• Energy Research
• 2018-2022close

This paper presents differences in calculations of annual heating and cooling energy need performed by numerical dynamic simulations software IDA ICE and those carried out by the modification of simple hourly method from EN ISO 13790 EN ISO 13790, widely used for determining building energy need. A simple model of a nearly-zero energy building was created and all heat gains and set-points that could lead to a mismatch in initial or boundary conditions were analysed. The impact of those on the annual heating and cooling energy need was examined by adding and/or removing every single one of them. Boundary conditions in numerical dynamic simulations were set up to match those in simple hourly method. Such an approach enables evaluation of differences in results and definition of their origin. The comparison of results has shown that in most cases, annual energy need for heating and cooling calculated using numerical dynamic simulations software differs from that calculated using EN ISO 13790. Among the others, more detailed heat accumulation model of heat gains in building’s envelope in IDA ICE software was marked as the main reason. Fact that solar heat gains seem to be underestimated by EN ISO 13790 and differences in heat transfer towards ground contribute to the differences in results as well.

The EN ISO 52016-1 standard presents a new simplified dynamic calculation procedure, whose aim is to provide an accurate energy performance assessment without excessively increasing the number of data required. The Italian National Annex to EN ISO 52016-1, currently under development, provides some improvements to the hourly calculation method; despite many works can be found in literature on the hourly model of EN ISO 52016-1, the National Annexes application has not been sufficiently analysed yet. The aim of the present work is to assess the main improvements introduced by the Italian National Annex and to compare the main results, in terms of energy need for space heating and cooling. To this purpose, an existing building representative of the Italian office building stock in Northern Italy was selected as a case study. The energy simulations were carried out considering both continuous and reduced operation of the HVAC systems. The options specified in the Italian National Annex were firstly applied one by one, and then all together. The variation of the energy need compared to the international base procedure is finally quantified. For the premises and the scope above discussed, the present work is intended to enhance the standardisation activity towards the adoption of more accurate and trustable calculation methods of the building energy performance.

Abstract The goal of the paper is to compare two different methods of calculating the linear transmittance of thermal bridges in order to evaluate the building energy need for heating. As a case study, it was considered an existing non-isolated residential building of ‘70 years consisting of 30 housing units. All the construction details of the building are known. The energy analysis of the building was carried out using a commercial software. The linear transmittance of the thermal bridges was determined both by the catalogue, provided by the software itself, and by the numerical finite-element evaluation according to UNI EN ISO 10211 standard using a 2-D numerical simulator. Through numerical analysis it is possible to evaluate in a detailed way all the thermal bridges present in the building and therefore it is possible to evaluate the approximation induced by the use of the catalogue. Results show that the detailed analysis leads to a transmission heat exchange through thermal bridges about eight times greater than that estimated through the catalogue and consequently to a higher building energy need of about 12%. The heating energy needs per unit area of the individual housing units were also compared.

