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Future energy systems will come with a 100% share of renewable energy and high integration of energy systems. District heating and cooling systems will be undeniable parts of the future energy systems, as they pave the bed for high-efficiency, low cost, and clean production. District heating systems may come into a wide range of designs in the future. Currently, most of the world’s district heating systems are based on the third generation design while everything in this framework is on the verge of a transition to the fourth generation. A large number of technologies for the future district heating systems has been proposed so far, among which low-, ultralow- and variable-temperature systems seem more of qualification. This study employs computational fluid dynamics to make a comprehensive examination of the compatibility of regular twin-pipes with various potential district heating schemes for future energy systems. The results show that both low- and ultralow-temperature systems could efficiently use regular twin-pipes commonly used in the third generation district heating systems, though the insulation of the pipe could be proportionally strengthened based on a techno-economic trade-off. In contrast, the results show that the thermal inertia of the pipe does not allow the variable-temperature district heating system to effectively operate when the transmission pipeline is longer than a limited length. Therefore, a regular heat distribution network may not be an appropriate host for a variable-temperature district heating scheme unless decentralized heat production units come into service.

The global energy matrix is going to embrace more and more renewable-based combined energy systems. Therefore, multi-generation energy systems, like CHPs (combined heat and power) could be extremely beneficial for such integrated energy systems. Also, the trend is toward 100% sustainable production where both renewable and waste energy sources are of special value. Especially, in Europe, waste incineration has received special attention over the past decades, as not only it is a smart method of waste disposal, but also a measure of cheap and environmentally friendly energy production. This study proposes a municipal waste-driven tri-generation (cold, heat, and power) system and assesses how this solution helps for easier integration of energy sectors and having a more sustainable chain of energy supply. Then, the solution is comprehensively analyzed over thorough thermodynamic, thermoeconomic, and thermoenvironmental investigations. The results of the assessments show that the proposed trigeneration system may effectively operate in any energy systems with simultaneous cold, heat, and power demands. Thermal, exergetic, fuel-to-power, fuel-to-heat, and fuel-to-cold efficiencies are found to be 83.28, 25.69, 23.49, 47.41, and 12.38%, respectively, while the payback period of 6 years is obtained based on the net present method.

Utilizing ultrasonic excitation as an active method for studying the rate of heat transfer has gained considerable attention recently. The present study investigated the effects of ultrasonic excitation on the heat transfer rate in a fin-and-flat tube heat exchanger experimentally. The performance of the heat exchanger was investigated with and without the presence of ultrasonic excitation. A comprehensive parameter study was attempted, so several parameters, including ambient temperature, flow rate, air passing velocity, Reynolds number, and Nusselt number, were studied in a relatively wide range. An adequate uncertainty test, as well as a validation assessment, is provided to certify the credibility of the obtained results and the hired facility. The results revealed that reducing the flow rate, ambient temperature, and air passing velocity on the heat exchanger increased the ultrasonic excitation’s effects. The highest heat transfer enhancement in the present experiment was 70.11%, measured at the lowest air passing velocity and ambient temperature with a Reynolds number 2166. The data presented in this paper will be useful for the optimal design of ultrasonic vibrating fin-and-tube heat exchangers.

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

This work reports a technical, economic, and environmental investigation of the possibility of using a recently developed smallscale crossflow wind turbine (CFWT) to supply the energy demand of buildings for different integration scenarios. For this purpose, three CFWT‐assisted building energy system configurations with heat pumps, with and without batteries, and two‐way interaction with the local grid in two residential building models in Iran and Germany are investigated. Triobjective optimization with a Nondominated Sorting Genetic Algorithm (NSGA‐II) is performed for finding the optimal configuration of the energy system in different configurations. For economic assessment, the Capital Budgeting Analysis method is used with four indicators, namely, payback period (PP), net present value (NPV), internal rate of return (IRR), and profitability index (PI). The results show that due to different energy market regulations and prices, different integration scenarios and system configurations can outperform others in Germany and Iran. Overall, due to the exchange rate instability and low energy tariff in Iran, in order for the project to be feasible, either the CFWT cost must fall to below 30% of its current cost or the local electricity price should increase significantly to get a Levelized cost of energy of as low as 0.6 $ kWh−1. Small‐scale wind turbines have tremendous potential as a sustainable and pollution‐free energy solution. This work conducts a technical, economic, and environmental investigation as well as multiobjective optimization of crossflow wind turbines and heat pumps to supply the energy demand for the household sector in Iran and Germany. The effect of capital expenditure, weather conditions, and energy tariffs are discussed.

