This review article presents a description of contemporary developments and findings related to the different elements needed in future 4th generation district heating systems (4GDH). Unlike the ...first three generations of district heating, the development of 4GDH involves meeting the challenge of more energy efficient buildings as well as the integration of district heating into a future smart energy system based on renewable energy sources. Following a review of recent 4GDH research, the article quantifies the costs and benefits of 4GDH in future sustainable energy systems. Costs involve an upgrade of heating systems and of the operation of the distribution grids, while benefits are lower grid losses, a better utilization of low-temperature heat sources and improved efficiency in the production compared to previous district heating systems. It is quantified how benefits exceed costs by a safe margin with the benefits of systems integration being the most important.
•Provides a review of 4th Generation District Heating (4GDH) in scientific papers.•Shows how 4GDH is an important integrated part of future sustainable energy systems.•Quantifies costs and benefits of 4GDH in a future sustainable energy system.•Shows how benefits exceed costs by a safe margin.•Shows the significant benefits of systems integration.
This paper aims to provide an overview of the costs and benefits of preparing existing space heating systems for low-temperature district heating. Necessary heating system improvements were assessed ...based on previous work carried out on the topic. This included evaluating the necessity of installing larger heating elements and improving heating system control. The costs of the identified heating system improvements were then estimated and compared with the savings achieved if district heating temperatures were lowered, from the perspective of both the total Danish energy system and the individual district heating customers. The investigations resulted in simple payback times of 1.2–4.3 years from an energy system perspective and 0.3–18.7 years for an individual district heating customer. The current study thus indicates that it is economically feasible to invest in an improved heating system control to enable a reduction in the district heating return temperatures.
•Low-temperature heating can be implemented at low costs from a long-term perspective.•Investments in heating systems are attractive from an energy system perspective.•Customer investments in heating systems should be motivated economically.
This study presents a field study of the performance of three multi-zone gas-fired comboheating systems that provide space heating and domestic hot water in three new single-family houses in the ...Greater Toronto Area in the Province of Ontario, Canada. Two systems are composed of a gas-fired condensing tankless water heater integrated with a smart air handling unit, while the third system is composed of a gas-fired condensing combi boiler integrated with a smart air handling unit. The performance of the three combo heating systems was monitored, analyzed and evaluated over one heating season. The gas consumption of the three systems were compared with traditional gas-fired heating systems (composed of forced-air gas furnace and gas storage tank water heater). Results showed that combo heating systems tested in this study are reliable, met the peak space heating load, improved the indoor thermal comfort by providing two independently controlled temperature zones and achieved significant gas savings compared to traditional natural gas heating systems. The annual gas consumption and greenhouse gas emissions of the combo heating systems tested in this study are less than the traditional gas-fired heating system (forced-air gas furnace and gas storage tank water heater) by up to 29%.
•The largest solar district heating market worldwide has been presented.•Characters of solar district heating plants in Denmark were summarized.•Possibility of solar district heating in smart ...renewable energy system was shown.•Potential trend of solar district heating plants in Denmark was discussed.
Large solar collector fields are very popular in district heating system in Denmark, even though the solar radiation source is not favorable at high latitudes compared to many other regions. Business models for large solar heating plants in Denmark has attracted much attention worldwide. Denmark is not only the biggest country in both total installed capacities and numbers of large solar district heating plants, but also is the first and only country with commercial market-driven solar district heating plants. By the end of 2017, more than 1.3 million m2 solar district heating plants are in operation in Denmark. Furthermore, more than 70% of the large solar district heating plants worldwide are constructed in Denmark. Based on the case of Denmark, this study reviews the development of large solar district heating plants in Denmark since 2006. Success factors for Danish experiences was summarized and discussed. Novel design concepts of large solar district heating plants are also addressed to clarify the future development trend. Potential integration of large solar district heating plants with other renewable energy technologies are discussed. This paper can provide references to potential countries that want to exploit the market for solar district heating plants. Policy-makers can evaluate the advantages and disadvantages of solar district heating systems in the national energy planning level based on the know-how and experiences from Denmark.
Central solar heating plants contribute to the reduction of CO
2-emissions and global warming. The combination of central solar heating plants with seasonal heat storage enables high solar fractions ...of 50% and more. Several pilot central solar heating plants with seasonal heat storage (CSHPSS) built in Germany since 1996 have proven the appropriate operation of these systems and confirmed the high solar fractions.
Four different types of seasonal thermal energy stores have been developed, tested and monitored under realistic operation conditions: Hot-water thermal energy store (e.g. in Friedrichshafen), gravel-water thermal energy store (e.g. in Steinfurt–Borghorst), borehole thermal energy store (in Neckarsulm) and aquifer thermal energy store (in Rostock). In this paper, measured heat balances of several German CSHPSS are presented. The different types of thermal energy stores and the affiliated central solar heating plants and district heating systems are described. Their operational characteristics are compared using measured data gained from an extensive monitoring program. Thus long-term operational experiences such as the influence of net return temperatures are shown.
Ambitious greenhouse gas emission reduction targets set by EU pose a significant challenge for the member countries. District heating as an efficient solution for heat supply and distribution can ...play a major part in meeting these targets. One key issue concerning district heating is the integration of renewables. The current study focuses on solar assisted district heating systems.
