Abstract: Small wind turbines are investigated as a possible solution for using wind energy at small scales in urban and suburban areas. Most turbines are suffering from a low aerodynamic performance due to turbulent and complex wind situations in cities. Therefore, increasing aerodynamic performance and reducing noise is an important factor to design small wind turbines. In order to optimize such turbines with respect to noise and efficiency it is important to understand the physical mechanisms. Measuring acoustic in urban environment it is hardly possible to obtain reproducible results, which are necessary for a comprehensively and profoundly investigation. Therefore, experimental studies have to been performed in anechoic wind tunnels. Those tunnels are mostly limited in size, which makes it quite difficult to investigate full small wind turbine models. Hence a model scale has to be used in order to measure the power and acoustic performance. For comparing the model scale results with original turbines, the same flow conditions around the airfoils are necessary. Due to the smaller size of the model scale the relative velocities of the blades are less, which can result in a laminar boundary layer. In order to force transition from laminar to turbulent, boundary layer trips can be used. The focus of this study is to examine and quantify the effect of boundary layer tripping on the aeroacoustics in case of small vertical axis wind turbines.
Abstract: CO2 is the main determining factor for global climate change. For this reason, the emissions of this gas have to be reduced as much and as quickly as possible. This paper discusses the possibility to realize a CO2-neutral heat and power supply for single and multi-family homes. There have been a lot of studies in the past, as well as several unsuccessful-attempts to commercialize such a system. However, this paper presents a new and simple 1 kWel setup for a smart combined heat and power (CHP) plant offers solutions for the deficiencies of previously published and demonstrated systems. A commercial pellets firing system is linked with an organic Rankine cycle (ORC), which is built with mass-produced parts. In addition, inexpensive and proven-in-use hot-water storage tanks are used as an energy buffer and for storage, resulting in reduced investment costs. Furthermore, we demonstrate that it is necessary to embed such a system into a smart home environment in order to achieve an efficient and profitable setup.
Abstract: The central heating units of buildings are typically replaced every 20 to 30 years. There exists a variety of solutions for fuel-and gas-based units, but it would be advantageous to be able to use renewable energies. This would become possible by the combination of planar carbon-fiber-based infrared (IR) radiant heating foils with a heat pump providing hot water. The main goal of our proposed overall control strategy is to increase the energy efficiency while maintaining the thermal comfort for the residents. We examined the electromagnetic compatibility of the heating foils and simulated the relative contributions of the amount of energy provided by the heat pump and by the heating foils to obtain a maximum coefficient of performance for the combined heating system.
Abstract: The transition from fossil generated energy towards regenerative energy sources is an important topic. Especially the generation from wind power plants and photovoltaic systems underlines the most important difference in comparison to conventional energy generation and distribution. One of the main characteristics of renewable energy sources is its decentralized generation, where existing distribution paths will become more and more a bottleneck in the future. The solution for this challenge is called smart grid and is driven by information, such as energy consumption, in order to match energy demand and supply. The SmartEco idea makes it possible to offload some of the energy’s surplus form the grid to individual customer homes in the context of the smart gird approach.
Abstract: Conventional ventilation systems with heat recovery used for building aeration exhibit characteristic disadvantages arising from their operating principle such as noise generation from bladed ventilators or remarkable pressure losses generated by heat exchangers. A novel concept that combines ventilators and heat exchanger in one compact friction ventilator that rotates in two separated ducts producing two opposed airflows and transferring thermal energy from the higher temperature airflow to the lower temperature level can overcome the mentioned shortcomings. In order to demonstrate the feasibility of a friction ventilator to operate as ventilation system with heat recovery computational fluid dynamics were used to analyze the resulting pressure jump and volume flow for different geometrical setups. An extensive grid dependency study for a defined operating point that represents the typical use has been carried out in order to improve the numerical results. Furthermore, the results were compared to experimental data whenever possible.
Abstract: Standard decentralized ventilation systems typically consist of two ventilators for inlet and exhaust air and a heat exchanger for the heat recovery. A recently developed device, a so called friction ventilator, combines these three elements into a single functional element. The ventilator consists of circular plates which are rotating centrally in between the inlet and the outlet duct of a ventilation system and generate a countercurrent flow in the two ducts. Furthermore, the discs act as a rotating heat exchanger between the two air flows. To increase understanding of the energy transfer from the rotating discs to the flow an experimental investigation on the effect of different rotor geometries was conducted. The study showed an interesting influence of the hub diameter on the characteristic curves with a higher pressure difference for an increase in diameter. The results of the heat recovery measurement however were only mildly affected by the hub geometry. Here the distance between the discs, the rotational speed of the discs and the volumetric flow seemed to have the greatest effect on heat recovery.
Abstract: A promising approach for increasing the energy efficiency of domestic households and buildings is to optimize the whole energy system by coupling of different heat sources and sinks. This procedure, known as heat integration, is state of the art in the industrial sector and is now applied to the residential sector. In this work several options for increasing the energy efficiency and for recovering waste heat are discussed. In order to reduce the primary energy demand different waste heat sources like domestic hot water or household appliances (refrigerators or freezers) were evaluated. The first step is the development of an advanced form of the stationary Pinch Analysis. This was subsequently applied to determine the thermodynamically possible energy saving for a single family home.
Abstract: The paper presents the results of an accompanying socio-scientific research of a one-year field test in a multiple dwelling, in which the energy saving potential of a newly developed smart heating system was examined. To draw conclusions about the user’s acceptance of the smart heating system, the residents of the test object were surveyed in terms of their attitude towards the smart heating system. With regard to user acceptance, we state an ambivalent relationship of the users to the new technology. On the one hand, they are delighted with the system and the increased comfort concerning room temperature. On the other hand, they think that the costs will increase with higher comfort. The analysis shows that adopting a new technology goes along with different, partly competing attitudes.
Abstract: Medium voltage grids are subject to a change in load situation due to the installation of decentralized generation plants. Predominantly load symmetry, active and reactive power as well as the required capacity of earth fault compensation is affected. Inverter-based plants as well as consumers using switching power supplies or phase control cause distortions of frequency. Simultaneously electrical energy storage is gaining importance within rural distribution networks to compensate fluctuating generation plants. A hybrid compensation system includes a transformer, a multi-phase inverter, diverse storage systems and a communication-capable control unit, which may be connected to the control center of the distribution system operator (DSO). It is object to current research activities to design and evaluate the functions of the superordinate control unit, which has to parametrize individual components, coordinate the energy flows between them and to embed several measuring instruments. Within the present work, basic considerations for design of system control are outlined.