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Abstract The characteristics of the wind at 10 m height were studied over a period of 32 months. The sampling interval was 20 ms and the averaging time was 10 min. Probability density functions are given for the speed, direction, inclination and intensity of turbulence of the wind. Frequency contour plots are given for wind speed vs solar time, wind speed vs wind direction, wind speed vs global solar irradiance and wind speed vs the intensity of turbulence of the wind. Differences between the results for day and night and between various seasons are examined.

Abstract The north wall of Chinese solar greenhouses (CSGs) plays an important role in maintaining their indoor thermal environment without additional heating during the wintertime. To enhance the heat storage/release capacity of the CSG wall and further improve the indoor thermal environment, an active-passive phase change thermal storage wall system has been developed in this study. The system was composed of 5 concentrating solar air collectors (CSACs), 6 tanks that were embedded in the north wall of the CSG and filled by phase change material (PCM), tubes linking the tanks and the CSACs and a centrifugal fan with variable-frequency drive (VFD). During the daytime, the solar energy was collected by the CSACs and stored in the tanks, whereas during the nighttime, the stored energy was released into the indoor environment of the CSG through a passive heat mode of the north wall or an active heat mode of the system. Then, a numerical model of the active-passive phase change thermal storage wall system has been developed. The simulation results were validated by the experimental data with the maximum relative error and average relative error being 5.6% and 3.9%, respectively. Furthermore, the heat release capacity characteristics in three cases with the air velocities of 2 m/s (Case A), 3 m/s (Case B) and 4 m/s (Case C) at indoor outlet for the active heat mode and a passive heating case (Case D) were chosen as the control groups for study. In the proposed wall, the heat release capacity of ventilation increased and that of inner surface of the wall declined with an increasing ventilation velocity. The total heat release capacities of the cases A, B and C were 38.12 MJ, 40.26 MJ, 42.00 MJ, respectively, higher than that of the case D (33.76 MJ). On the other hand, the calculated temperature distribution indicated that there was no thermal-stable layer within depth of the 360 mm in the wall due to an apparent temperature variation of the PCM layer by ventilation. These results suggested that the proposed system could effectively promote the heat storage/release capacity of the middle layer of the wall.

Abstract Climate responsive strategies contained in traditional native dwellings can provide theoretical basis for the development of sustainable buildings. This study focused on a quantitative analysis of cliff-side cave dwellings located in cold region of China. Field measurements in summer and winter were carried out. Based on the monitoring data, thermal environment of the cave dwelling and thermal characteristics of the adobe massive building envelope were evaluated. Results showed that the cliff-side cave dwelling was well adapted to local environment for its good ability of thermal insulation under the natural conditions. Furthermore, in order to assess the whole annual thermal performance and thermal comfort level, numerical simulations on the cliff-side cave dwelling models was also performed using the software Energyplus. Results showed that 52.50% time of the year was comfortable of the living room. Meanwhile, some technical strategies of making full use of solar energy and natural ventilation was proposed in the end of this paper, which can provide technical support for the regeneration design of traditional residential buildings.

A data-driven approach for maximization of the power produced by wind turbines is presented. The power optimization objective is accomplished by computing optimal control settings of wind turbines using data mining and evolutionary strategy algorithms. Data mining algorithms identify a functional mapping between the power output and controllable and non-controllable variables of a wind turbine. An evolutionary strategy algorithm is applied to determine control settings maximizing the power output of a turbine based on the identified model. Computational studies have demonstrated meaningful opportunities to improve the turbine power output by optimizing blade pitch and yaw angle. It is shown that the pitch angle is an important variable in maximizing energy captured from the wind. Power output can be increased by optimization of the pitch angle. The concepts proposed in this paper are illustrated with industrial wind farm data.

Cost of energy generated from offshore wind is impacted by maintenance cost to a great extent. Cost of maintenance depends primarily on the strategy for performing maintenance. In this paper a maintenance cost model for offshore wind turbine components following multilevel opportunistic preventive maintenance strategy is formulated. In this strategy, opportunity for performing preventive actions on components is taken while a failed component is replaced. Two kinds of preventive actions are considered, preventive replacement and preventive maintenance. In the former, components that undergo that action become as good as new (i.e., the replaced components, are not just as good as new, but are actually new), but in the latter, ages of components are reduced to some degree depending on the level of maintenance action. Total cost associated with maintenance depends on the setting of age groups that determine which component should be preventively maintained and to what degree. Through optimum selection of the number of age groups, cost of maintenance can be minimized. A model is formulated where total maintenance cost is expressed as a function of number of age groups for components. A numerical study is used to illustrate the model. The results show that total cost of maintenance is significantly impacted by number of age groups and age thresholds set for components.

Abstract The Cost of Energy is a major concern for the electric power industry. Customers are sensitive to the cost of renewable energy, which is typically more expensive than conventional energy generation due to the variability and uncertainty associated with their sources. Power Purchase Agreements (PPAs) are developed to balance the energy price and associated risks with poewr gerneation and transmission. The energy delivery limits imposed by current PPAs impact the Levelized Cost of Energy (LCOE) in ways that are not accomodated by existing LCOE models. In this work, a new cost model is developed to evaluate the LCOE from a wind power source under a PPA contract. The application of the model to real wind farms demonstrates that the actual LCOE depends on the defined minimum/maximum energy purchase limitations within a PPA contract. The developed cost model can be used as a basis for setting appropriate PPA terms, such as a price schedule and performance metrics. Hence, it can help the Seller to negotiate penalties and energy price within their PPAs.

Abstract The main goal of this study is to investigate the effect of boiler design by smoke tube addition on combustion characteristics and emissions in a small scale pellet boiler. In this context, flame/smoke tube pellet-fuelled boilers with two different constructions were designed, manufactured and tested. In the design of the boilers, the first passes of gases without smoke tubes (Boiler-1) and with smoke tubes (Boiler-2) were considered. The effect of different gas passes of the boilers on flame temperature, flue gas temperature, thermal efficiency, and flue gas emissions of O2, CO, CO2 and NOx were investigated and results were compared with each other. The results showed that adding smoke tubes to the first pass of the boiler decreased the average flue gas temperatures from 87.6 °C to 76.9 °C. The thermal efficiency of the Boiler-2 geometry reached a value of 92.3% and was nearly 1.3% higher than the Boiler-1 geometry. CO emissions increased up to 205 ppm from 166 to 371 ppm by addition of smoke tubes to the first pass of the Boiler-1. It was observed that smoke tubes addition to the first pass of the boiler did not affect the NOx emissions significantly, which were about 45–47 ppm.