Frederick University

Nicosia, Cyprus

Frederick University

Nicosia, Cyprus
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Fyrillas M.M.,Frederick University
Heat Transfer Engineering | Year: 2017

We address the two-dimensional heat conduction problem due to a periodic array of isothermal pipes buried in a conductive medium. The upper surface of the medium is subjected to convection with a uniform heat transfer coefficient, and the lower surface is insulated. Similar to the concept of critical thickness associated with a slab embedded with isothermal strips, we show that there exists a critical depth such that the heat transfer rate is maximized. As the Biot number tends to infinity, the critical depth approaches zero for a single pipe buried in a semi-infinite medium. For a periodic array of isothermal pipes, there is also a critical Biot number beyond which the critical depth is zero. Furthermore, insulating the pipes reduces the critical depth, and the heat transfer rate does not vary significantly with respect to the depth. © 2017 Taylor & Francis Group, LLC

Kylili A.,Frederick University | Fokaides P.A.,Frederick University | Christou P.,Frederick University | Kalogirou S.A.,Cyprus University of Technology
Applied Energy | Year: 2014

Infrared thermography (IRT) has met an extensive popularity among the non-destructive technologies for building diagnostics, especially with the increasing concerns of energy minimisation and low energy consumption of the building sector. Its popularity for a broad range of applications can be attributed to its non-contact safe nature, its usefulness and effectiveness, as well as the energy and cost savings it can achieve. This paper reviews the state-of-the-art literature and research regarding the passive and active infrared thermography. The fundamentals of IRT are thoroughly explained and the thermographic process for building diagnostics is presented. This work also presents the fields of applicability of IRT with a focus on the building sector, as well as the advantages, limitations and potential sources of errors of IRT employment. Additionally previous non-destructive testing (NDT) studies that employed passive, active pulsed, and active lock-in thermographies for building diagnostics are presented. A review of the thermal image analysis methods and the future trends of thermal imaging are also included in this work. It can be concluded that while IRT is a useful tool for the characterisation of defects in the building sector, there is great prospect for the development of more advanced, effective and accurate approaches that will employ a combination of thermography approaches. © 2014 Elsevier Ltd.

Fokaides P.A.,Frederick University | Papadopoulos A.M.,Aristotle University of Thessaloniki
Energy and Buildings | Year: 2014

The establishment of a methodology for the calculation of the cost-optimal insulation thickness of building elements has been a subject of interest for some years. Many studies have been conducted on the ideal insulation thickness and been based on specific assumptions and approaches. The introduction of the Energy Performance of Buildings Directive recast (2010/31/EC) in May 2010, leads to the compulsory implementation of a specific methodology for this purpose by all European Union member states (Article 5, EPBD recast). Therefore, a study on this subject was conducted, to evaluate the results of previous studies and the strengths and weaknesses of the previous methodologies and to determine how the methodologies should be further developed to provide more reliable results. Additionally, a derived model was validated by a parametric study that examined all possible aspects that could potentially affect the end results. The minimum requirements of the insulation thickness for three selected European cities were also compared to the results of the proposed model applied to these cities. The results show that the proposed model provides a better compromise between simplicity and accuracy, leading at the same time to significantly lower U-values and therefore to improved energy efficiency of the buildings. © 2013 Elsevier B.V. All rights reserved.

Charalambous C.,Frederick University | Fleszar K.,American University of Beirut
Computers and Operations Research | Year: 2011

A new heuristic algorithm for solving the two-dimensional bin-packing problem with guillotine cuts (2DBPG) is presented. The heuristic constructs a solution by packing a bin at a time. Central to the adopted solution scheme is the principle of average-area sufficiency proposed by the authors for guiding selection of items to fill a bin. The algorithm is tested on a set of standard benchmark problem instances and compared with existing heuristics producing the best-known results. The results presented attest to the efficacy of the proposed scheme. © 2010 Elsevier Ltd. All rights reserved.

Kylili A.,Frederick University | Fokaides P.A.,Frederick University
Sustainable Cities and Society | Year: 2015

The European "Smart Cities & Communities Initiative" of the Strategic Energy Technology Plan (SET-Plan) supports cities and regions in taking ambitious measures to progress by 2020 towards a 40% reduction of greenhouse gas emissions through sustainable use and production of energy. This initiative aims to pool resources to support the demonstration of energy, transport and information and communication technologies in European urban areas. In this effort, the zero energy buildings (ZEB) are expected to play a crucial role. The main objective of this paper is to present the potential contribution of the ZEB principle towards achieving smart cities in Europe. In terms of this study, the evolution of building standards towards the ZEB concept will be presented, followed by discussions regarding the provisions of a SET-Plan smart city and the ZEB definition. Additionally, past studies discussing on the role of zero energy buildings in smart energy regions will also be reviewed. The conclusions of the analysis on the potential of ZEBs in SET-Plan smart cities will provide some useful insight towards the actions required in the building assessment methodologies' developments, in order to achieve the envisioned smart cities in Europe. © 2014 Elsevier Ltd. All rights reserved.

