temperature from 78 to 67 °C and, for 98% of the year, to below 60 °C. However for the temperatures below 60 °C a low-temperature DH substation is required for DHW (domestic hot water) heating. This research shows that renewable sources of heat can be integrated into the DH system without problems and contribute to the fossil-free heating sector already today.
The city of Pécs in Hungary has developed an energy strategy to be implemented in the years to come which proposes structural changes in both the supply and demand sides. This paper offers a model based on the proposed system aimed at providing a basis for comparison for decision-makers. The model has been developed with the help of energy system analysis tool energyPRO, and covers the three basic sectors of heat, electricity and transport. It shows the energy system of Pécs in terms of hourly production and demand levels – and these values enable the model to analyse intermittent energy sources. The model is also validated – to ensure that it is satisfactory for the simulation of future energy systems. It analyses two scenarios – one where the city does not implement the changes proposed in the strategy, and one where it does. The paper compares the two scenarios based on sustainability, energy security and affordability.
Danish municipal heat planning empowers municipalities to implement locally appropriate energy solutions that are the best fit for the locality as a whole and the individual consumers served. Supportive policies and actions at the national and local levels have encouraged heat planning that confers significant autonomy to local governments. By examining how power is distributed and shared by different levels of governments in the planning process, this paper investigates how comprehensive energy planning in Denmark has supported the development of highly cost-effective district heating systems. Lessons from the Danish approach to heat planning are considered for their relevance to the United States, where significant technical district heating potential exists, yet remains well outside the typical energy policy discussions. While the specific Danish political context may not be transferable to other locations, the practical aspects of power sharing, socio-economic cost–benefit analyses, and communal decision-making may inform approaches to local heat planning around the world.
This paper defines the concept of 4th Generation District Heating (4GDH) including the relations to District Cooling and the concepts of smart energy and smart thermal grids. The motive is to identify the future challenges of reaching a future renewable non-fossil heat supply as part of the implementation of overall sustainable energy systems. The basic assumption is that district heating and cooling has an important role to play in future sustainable energy systems – including 100 percent renewable energy systems – but the present generation of district heating and cooling technologies will have to be developed further into a new generation in order to play such a role. Unlike the first three generations, the development of 4GDH involves meeting the challenge of more energy efficient buildings as well as being an integrated part of the operation of smart energy systems, i.e. integrated smart electricity, gas and thermal grids.
According to some future Danish energy scenarios, biomass will become one of the two main pillars of the future energy system accompanied by wind power. The biomass can be used for generating heat and electricity, and as a transportation fuel in a future energy system according to the scenarios. This article compares the value of using biomass as a heat source and for electricity generation in a 100% renewable energy system context. The comparison is done by assuming an incremental decrease in the biomass available for the electricity and heat sector, respectively. The assumed scenarios for the decrease of biomass are made by use of an hourly energy system analysis model, EnergyPLAN. The results are shown in terms of system configuration, biomass fuel efficiency, system cost, and impacts on the export of electricity. It is concluded that the reduction of biomass in the heat sector is better than the alternative reduction in the electricity sector in every aspects except biomass fuel efficiency.
Scenario-making is becoming an important tool in energy policy making and energy systems analyses. This article probes into the making of scenarios for Denmark by presenting a comparison of three future scenarios which narrate 100% renewable energy system for Denmark in 2050; IDA 2050, Climate Commission 2050, and CEESA (Coherent Energy and Environmental System Analysis). Generally, although with minor differences, the scenarios suggest the same technological solutions for the future such as expansion of biomass usage and wind power capacity, integration of transport sector into the other energy sectors. The methodologies used in two academic scenarios, IDA 2050 and CEESA, are compared. The main differences in the methodologies of IDA 2050 and CEESA are found in the estimation of future biomass potential, transport demand assessment, and a trial to examine future power grid in an electrical engineering perspective. The above-mentioned methodologies are compared in an evolutionary perspective to determine if the methodologies reflect the complex reality well. The results of the scenarios are also assessed within the framework of “radical technological change” in order to show which future scenario assumes more radical change within five dimensions of technology; technique, knowledge, organization, product, and profit.
The utilisation of biomass poses large challenges in renewable energy systems while buildings account for a substantial part of the energy supply even in 100% renewable energy systems. In this paper the focus is on how the heating sector can reduce its consumption of biomass, thus leaving biomass for other sectors, but while still enabling a 100% renewable energy system. The analyses of heating technologies shows that district heating (DH) systems are important in limiting the dependence on biomass and create cost effective solutions. DH systems are especially important in renewable energy systems with large amounts of fluctuating sources as it enables fuel efficient and low cost energy systems with thermal heat storages. DH increases the efficiency with the use of combined heat and power production (CHP), while reducing the biomass demand by enabling the use of other renewable resources such as large-scale solar thermal, large heat pumps, geothermal heat, industrial surplus heat, and waste incineration. Where the energy density in the building stock is not high enough for DH to be economical, geothermal heat pumps can be recommended for individual heating systems, even though biomass consumption is higher than the DH solutions.
