1,721,026 research outputs found
Towards a 100% renewable island power system with energy storage::modelling, optimization, and cost analysis
No full textA Danish island, Aero, has wind power more than it needs, but still has to import power from the mainland due to the balance issue of the island. In addition, Aero has just set up an e-ferry to facilitate transportation between the island and the mainland over a 20 km distance. This paper will study the minimum storage that will be needed to support the balance of its 100% renewable-based energy system, i.e., reduce the power import from the mainland to zero. The analysis will include different storage technologies with different efficiencies, such as Lithium-ion battery (close to 100% round-trip efficiency) and high-temperature thermal storage (about 41% round-trip efficiency) since they require different optimization models. The results show that for the case with a low round-trip efficiency, more wind power will be required in order to be 100% self-sufficient. In addition, as the self-sufficiency (the percentage of the total energy consumption that is supplied by the island itself) goes up, the required size of the storage goes up even quicker.</p
Post-evaluation of the energy retrofit process in three public schools in Denmark
No full textConsidering that over 80% of buildings in Denmark were built before the 1980's, a holistic energy retrofitting of the existing building stock is a major milestone to attain the energy and environmental targets of the country. In this work, a case study of three public schools is considered for post-retrofit process evaluation. The three schools were heavily retrofitted by September 2018 with energy conservation and improvement measures implemented targeting both, the building envelope and various energy systems. A technical evaluation of the energy retrofit process in the schools was carried out, considering one year of operation after the completion of the retrofitting work. Actual data from the heating and electricity meters in the schools was collected and compared with the pre-retrofit design numbers which rely majorly on static tabulated numbers for savings evaluation. It was shown that the retrofit design numbers largely overestimate the attained savings, where the average performance gap between the expected and the real numbers for the three schools is around 61% and 136% for annual heating and electricity savings respectively. On the other hand, an alternative approach was proposed where calibrated dynamic energy performance models, developed for the three schools in EnergyPlus, were used to simulate the impact of implementing the retrofit measures. It was shown that implementing this approach could predict much better the impacts of the retrofit process with an average gap of around 17% for heating savings and 21% for electricity savings. Based on the post-retrofit process evaluation in the three schools, it was concluded that using dynamic model simulations has the potential of lowering the performance gap between the promised and the real savings compared to static tabulated approaches, although the savings are still generally over-estimated in both approaches.</p
Experimental and numerical investigation of a PCM module for ventilation systems
No full textIn the last decades, there is an increasing demand for innovative, efficient, and environmentally friendly cooling technologies as alternatives to the conventional compressor-based technologies. In this study, a theoretical and experimental investigation of a Phase Change Material(PCM) based module for a ventilation system is presented. A latent thermal energy storage unit with PCM is used as an add-on-module to a ventilation system to provide additional cooling capacity. The ventilation system is used to direct cold air from the outside through the PCM module to solidify the PCM during night time. During day time, the room supply air can be cooled down by passing it through the PCM module. An actual application employing the considered PCM module is investigated, where PCM is encapsulated in rectangular containers, each with 2kg of PCM. The PCM containers are placed inside the supply air stream of a ventilation unit. A one-dimensional numerical model is developed to predict the dynamic performance of the PCM-driven ventilation system. In addition, the model is calibrated and validated with data collected from an experimental application. It was shown that the developed model predicts well the system performance with an average deviation of less than 2% for the PCM temperature and less than 4% for the air temperature.</p
District-scale lake water free cooling in Zurich, Switzerland: System performance simulation and techno-economic feasibility
No full textObject-oriented modeling and performance evaluation of a PCM-based ventilation system
