Evaluation of building envelope energy performance through extensive simulation and parametrical analysis

More than 30% of the final energy uses in the European Union are due to the building energy consumptions. In order to reduce their energy impact and improve their efficiency, the design activity has been given a large importance, both for new buildings or refurbishment projects. Moreover, besides these goals, during the last years the indoor comfort conditions have assumed a more and more relevant significance for professionals in the building design. That required the development of properly detailed instruments of analysis, such as building energy simulation tools (BES). Generally, the more complex a tool, the higher the number of required inputs but not all of them are always available in the early design stages. For this reason, BES codes have been used also to elaborate simpler models. This research analyses the possibilities given by an extensive use of the BES for the evaluation of the building envelope energy performance and some of the different issues related to BES. The first topic discussed is related to the external boundary conditions in BES, in particular the definition of a representative weather file for the description of the external environment and of the modelling of the heat transfer through the ground. The second topic analyses the problems of the validation of the results provided by BES tools and the relative accuracy introduced by the choice of a specific code. The comparison between BES software is carried out both considering the outputs of a whole thermal zone, such as heating and cooling energy needs and peak loads and the time of their occurrences, and the response of a single component (i.e., opaque walls and glazings). Finally, the coherence between the energy needs elaborated by means of BES tools and those by the quasi-steady state model presented in the technical Standard EN ISO 13790:2008 is studied and some correction factors are proposed for this simplified method

Development of sets of simplified building models for building simulation

This work proposes a method to manage the complexity of variables involved in building simulation studies and to identify groups of simplified building models suitable to have statistically significant results. The method is described by means of an applicative example, whose aim is the definition of a set of configurations appropriate for the analysis of TRNSYS and EnergyPlus discrepancies in monthly energy needs, hourly peak loads and time of occurrences of hourly peak loads – for both heating and cooling. The proposed procedure for the definition of a reference set of building configurations moves on from the selection of a set of candidate variables describing the building envelope characteristics, paying attention to implications of each choice and to cross-correlations among variables. This is obtained by means of a screening analysis with a simple statistical index (Spearman’s rank correlation coefficient). Two sample sizes are considered in order to evaluate the effects on the selection procedure. For each of the six considered outputs, the most significant group of configuration variables is identified, and the differences among those groups are described

Long term evaluation of building energy performance : comparison of the test reference year and historical data series in the North Italian climates

The pursuit of better energy performance of buildings led o the recourse to more detailed instruments of analysis, requiring more complex and detailed inputs, such as the hourly weather data. In this work, the representativeness of the test reference year (TRYEN) weather data, recently developed in Italy in accordance with the procedure proposed by EN ISO 15927-4:2005, has been studied evaluating the energy performance – energy needs and peak loads – of a set of different simplified reference buildings by means of TRNSYS simulation code, using both the TRYEN and the TRYEN source multi-year collected weather series for 5 north Italian locations. The results have been analysed by means of both descriptive and inferential statistics. The variability of energy performance has also been correlated with the envelope characteristics, in order to estimate a sensitivity of the different buildings to the weather data variability

Evaluation of building envelope energy performance through extensive simulation and parametrical analysis

More than 30% of the final energy uses in the European Union are due to the building energy consumptions. In order to reduce their energy impact and improve their efficiency, the design activity has been given a large importance, both for new buildings or refurbishment projects. Moreover, besides these goals, during the last years the indoor comfort conditions have assumed a more and more relevant significance for professionals in the building design. That required the development of properly detailed instruments of analysis, such as building energy simulation tools (BES). Generally, the more complex a tool, the higher the number of required inputs but not all of them are always available in the early design stages. For this reason, BES codes have been used also to elaborate simpler models. This research analyses the possibilities given by an extensive use of the BES for the evaluation of the building envelope energy performance and some of the different issues related to BES. The first topic discussed is related to the external boundary conditions in BES, in particular the definition of a representative weather file for the description of the external environment and of the modelling of the heat transfer through the ground. The second topic analyses the problems of the validation of the results provided by BES tools and the relative accuracy introduced by the choice of a specific code. The comparison between BES software is carried out both considering the outputs of a whole thermal zone, such as heating and cooling energy needs and peak loads and the time of their occurrences, and the response of a single component (i.e., opaque walls and glazings). Finally, the coherence between the energy needs elaborated by means of BES tools and those by the quasi-steady state model presented in the technical Standard EN ISO 13790:2008 is studied and some correction factors are proposed for this simplified method

Clustering of European climates and representative climate identification for building energy simulation analyses

This research presents a methodology to cluster weather climates with the purpose of generating homogeneous and distinct groups suitable for the selection of representative cities, to use as reference for robust generalization of building simulation findings. The proposed methodology is based on Hierarchical Clustering and Kolmogorov-Smirnov tests, applied to dry bulb temperature, water vapour partial pressure and solar irradiation data. As an example, a dataset with more than 300 European climates is analysed, a new classification is prepared and compared with the well-known Köppen-Geiger system. Results on this paper provide preliminary indications of the large potential of this approach to identify representative cities for Building Energy Simulation analyses

Analysis and improvement of the representativeness of EN ISO 15927-4 reference years for building energy simulation

Representativeness of weather inputs is crucial to limit the global uncertainty of building energy simulation results. The length of the multi-year weather data series and the methodology used for the typical month selection largely influence the results of the reference year development process. In this work, we investigate two possible modifications to the EN ISO 15927-4:2005 procedure aimed at improving the representativeness of reference year heating and cooling needs. The first modification maintains the reference years independent of their final use while the second one leads to the development of specific weather files for heating or cooling analyses by introducing weighting coefficients for the different weather parameters. The study is performed for five North Italy localities with 10 or less years in the data-set and for a sample of 48 simplified buildings. Both proposed modifications brought improvements to the representativeness of the reference year results

Analysis of the building smart readiness indicator calculation: A comparative case-study with two panels of experts

The last release of the Energy Performance of Buildings Directive 2018/844/EU stated that smart buildings will play a crucial role in the future energy systems. Consequently, the Directive introduced the Smart Readiness Indicator in order to provide a common framework to highlight the value of building smartness across Europe. The methodology for the calculation of the Smart Readiness Indicator is currently under development and therefore not yet officially adopted at the European Union level. In this context, the current research analyzed the second public release of the proposed methodology, discussing the feasibility of its implementation and the obtained results through a practical application. Specifically, the methodology was applied to a nearly zero-energy office building located in Italy, and the evaluation was carried out in parallel by two different expert groups composed by researchers and technical building systems specialists. With the aim of analyzing the impact of subjective evaluations on the calculated indicator, a two-step assessment was adopted: in a first phase the two groups worked separately, and only in a second phase they were allowed to compare results, discuss discrepancies and identify the difficulties in applying the methodology. As the main outcome of this research, a set of recommendations are presented for an effective broad implementation of the Smart Readiness Indicator, able to increase the relevance of its evaluation and effectiveness, as well as to enhance the comparability of smart readiness of buildings through the definition of benchmarks and to integrate with other measurable key indicators, especially concerning energy flexibility