Aalborg Municipality, Denmark is investigating ways of switching to 100% renewable energy supply over the next 40 years. Analyses so far have demonstrated a potential for such a transition through energy savings, district heating (DH) and the use of locally available biomass, wind power and low-temperature geothermal resources. The analyses have also demonstrated that the municipality will still rely heavily on surrounding areas for electric load balancing assistance. With a departure in a previously elaborated 100% renewable energy scenario, this article investigates how absorption heat pumps (AHP) and compression heat pumps (HP) for the supply of DH impact the integration of wind power. Hourly scenario-analyses made using the EnergyPLAN model reveal a boiler production and electricity excess which is higher with AHPs than with HPs whereas condensing mode power generation is increased by the application of HPs rather than AHP.
Denmark’s long-term energy goal is to develop an energy system solely based on renewable energy sources by 2050. To reach this goal, energy savings in buildings is essential. Therefore, the focus on energy efficient measures in buildings and net zero energy buildings (NZEBs) has increased.Most buildings in Denmark are connected to electricity grids and around half are connected to district heating (DH) systems. Connecting buildings to larger energy systems enables them to send and receive energy from these systems. This paper’s objective is to examine how excess heat production from NZEBs influences different types of DH systems.In the analysis three different types of DH systems are analyzed, and three technology development scenarios for each are created. The examination is from a technical perspective and looks into how the overall heat production within DH areas is affected by the NZEBs excess heat production from solar thermal collectors.The main findings are that the excess heat from NZEBs can benefit DH systems by decreasing the production from production units utilizing combustible fuels. In DH areas where the heat demand in summer months is already covered by renewable energy, adding seasonal heat storage is essential to utilize the NZEB production.
Increasing penetration of fluctuating energy sources for electricity generation, heating, cooling and transportation increase the need for flexibility of the energy system to accommodate the fluctuations of these energy sources. Controlling production, controlling demand and utilising storage options are the three general categories of measures that may be applied for ensuring balance between production and demand, however with fluctuating energy sources, options are limited, and flexible demand has also demonstrated limited perspective. This article takes its point of departure in an all-inclusive 100% renewable energy scenario developed for the Danish city Aalborg based on wind power, bio-resources and low-temperature geothermal heat. The article investigates the system impact of different types of energy storage systems including district heating storage, biogas storage and electricity storage. The system is modelled in the energy systems analyses model energyPRO with a view to investigating how the different storages marginally affect the amount of wind power that may be integrated applying the different storage options and the associated economic costs. Results show the largest system impact but also most costly potential are in the form of electricity storages.
Distributed cogeneration has played a key role in the implementation of sustainable energy policies for three decades. However, increasing penetration levels of intermittent renewables is challenging that position. The paradigmatic case of West Denmark indicates that distributed operators are capitulating as wind power penetration levels are moving above 25%; some operators are retiring cogeneration units entirely, while other operators are making way for heat-only boilers. This development is jeopardizing the system-wide energy, economic, and environmental benefits that distributed cogeneration still has to offer. The solution is for distributed operators to adapt their technology and operational strategies to achieve a better co-existence between cogeneration and wind power. Four options for doing so are analysed including a new concept that integrates a high pressure compression heat pump using low-temperature heat recovered from flue gasses in combination with an intermediate cold storage, which enables the independent operation of heat pump and cogenerator. It is found that an electric boiler provides consistent improvements in the intermittency-friendliness of distributed cogeneration. However, well-designed heat pump concepts are more cost-effective than electric boilers, and in future markets where the gas/electricity price ratio is likely to increase, compression heat pumps in combination with intermediate thermal storages represent a superior potential for combining an intermittency-friendly pattern of operation with the efficient use of electricity in heating and cooling production.
In Denmark, the integration of wind power is affected by a large amount of cogeneration of heat and power. With ancillary services supplied by large-scale condensation and combined heat and power (CHP) plants, a certain degree of large-scale generation is required regardless of momentary wind input. A lowered district heating demand and thereby lowered CHP-bound electricity generation would appear to increase the possibility of integration wind power but due to the ancillary services supplied by CHP plants, the situation is in fact the opposite. Heat savings may not be technically feasible, if a certain production is required regardless of whether over-all electricity generation is sufficient. This article analyses this and although heat savings do have a negative impact on the amount of wind power the system may integrate a given moment in certain cases, associated fuel savings are notable and by far supersede the 'loss' in wind power integration.
