• Energy Research

The present work introduces an innovative yet feasible heating system consisting of a ground source heat pump, borehole thermal energy storage, an auxiliary heater, radiators, and ventilation coils. The concept is developed by designing a new piping configuration monitored by a smart control system to reduce the return flow temperature and increase the temperature differential between the supply and return flows. The radiators and ventilation heating circuits are connected in series to provide the heat loads with the same demand. The investigation of the proposed model is performed through developed Python code considering a case study hospital located in Norway. The article presents, after validation of the primary heating system installed in the hospital, a parametric investigation to evaluate the effect of main operational parameters on the performance metrics of both the heat pump and the total system. According to the results, the evaporator temperature is a significant parameter that considerably impacts the system performance. The parametric study findings show that the heat pumps with a thermal capacity of 400 kW and 600 kW lead to the highest heat pump and total seasonal performance factors, respectively. It is also observed that increasing the heat pump capacity does not affect the performance indicators when the condensation temperature is 40 °C and the heat recovery is 50%. Moreover, choosing a heat pump with a smaller capacity at the heat recovery of 75% (or higher) would be an appropriate option because the seasonal performance values are not varied by changing the heat pump capacity. The results reveal that reducing return temperature under a proper parameters selection results in substantially higher seasonal performance factors of the heat pump and total system. These outcomes are in-line with the United Nations sustainable development goals including Sustainable Cities and Communities.

Abstract In the present study, a novel solar-based building energy system, which is integrated with both electricity and district heating grids, is proposed and modeled. The solar system uses photovoltaic-thermal panels and has neither a battery nor a heat pump. The elimination of the battery and heat pump is proposed to reduce the cost of the system to motivate the building owners to adopt the solution as a cheaper energy system for their buildings. In this way, the building energy system would be able not only to produce a major portion of the heat and electricity demands of the households but also to supply its excess production to the grids to decrease the energy bill of the building. As district heating systems are on the verge of a transformation to their next generations, it is important to know how this system would respond to the future designs and standards of district heating systems. That is why the simulations are accomplished based on different district heating integration scenarios, i.e. existing, low-temperature, and ultralow-temperature district heating systems. For doing the simulations and comparative analysis on the performance of the system in various dynamic operating conditions, TRNSYS software is employed. The results show that the ultralow-temperature district heating model is the most suitable case for integration with the proposed system. In this case, the building energy systems will supply over 400 m3 hot water to the heat network and about 1940 kWh surplus electricity to the power grid over an entire year. Due to a lower panel temperature, the system produces the largest amounts of electricity and heat (3647.4 kWh and 9118.5 kWh) compared to the other two cases. The maximum overall efficiency values of 74.51%, 62.35%, and 52.35% for ultralow-, low-, and the 3rd generation-district heating models are achieved.

Abstract This study introduced an innovative yet feasible and cost-effective solution to make a big step forward in the state-of-art of smart energy buildings and obtain a real meaning of net-zero energy building. In this study, the main cornerstones of the developed solution combined the following technologies: the use of novel trigeneration solar collectors without a battery, a very clever method of heat pump integration with minimal size and cost required, and two-way interaction of the building with local energy networks. Different system configurations based on the included components were suggested and analyzed for an apartment building in Denmark. A thorough techno-economic and environmental evaluation of the proposed solution and the most competent ones already proposed for the same application was carried out to rank the best configuration from various facets. A comparative parametric study was accomplished to examine and compare the variation of performance indicators with significant decision variables. In addition, the tri-objective optimization was implemented for each configuration to specify the best optimum condition from energy, economic, and environmental standpoints. According to the economic results, the configurations integrated with battery and regular heat pumps were not favorable due to the highest total cost and the payback period. Here, the proposed system, owing to its resilient energy trade possibility with the energy networks and the scaled-down heat pump, gave larger energy-saving and CO2 emission reduction rates of 16.6% and 21.6%, respectively. The multi-objective optimization showed that the capacities of the battery and the cold storage were the most effective parameters on the performance of the system.

Abstract Recovery of waste heat in large industrial plants is nowadays an important topic of thermal optimization. In the present study, energy, exergy, and exergoeconomic analysis of an integrated system, Tehran's waste-to-energy power plant coupled with an organic Rankine cycle (ORC), is analyzed. Parametric study of essential parameters (moisture content, pinch point temperature differences of the HROG, steam generator's superheat temperature difference, and steam turbine inlet pressure) is performed thermodynamically. The best system performance achieved using R123 as the working fluid of ORC. After implementation of the waste-heat-recovery system into the WtE plant, with R123 the energy and exergy efficiencies increase from 17.27% to 19.51% and 14.49%–16.36%, respectively. Exergy analysis reveals that the gasifier and steam generator are the main source of exergy destruction in the overall system. Additionally, the results of single-objective optimization based on maximum exergy efficiency and minimum total product unit cost were calculated. Furthermore, multi-objective optimization based on genetic algorithm using MATLAB software is implemented to find the optimum point with respect to exergy efficiency and total product unit cost as the objective functions. The exergy efficiency and total product unit cost at the optimum point, considering multi-objective optimization, are 19.61% and 24.65 $/GJ, respectively.

