1,721,032 research outputs found
Extensive Comparative Analysis Of Two Building Energy Simulation Codes For Southern Europe Climates: Heating And Cooling Energy Needs and Peak Loads Calculation In TRNSYS And EnergyPlus
Full text linkIn order to evaluate the energy performance of buildings, both in heating and in cooling periods, the simulation codes can be used. Moreover, in accordance with the technical Standard EN ISO 13790:2008, the simulation codes can be employed for refining the steady-state methods, and particularly the utilization factors estimations, in accordance with the procedure proposed. As the various simulation codes implement different capabilities and refer to different mathematical models and calculation assumptions, the necessary validation steps which are used for diagnostic purposes are not enough to ensure the agreement of the results over a wider range of configurations and conditions. The main dynamic simulation codes have been generally evaluated according to the Standard ANSI/ASHRAE 140:2007 (BESTEST). By this approach the user can choose a software among those successfully tested, giving acceptable deviations between the computed output and the reference values for a selected number of reference buildings defined in the Standard. However the number of those reference building configurations is limited and the considered features are not representative of the common building stock present for instance in Southern Europe. Moreover, as those configurations were selected for diagnostic purposes, they are expected to produce unacceptable biasing when considered with statistical approaches in order to improve the quasi steady state approaches as the one proposed in the technical standard EN ISO 13790:2008. In this work a procedure to identify the main causes of deviation has been developed and has been applied to two well-known dynamic simulation software: TRNSYS (version 16.1) and EnergyPlus (version 7). The approach is based on a factorial plan of comparison aimed to investigate the main variables related to the envelope of the building and its behavior: variations in geometry and boundary conditions (dimensions and orientation of the glazing, amount of dispersing surface) envelope characteristics (walls insulation and heat capacity, insulation and solar transmittance of glazings) internal gains. From the combination of the values of the above variables, more than 1600 different configurations have been obtained for two Italian climatic conditions, each of which providing monthly values for heating and cooling needs and for heating and cooling peak loads. Thanks to the large number of configurations, the monthly heating and cooling energy needs and peak loads have been analysed with inferential statistics, which allowed to evaluate the agreement between the outputs and to characterize the weight of the different variables in causing the deviations found
Influence of the representativeness of reference weather data in multi-objective optimization of building refurbishment
Full text linkEnergy saving measures properly applied to the existing building stock can bring noticeable savings. In particular, optimal cost-effective solutions can be found through multi-objective optimization techniques, such as those based on genetic algorithms (GA), coupled with building energy simulation (BES). Although the robustness of GA multi-objective optimizations to the quality of the inputs is discussed in the literature, the role of the weather data file is not investigated in detail. For this reason, this work analysed the extent to which the method adopted for the development of reference weather data for BES can affect the optimal solutions. Considering a group of simplified building configurations and the location of Trento, Italy, many multi-objective optimizations are performed. The results show changes to both Pareto fronts and optimal retrofit solutions
Building Simulation Applications BSA 2019 - Proceedings of 4th IBPSA-Italy conference
Full text linkUnlike the previous editions,the fourth Building Simulation Applications BSA 2019 Conference took place in June, from 19th to 21st, instead of during the winter period. For the biennial conference hosted by the Free University of Bozen-Bolzano, IBPSA Italy had to double its efforts, considering its concurrent commitment to the organization of Building Simulation 2019 in Rome. Even so, BSA 2019 featured more than 60 participants and around 130 different authors, with a significant presence of delegates from abroad and, in particular, from Austria. A different review process was introduced, with the full paper submission and review following the conference. Based on this, only 40 out of the 54 works presented during the conference in two parallel sessions were accepted for inclusion in this proceedings book
From energy signature to cluster analysis: comparison between different clustering algorithms
No full textThe energy audit on the existing buildings has become a priority in the last years, as consequence of the adoption of the European Directives about building energy efficiency. In particular, in Italy, public buildings are often the most inefficient ones among the stock and, thus, those with the highest potential for improvements. Many methods can be applied to perform an energy diagnosis; one of them is “Energy Signature” simplified method, ES, described in the Annex B of the technical standard EN 15603:2008. The ES can actually be seen as a very simplified model of the building, based on a linear regression between energy consumption and degree days in a set of reference periods. If applied year after year, the ES allows a fast detection of system faults, changes of use pattern, and to assess the efficacy of different energy management strategies or retrofitting interventions, discounting the effect