Combined heat and power (CHP) plants with thermal stores may be suitable for sustainable energy production and the accommodation of fluctuating renewable energy sources. At the moment, in the UK, only a few CHP plants have thermal stores. Previous research has shown that thermal stores can improve the economics of CHP plants in the UK under the current market conditions. However, currently, it is only beneficial for CHP plants to sell their electricity to a third party, a Licensed Electricity Supplier, rather than to sell it directly to the power exchange market at prices which are much higher. If CHP plants aggregate, direct access to the power exchange market can become economically viable hence there is the possibility that thermal stores could further improve the economics of CHP plants under an aggregated electricity dispatch. This work firstly explains the conditions under which such plants could aggregate and act as a large power plant in the UK market, and secondly explores the most economic-size of gas engine and thermal store, in the case of aggregation, using energyPRO software and Excel spreadsheets. The work suggests that direct access to the power exchange market can improve the economics of the CHP plants. The highest Net Present Value (NPV), without heat dissipation, for a CHP plant exporting its electricity to the grid for a community heating load of 20GWh, is more than £5m, and is obtained for a 6MW engine with a 28.2MWh (900m3) thermal store. The research suggests that such high electricity prices could make even larger plants more profitable than that; however, this can happen only if some of the produced heat is dissipated.
Efficient heat supply systems based on renewable energy sources are an important element of future energy systems that do not depend on fossil fuels. End-use energy savings and the expansion of district heating are often mentioned as measures to make the heat supply sector in Denmark more sustainable. In this paper, the impacts of expanding district heating and implementing end-use energy savings are evaluated in relation to an existing local energy system as well as a local renewable energy system in the short term. The results show that end-use energy savings and district heating expansion combined in the existing energy system improve the overall fuel efficiency of the system. Similar effects are observed in relation to the renewable energy system. The assessment of the associated costs indicates that the district heating supply costs are higher than or at about the same level of the extra costs of heat demand reduction measures. It is necessary to then discuss how building owners, utilities and other local actors can be motivated to invest in such socio-economically feasible heat savings. The paper also indicates that (municipal) energy planning in Denmark will have to be approached more strategically in the near future.
There has been discussion about the extent to which combined heat and power (CHP) plants with thermal stores are suitable for sustainable energy production. At the moment, in the UK the development of this type of plant is limited. This paper analyses the economics and optimum size of CHP operating with gas engines and thermal stores in British market conditions. This is achieved using energyPRO software. It is shown that, due to the big differences in electricity prices between day and night, the use of thermal stores could be profitable in the UK. The economical size of CHP plant for a district or community heating load of 20,000MWh per year is found to be a 3MWe gas engine with a 7.8MWh thermal store. In this case the analysis reveals that the use of a thermal store more than doubles the return on investments (as measured in net present value) compared with the same size of a plant without a thermal store. It is concluded that thermal stores can improve the overall economics of CHP plants in present British circumstances.
It is technically possible to decrease the Danish fossil fuel consumption by 50 % within less than 20 years, without a decrease in the material standard of living and without nuclear power. Although Denmark followed an active and internationally praised energy policy, 1987 will probably see a Danish record in fossil fuel consumption, beating the old record from before the first energy crisis in 1973. Nevertheless there has been some success in developing conservation methods and renewable energy technologies like wind power and biogas—based village energy plants—and therefore it now seems technically possible to initiate a strategy for reduced consumption of fossil fuels. The present sectorized and centralized organization of energy systems makes the supply side based on fossil fuels dominate over consumer-oriented conservation technologies blocking effective conservation strategies. It is therefore necessary to regionalize and decentralize the energy systems in order to synchronize conservation, supply-side energy efficiency and renewable energy use, and in that way effectively reduce the consumption of fossil fuel.
This article presents a model of natural ventilation of buildings at the stage of design and a consequence of the behaviour of the occupants. An evaluation is made by coupling multizone air modelling and thermal building simulation using a deterministic set of input factors comprising among others climate, local environment, building characteristics, building systems, behaviour of occupants and heat loads. Selected deterministic input factors are varied to generate additional information applied in an optimization loop.With that, it is found that the optimal solution depends to a great extent on the possibility of optimization of the behaviour of occupants, and to a lesser extent on the design of the building.
