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Passive solar elements for both direct and indirect gains, are systems used to maintain a comfortable living environment while saving energy, especially in the building energy retrofit and adaptation process. Sunspaces, thermal mass and glazing area and orientation have been often used in the past to guarantee adequate indoor conditions when mechanical devices were not available. After a period of neglect, nowadays they are again considered as appropriate systems to help face environmental issues in the building sector, and both international and national legislation takes into consideration the possibility of including them in the building planning tools, also providing economic incentives. Their proper design needs dynamic simulation, often difficult to perform and time consuming. Moreover, results generally suffer from several uncertainties, so quasi steady-state procedures are often used in everyday practice with good results, but some corrections are still needed. In this paper, a comparative analysis of different solutions for the construction of verandas in an existing building is presented, following the procedure provided by the slightly modified and improved Standard EN ISO 13790:2008. Advantages and disadvantages of different configurations considering thermal insulation, windows typology and mechanical ventilation systems are discussed and a general intervention strategy is proposed. The aim is to highlight the possibility of using sunspaces in order to increase the efficiency of the existing building stock, considering ease of construction and economic viability.
Energy Performance of Verandas in the Building Retrofit Process (PDF Download Available). Available from: https://www.researchgate.net/publication/303093420_Energy_Performance_of_Verandas_in_the_Building_Retrofit_Process [accessed Jul 5, 2017].
In den vergangenen Jahren ist das technische Gas Schwefelhexafluorid (SF6) immer wieder Gegenstand von Diskussionen des Klimaschutzes und der technischen Notwendigkeit für den Betrieb von Schaltanlagen gewesen und wird dies wohl auch noch für längere Zeit bleiben. Das Gas, welches sich aus einem Schwefelatom und sechs Fluoratomen zusammensetzt, wird seit Ende der sechziger 1960er Jahre in Schaltanlagen der Mittel- und Hochspannung eingesetzt. So günstig dessen Eigenschaften im technischen Einsatz auch sind, so klimaschädlich ist es beim Entweichen in die Atmosphäre. SF6 ist das Klimagas mit dem größten bekannten Treibhauspotenzial, es weist ein CO2-Äquivalent (GWP) von 23.900 und eine atmosphärische Lebensdauer von ca. 3.200 Jahren auf. Neben nur wenig verbliebenen Anwendungen in Industrie, Militär und Medizin kommt es heute hauptsächlich bei der elektrischen Energieversorgung als Isolier- und Lichtbogenlöschgas in Schaltanlagen von Übertragungs- und Verteilnetzen zum Einsatz. Grund genug die technische Notwendigkeit, mögliche Alternativen und Konsequenzen drohender Verbote zu diskutieren. In diesem Artikel werden zunächst die Grundlagen moderner SF6- Hochspannungsschaltanlagen vorgestellt, die Klimabelastung durch entweichendes SF6 evaluiert, ein Überblick über den Stand der Forschung gegeben und mögliche Konsequenzen eines Verbotes von Schwefelhexafluorid in der Energieversorgung diskutiert.
Optimal microgrid scheduling with peak load reduction involving an electrolyzer and flexible loads
(2016)
This work consists of a multi-objective mixed-integer linear programming model for defining optimized schedules of components in a grid-connected microgrid. The microgrid includes a hydrogen energy system consisting of an alkaline electrolyzer, hydrogen cylinder bundles and a fuel cell for energy storage. Local generation is provided from photovoltaic panels, and the load is given by a fixed load profile combined with a flexible electrical load, which is a battery electric vehicle. The electrolyzer has ramp-up constraints which are modeled explicitly. The objective function includes, besides operational costs and an environmental indicator, a representation of peak power costs, thus leading to an overall peak load reduction under optimized operation. The model is used both for controlling a microgrid in a field trial set-up deployed in South-West Germany and for simulating the microgrid operation for defined period, thus allowing for economic system evaluation. Results from defined sample runs show that the energy storage is primarily used for trimming the peak of electricity drawn from the public grid and is not solely operated with excess power. The flexible demand operation also helps keeping the peak at its possible minimum.
