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[en] Exhaust gas recirculation (EGR) strategy has been recently employed in natural gas SI engines as an alternative to lean burn technique in order to satisfy the increasingly stringent emission standards. However, the effect of EGR on some of engine performance parameters compared to lean burn is not yet quite certain. In the current study, the effect of both EGR and lean burn on natural gas SI engine performance was compared at similar operating conditions. This was achieved numerically by developing a computer simulation of the four-stroke spark-ignition natural gas engine. A two-zone combustion model was developed to simulate the in-cylinder conditions during combustion. A kinetic model based on the extended Zeldovich mechanism was also developed in order to predict NO emission. The combustion model was validated using experimental data and a good agreement between the results was found. It was demonstrated that adding EGR to the stoichiometric inlet charge at constant inlet pressure of 130 kPa decreased power more rapidly than excess air; however, the power loss was recovered by increasing the inlet pressure from 130 kPa at zero dilution to 150 kPa at 20% EGR dilution. The engine fuel consumption increased by 10% when 20% EGR dilution was added at inlet pressure of 150 kPa compared to using 20% air dilution at 130 kPa. However, it was found that EGR dilution strategy is capable of producing extremely lower NO emission than lean burn technique. NO emission was reduced by about 70% when the inlet charge was diluted at a rate of 20% using EGR instead of excess air.
[en] A nonlinear adaptive excitation controller is proposed to enhance the transient stability and voltage regulation of synchronous generators with unknown power angle and mechanical power input. The proposed method is based on a standard third-order model of a synchronous generator which requires only information about the physical available measurements of relative angular speed, active electric power, infinite bus and generator terminal voltages. The operating conditions are computed online using the above physical available measurements, the terminal voltage reference value and the estimate of the mechanical power input. The proposed design is therefore capable of providing satisfactory voltage in the presence of unknown variations of the power system operating conditions. Using the concept of sliding mode equivalent control techniques, a robust decentralized adaptive controller which insures the exponential convergence of the outputs to the desired ones, is obtained. Real-time experimental results are reported, comparing the performance of the proposed adaptive nonlinear control scheme to one of the conventional AVR/PSS controller. The high simplicity of the overall adaptive control scheme and its robustness with respect to line impedance variation including critical unbalanced operating condition and temporary turbine fault, constitute the main positive features of the proposed approach.
[en] Mass housing does not satisfy energy efficiency. This article proposes a system of social ecological economic factors in assessing the housing construction energy efficiency. A performance evaluation criteria list has been developed. This toolkit consists of 4 groups. The authors of the given work have made an attempt to develop an inventory for evaluating the energy efficiency projects. The social ecological economic factors are taken into account in opposition of other assessment systems. The housing construction projects evaluation is based on the costs spent during the building life cycle. This criterion can be considered by the construction investors when making the projects decisions. (paper)
[en] In order to achieve the goal of energy saving and emission reduction and energy efficient utilization, taking a 58MW swirl pulverized coal boiler as the research object, the three-dimensional model of the rotor is established. According to the principle of CFD, basic assumptions and boundary conditions are selected, the temperature field in the furnace of 6 kinds of working conditions is numerically solved, and the temperature distribution in the furnace is analyzed. The calculation results show that the temperature of the working condition 1 is in good agreement with the experimental data, and the error is less than 10%,the results provide a theoretical basis for the following calculation. Through the comparison of the results of the 6 conditions, it is found that the working condition 3 is the best operating condition of the pulverized coal boiler. (paper)
[en] The analysis of the technical condition of the fixed assets of the housing and communal sector of the country is presented, the main part of which are civil buildings. It is shown that the housing stock does not meet modern requirements of thermal engineering standards, energy saving and energy efficiency of buildings. To create the necessary microclimate of living quarters with a comfortable living environment, most civil buildings built at different times need modernization. To effectively carry out overhaul requires a comprehensive approach to the technology of repair and construction with the use of modern energy-saving technologies and materials. Effective implementation of thermal insulation of enclosing structures should be preceded by a detailed survey of the technical condition of facilities with the issuance of scientifically grounded recommendations based on modern scientific achievements in this field, for the further development of a technical task for the design of these works. (paper)
[en] The temperature rise of solar panels can cause significant reduction in the energy generation especially for the countries located in tropical climate region. It is more effective to use water-film for cooling the front surface of solar panels, but the energy consumption of the water-cooled photovoltaic system (WCPV) needs to be reduced to obtain a higher net energy gain. In this study, a discrete water-supply water-cooling system (D-WCPV) has been proposed to reduce the energy consumption of the water pump and to improve the performance of a retrofit or building integrated photovoltaic system through reduction of the panel temperature. The discrete mechanism utilises a relay to switch on the power supply of the water pump whenever the temperature of the solar panel has reached the threshold of 45 °C. It is found that minimum flow rate for the D-WCPV is 8 L/min to form a full coverage of water on the surface of the solar panel for providing an uniform cooling effect and hence providing a better performance improvement. A comparison has also been made for the continuous water-supply water-cooling system (C-WCPV) and D-WCPV. D-WCPV has two advantages over C-WCPV as follows: 1) the energy consumption of the water pump operating at flow rate of 8 L/min has been reduced by 86.7% from 0.057 kWh/h to 0.0076 kWh/h and (2) the net energy gain (NEG) of the system at solar irradiation ranging from 806 Wh/m2 to 950 Wh/m2 has been increased by 80.2% from 5.5% to 10.0%. (paper)
