Energies2014, 7(4), 2449-2475; doi:10.3390/en7042449 (doi registration under processing) - published online 17 April 2014 Show/Hide Abstract
Abstract: Transportation electrification has become an important issue in recent decades and the large scale deployment of electric vehicles (EVs) has yet to be achieved. The smart coordination of EV demand addresses an improvement in the flexibility of power systems and reduces the costs of power system investment. The uncertainty in EV drivers’ behaviour is one of the main problems to solve to obtain an optimal integration of EVs into power systems. In this paper, an optimisation algorithm to coordinate the charging of EVs has been developed and implemented using a Genetic Algorithm (GA), where thermal line limits, the load on transformers, voltage limits and parking availability patterns are taken into account to establish an optimal load pattern for EV charging-based reliability. This methodology has been applied to an existing residential low-voltage system. The results indicate that a smart charging schedule for EVs leads to a flattening of the load profile, peak load shaving and the prevention of the aging of power system elements.
Energies2014, 7(4), 2436-2448; doi:10.3390/en7042436 (doi registration under processing) - published online 17 April 2014 Show/Hide Abstract
Abstract: The influences of various evaporators on the system responses of a 50 kW ORC system using R-245fa are investigated in this study. First the effect of the supplied hot water flowrate into the evaporator is examined and the exit superheat on the system performance between plate and shell-and-tube evaporator is also reported. Test results show that the effect of hot water flowrate on the evaporator imposes a negligible effect on the transient response of the ORC system. These results prevail even for a 3.5-fold increase of the hot water flowrate and the system shows barely any change subject to this drastic hot water flowrate change. The effect of exit superheat on the ORC system depends on the type of the evaporator. For the plate evaporator, an exit superheat less than 10 °C may cause ORC system instability due to considerable liquid entrainment. To maintain a stable operation, the corresponding Jakob number of the plate heat evaporator must be above 0.07. On the other hand, by employing a shell and tube heat evaporator connected to the ORC system, no unstable oscillation of the ORC system is observed for exit superheats ranging from 0 to 17 °C.
Energies2014, 7(4), 2421-2435; doi:10.3390/en7042421 (doi registration under processing) - published online 17 April 2014 Show/Hide Abstract
Abstract: A mathematical model was developed to describe batch and continuous fermentation of glucose to organic acids with Clostridium tyrobutyricum. A modified Monod equation was used to describe cell growth, and a Luedeking-Piret equation was used to describe the production of butyric and acetic acids. Using the batch fermentation equations, models predicting butyric acid selectivity for continuous fermentation were also developed. The model showed that butyric acid production was a strong function of cell mass, while acetic acid production was a function of cell growth rate. Further, it was found that at high acetic acid concentrations, acetic acid was metabolized to butyric acid and that this conversion could be modeled. In batch fermentation, high butyric acid selectivity occurred at high initial cell or glucose concentrations. In continuous fermentation, decreased dilution rate improved selectivity; at a dilution rate of 0.028 h−1, the selectivity reached 95.8%. The model and experimental data showed that at total cell recycle, the butyric acid selectivity could reach 97.3%. This model could be used to optimize butyric acid production using C. tyrobutyricum in a continuous fermentation scheme. This is the first study that mathematically describes batch, steady state, and dynamic behavior of C. tyrobutyricum for butyric acid production.
Energies2014, 7(4), 2377-2420; doi:10.3390/en7042377 - published online 15 April 2014 Show/Hide Abstract
Abstract: Smart Grids are becoming a reality all over the world. Nowadays, the research efforts for the introduction and deployment of these grids are mainly focused on the development of the field of Smart Metering. This emerging application requires the use of technologies to access the significant number of points of supply (PoS) existing in the grid, covering the Low Voltage (LV) segment with the lowest possible costs. Power Line Communications (PLC) have been extensively used in electricity grids for a variety of purposes and, of late, have been the focus of renewed interest. PLC are really well suited for quick and inexpensive pervasive deployments. However, no LV grid is the same in any electricity company (utility), and the particularities of each grid evolution, architecture, circumstances and materials, makes it a challenge to deploy Smart Metering networks with PLC technologies, with the Smart Grid as an ultimate goal. This paper covers the evolution of Smart Metering networks, together with the evolution of PLC technologies until both worlds have converged to project PLC-enabled Smart Metering networks towards Smart Grid. This paper develops guidelines over a set of strategic aspects of PLC Smart Metering network deployment based on the knowledge gathered on real field; and introduces the future challenges of these networks in their evolution towards the Smart Grid.
Energies2014, 7(4), 2362-2376; doi:10.3390/en7042362 - published online 14 April 2014 Show/Hide Abstract
Abstract: Windows are the primary aperture to introduce solar radiation to the interior space of a building. This experiment explores the use of EnergyPlus software for analyzing the illuminance level on the floor of a room with reference to its distance from the window. For this experiment, a double clear glass window has been used. The preliminary modelling in EnergyPlus showed a consistent result with the experimentally monitored data in real time. EnergyPlus has two mainly used daylighting algorithms: DElight method employing radiosity technique and Detailed method employing split-flux technique. Further analysis for illuminance using DElight and Detailed methods showed significant difference in the results. Finally, we compared the algorithms of the two analysis methods in EnergyPlus.
Energies2014, 7(4), 2343-2361; doi:10.3390/en7042343 - published online 14 April 2014 Show/Hide Abstract
Abstract: Cool roofs represent an acknowledged passive cooling technique to reduce building energy consumption for cooling and to mitigate urban heat island effects. This paper concerns the evaluation of the dynamic effect of new cool roof clay tiles on building thermal performance in summer and winter conditions. To this end, these properties have been analyzed on traditional roof brick tiles through an indoor and outdoor two-year long continuous monitoring campaign set up in a residential building located in central Italy. The analysis and the cooperation with industrial companies producing brick tiles and reflective coatings allowed the production of a new tile with notable “cool roof” properties through the traditional industrial manufacturing path of such tiles. Notable results show that during summer the high reflection tiles are able to decrease the average external roof surface temperature by more than 10 °C and the indoor operative temperature by more than 3 °C. During winter the average external surface temperature is lower with high reflection tiles by about 1 °C. Singular optic-thermal phenomena are registered while evaluating the dynamics of the cool roof effect. Interesting findings show how the sloped cool roof application could suggest further considerations about the dynamic effect of cool roofs.