of weather variations. When the stock of buildings is large, individual energy audits can be too much onerous and time consuming and building simulation impracticable. For this reason, ES can be combined with clustering techniques in order to identify groups of buildings with similar behaviour among which a reference cases can be identified and deeply investigated either experimentally or through detailed building simulation (BS). In this respect, ES and clustering can be seen as the key element to allow the extension of BS also to the analysis of building stocks. In this work, ES and different clustering techniques have been used to analyse a set of 41 schools in the province of Treviso, north of Italy, pointing out the buildings features most affecting their energy signatures through multiple linear regressions. A comparison between two non-hierarchical clustering algorithms, K-means and K-medoids, has been conducted. Particular attention has been paid to the approaches for the evaluation of closeness of schools in the same group and the identification of the reference school for each set. As final outcome of this research, the impact of the clustering algorithms is discussed, in order to assess to which extent the selection of the schools with the most representative energy signatures can be affected by the choice of the data mining techniques
Numerical and experimental analysis on poultry freezing time
No full textCooling and freezing food is one of the most widely discussed topics in the refrigeration literature. Some semi-empirical models have been proposed to estimate the total freezing time but the achievable results can be significantly different depending on the model used. This paper focuses on the freezing time of poultry
products. Thanks to a calibrated numerical approach, this paper intends to assess some classic semi-analytical models commonly used to evaluate the food freezing time, whose accuracy relies on some empirical parameters obtained by curve-fitting experimental data. In this work, some original experimental data on packed poultry samples are collected. Afterwards, a numerical 3D model is calibrated against the experimental results. Then the numerical procedure is adapted and used to carry out a comparison between some existing models for infinite slab geometry and to investigate the effect of the sample dimension
Robustness of multi-objective optimization of building refurbishment to solar radiation model
No full textThe energy saving potential of existing buildings in highly urbanized world areas stimulates interest in the introduction of renovation measures. Due to the high economic impact of those interventions, special attention has to be paid to balance energy and economic
performance, leading to the definition of the best combination through multi-objective approach. The recourse to building simulation, to improve the resolution and discrimination capability between different renovation configurations, forces us to consider the quality of the input data and leads to robustness issues for the optimal solution. In this regard, a reliable estimation of the global irradiation incident on various tilted surfaces is essential in order to account for the solar heat gains. Nonetheless, many meteorological stations
monitor only global solar radiation on a horizontal plane. As a consequence, a variety of mathematical and empirical models have been proposed in the literature for both the subdivision of horizontal solar irradiation into direct and diffuse components and for the calculation of irradiation on tilted surfaces. Besides introducing intermodal uncertainty, no pair of diffuse and tilt irradiation models can provide results with the same reliability for worldwide localities different from those considered for the definition of each model.
This research work investigates the extent to which the choice of solar irradiation models affects the confidence levels of the optimal solutions provided by multiobjective optimizations. With this purpose, several multiobjective optimizations are carried out with different solar irradiation models. Semi-detached houses, penthouses and intermediate flat in multi-storey buildings are analyzed with the purpose of broadening the representativeness of the conclusions
Thermal dynamic transfer properties of the opaque envelope: Analytical and numerical tools for the assessment of the response to summer outdoor conditions
No full textThe reliable estimation of buildings energy needs for cooling is a crucial issue in the implementation of the EPB Directive 2010/31/EU (formerly 2002/91/EC), especially in central and southern Europe climates. On this purpose one of the main topics is to predict the behavior of the opaque envelope subjected to variable boundary conditions. The EN ISO 13786:2007 technical standard assumes sinusoidal boundary conditions and introduces dynamic thermal characteristics. The aim of this paper is to assess the deviation arising by the use of different approaches for the calculation of the dynamic thermal characteristics of an opaque envelope element under periodic non sinusoidal boundary conditions. The EN ISO 13786 procedure has been firstly applied by decomposing the external forcing temperature by means of the Fast Fourier Transform (FFT) analysis. A comparison with different approaches, such as Finite Difference Methods (FDM) and Transfer Function Methods (TFM), has been carried out. The predictions of the EN ISO 13786 with a sinusoidal forcing temperature (i.e., standard approach) have also been assessed, comparing the results to the ones obtained through the FFT analysis. Furthermore, corrections to the periodic thermal transmittance and to the time shift have been proposed, in order to improve the explicative worth of those parameters
