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•Applicable objective functions and their relations at the level of district.•Optimization of distributed integration into districts.•Optimal network configuration and component ...selection to design a district.•Optimal management, operation and planning and subsystem building blocks.•Widely-used optimization tools for district heating and cooling.
Modelling, simulation and optimization of an isolated building separated from the district in which they operate is no longer of interest as a view point of improved efficiency, economic benefits and exploitation of renewable energy resources. Instead, district energy systems have the capacity to obtain several benefits, regarding the practical, environmental and safety by taking advantage of large poly-generation energy conversion technologies. The use of optimization techniques to design such high-efficient systems is strongly motivated by minimizing of the cost for the required infrastructures, minimizing emission, and maximizing the generation or efficiency but is particularly challenging because of the technical characteristics and the size of the real world applications. In this paper, different types of optimization problems, constraints and techniques as well as the optimization tools used in district energy systems are discussed.
A net-zero energy district is any neighborhood where the consumption of the buildings is offset by on-building generation on an annual basis. In this study, a net-zero energy district is identified ...among the set of optimal solutions and the effects of storage on its performance is investigated. It is assumed the model simultaneously optimizes the location of host buildings (energy generators), type of technologies and associated size, and the energy distribution network layout together with the optimal operating strategy. The optimization model addresses all technologies with a special focus on the effect of application of energy storage. Two types of energy storage are considered inside each building: thermal energy storage (hot water tank) and electrical energy storage (battery bank). The model is applied to the new part of a district energy system located in Switzerland. The best integrated district energy systems are presented as a set of Pareto optimal solutions by minimizing both the total annualized cost and equivalent CO2 emission while ensuring the reliable system operation to cover the demand. The results indicated that selection of the proposed optimal district energy system along with the storage brings great economic and environmental benefits in comparison to all other scenarios (conventional energy system, stand-alone system, and net zero-energy without storage).
•A multi-level procedure is proposed for energy optimization of a new district.•Type, size, and location of the equipment are all taken into account.•An optimal design of a net-zero energy district is presented with and without storage.•A case study with seven buildings is presented to show the applicability of methodology.•The results are compared to the optimal design of a stand-alone district.
In this paper, an annual comparative analysis for the coefficient of performance (COP) and the energy consumption are presented for two direct expansion heat-pump water heating systems: ...solar-assisted heat pump, and air-source heat pump. Two main research questions are addressed: (1) How does each system's performance differ from the other system under the same conditions? and (2) How does the climate affect the performance of an individual system to help the designer choose the more energy efficient water heater for a specific location? To make those water heaters comparable, all design parameters for both heat pumps are assumed to be the same with identical components. A sensitivity analysis is also carried out for various factors such as irradiance, ambient temperature, collector/evaporator area, wind speed, and compressor rotational speed considering three different hot water tank temperatures. The results for both heat pump water heating systems show that the climate (different months) plays the key role on the annual performance. Changes in irradiance and ambient temperature as well as the wind speed throughout the year can increase the COP by up to 33 % (from 2.1 to 2.8) under certain conditions for the case study with moderate weather. Therefore, the benefits from the local weather should be investigated before choosing the design variables and proper source (solar thermal, air) for the heat pump. Nearly the same results were obtained for both type of water heaters with slightly better performance of air heat pump in colder months of the year (December to February).
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•Economic viability and environmental effects of a biomass-powered tri-generation system.•Developing a methodology for incorporating reliability, availability, and maintainability (RAM) analysis with ...optimization techniques.•A flexible modular design strategy adjustable to various types of energy inputs for hydrogen, heat, and electricity generation.•Incorporation of other operational criteria such as mean time for logistics, mean time to preventive maintenance.•Establishment of a platform for extending the integrated RAMS optimization approach to other phases of the project other than design.
For green hydrogen energy systems driven by renewables, despite the complexities in design and operations, uncertainties related to availability of infrastructures or seasonality of resources are significant as well as the uncertainties in technical side such as adoption of technologies for energy generation, conversion, and storage. Such uncertainties put the economy and sustainability of these systems under shadows. Consequently, it has been attempted to balance and offset the impacts of uncertainties by means of providing the side products such as hydrogen. An enviro-economic optimization considering reliability, availability, and maintenance of a biomass-gasification-driven combined heating, hydrogen, and electricity system is considered in this study. The emission penalty cost as well as the electricity and hydrogen generation revenues are also pinpointed as part of the objective function which is the total cost. Such costs incorporate capital cost for purchase and installation of all modules, primary fuel (High Heat Value Woods) purchase, and transportation costs. Probabilistic approach using Weibull function is used for modeling reliability for the whole system. The most optimal values for total cost, hydrogen and electrical modules incomes, rated capacities, utilization times, reliability and maintainability indicators such as mean time to failure and maintenance intervals for modules are derived and compared. The sensitivity to performance parameters and sizing characteristics of those three modules are also investigated. The results support this notion that if there are opportunities to sell hydrogen, it is advantageous to integrate hydrogen module to the heating and power co-generation. The results show that minimum cost is obtained by devoting less rated capacities and utilization times to electricity modules in favor of increasing the hydrogen module utilization times and flow rates.