No full textThe buildings sector is a large energy consumer, so improving the building block energy performance through implementing energy-efficient techniques would aid in attaining the energy and environmental goals. Among energy-saving technologies, Latent Thermal Energy Storage (LTES) systems have drawn great attention to be applied in buildings as they enable more efficient and cost-effective thermal management by reducing energy use or shifting peak loads. Particularly, Phase Change Material (PCM), as a storage medium in LTES systems, has received considerable attention in recent research studies and investigations. This study aims at modelling and assessment of a PCM-driven ventilation system. An energy storage system with four PCM stacks was modelled using Modelica language considering the physical and operational parameters. Subsequently, the influence of parameters on PCM temperature was evaluated by sensitivity analysis. Using collected data from a system experiment, unknown parameters for the first stack were estimated on the first 3 days and validated on the following 2 days through minimizing Root Mean Square Error (RMSE) of predicted PCM temperature to the measured temperature using a genetic algorithm. The estimated parameters were applied to the four stacks and developed ventilation system was then validated based on the 5-day measurements from experimental setup. The overall system performance was simulated and assessed and the PCM thermal energy storage capacity was evaluated. Results showed that the object-oriented Modelica model yields a sufficient accuracy in capturing the thermal behavior of the PCM-based energy storage system. For each stack, the RMSE of predicted PCM temperature compared to measurements are 0.277 °C, 0.332 °C, 0.332 °C and 0.410 °C respectively.</p
Towards a 100% renewable island power system with energy storage::modelling, optimization, and cost analysis
No full textA Danish island, Aero, has wind power more than it needs, but still has to import power from the mainland due to the balance issue of the island. In addition, Aero has just set up an e-ferry to facilitate transportation between the island and the mainland over a 20 km distance. This paper will study the minimum storage that will be needed to support the balance of its 100% renewable-based energy system, i.e., reduce the power import from the mainland to zero. The analysis will include different storage technologies with different efficiencies, such as Lithium-ion battery (close to 100% round-trip efficiency) and high-temperature thermal storage (about 41% round-trip efficiency) since they require different optimization models. The results show that for the case with a low round-trip efficiency, more wind power will be required in order to be 100% self-sufficient. In addition, as the self-sufficiency (the percentage of the total energy consumption that is supplied by the island itself) goes up, the required size of the storage goes up even quicker.</p
Post-evaluation of the energy retrofit process in three public schools in Denmark
No full textConsidering that over 80% of buildings in Denmark were built before the 1980's, a holistic energy retrofitting of the existing building stock is a major milestone to attain the energy and environmental targets of the country. In this work, a case study of three public schools is considered for post-retrofit process evaluation. The three schools were heavily retrofitted by September 2018 with energy conservation and improvement measures implemented targeting both, the building envelope and various energy systems. A technical evaluation of the energy retrofit process in the schools was carried out, considering one year of operation after the completion of the retrofitting work. Actual data from the heating and electricity meters in the schools was collected and compared with the pre-retrofit design numbers which rely majorly on static tabulated numbers for savings evaluation. It was shown that the retrofit design numbers largely overestimate the attained savings, where the average performance gap between the expected and the real numbers for the three schools is around 61% and 136% for annual heating and electricity savings respectively. On the other hand, an alternative approach was proposed where calibrated dynamic energy performance models, developed for the three schools in EnergyPlus, were used to simulate the impact of implementing the retrofit measures. It was shown that implementing this approach could predict much better the impacts of the retrofit process with an average gap of around 17% for heating savings and 21% for electricity savings. Based on the post-retrofit process evaluation in the three schools, it was concluded that using dynamic model simulations has the potential of lowering the performance gap between the promised and the real savings compared to static tabulated approaches, although the savings are still generally over-estimated in both approaches.</p
Experimental and numerical investigation of a PCM module for ventilation systems
No full textIn the last decades, there is an increasing demand for innovative, efficient, and environmentally friendly cooling technologies as alternatives to the conventional compressor-based technologies. In this study, a theoretical and experimental investigation of a Phase Change Material(PCM) based module for a ventilation system is presented. A latent thermal energy storage unit with PCM is used as an add-on-module to a ventilation system to provide additional cooling capacity. The ventilation system is used to direct cold air from the outside through the PCM module to solidify the PCM during night time. During day time, the room supply air can be cooled down by passing it through the PCM module. An actual application employing the considered PCM module is investigated, where PCM is encapsulated in rectangular containers, each with 2kg of PCM. The PCM containers are placed inside the supply air stream of a ventilation unit. A one-dimensional numerical model is developed to predict the dynamic performance of the PCM-driven ventilation system. In addition, the model is calibrated and validated with data collected from an experimental application. It was shown that the developed model predicts well the system performance with an average deviation of less than 2% for the PCM temperature and less than 4% for the air temperature.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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