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• Computing the Wave-Kernel Matrix Functions

  P. Nadukandi, N. Higham

  SIAM journal on scientific computing (2018). Vol. 40 (6), pp. A4060-A4082

  
  

  Abstract

  We derive an algorithm for computing the wave-kernel functions cosh \surd A and sinhc\surd A for an arbitrary square matrix A, where sinhcz = sinh(z)/z. The algorithm is based on Pad\'e approximation and the use of double angle formulas. We show that the backward error of any approximation to cosh \surd A can be explicitly expressed in terms of a hypergeometric function. To bound the backward error we derive and exploit a new bound for \| Ak\| 1/k that is sharper than one previously obtained by Al-Mohy and Higham [SIAM J. Matrix Anal. Appl., 31 (2009), pp. 970-- 989]. The amount of scaling and the degree of the Pad\'e approximant are chosen to minimize the computational cost subject to achieving backward stability for cosh \surd A in exact arithmetic. Numerical experiments show that the algorithm behaves in a forward stable manner in floating-point arithmetic and is superior in this respect to the general purpose Schur--Parlett algorithm applied to these functions.

  Abstract
  We derive an algorithm for computing the wave-kernel functions cosh \surd A and sinhc\surd A for an arbitrary square matrix A, where sinhcz = sinh(z)/z. The algorithm is based [...]

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• Energy efficiency, indoor thermal comfort and influence of user habits in retrofitting of social housing blocks: Case study in the Metropolitan Area of Barcelona

  X. Cipriano, J. Carbonell, J. Cipriano, D. Pérez

  A quarterly newsletter of the IEA-AIVC. (2010).

  
  

  Abstract

  The Mediterranean seaside cities like the towns placed at the Metropolitan region of Barcelona have soft winters and variable summers which change from hot to very hot. Historically, summer comfort in dwellings was reached through passive cooling strategies and reducing the activity of the citizens during the hottest hours (the siesta). At the beginning of the 20th and until the building regulations appear, most of the constructed buildings were designed without any energy saving criteria, therefore, summer and winter passive were scrapped.

  Abstract
  The Mediterranean seaside cities like the towns placed at the Metropolitan region of Barcelona have soft winters and variable summers which change from hot to very hot. Historically, [...]

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• L'ús actual de l'energia solar. Aplicacions als edificis

  X. Cipriano, J. Cipriano

  L'Atzavara (2004). Vol. 12, pp. 51-60

  
  

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• Monitoring and modelling energy efficiency of municipal public buildings: case study in Catalonia region

  X. Cipriano, J. Carbonell, J. Cipriano

  International Journal of Sustainable Energy (2009). Vol. 28 (1-3), pp. 3-18

  
  

  Abstract

  Energy efficiency benchmarking can be used to monitor changes in the overall efficiency of buildings. Benchmarking models, based on energy efficiency indicators, are valuable tools for both public and private stakeholders because they allow an improvement in the building energy management. For the last decade, some governments have used these tools to define their building regulations (Santamouris, M., et al., 2005. Energy performance of residential buildings book. UK: James and James/Earthscan. ISBN: 1-902916-49-2, Chung, W., Hui, Y.V., and Miu Lam, Y., 2006. Benchmarking the energy efficiency of commercial buildings. Applied Energy, 83, 1–14). This paper tries to go further, integrating a benchmarking and a modelling process, into the same energy efficiency analysis. The connections between the energy use intensities (EUIs) and the characteristic building factors are modelled using neural network techniques. The process is divided into two stages: the data acquisition stage and the benchmarking and modelling stage. The benchmarking and modelling stage is focused on the adjustment of these EUIs within the climatic conditions (with a severity climate index method) and the development of a prediction model for calculating the relationship between these climate-adjusted EUIs and the significant factors of a building. In order to validate this methodology, an application to schools in Catalonia is presented. Additionally, the use of the artificial neural network (ANN) benchmark model for predicting potential energy savings from retrofit projects was evaluated. Some of the input variables were modified to reflect potential energy savings from a retrofit project, and the new input set was simulated with the ANN model. The preliminary results show that the developed ANN model can be used to predict energy savings from retrofit projects

  Abstract
  Energy efficiency benchmarking can be used to monitor changes in the overall efficiency of buildings. Benchmarking models, based on energy efficiency indicators, are valuable [...]