Centralised and distributed solar collectors in an existing district heating system are investigated. The effects of reducing supply temperature are studied in two scenarios. Outdoor dependent supply temperature level (115-80 °C) and low supply temperature level (65 °C) are considered. Both distributed and centralised systems are defined with same investment costs, but different capacities due to differences in unit costs (€/kW). The aim is to study cost-efficient solutions for integrating solar heating an existing district heating system.
Heat demand consisting of space heating and domestic hot water consumption, solar collectors and district heating network itself are all modelled by dedicated models in order to provide realistic input for a techno-economic analysis.
Investigation is based on a case study of a local district heating system in Finland with an annual heat consumption of 1.2 GWh and a heat demand density of 0.74 MWh/m.
•Solar assisted district heating was studied for an existing district heating system.•Performance of distributed and centralised solar collector systems was evaluated.•Centralised collector systems can provide cost savings from 7 to 21%.•Pay-back times between 10 and 11 years for centralised systems were recorded.•Low temperature distribution gave a boost in performance for centralised collectors.
•A generic multivariable thermal-economic optimization approach was developed.•The influences of different aim functions on the varied optimal results were shown.•Sensitivity analysis of the key ...design parameters was carried out.•The optimal heat price could provide practical reference for the end-use consumers.•The system levelized cost of heat can be reduced by 5–9% in this study.
Large-scale solar heating plants for district heating networks have gained great success in Europe, particularly in Denmark. A hybrid solar district heating plant with 5960 m2 flat plate collectors and 4039 m2 parabolic trough collectors in series was built in Taars, Denmark in 2015. The solar heating plant was used as a reference case in this study. A validated TRNSYS-GenOpt model was set up to optimize the key design parameters of the plant, including areas of both collector types, storage size, orientation of the parabolic trough collectors and so on. This study introduces a generic method to optimize the hybrid solar district heating systems based on levelized cost of heat. It is found that the lowest net levelized cost of heat of hybrid solar heating plants could reach about 0.36 DKK/kWh. The system levelized cost of heat can be reduced by 5–9% by use of solar collectors in the district heating network in this study. The results also show that parabolic trough collectors are economically feasible for district heating networks in Denmark. The generic and multivariable levelized cost of heat method can guide engineers and designers on the design, construction and control of large-scale solar heating plants.
•Machine Learning is used for energy use prediction of a solar-assisted heat pump.•Attention mechanism and time series decomposition is used to improve model accuracy.•Various combinations of input ...features are compared.•Results can provide valuable insights for developing Neural Network models.
With improved insulation of building envelopes and the use of low-temperature space heating systems, the share of energy use for domestic hot water (DHW) production in buildings has increased significantly, and nearly become the most energy-expensive service in modern buildings. Early prediction of the energy use for DHW is required for many advanced applications such as smart control, demand-side management, and optimal operation of electric or heat storage. However, predicting energy use of the solar-assisted water heating system is more challenging than typical DHW systems, as it is strongly affected by two stochastic phenomena, demand pattern and solar radiation.
Given the increasing use of solar-assisted water heating systems, this paper aims to evaluate the potential to predict energy use in such systems using a novel machine learning approach. In this novel model, a Long-Short Term Memory (LSTM) neural network is enhanced by (1) implementing the attention mechanism, a recent development in deep learning inspired by human vision to pay selective attention to the input data, and (2) decomposition of input data into sub-layers. The performance of simple LSTM neural network, Attention-based LSTM neural network (ALSTM) and Attention-based LSTM using decomposed data (ALSTM-D) are compared to a Feed-Forward neural network as a baseline model. Results show that LSTM, ALSTM and ALSTM-D models have a Mean Absolute Error (MAE) of 25%, 28% and 41% lower than Feed-Forward model, respectively. These results indicate the superior performance of the proposed ALSTM-D model over conventional models for solar-assisted DHW systems.
•China faces challenges to supply clean building heating services to its citizens.•All building heating solutions have a great potential.•The choice of building heating solutions in China is affected ...by spatial parameters.•It is essential to use spatial analysis to find proper building heating solutions.
With continuing of urbanization, improving of life quality as well as combating against air pollution, China is facing comprehensive challenges to supply modern clean heating to a majority of its citizens. For space heating solutions, currently in urban areas of north China, coal based district heating is prevalent. In urban areas of south China, distributed heating solutions are used. In rural areas, de-centralized coal stoves and biomass stoves are still commonly used. As renewable building heating solution, ground source heat pumps are installed for large scale applications. Building floor areas heated by ground source heat pumps increased tremendously during past ten years. Air source heat pump is being promoted in north Chinese rural areas as part of coal to clean heating project. Solar water heater and electric water heater for domestic hot water supply is widely used in north China and gas water boiler is widely used in south China. A series of policies have encouraged clean fossil fuel district heating in north China. National development plans are also supporting and subsidizing renewable heating technology such as heat pumps. Different building heating technologies have their own advantages and disadvantages from techno-economic and environmental perspectives. The choice of building heating solutions for different geolocations of China is strongly affected by spatial parameters such as local climate condition, population distribution, natural resource availability etc. Therefore, a spatial data analysis method is essential to help stakeholders decide proper building heating solutions in different parts of China by key performance indicators reflecting lower primary energy use, economic affordability and lower environmental impact.
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