Aalborg Municipality, Denmark, wishes to investigate the possibilities of becoming independent of fossil fuels. This article describes a scenario for supplying Aalborg Municipality’s energy needs through a combination of low-temperature geothermal heat, wind power and biomass. Of particular focus in the scenario is how low-temperature geothermal heat may be utilised in district heating (DH) systems. The analyses show that it is possible to cover Aalborg Municipality’s energy needs through the use of locally available sources in combination with significant electricity savings, heat savings, reductions in industrial fuel use and savings and fuel-substitutions in the transport sector. With biomass resources being finite, the two marginal energy resources in Aalborg are geothermal heat and wind power. If geothermal heat is utilised more, wind power may be limited and vice versa. The system still relies on neighbouring areas as an electricity buffer though.The costs of the scenario are at a comparable level with the reference situation, but with significantly higher needs for investments and lower fuel costs. Implementation of the scenario would therefore have a positive socio-economic impact as investments are more local labour-intensive than fuel supply.
Ideal cycles are a very important tool in performance analysis, comparison and development of actual thermodynamic systems. Carnot cycle has been recognized as one of the bases of thermodynamic science. One of the main draw backs of Carnot cycle has been corrected by Lorenz cycle, namely, the isothermal heat sources have been replaced by polytropic ones.
The dual absorption system has all the advantages of the absorption cooling system, however, it avoids the use of the water consuming cooling tower. Absorption system is one of the strong alternatives to CFSs, since it utilizes refrigerants which has no bad effects on the ozone layer. It also, utilizes waste heat and solar energy as main driving power. The characteristics of such a system has been recently studied without introducing the basic ideal cycles. In this work Carnot and Lorenze cycles have been developed for this new absorption system. The graphical representation onT-s, PTX and lnP-1/T diagram have been also reported.
Also, the conventional expression used for the coefficient of performance of the ideal absorption cycle has been corrected on a rigorous basis of first and second laws of thermodynamics.
An analysis of seven different technologies is presented. The technologies integrate fluctuating renewable energy sources (RES) such as wind power production into the electricity supply, and the Danish energy system is used as a case. Comprehensive hour-by-hour energy system analyses are conducted of a complete system meeting electricity, heat and transport demands, and including RES, power plants, and combined heat and power production (CHP) for district heating and transport technologies. In conclusion, the most fuel-efficient and least-cost technologies are identified through energy system and feasibility analyses. Large-scale heat pumps prove to be especially promising as they efficiently reduce the production of excess electricity. Flexible electricity demand and electric boilers are low-cost solutions, but their improvement of fuel efficiency is rather limited. Battery electric vehicles constitute the most promising transport integration technology compared with hydrogen fuel cell vehicles (HFCVs). The costs of integrating RES with electrolysers for HFCVs, CHP and micro fuel cell CHP are reduced significantly with more than 50% of RES.
The Danish city Frederikshavn is aiming at becoming a 100% renewable energy city. The city has a number of energy resources including a potential for off-shore wind power, waste and low-temperature geothermal energy usable as heat source for heat pumps producing district heating.In this article, a technical scenario is described and developed for the transition of Frederikshavn’s energy supply from being predominantly fossil fuelled to being fuelled by locally available renewable energy sources. The scenario includes all aspects of energy demand in Frederikshavn i.e. electricity demand, heat demand, industrial demand as well as the energy demand for transportation.The locally available energy resources are deliberated and an energy system is designed and analysed with an energy systems analysis model on an aggregate annual level as well as on an hourly basis. Particular attention is given to the use of geothermal energy in the area. It is shown, that the use of geothermal energy in combination with an absorption heat pump shows promise in a situation where natural gas supply to conventional cogeneration of heat and power (CHP) plants decreases radically.
This paper presents the methodology and results of the overall energy system analysis of a 100% renewable energy system. The input for the systems is the result of a project of the Danish Association of Engineers, in which 1600 participants during more than 40 seminars discussed and designed a model for the future energy system of Denmark. The energy system analysis methodology includes hour by hour computer simulations leading to the design of flexible energy systems with the ability to balance the electricity supply and demand. The results are detailed system designs and energy balances for two energy target years: year 2050 with 100% renewable energy from biomass and combinations of wind, wave and solar power; and year 2030 with 50% renewable energy, emphasising the first important steps on the way. The conclusion is that a 100% renewable energy supply based on domestic resources is physically possible, and that the first step towards 2030 is feasible to Danish society. However, Denmark will have to consider to which degree the country shall rely mostly on biomass resources, which will involve the reorganisation of the present use of farming areas, or mostly on wind power, which will involve a large share of hydrogen or similar energy carriers leading to certain inefficiencies in the system design.