[en] Highlights: • Energy consumption (Qc) and thermal comfort (PMV) of a TAC system were evaluated. • The optimization aim was to achieve thermally comfort at lowest energy consumption. • RSM and TOPSIS methods were applied for operating optimization of the TAC system. • RSM method used 9 cases saving 74% of computation cost compared to TOPSIS. The operating parameters of task/ambient air conditioning (TAC) systems including supply air temperature (ts) and air flow rate (Qs) were reported to have critical effects on energy savings and thermally comfortable environment. Due to the existing contradictions between these two aspects, a multi-objective study should be carried out to realize consuming minimum energy and at the same time to guarantee the thermal comfort level at suitable range. Two optimization methods were adopted in this study, one is the response surface methodology (RSM), and the other is the technique for order preferences by similarity to an ideal solution (TOPSIS) method. The objective of this study was to compare the pros and cons of these two methods. It was found that the optimum operating parameters obtained using RSM method were 26 °C (ts) and 28.94 l/s (Qs), corresponding to energy consumption (Qc) of 46.89 W and PMV of 0.11; while that obtained using TOPSIS method were 26 °C (ts) and 30 l/s (Qs), corresponding to energy consumption (Qc) of 49.64 W and PMV of 0.09. Furthermore, compared with TOPSIS method, there were only 9 cases used in RSM method saving 74% of computation cost.
[en] The daylighting performance, besides the thermal comfort of the buildings is extraordinarily needed to be determined at the early phases of design. In addition, the building envelope is playing a vital mediator between the building and other the surrounding conditions whether perceptible as climate change or intangible like cultural heritage identity. So that, studying responsive architecture for sustainable buildings by developing the daylighting performance, and reducing the energy consumption of the buildings are important scopes for getting rid of Carbon dioxide (CO2) emissions to adapt and mitigate climate change and occupants’ satisfaction. Currently, the hot-desert countries are carrying out the design strategies based on the fully glazed office buildings as in the United Arab Emirates (UAE), which is called ‘the International Style’, was established for another climate. This causes an inefficient building performance coupled with identity crises. Furthermore, the artificial lighting and thermal comfort are two of the primary energy demands in the office buildings. In terms of both productivity and human comfort, the occupants ‘satisfaction with their surrounding workplace is vital. So that, any strategy aims at decreasing exaggerated solar radiations and improving availability of daylight is deemed a sustainable strategy for design. Furthermore, there are limited performance evaluation tools offered to architects at the early phases of design. In this light, the state-of-the-art “Digital Age “has applied smarter and more interactive “building envelopes “to ensure environmental control and comfort. So that, this paper focuses on this problem in Hot - Arid countries. (paper)
[en] The next level of energy performance of new buildings within the European Union will be the Nearly Zero-Energy Building (NZEB). A lot of work has been spent on pilot and demonstration buildings on this and even higher energy performance levels throughout many EU countries. However, most of the high performance buildings realised so far result in additional investment costs when compared to the current national minimum energy performance requirements. The considerably higher investment costs are one of the main barriers to the early application of the NZEB-level in Europe. The EU Horizon 2020 project CoNZEBs works on technical solution sets that result in lower investment costs for NZEBs, bringing the costs close to those of conventional new buildings. The project focus is on multi-family houses. In each of the four participant countries Germany, Denmark, Italy and Slovenia a team of researchers is analysing which sets of market-ready technologies at the building envelope, the services systems for heating, domestic hot water, ventilation and cooling (where required) in combination with renewable energy systems can fulfil the NZEB requirements at lower costs than those incurred by the national mainstream NZEB application. Additional efforts are being spent on the life-cycle costs and the life-cycle analysis of the solution sets, as well as on the impact of future developments of primary energy factors, energy costs and technology efficiencies. Since details of the CoNZEBs work are presented in several additional papers, this document gives an overview of the different tasks and results that are available so far. (paper)
[en] Due to the intense pressure from energy shortage and environmental protection, an accurate prediction of building energy consumption is crucial for different energy conservation applications and policies. Besides simulation models and traditional statistical approaches, a data-driven modelling based on energy records provides new opportunities for predicting the building energy demand. This research is conducted based on the whole procedure of data mining with limited datasets, by making use of machine learning techniques and mathematical statistics. Especially, regarding the temporal and the architectural scales, models can be categorized into the short-term prediction, medium-term prediction and long-term prediction of classified energy consumptions, which also represent different modelling characteristics derived from mass data, limited data and poor data respectively. During the modelling process, the fuzzy C-means clustering and the interdisciplinary Lorenz curve were utilized to recognize different energy patterns. Afterwards, models of the nonlinear Support Vector Regression, the Grey model and the traditional polynomial regression were utilized respectively to output the predicted sequence. In summary, with datasets in current energy platforms, this paper presents a study of data-driven models based on energy records considering the nonlinear and uncertain features of different multi-dimensional models. (paper)