Impact of solar irradiation models on building refurbishment measures from multi-objective optimization
Full text linkThe European energy regulations encourage the refurbishment of existing buildings in order to ensure a reduction of the energy use. The choice of the optimal solutions is actually a trade-off problem between conflicting goals. For this reason, multiobjective optimization techniques can be coupled with building energy simulation (BES). However, even if validated BES codes are used, some discrepancies arise due to the accuracy of implemented models, such as those related to the elaboration of solar irradiation profiles. This research work investigates the extent to which the choice of solar irradiation models can affect the robustness of the Pareto front for several building configurations in two Italian climates. The results highlight the building characteristics reducing the robustness of Pareto front solutions. Nonetheless, the analysis shows a low sensitivity of cost and energy optimal solutions to the uncertainty introduced by solar models
Assessment and Mapping of the Urban Heat Island Effect: A Preliminary Analysis on the Impact on Urban Morphology for the City of Turin, Italy
No full textUrban Heat Island (UHI) effects, intensified by growing urbanization, significantly impact thermal comfort and energy demand in cities. To accurately model these effects in building performance and urban energy simulations, precise weather data and boundary conditions are essential. Although weather stations in city centers are increasingly used to develop typical meteorological years, they often fail to capture the microclimate variations across urban areas. New tools and methods are thus needed to help building professionals and municipalities assess UHI severity, use more representative weather data, and evaluate the impact of buildings on the urban microclimate. Among available tools for UHI impact assessment, Computational Fluid Dynamics (CFD) models offer detailed analysis but are computationally intensive and impractical for largescale, year-round studies. Conversely, equivalent RC networks are more computationally efficient but still require extensive inputs, limiting their widespread use in large cities. This research introduces a new workflow using correlations to estimate UHI effects from rural weather data. The MIT Urban Weather Generator (UWG) was used to simulate UHI in representative districts, with the results employed to develop correlations for mapping local microclimates across urban areas. The proposed methodology is preliminary applied to the Italian city of Turin, focusing primarily on the correlation between urban morphology and the UHI phenomena (i.e., paying attention to those variables with the most significant effects on the local urban microclimate, according to the literature). The UHI impact has been quantified in terms of differential heating and cooling degree-days with respect to the rural environment. Results prove that with a training set of about 5 % of the city, modelled in detail with UWG, developed correlations appear robust enough to describe the phenomenon for residential districts of Turin
From Energy Signature To Cluster Analysis: An Integrated Approach
Full text linkEnergy audits of existing buildings are especially important in the case of public buildings and in particular in the case of schools, where a more efficient use of energy implies unquestionable benefits to public budgets. Schools audit can drive public administrator to better address retrofit investments facilitating the choices of energy efficiency measures in the renovation or operation phase. However, energy audit of existing buildings can be onerous when the number of buildings is large and requires extensive monitoring campaigns, field surveys and energy performance calculation. A simplified method for building energy diagnosis is the Energy Signature (ES) method described in annex B of standard EN 15603:2008. According to this approach heating and cooling energy uses of a given building are correlated to climatic data over a suitable period. Plotting for several time periods the average heating or cooling power versus average external temperature provides useful information on building energy performance and allows fast detection of malfunctions or of changes on the building operation/features, as well as the verification of the efficacy of any retrofit intervention. Although the method is preferably adopted for constant internal temperature, as in the case of fixed temperature set-point, and when external temperature is the most influential parameter, as for buildings with stable internal gains and relatively low passive solar gains, it can be applied recording energy use for heating or cooling, and accumulated temperature difference between indoor and outdoor, at average regular intervals. These intervals can be as small as one hour, but for manual monitoring, a week is often used. The ES is the best fitting linear regression between energy use and external temperature or cumulated temperature differences. Thus, intercept and slope are the two characteristic parameters of the specific ES of a building. In this paper, the building energy signature parameters have been used to analyze a large set of school buildings and to define the characteristics most influential on the energy needs. In particular, the weekly energy consumption for heating of a set of 60 school buildings located in the province of Treviso, North East of Italy, have been considered. A cluster analysis based on multiple regression has then been used to identify the buildings subsets homogeneous as for the features affecting the signature parameters. Each cluster has then been analyzed in order to customize the best retrofit measures combination and the potential energy savings
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