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• Design methodology for low cost tubular digesters

  J. Martí-Herrero, J. Cipriano

  Bioresource Technology (2012). Vol. 108, pp. 21-27

  
  

  Abstract

  The aim of this paper is to present a novel, universal, methodology for the design of low cost tubular digesters. This method improves on the established methodology by avoiding assumptions that tend to reduce the final hydraulic retention time (HRT) of digesters once installed. This work recommends designing the digester using trench cross-sectional area and proposes an optimization of the trench dimensions with respect to the angle of the walls and the relationship between the length of the biogas bell and the top width of the trench. The influence of the biogas pressure is considered. A simple geometrical analysis is presented that, by parameterization, can be applied in a wide range of situations.

  Abstract
  The aim of this paper is to present a novel, universal, methodology for the design of low cost tubular digesters. This method improves on the established methodology by avoiding [...]

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• An outdoor Test Reference Environment for double skin applications of Building Integrated PhotoVoltaic Systems

  J. Bloem, C. Lodi, J. Cipriano, D. Chemisana

  Energy and Buildings (2012). Vol. 50, pp. 63-73

  
  

  Abstract

  This article presents and discusses an outdoor Test Reference Environment (TRE) for double skin applications of Building Integrated PhotoVoltaic (BIPV) Systems. From the experience gained during the past 20 years in several EC research projects, an experimental tested design for a common Test Reference Environment is proposed. This outdoor test set-up allows the assessment of experimental data for electrical and thermal performance evaluation of photovoltaic systems integrated as double skin applications in the building envelope. The specific design of the Test Reference Environment makes it possible to study in a harmonised way through electrical and thermal energy flow analysis, the impact of different materials for PV modules and construction design of building envelopes. The energy balance for BIPV double skin applications is presented as well. The experimental data has been used for validation of modelling work by several academic groups which has resulted in an improved knowledge on the heat transfer, in particular the convective heat exchange coefficient for the specific double skin boundary conditions.

  Abstract
  This article presents and discusses an outdoor Test Reference Environment (TRE) for double skin applications of Building Integrated PhotoVoltaic (BIPV) Systems. From [...]

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• Modelling the heat dynamics of a monitored Test Reference Environment for Building Integrated Photovoltaic systems using stochastic differential equations

  C. Lodi, P. Bacher, J. Cipriano, H. Madsen

  Energy and Buildings (2012). Vol. 50, pp. 273-281

  
  

  Abstract

  This paper deals with grey-box modelling of the energy transfer of a double skin Building Integrated Photovoltaic (BIPV) system. Grey-box models are based on a combination of prior physical knowledge and statistics, which enable identification of the unknown parameters in the system and accurate prediction of the most influential variables. The experimental data originates from tests carried out with an air-based BIPV system installed in a Test Reference Environment. BIPV systems represent an interesting application for achieving the requirements of the EU EPBD Directive. Indeed, these systems could reduce the ventilation thermal losses of the building by pre-heating the fresh air. Furthermore, by decreasing PV module temperature, the ventilation air heat extraction can simultaneously increase electrical and thermal energy production of the building. A correct prediction of the PV module temperature and heat transfer coefficients is fundamental in order to improve the thermo-electrical production. The considered grey-box models are composed of a set of continuous time stochastic differential equations, holding the physical description of the system, combined with a set of discrete time measurement equations, which represent the data driven part. In the present work, both one-state and two-state non-linear grey-box models are considered. In order to validate the results, the residuals are analysed for white-noise properties.

  Abstract
  This paper deals with grey-box modelling of the energy transfer of a double skin Building Integrated Photovoltaic (BIPV) system. Grey-box models are based on a combination [...]