Papadakis A.P.,Frederick University
Journal of Plasma Physics | Year: 2013

The streamer propagation in point-plane, non-uniform gaps under high applied electric fields, prior to the impact of primary streamer on cathode, is analyzed. The configuration used is an anode hyperboloid with 50-μm radius of curvature, and a flat plate as the cathode. The applied voltage is 130-kV direct current, and an initial electron is assumed to exist close to the anode in ambient air. The geometry used is a two-dimensional axisymmetry with a gap of 5 cm between the anode and the cathode. It is shown that the streamer is formed on the anode tip as expected, and midway toward the cathode, it separates into two streamers, the primary streamer that continues its propagation toward the cathode, and the branched streamer expanding radially toward the outer boundaries. The qualitative behavior of the discharge is analyzed in terms of streamer speeds, radial and axial electric fields, charged particle densities, and conductive currents. A branched streamer plasma structure was observed along the path of the primary plasma structure expanding radially outwards. Copyright © 2012 Cambridge University Press.

Fokaides P.A.,Frederick University | Kylili A.,Frederick University
Energy Policy | Year: 2014

Grid parity is defined as the threshold at which a grid-connected renewable energy sources (RES) system supplies electricity to the end user at the same price as grid-supplied electricity. Predictions from the 2006 time-frame expected retail grid parity for solar in the 2016 to 2020 era, but due to rapid downward pricing changes, more recent calculations have forced dramatic reductions in time scale, and the suggestion that solar has already reached grid parity in a wide variety of locations. This study presents aspects of achieving grid parity in insular energy systems, based on a case study applied in Cyprus. The analysis presents the variation of the manufacturing cost, the selling price of the produced energy, and the performance of the solar panels to examine the conditions of accomplishing grid parity event. It is also concluded that grid parity may be easier achieved in insular energy systems due to the higher cost of primary energy. © 2013 Elsevier Ltd.

Panaoura A.,Frederick University
Computers in Human Behavior | Year: 2012

The present study investigates the improvement of students' mathematical performance by using a mathematical model through a computerized approach. We had developed an intervention program and 11 years students worked independently on a mathematical model in order to improve their self-representation in mathematics, to self-regulate their performance and consequently to improve their problem solving ability. The emphasis of using the specific model was on dividing the problem solving procedure into stages, the concentration on the students' cognitive processes at each stage and the self-regulation of those cognitive processes in order to overcome cognitive obstacles. The use of the computer offered the opportunity to give students general comments, hints and feedback without the involvement of their teachers. Students had to communicate with a cartoon animation presenting a human being who faced difficulties and cognitive obstacles during problem solving procedure. Three tools were constructed for pre- and post-test (self-representation, mathematical performance and self-regulation). There were administered to 255 students (11 years old), who constituted the experimental and the control group. Results confirmed that providing students with the opportunity to self-reflect on their learning behavior when they encounter obstacles in problem solving is one possible way to enhance students' self-regulation and consequently their mathematical performance. © 2012 Elsevier Ltd. All rights reserved.

Fyrillas M.M.,Frederick University
International Journal of Heat and Mass Transfer | Year: 2010

We address the problem of two-dimensional heat conduction in a solid slab embedded with a periodic array of isothermal pipes of general cross-section. The objective of this work is two-fold: to develop a numerical procedure through which we can obtain the shape factor associated with a given configuration and, to develop a numerical shape optimization algorithm through which we can compute shapes that extremize the transport rate. The shape factor is obtained by first transforming the periodic array of pipes into a periodic array of strips using the generalized Schwarz-Christoffel transformation and, subsequently, by developing an integral equation of the first kind for the temperature gradient using the boundary element method. The integral equation is solved both numerically and analytically/asymptotically with excellent agreement between the results. The shape optimization problems, which are formulated with respect to the parameters of the generalized Schwarz-Christoffel transformation, are solved numerically to compute the shape that maximizes the cross-sectional area and the shape that minimizes the perimeter of the cross-section, given the shape factor and the distance between two consecutive pipes. It is inferred that the problems are adjoint to the transport rate minimization and transport rate maximization problems, respectively. The optimal shapes are computed numerically and validated with available analytical and numerical results for a single pipe. Furthermore, motivated by the analytical result, we propose a parametric set of equations that describe well the optimal shapes. The versatility of the Laplace equation suggests that similar formulations have applications in continuum mechanics, electricity, hydraulics and drug reduction. © 2009 Elsevier Ltd. All rights reserved.

Papadopoulos H.,Frederick University | Haralambous H.,Frederick University
Neural Networks | Year: 2011

This paper proposes an extension to conventional regression neural networks (NNs) for replacing the point predictions they produce with prediction intervals that satisfy a required level of confidence. Our approach follows a novel machine learning framework, called Conformal Prediction (CP), for assigning reliable confidence measures to predictions without assuming anything more than that the data are independent and identically distributed (i.i.d.). We evaluate the proposed method on four benchmark datasets and on the problem of predicting Total Electron Content (TEC), which is an important parameter in trans-ionospheric links; for the latter we use a dataset of more than 60000 TEC measurements collected over a period of 11 years. Our experimental results show that the prediction intervals produced by our method are both well calibrated and tight enough to be useful in practice. © 2011 Elsevier Ltd.

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