1,720,963 research outputs found
Advanced modeling and energy-saving-oriented assessment of control strategies for air-cooled chillers in space cooling applications
Full text linkChillers are reference technologies to meet the demand for space cooling in the tertiary and commercial sectors.
Meantime, being power-to-cold technologies, they could increase the flexibility of these buildings in those contexts of a high share of electricity from renewable energy sources through new control strategies. To reliably assess the achievable energy savings in these novel applications, models capable of simulating not only the steady-state operation but also the dynamic response are required. However, the operation of these systems is usually evaluated through highly simplified models, also omitting controls. To fill this gap, this paper proposes an integrated thermodynamic and control modeling for an air-cooled chiller, accounting for usual and innovative
control strategies. To show the capabilities of the model, an air-cooled chiller serving an office in the Mediterranean area is assumed. Both a variable-speed chiller and a constant-speed chiller with sequential control for compressors are simulated. Results show that for a variable-speed chiller, the set point for the supplied cold water is met, and the thermal inertia of the hydronic loop affects the reaching of the steady-state operation. In the case of a constant-speed chiller with sequential control, the number of “ON-OFF” cycles for each compressor is monitored and the minimum inertia of the hydronic loop for the safe operation of compressors is found. The analysis reveals that a variable temperature setpoint for the supplied water allows for a percentage increase in the energy performance between 10.8% and 60.3%. The proposed model enables the analysis of innovative controls aimed at improving energy savings and increasing building flexibility
Integrated Thermodynamic and Control Modeling of an Air-to-Water Heat Pump for Estimating Energy-Saving Potential and Flexibility in the Building Sector
Full text linkReversible heat pumps are increasingly adopted for meeting the demand for space heating and cooling in buildings. These technologies will play a key role not only in the decarbonization of space air conditioning but also in the development of 100% renewable energy systems. However, to assess the achievable benefits through the adoption of these technologies in novel applications, reliable models are needed, capable of simulating both their steady-state operation and dynamic response at different conditions in terms of heating loads, outdoor temperatures, and so on. The operation of heat pumps is often investigated by highly simplified models, using performance data drawn from catalogs and paying scarce attention to the critical influence of controllers. In this respect, this paper proposed an integrated thermodynamic and control modeling for a reversible air-to-water heat pump. The study considered a heat pump alternatively equipped with variable-speed compressors and constant-speed compressors with sequential control. The developed modeling was then used to investigate the operation of an air-to-water heat pump serving an office building in Italy. Results show that the model provided insights into the transient operation of variable-speed heat pumps (e.g., the settling time). Regarding constant-speed heat pumps, the model provided hints of interest to the control engineer to prevent, in the examined case study, the risk of quick compressors cycling on low-load heating days or when low-temperature heating devices are supplied. Finally, using a control strategy based on a heating curve for the variable-speed heat pump, results show the potential for a sensible increase in the average coefficient of performance, from 17% up to 50%
State of art and economic evaluation of wave energy converters. A case study
No full textThe even increasing energy demand in the world is a relevant problem for the modern society. The energy supply from fossil fuels has become a critical aspect due to the progressive reduction of reserves and political instability among the Countries. For these reasons, the exploitation of renewable energy sources is looked with a great interest. In this context, solar, wind, geothermal, hydropower, and biomass can be successfully used through commercial technologies. Other potential renewable energy sources could have potential applications in the next future. Among these, sea wave is considered a very promising energy source, especially for small islands. In this context, the paper propones a new configuration of wave energy converter, analyzing the economic aspects for a potential realization in the Mediterranean Sea
Online Estimation of the Mechanical Parameters of an Induction Machine Using Speed Loop characteristics and Recursive Least Square Technique
No full textThis paper presents a novel approach for estimation of mechanical parameters, inertia and friction coefficient of an Induction Machine (IM) using speed loop characteristics and Recursive Least Square (RLS) estimator. Using the 5th order dynamic equation for Induction Machine and the forgetting factor based RLS algorithm the technique herein proposed employs the speed of the machine and the torque as the inputs for the estimator. Results obtained compares the estimated parameters with the actual parameters under multiple step varying and exponentially varying scenarios. Upon analyzing the results, the validity and the effectiveness of the proposed identification technique is confirme
Enhanced Current Loop PI Controllers with Adaptive Feed-Forward Neural Network via Estimation of Grid Impedance: Application to Three-Phase Grid-Tied PV Inverters
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Improving the speed estimation by load torque estimation in induction motor drives: an MRAS and NUIO approach
No full textThis paper proposes the application of the NUIO inside a FOC induction motor drive for the simultaneous estimation of the load torque and the rotor speed. The idea is to estimate at first the speed with the current model in parallel with a reference model developed on the basis of the voltage model of the induction machine. Then, the estimated speed is given as input to a nonlinear unknown input observer (NUIO) to estimate the load torque. This estimation is then used to correct the previous estimation of the speed. Simulation and experimental results confirm the goodness of the method for an extended range of speed and different load torque, and they confirm the reduction of error in transient and steady state with respect to a simple MRAS scheme without NUIO
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