Exergetic analysis of a desiccant cooling system: searching for performance improvement opportunities

The current increase of the energy consumption of buildings requires new approaches to solve economic, environmental and regulatory issues. Exergy methods are thermodynamic tools searching for sources of inefficiencies in energy conversion systems that the current energy techniques may not identify. Desiccant cooling systems (DCS) are equipments applied to dehumidifying and cooling air streams, which may provide reductions of primary energy demand relatively to conventional air‐conditioning units. In this study, a detailed thermodynamic analysis of open‐cycle DCS is presented. It aims to assess the overall energy and exergy performance of the plant and identify its most inefficient sub‐components, associated to higher sources of irreversibilities. The main limitations of the energy methods are highlighted, and the opportunities given by exergy approach for improving the system performance are properly identified. As case study, using a pre‐calibrated TRNSYS model, the overall energy and exergy efficiency of the plant were found as 32.2% and 11.8%, respectively, for a summer week in Mediterranean climate. The exergy efficiency defect identified the boiler (69.0%) and the chiller (12.3%) as the most inefficient components of the plant, so their replacement by high efficient systems is the most rational approach for improving its performance. As alternative heating system to the boiler, a set of different technologies and integration of renewables were proposed and evaluated applying the indicators: primary energy ratio (PER) and exergy efficiency. The heating system fuelled by wood was found as having the best primary energy performance (PER = 109.6%), although the related exergy efficiency is only 11.4%. The highest exergy performance option corresponds to heat pump technology with coefficient of performance (COP) = 4, having a PER of 50.6% and exergy efficiency of 28.2%. Additionally, the parametric analyses conducted for different operating conditions indicate that the overall irreversibility rate increases moderately for larger cooling effects and more significant for higher dehumidification rates. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of Time Delays in a Dynamical Heart Model

In this work, a dynamical model of the heartbeat is studied using nonlinear dynamics and considering the time delays inherent in the system. Two fixed points are associated to sustained oscillations which might be interpreted as the diastole and systole These parameters are associated with blood flow in human body called arterial pressure and are very important in the cardio-vascular diagnostic.     

AH-questionnaire: An adaptive hierarchical questionnaire for learning styles

One of the main concerns when providing learning style adaptation in Adaptive Educational Hypermedia Systems is the number of questions the students have to answer. Most of the times, adaptive material available will discriminate among a few categories for each learning style dimension. Consequently, it is only needed to take into account the general tendency of the student and not the specific score obtained in each dimension. In this context, we present AH-questionnaire, a new approach to minimize the number of questions needed to classify student Learning Styles. Based on the Felder-Silverman’s Learning Style Model, it aims at classifying students into categories in spite of providing precise scores. The results obtained in a case study with 330 students are very promising. It was possible to predict students’ learning style preference with high accuracy and only a few questions.     

Constant component of the phase voltage in ore-processing furnaces producing phosphorus and calcium carbide

For the example of phosphorus and carbide furnaces, we consider the variation of the constant component U _cc in the phase voltage of an ore-processing furnace with a closed charge hole. The magnitude and direction of U _cc depend on the reactions of the electrode with different components in the reaction zone and also on the development and combustion of the electric arc.     

Sustainability in bridge construction processes

Sustainability must be seen as a global issue. In order to achieve that goal, it is necessary to apply its principles to all industrial activities, including those that are not traditionally engaged with such guidelines, which is the case of Bridge Construction. This paper evaluates the consumption of steel and energy and the emissions of carbon dioxide due to the use of movable scaffolding systems (MSS) in the Bridge Construction industry. The values obtained considering the use of conventional MSS are compared with the ones obtained using a new sustainable technology which is herein synthetically described—the organic prestressing system (OPS). In order to compare the sustainability of the two systems, a prediction of the material and energy consumptions, and CO₂ emissions for traditional MSS and for MSS equipped with OPS is performed until 2025.     

Dead-time-compensator for unstable MIMO systems with multiple time delays

In this paper a new dead-time-compensator to deal with unstable time delay systems is presented. The result is an extension to multiple-input multiple-output systems with multiple and different time delays of a previous result already reported for single-input single-output systems. There are two key issues: the system instability and the presence of different time delays in each signal channel. The proposed approach is developed in three steps. First, a non-delayed output plant is predicted. This predictor is a stable dead-time-compensator coping with multiple and arbitrary delays in all the signal channels. Then, a stabilizer controller is easily designed for the resulting non-delayed plant. For this stabilized plant, the control performance is improved in order to achieve some output tracking and regulation requirements. The results are illustrated by two examples showing their applicability to unstable multiple-input multiple-output multi-delayed plants, which is the main novelty of the proposed approach.