Abstract In the present study, innovative energy efficiency enhancement methods and cleaner production in conventional waste-fired CHP plants are presented. This includes the medium- and low-grade solar thermal systems and flue gas condensation for feedwater heating in different arrangements. The article presents a thorough thermodynamic, economic, and environmental assessment of all the possible scenarios and then ranks the best solutions in different aspects. For making the results reliable, the solutions are applied to a waste-fired CHP plant in Denmark. For this, a transient simulation of the proposed configurations is performed via TRNSYS software for an entire year. The results indicate that the proposed models can produce more power and heat than the conventional plant but with different effectiveness factors. According to the economic results, a design consisting of a flue gas condensation circuit and parabolic trough collectors for the open and closed feedwater heater form the best configuration. The exergy assessment results indicate that the waste incinerator with annual irreversibility of 128.4 GWh is the most important component exergetically. Finally, the parametric study results show that the increase of incineration temperature significantly affects the power and heat exergy efficiency ratios.

Abstract The aim of this study is to increase the power generation/exergy efficiency and reduce total product cost/environmental contamination of solid oxide fuel cells. Accordingly, three integrated systems are proposed and analyzed from energy, exergy, exergoeconomic, and environmental viewpoints through the parametric study. The first model assesses the combination of a gasifier with a solid oxide fuel cell. In the second model, waste heat of the first model is reused in the Stirling engine to enhance the efficiency and power generation. The last model proposes reuse of the surplus power of the Stirling engine in a proton exchange membrane electrolyzer for hydrogen production. Considering total product cost, exergy efficiency, and hydrogen production rate as the objective functions, a multi-objective optimization is applied based on the genetic algorithm. The results indicate that at the optimum operating condition, the exergy efficiency of the model (a), (b), and (c) is 28.51%, 39.51%, and 38.03%, respectively. Corresponding values for the energy efficiency and the emission rate of the models are 31.13%, 67.38%, 66.41%, 1.147 t/MWh, 0.7113 t/MWh, 0.7694 t/MWh. At the optimum solution point, total product cost associated with the model (a), (b), and (c) is 19.33 $/GJ, 18.91 $/GJ, and 24.93 $/GJ, respectively. If the hydrogen production rate and total product cost considered as the objective functions, at optimum solution point, the rate of hydrogen production and overall product cost would be 56.5 kg/day and 41.76 $/GJ, respectively. Overall, the proposed integrated systems demonstrate decent functionality both in thermodynamic, environmental, and economic aspects.

Abstract In this study, an integrated renewable energy system is proposed by integrating Tehran’s waste-to-energy plant with a solar chimney power plant. The integration is performed by exploiting warm air of the condensers cooling air for injecting under the turbine of solar chimney power plant. The proposed system is analyzed from energy, exergy, exergoeconomic, and environmental viewpoints through the parametric study. Exergy efficiency, net power output, solar chimney power plant power output, total product cost and cost rates of the system are plotted and compared during the night and daytime. Additionally, influence of the effective parameters is examined on the CO2 emissions indicator. Subsequently, the proposed system is optimized by multi-objective optimization method using a developed MATLAB code based on a genetic algorithm. Four effective design parameters are presumed for multi-objective optimization purpose and exergy efficiency along with total cost rate are considered as the objective functions. Accordingly, a group of the optimal solution points is gathered as a Pareto frontier and the most favorable solution points are ascertained from an exergy/exergoeconomic viewpoints. In addition, a point which is well-balanced between the conflicting objectives is selected as the final solution. Eventually, scatter distribution of the effective parameters are presented to have a better outlook of optimal ranges of the parameters. Results indicate that exergy efficiency of the system is higher during the nighttime while total product cost is lower during the daytime. Results further indicate, turbine inlet pressure has the highest impact on the CO2 emissions and the solar chimney power plant has the highest exergy destruction. Results of the multi-objective optimization demonstrate that at the best solution point, exergy efficiency and total cost rate of the system are 7.56% and 406.8 $/h. Furthermore, analyzing scatter distribution of the effective parameters reveals that higher values of the superheater temperature difference may be a better choice for designing the system.