District heating-connected waste incineration plants face a serious operating challenge during the warmer months of the year when the heating load is quite low. The challenge is the difficulty of managing the extra municipal solid waste to be disposed of, exposing great pressure and cost on the plant. Conventionally, the solution is either burning the surplus waste and providing the extra cooling required for the condenser with a summer chiller and paying the tax of the total heat generation of the plant, or paying other industries to burn the waste for their specific applications. Both of these solutions are, however, costly. In this study, to address this challenge the utilization of the extra available resources of waste incineration plants for district cooling supply is proposed. Then, the proposed solution is analyzed from the thermodynamic and economic points of view. The feasibility of the proposal is investigated for a real waste incineration plant in Denmark and its 50 neighboring office/service buildings as the case study. The simulations are done based on real hourly data of the plant and economic parameters. The results show that for the case study for a plant with a thermal capacity of 73 MW, a district cooling with a peak load of over 20 MW could be perfectly supplied. The payback period of the proposed solution, including the cost of piping, absorption chiller, etc., can be as short as five years.

In this research, for the first time, the impact of wavy orientations on the entropy generation and exergy destruction of the wavy microchannel working with various types of aqueous nanofluid is addressed. To this end, two Left–Right and Up–Down wavy microchannels were developed, and the laminar flows of silver, aluminum oxide, and hybrid silver-aluminum oxide nanofluids, each with concentrations of 1%, 2%, and 3%, were numerically simulated using the multi-phase mixture model. The simulation was carried out at constant pumping powers of 0.05 W, 0.15 W, 0.25 W, and 0.35 W, and the inlet temperature of 300 K. The results demonstrated that the total exergy destruction for the Left–Right wavy microchannel is on average 20% lower than the Up-Down one. In both of the microchannels, using nanofluid decreases the destructed exergy, with the largest irreversibility reduction related to the silver nanofluid case. Also, utilizing nanofluids increases the effectiveness number, while raising the pumping power declines it. Moreover, the values of the effectiveness number are higher for the Up-Down wavy microchannel compared to those of the Left–Right one. Finally, for 3% silver nanofluid at pumping power of 0.05 W in the Left–Right wavy microchannel, the highest value of second law efficiency is obtained, while it is lowest for the water at pumping power of 0.35W in the Up–Down wavy microchannel.

The combination of a waste-driven hybrid heat and power plant with a small organic Rankine cycle unit was recently proposed and investigated from a thermodynamic perspective. The present study provides a more comprehensive assessment from system operation through considering the energy, exergy, exergoeconomic, and exergoenvironmental (4E) aspects in a revised design of this concept to obtain a bigger picture of the system’s technical, economic, and environmental effects on existing and future energy systems. The revised design includes a flue gas condensation unit and alternative friendly organic working fluids. For this, the hybrid plant is modeled for its thermal, economic, and environmental performances. Then, the exergy losses and environmental effects of the system are scrutinized, the cost of losses and pollutions are predicted, and lastly, sorts of solutions are introduced to improve the exergoeconomic and exergoenvironmental performances of the system. The results indicate that the highest share of exergy destruction relates to the incineration (equipped with a steam generator) with a levelized cost of approximately USD 71/h for a power plant with almost 3.3 megawatt electricity output capacity. The hybridization proposal with the flue gas condensation unit increases the sustainability index of the system from 1.264 to 1.28.

The rapid globalization of the energy crisis and the adverse effects of global warming have caused the need for non-conventional energy resources to be felt more than ever. As a result of this, vertical axis wind turbines (VAWT) have received much attention over the recent decades, and have thus been more developed and used worldwide. The cross-flow wind turbine (CFWT) is a wind turbine in the category of VAWTs, and perfectly suitable for urban applications due to its simplicity, high starting torque at low wind speed, and self-starting capability, even though its low power coefficient as its main drawback has slowed down its widespread use so far. The main aim of this paper is to review the scientific literature and recent developments in the field of CFWTs. The governing equations and turbulence models for the simulation of the turbine are discussed and various wind resource assessment methods for estimating potential site locations, different aspects, and wind energy harvesting systems from buildings are debated. The research gaps, challenges, and future possible works on such turbines and their applications are discussed. Investigations indicate that changing the rotor geometric parameters and adding innovative augmentation devices have been the most widely addressed approaches for making performance enhancement of the wind turbine in the literature. The critical performance-affecting parameters are improved by various innovative designs of the turbine structure or blades, as well as several augmentation techniques, such as guide nozzle, casing, windshield, guide vane, deflector, cowling, etc.

In this paper, the performance enhancement of a particular type of heater, i.e., water bath heater, with a wide range of industrial applications is proposed and assessed. The idea is centered around using an alternative working fluid with better heat transfer characteristics (heat transfer oil—HTO) to quantify the impacts not only from a technical point of view but also from an economic perspective. The indirect heater of Arkan CGS (located in North Khorasan province of Iran) is selected as the case study, and its laboratory model is constructed by dimensional analysis. The thermal analysis is done at different fluid flow rates in the heating coil of the experimental setup. The results are verified by both numerical simulation and available empirical correlation. The results show that using HTO as the heating medium leads to heater efficiency improvement by up to 158%, and it will also lead to energy savings of up to 36.5%. A comprehensive economic analysis is carried out based on the technical results. It is found that the internal rate of return and dynamic payback period are in the ranges of 42–67% and 1.53–2.17 years, respectively.