فصلنامه مهندسی و مدیریت انرژی
سال ششم شماره 2 (پیاپی 20، تابستان 1395)

For proper and efficient utilization of wind power, the prediction of wind speed is very important. Wind is one of the main sources of energy in the world, but the wind turbines have a lack of reliability, continuity and homogeneity in power production. On the other hand, sudden changes of wind speed, lead to risk for wind turbine units health. Therefore, the prediction of wind speed for turbine maintenance and planning for production is very important. This paper provides a new method for predicting the wind speed. The technique is based on combining genetic algorithm and neural network. The previous wind speed information is used as inputs to Long-Step prediction (multi-day) of the wind speed. The proposed method was tested based on actual data collected from the MAPNA Co wind farm. Simulation results show the accuracy of the proposed model in predicting the wind speed. The accuracy of prediction models, based on root mean squared error (RMSE), is 0.96 meters per second. The results of the recurrent neural network genetic algorithm (RNNGA) method were compared with some reference methods which this model with less input data (wind speed), has the same or better accuracy.

Office buildings in the construction sector are the largest consumer of energy. So providing solutions for energy efficiency, improving performance and correcting the operation pattern can reduce energy consumption and improve occupants comfort in these buildings. Using Design builder and CFD simulation software and recording devices, the study has analyzed the environment quality parameters (temperature, humidity and air pressure) to calculate the amount of energy required in a smart building. First the current state of the environment is evaluated. In the next steps the building energy bills analyzed, also simulation and calculation of building loads and ultimately provide solutions to energy audits and energy efficiency of buildings have been discussed. The objective of this study is to review ways to reduce energy consumption in such buildings. The simulation in this study shows that with proper planning and management of energy consumption in intelligent office buildings, there is a possibility of reducing more than 35 to 40% of annual energy consumption. However the most of the savings are in the cooling and lighting sectors in such buildings.

The shape and geometry of the flow field have considerable effects on the transfer rate of the reactants toward the catalyst layer and consequently the performance of the polymer electrolyte membrane (PEM) fuel cell. In this study, a novel PEM fuel cell with pin-type flow field is proposed in order to reduce the wake regions, increase the oxygen transfer rate into the catalyst layer and the current density, and finally improve the fuel cell performance. To assess the performance of the proposed fuel cell, it is numerically simulated based on the computational fluid dynamics and the single-domain approaches and compared with that of a PEM fuel cell with parallel channels for the same geometry and operating conditions. The numerical results show that oxygen transfer rate into the gas diffusion layer and cathode catalyst layer is increased due to the existence of the pins in the proposed flow field. Comparing with the parallel channels, the pin-type fuel cell has an improved performance as the current density is increased, especially for high current density value. However, the pin-type fuel cell exhibits a higher pressure drop and non-uniform distribution of the current density.

In this study, an experimental system that includes evacuated tube heat pipe solar collector, is constructed and tested under weather conditions of Sanandaj in 21 August, 30 August and 7 September. Then a mathematical model, based on energy and exergy balance equations have been developed and the theoretical results were compared with experimental ones. The obtained results showed that the optimum number of vacuum tubes in weather conditions of Sanandaj is equal to 15. In the final hours of the day exergic efficiency is high. The effect of collector fluid mass rate on its efficiency is little at the beginning hours of the day and gradually increases over time. Also, the effect of this parameter is much more in lower values. Finally, the results of mathematical model developed to simulate the performance of evacuated tube heat pipe solar collector were compared experimental results and a good agreement was observed in terms of standard error and maximum relative error.

Photovoltaic/thermal (PV/T) systems are a hybrid of solar collectors and photovoltaic panels which convert radiant energy into both electricity and heat. The objective of this work is to simulate a water-based flat plate photovoltaic/thermal collector with glass cover and without it and investigate the influence of four parameters of solar irradiation, packing factor, ambient temperature and mass flow rate on the performance of this system. The accuracy of the model has been validated with the available data in the literature where good agreement between the results has been achieved. The results showed that energy efficiency of the glazed photovoltaic/thermal collector is higher than unglazed one and its exergy efficiency is lower. Results also showed that increasing solar irradiation and packing factor lead to increase in energy and exergy efficiencies while increasing ambient temperature leads to an increase in energy efficiency and decrease in exergy efficiency. Moreover, it was found that there is an optimum mass flow rate to maximize exergy efficiency. The value of the optimum mass flow rate is larger in the case of the unglazed system compared to that of glazed one.

Energy shortage is one of the fundamental challenges of human beings in which finding a new way for optimum utilization of unique energy resources and cogeneration can be terminated to the reservation of energy or cogeneration purposes. In this paper, by using the combined Ejector Refrigeration Cycle (ERC) and Organic Rankine Cycle (ORC), in addition to producing power from Organic Rankine Cycle, we will use the waste heat recovery of condenser in the ORC for the purposes of generating cooling capacity in the ERC. Actually, the condenser of the ORC works as the evaporator of the ERC. We have considered isobutane as a working fluid of ERC and also R113, R141b, R11, R123, R245fa, R114, and isobutane as working fluids of ORC. The maximum Combined Cycle Performance is obtained when we would use isobutane and R113 as working fluids in ERC and ORC, respectively. In this case, ORC Efficiency, Combined Cycle Efficiency, and Cycle Coefficient of performance will be 19.97%, 34.69% and 0.3683, respectively.In addition to energetic analysis’ point of view, from the exergetic analysis’ one, the combined usage of R113 and isobutene by having the highest efficiency of 52.53% is an appropriate working fluids, too. Also a parametric analysis is performed for the cycle performances, based on the operational parameters of combined cycle.