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• Approaches to evaluate building energy performance from daily consumption data considering dynamic and solar gain effects

  S. Danov, J. Carbonell, J. Cipriano, J. Martí-Herrero

  Energy and Buildings (2013). Vol. 57, pp. 110-118

  
  

  Abstract

  A method for determining the total heat loss coefficient, the effective heat capacity and the net solar gain of a building is presented. The method uses a linear regressions approach based on daily energy consumption combined with readily available meteorological data. The effective heat capacity of the building is evaluated by correlating the energy consumption and outdoor temperature changes from the previous day. The net solar gain of the building is assessed by analysing the data separated into groups by amount of daily solar irradiation. Corrected total heat loss coefficient is determined by explicitly including in the building's energy balance the accumulated heat and the solar gain. The method has been applied to the analysis of nine public buildings in Spain. An improvement of the estimated heat loss coefficient due to the corrections is observed. The effective heat capacity normalised by the building area is shown to be a useful indicator of the building operation, detecting continuous or intermittent heating. The estimated parameters in this study can enable specific benchmarking, detecting opportunities for energy savings and evaluating their potential. With the increasing implementation of smart metering technologies, the method is promising for application to the analysis of large building stocks.  

  Abstract
  A method for determining the total heat loss coefficient, the effective heat capacity and the net solar gain of a building is presented. The method uses a linear regressions [...]

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• Numerical analysis of the most appropriate heat transfer correlations for free ventilated double skin photovoltaic façades

  J. Cipriano, G. Houzeaux, D. Chemisana, C. Lodi, J. Martí-Herrero

  Applied thermal engineering (2013). Vol. 57 (1-2), pp. 57-68

  
  

  Abstract

  Double skin façades with photovoltaic integrated systems are building components which combine functions of the building envelope with electricity and thermal energy generation. The heat transfer modelling of these components, especially under free convection situations, raises a high complexity and is one of the main drawbacks for a massive dissemination of this technology. Many attempts to fill this gap have been undertaken and some mathematical correlations allowing evaluating average Nusselt numbers and air mass flow rate have been obtained in the last decades. However, very few studies faced a detailed analysis of the valid range of these mathematical expressions and of the restrictions entailed. This paper introduces a methodology to analyse the valid range of the existing mathematical correlations for the convective heat transfer coefficients and for the air mass flow rate in laminar and transition to turbulent free convection, and provides an evaluation of the effect of the asymmetry of the wall boundary conditions. A specific numerical code, based on a stabilized finite element formulation (FEM), is used to solve the incompressible Navier–Stokes equations within the air gap and to determine the accuracy of the existing heat transfer correlations. This evaluation was preceded by an extensive bibliographic research as well as a detailed validation of the physical and numerical hypothesis adopted in the finite element code.

  Abstract
  Double skin façades with photovoltaic integrated systems are building components which combine functions of the building envelope with electricity and thermal [...]

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• Evaluation of a multi-stage guided search approach for the calibration of building energy simulation models

  J. Cipriano, G. Mor Martinez, D. Chemisana, D. Pérez, G. Gamboa, X. Cipriano

  Energy and Buildings (2015). Vol. 87, pp. 370-385

  
  

  Abstract

  This paper is focused on increasing the knowledge on methods for calibrating BES models and to get more insights of different approaches for the optimization of the calibration process. The paper will be centred in the evaluation of a multistage guided search approach. It defines an iterative optimization procedure which starts with the assignment of probabilistic density functions to the unknown parameters, followed by a random sampling and running batch of simulations. It then finishes with an iterative uncertainty and sensitivity analysis combined with a re-assignment of the ranges of variation of the strong parameters. The procedure converges when no new influencing parameters are found. This method is applied to a real case study consisting of an unoccupied office building located in Lleida (Spain). The measured indoor temperature has been used to determine the uncertainty and precision of the method. The effect of the size of the sampling, the number of iterations and the parameters of the global sensitivity method are analyzed in detail. The results of this paper exemplify the degree of accuracy of multistage guided search approaches, and illustrate the reasons how these analyses can contribute to the improvement of more refined calibration methods.

  Abstract
  This paper is focused on increasing the knowledge on methods for calibrating BES models and to get more insights of different approaches for the optimization of the [...]

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