Volume 7, Issue 5, September 2015
Index of content:
- REGULAR ARTICLES
7(2015); http://dx.doi.org/10.1063/1.4929957View Description Hide Description
Variability and intermittency of wind is the main challenge for making a reliable wind power forecasting (WPF). Meteorological and topological complexities make it even harder to fit any forecasting algorithm to one particular case. This paper presents the comparison of three short term WPF models based on three wind farms in China with different terrains and climates. The sensitivity effects of training samples on forecasting performance are investigated in terms of sample size, sample quality, and sample time scale. Then, their adaptabilities and modeling efficiency are also discussed under different seasonal and topographic conditions. Results show that (1) radial basis function (RBF) and support vector machine (SVM) generally have higher prediction accuracy than that of genetic algorithm back propagation (GA-BP), but different models show advantages in different seasons and terrains. (2) WPF taking a month as the training time interval can increase the accuracy of short-term WPF. (3) The change of sample number for the GA-BP and RBF is less sensitive than that of the SVM. (4) GA-BP forecasting accuracy is equally sensitive to all size of training samples. RBF and SVM have different sensibility to different size of training samples. This study can quantitatively provide reference for choosing the appropriate WPF model and further optimization for specific engineering cases, based on better understanding of algorithm theory and its adaptability. In this way, WPF users can select the suitable algorithm for different terrains and climates to achieve reliable prediction for market clearing, efficient pricing, dispatching, etc.
A simple methodology for capacity sizing of cogeneration and trigeneration plants in hospitals: A case study for a university hospital7(2015); http://dx.doi.org/10.1063/1.4930064View Description Hide Description
Energy efficiency applications have great importance for facilities that utilize large amount of electrical and heat energy. Cogeneration (so called Combined Heat and Power; abbreviated as CHP) plants with gas engines are capable of generating both electrical and heat energy simultaneously using a single fuel input. In recent years, the realization of license exemption for facilities willing to produce electricity just for their energy demands by ensuring the condition of 80% total efficiency, low carbon emission of systems contain gas engines, rapid operation for synchronization and shortness of payback periods make cogeneration and trigeneration (so called Combined Cooling, Heat and Power; abbreviated as CCHP) plants more popular. This paper (i) briefly reviews cogeneration and trigeneration plants and their advantages, (ii) presents a novel methodology to determine the optimal capacity ratings for the plants by using the energy consumption profile, (iii) illustrates the calculation procedures including economic profit, thermal efficiency, and electricity generation of the selected system, and (iv) suggests the optimal capacity, plant placement and configuration for a medium-scale hospital. The energy savings potential at the university hospital is estimated as 19.66% and 19.52% with the use of natural gas based cogeneration and trigeneration plant, respectively.
Effect of solar area concentration ratio on performance of a conventional solar still with air humidification-dehumidification7(2015); http://dx.doi.org/10.1063/1.4930136View Description Hide Description
The high demand for drinking water increased the need to develop new economic methods for water desalination. Conventional solar stills suffer from latent heat losses resulting from water-vapor condensation on the inner surface of the glazing. Using open humidification-dehumidification process with conventional solar stills is a potential area in water desalination nowadays. Integrating a vertical duct to the still for generating a natural draft and solar-air preheater improved its performance. The effect of the solar area concentration ratio on the still performance with heater was studied thoroughly compared to no heater as a reference. Using a condenser in the duct prevents latent heat losses on the inner surface of the glazing and utilizes it to preheat the feed water. This arrangement improved the still productivity. A model was generated to describe the efficiency of the system using three area concentration ratios: 0.5, 0.625, and 0.75. The results showed that the still productivity increased proportionally with the area concentration ratio with average productivity of 5.5 l m−2 day.