Face aux défis énergétiques auxquels le monde est aujourd'hui confronté, la conception énergétique des bâtiments est l'un des enjeux majeurs. Le véritable défi des années à venir est sans aucun doute la réduction des besoins en énergie fossile primaire et de l'empreinte carbone dont le secteur du bâtiment est responsable d’une grande partie. Afin de garantir les performances énergétiques et apporter des solutions techniques adéquates, la prédiction de la consommation énergétique doit être de plus en plus réaliste. En l’occurrence, la modélisation thermique des bâtiments doit tenir compte des conditions intérieures et extérieures de ses environnements proches. Ce travail de recherche porte donc sur le développement d’un modèle de simulation du microclimat urbain dans le cas des rues canyons et des cours intérieures. Ce modèle est intégré dans le logiciel de simulation thermique dynamique TRNSYS 18 pour étudier l’impact de ce microclimat sur les performances énergétiques du bâtiment. Une étude bibliographique sur les modèles microclimatiques existants dans la littérature a été réalisée. Ceci a montré que le problème majeur réside dans le temps de calcul et l’interopérabilité. En effet, un modèle nodal a été développé par le langage de programmation Python et puis intégré au logiciel TRNSYS 18 pour étudier l’impact du microclimat dans le cas des rues canyons sur les performances énergétiques des bâtiments. Les résultats montrent une cohérence satisfaisante du modèle développé par rapport à des études expérimentales qui existent dans la littérature. Ce modèle a ensuite été utilisé pour effectuer une étude paramétrique dans le cas de cette typologie de rue et pour quantifier ainsi l’impact sur les besoins énergétiques de chauffage et de refroidissement des bâtiments étudiés. A l’instar du modèle précédent, un modèle zonal a été aussi développé et il porte sur la modélisation des cours intérieures dans le cas des bâtiments types « Riad ». Ce modèle a été comparé avec des simulations CFD par le logiciel ENVI-met. Les résultats obtenus ont été très pertinents. Ensuite une étude a été réalisée sur l’impact de la forme des cours intérieures et des paramètres microclimatiques sur les besoins énergétiques de ces bâtiments. En fin, un quartier type Canyon avec des bâtiments comprenant des cours intérieures situé à la ville de Tanger (Maroc) a fait l’objet d’un cas d’étude par l’application de l’ensemble des modèles développés. Les principaux résultats de ce travail de recherche dévoilent clairement la nécessité de la prise en compte du microclimat urbain pour une meilleure estimation des performances énergétiques des bâtiments. Les modèles développés et intégrés dans le logiciel TRNSYS 18 présentent donc un compromis intéressant par rapport aux logiciels existants. Il a été aussi démontré qu’il y a une forte interaction entre la conception énergétique urbaine et l’enveloppe des bâtiments. Le choix des paramètres microclimatiques peut être déterminant sur le comportement hygro-thermo-aéraulique des bâtiments. Ces modèles développés restent à la portée des ingénieurs concepteurs et des chercheurs pour les implémenter facilement dans les outils de simulations thermiques dynamiques des bâtiments. To face up to the energy challenges confronting the world today, buildings' energy design is one of the major issues. The real challenge in the coming years is undoubtedly the reduction of primary fossil energy needs and of carbon footprint in which the building sector is responsible for a large part. In order to ensure energy performance and provide adequate technical solutions, the prediction of energy consumption must be more and more realistic. In this case, buildings' thermal modelling must take into account the indoor and outdoor conditions of their surrounding environments. This research work therefore focuses on the development of an urban microclimate simulation model for canyon streets and courtyards. This model is integrated into the dynamic thermal simulation software TRNSYS 18 to study the impact of this microclimate on the building's energy performance. A bibliographic review of the existing microclimatic models in the literature has been carried out. This has shown that the major problem lies in computing time and interoperability. Indeed, a nodal model was developed using the Python programming language and then integrated into the TRNSYS 18 software to study the impact of microclimate on the buildings energy performance in the case of canyon streets. The obtained results show a satisfactory coherence between the developed model and experimental studies existing in the literature. This model was then used to carry out a parametric study in this street typology and thus quantify the impact on the heating and cooling energy needs of the studied buildings. Like the previous model, a zonal model has also been developed and it concerns the modeling of interior courtyards in the case of "Riad" type buildings. This model was compared with CFD simulations by the ENVI-met E software and the results were very relevant. Afterwards, a study was carried out on the impact of the courtyard form and microclimatic parameters on such buildings' energy needs. Finally, a Canyon-type neighborhood of buildings with courtyards located in Tangier City was the subject of a case study through the application of all the developed models. The main results of this research work clearly reveal the need to take into account the urban microclimate for a better estimation of the buildings' energy performance. The developed and integrated models in TRNSYS 18 present then an interesting compromise compared to the existing software. It has also been shown that there is a strong interaction between urban energy design and building envelope. The choice of microclimatic parameters can be a determining factor on the hygro-thermo-aerodynamic behavior of buildings. These developed models remain within the reach of engineers and researchers for easy implementation in dynamic thermal simulation tools for buildings.

Abstract Since the early 20th century, many studies have been conducted on sky temperature models and sky emissivity. These models are related to local weather conditions and specific sites. Therefore, the existing variations among the models have been an important factor for the development of new models for different locations. The existing models do not cover the whole planet even though sky temperature assessment is necessary to evaluate the net radiative heat transfers between surfaces and sky vault. So, considering building energy performance, radiative cooling and other engineering purposes, the evaluation of sky temperature is fundamental and needs to be properly accounted. This study aims at providing a critical review about the existing correlations for the calculation of sky emissivity and sky temperature, referring to different climatic conditions. Firstly, available correlations were classified and described. Some models were then applied to various significant locations all over the world to highlight differences as far as sky emissivity and sky temperatures. Subsequently, some correlations were implemented in a dynamic simulation code, to assess their influence on building annual energy needs. For this reason, a sample building was considered and the influence of different correlations on heating and cooling energy demands was investigated. The results were compared with the sky temperature values obtained by applying the standard ISO 13790, which suggests simplified correlations when the sky temperature is not available from climatic data. Comparing the analyzed models, significant deviations were found: from 10.8 °C to 19.7 °C under clear sky conditions and from 7 °C to 17.2 °C under cloudy sky conditions.

Abstract The aim of this study is to demonstrate the requirement to integrate the urban microclimate to predict the energy needs of buildings. To do this, an integrated approach in TRNSYS software was developed and compared with existing experimental results of a street canyon. Afterwards, a case study was carried out in the case of a street canyon located in the city of Tangier in Morocco. The impact of the aspect ratio on the temperature of the building surfaces and the radiation absorbed by them was examined. The results show that there is greater radiation absorption on the building facades in street canyons than on those of stand-alone buildings. These effects lead to higher surface temperatures in street canyons, resulting in increased cooling energy needs in summer and reduced heating energy needs in winter.