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This study applies a mathematical programming procedure to model the optimal design and planning of a new district which satisfies two features of the 4th generation district heating systems: energy ...reciprocity and on-site generation. The aim of the computational model is to investigate the effect of energy reciprocity (energy exchange among the buildings) as well as to find the best way to select the equipment among various candidates (capacities), the pipeline network among the buildings, and their electrical connections. The objective function includes the annualized overall capital and operation costs for the district along with the benefits of selling electricity to the grid. The distributed energy supply consists of heating, cooling, and power networks, several CHP technologies, solar array, chillers, and auxiliary boilers. The performance of the model for poly-generation was evaluated for designing the new part of Suurstoffi district situated in Risch Rotkreuz, Switzerland with seven residential and office complexes under four different scenarios. Allowing heat exchange among the buildings leads to 25% reduction in total annualized cost and 5% reduction in emission compared to the conventional districts. Removing the network and installation of PV and CHPs results in 9% reduction in emission and 11% reduction in cost. Simultaneous heat and electricity exchange results in a higher reduction in total annualized cost equal to 40% of the base scenario.
•Optimal design of a new 4th generation district heating focusing on energy reciprocity.•Selection, placement, operation of plants, and power and heating networks.•Effects of heat and electricity exchange on total annualized cost and emission.•Analysis of a real case study for 7 buildings in new part of Suurstoffi district.•40% reduction in cost and 11% reduction in CO2 emission in optimal design.
The negative impact of human activities on the environment receives tremendous attention, especially on the increased global temperature. To combat climate change, clean and sustainable energy ...sources need to be rapidly developed. Solar energy technology is considered as one of the ideal candidates, which directly converts solar energy into electricity and heat without any greenhouse gas emissions. In both areas, high-performance cooling, heating and electricity generation is one of the vital needs. Modern nanotechnology can produce metallic or nonmetallic particles of nanometer dimensions which have unique mechanical, optical, electrical, magnetic, and thermal properties. Studies in this field indicate that exploiting nanofluid in solar systems, offers unique advantages over conventional fluids. In this paper, the applications of nanofluids on different types of solar collectors, photovoltaic systems and solar thermoelectrics are reviewed. Beside the wide range of energy conversion, the efforts done on the energy storage system (ESS) have been reviewed. In the field of economics, nanotech reduces manufacturing costs as a result of using a low temperature process.
•Proposed an MILP model for integration of heating sides and cooling sides.•Optimal combination of heating and cooling equipment as well as the network.•Investigation of the effect of cold and hot ...thermal energy storage on cost and emission.•A comparison among conventional, heat-driven, solar-driven, and hybrid generations.•Analysis of cooling distribution network, electrical network, and grid interaction.
An optimal design and well-scheduled district cooling system is crucial for the success of the implementation of such systems especially when the cooling plant(s) are intended to be connected to a group of newly-built consumers. In order to supply such customers the required cooling load, a huge capital and operation investment in district cooling network is a necessity if the cooling network is separated from the heating production units. One solution scheme is to take advantage of the heating generation units, which are off during summer to drive the cooling equipment. However, among various design parameters, the most important one is the desirable configuration of the district of interest: best selection and combination of the heating and cooling generation equipment. A least-annualized-cost mathematical approach based on the mixed integer linear programming (MILP) is described in this paper to determine the optimal integration as well as the optimal control of the flow and the storage. The test case study showed that the methodology was effective to give a huge savings in both total annual cost and emission for a wide range of designs. More than 67% of CO2 emission reduction is achieved through the hybrid heat and solar-driven arrangement.
•Underground green hydrogen storage in various geological formations.•Challenges associated with underground hydrogen storage.•Requirement for extensive studies to understand hydrogen interactions ...with microorganisms.•Reviewing the various past and present hydrogen storage industrial projects and sites.•Importance of incorporating hybrid energy systems into hydrogen storage.•Past and future of integrated underground green hydrogen storage within this dynamic energy landscape.
One of the major challenges in harnessing energy from renewable sources like wind and solar is their intermittent nature. Energy production from these sources can vary based on weather conditions and time of day, making it essential to store surplus energy for later use when there is a shortfall. Energy storage systems play a crucial role in addressing this intermittency issue and ensuring a stable and reliable energy supply. Green hydrogen, sourced from renewables, emerges as a promising solution to meet the rising demand for sustainable energy, addressing the depletion of fossil fuels and environmental crises. In the present study, underground hydrogen storage in various geological formations (aquifers, depleted hydrocarbon reservoirs, salt caverns) is examined, emphasizing the need for a detailed geological analysis and addressing potential hazards. The paper discusses challenges associated with underground hydrogen storage, including the requirement for extensive studies to understand hydrogen interactions with microorganisms. It underscores the importance of the issue, with a focus on reviewing the the various past and present hydrogen storage projects and sites, as well as reviewing the modeling studies in this field. The paper also emphasizes the importance of incorporating hybrid energy systems into hydrogen storage to overcome limitations associated with standalone hydrogen storage systems. It further explores the past and future integrations of underground storage of green hydrogen within this dynamic energy landscape.
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