The energy supply of Offenburg University of Applied Sciences (HS OG) was changed from separate generation to trigeneration in 2007/2008. Trigeneration was installed for supplying heat, cooling and electrical power at HS OG. In this paper, trigeneration process and its modes of operation along with the layout of the energy facility at HS OG were described. Special emphasis was given to the operation schemes and control strategies of the operation modes: winter mode, transition mode and summer mode. The components used in the energy facility were also outlined. Monitoring and data analysis of the energy system was carried out after the commissioning of trigeneration in the period from 2008 to 2011. Thus, valuable performance data was obtained.
Proton Exchange Membrane Fuel Cell (PEMFC) is one of the most promising technologies for sustainable energy production due to the high power density, low operative temperature and more convenient use for several applications. Nevertheless, the high generated current that characterizes PEMFC requires a specific power conditioning. In addition, specific controller must be designed to fit with system operative points changing associated with the variation of this high current. To deal with this challenge, in this paper, an electrochemical system composed of a Proton Exchange Membrane Fuel Cell (PEMFC) feeding via two phases IBC has been proposed and investigated. For robustness, the used IBC for fuel cell voltage regulation is controlled by linear quadratic regulator (LQR). Then, genetic algorithms technique is applied to optimize the LQR controller parameters giving optimal control coefficients and can if necessary be adjusted according to each working situation change. The model of the entire system is studied using Matlab/Simulink environment. The simulation’s comparative standard and robustness results both demonstrate that the proposed GA-based LQR controller outperforms the conventional PI in terms of performance metrics (overshoot reduction: between 58.93% and 97.09%; response time reduction: between 56.40% and 77.00% and ripple reduction: between 84.00% and 94.86%).
Die Hochschule Offenburg begleitet seit Juli 2006 in Zusammenarbeit mit dem Fraunhofer ISE in Freiburg und der HfT Stuttgart die solar unterstützte Klimatisierung der Festo AG & Co. KG in Esslingen. Die Anlage wurde im Rahmen des Forschungsvorhabens „Solarthermie2000plus“ vom Bundesumweltministerium gefördert. Dabei wurde die bereits bestehende Adsorptionskälteanlage, die bisher mit Kompressorabwärme und Gaskesseln betrieben wurde, durch eine Solaranlage als drittem Wärmelieferanten ergänzt.
Electric arc furnaces (EAF) are complex industrial plants whose actual behavior depends upon numerous factors. Due to its energy intensive operation, the EAF process has always been subject to optimization efforts. For these reasons, several models have been proposed in literature to analyze and predict different modes of operation. Most of these models focused on the processes inside the vessel itself. The present paper introduces a dynamic, physics-based model of a complete EAF plant which consists of the four subsystems vessel, electric system, electrode regulation, and off-gas system. Furthermore the solid phase is not treated to be homogenous but a simple spatial discretization is employed. Hence it is possible to simulate the energy input by electric arcs and fossil fuel burners depending on the state of the melting progress. The model is implemented in object-oriented, equation-based language Modelica. The simulation results are compared to literature data.
In the dual membrane fuel cell (DM-Cell), protons formed at the anode and oxygen ions formed at the cathode migrate through their respective dense electrolytes to react and form water in a porous composite layer called dual membrane (DM). The DM-Cell concept was experimentally proven (as detailed in Part I of this paper). To describe the electrochemical processes occurring in this novel fuel cell, a mathematical model has been developed which focuses on the DM as the characteristic feature of the DM-Cell. In the model, the porous composite DM is treated as a continuum medium characterized by effective macro-homogeneous properties. To simulate the polarization behavior of the DM-Cell, the potential distribution in the DM is related to the flux of protons and oxygen ions in the conducting phases by introducing kinetic and transport equations into charge balances. Since water pressure may affect the overall formation rate, water mass balances across the DM and transport equations are also considered. The satisfactory comparison with available experimental results suggests that the model provides sound indications on the effects of key design parameters and operating conditions on cell behavior and performance.