•A quantitative internal IRT method for determining in-situ U-values is proposed.•It can be used for both existing and new building envelopes.•The deviation (1–4%) was found to be smaller than that ...of alternative IRT methods.•The execution time was shorter than that of other methods for determining U-value.
The thermal behaviour of a building is often underestimated or neglected during its construction and operation stages. In recent years, the heat flux meter (HFM) method has been commonly used to determine the U-value, a key parameter for assessing the thermal quality of the building envelope in steady-state conditions. However, this non-invasive test takes at least 72h to execute, the accuracy is 14–28%, and it is not reliable for non-homogeneous building elements. An alternative technique is based on infrared thermography (IRT). Although it is generally used for qualitative analysis, quantitative internal IRT methods may also be adopted for in-situ measurement of the U-value. This research presents a method for determining in-situ U-values using quantitative internal IRT with a deviation of 1–2% for single-leaf walls and 3–4% for multi-leaf walls. It takes 2–3h and can be used to provide information about the building envelope for the future refurbishment of existing buildings or to check the thermal behaviour of new building façades according to their design parameters.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Building energy policies play a key role in reducing energy consumption in the EU building sector towards climate neutrality goals. This study conducts a comparative analysis of building regulations ...across EU Member States, with a focus on the building envelope efficiency. It examines thermal transmittance limits for windows, walls, floor, and roof to highlight regulatory differences and propose ways to improve harmonization. Challenges arise from the lack of a centralised data source, needing reliance on national regulations and similar studies to fill gaps and increase compliance with the Energy Performance of Buildings Directive (EPBD). Integrating data from various sources, including national reports and scientific literature, the study clarifies the current regulatory landscape for new and existing buildings, stressing the importance of improving the efficiency of the building envelope to minimise energy losses, and includes national climate zones for comprehensive coverage of regional climates. Variability in regulations underlines the need for a higher uniformity. Suggested steps include the development of a unified climate zone system, the establishment of guidelines for each zone, and the definition of harmonized thermal transmittance limits to facilitate a consistent regulatory framework. While this study focuses primarily on thermal transmittance, it provides a basis for future research efforts to address differences in European building codes and progress towards climate neutrality. Future developments could include the analysis of additional parameters to provide a holistic view of building energy performance and regulations supporting sustainability goals in the EU.
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•Envelope requirements are determinant to achieve climate neutrality in Europe.•High variability characterizes building energy requirements across Member States.•Climate-consistent thermal transmittance limits can increase energy savings in buildings.•Targeted guidance is required for establishing interventions on the envelope.•Harmonization of envelope requirements aid compliance with European regulations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•U-value estimation is crucial for energy diagnosis of existing buildings.•Heat flux meter method allows in situ measurements of actual U-value.•In situ measurements of U-value can be affected by ...some relevant metrological issues.•Uncertainties of in situ measurements of U-value depend on operative conditions.
Energy audits and check of energy performances are more and more urgent for achieving energy saving in existing buildings. In this context, it is very important to estimate U-value of buildings and, to this aim, different approaches are available. U-value is mainly estimated from the knowledge of thermal properties of the single layers of the wall using design data or analogies with similar buildings. To get a more accurate estimation, field analyses should be made like endoscopic investigation or logs. Nowadays, also in situ measurement of U-value using heat flow meters are available. Such measurements involve quite simple operational and calculation issues but, on the other hand, the disadvantage of long duration times and not negligible measurement uncertainties. In this paper, the authors present the results of an experimental campaign aimed both to assess the metrological performance of HFMs and to evaluate the influence of the ambient conditions. Furthermore, in situ U-values have been compared with the estimated ones from design data and field analyses. The results of the test show a good behavior of HFMs when tests are conducted according to ISO 9869. Nevertheless, operative measurement conditions and characteristics of the envelope component under investigation can strongly affect in situ U-value accuracy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper reviews the main energy-related features of building-integrated photovoltaic (BIPV) modules and systems, to serve as a reference for researchers, architects, BIPV manufacturers, and BIPV ...designers. The energy-related behavior of BIPV modules includes thermal, solar, optical and electrical aspects. Suitable standardization to evaluate heat transfer and solar heat gain by BIPV modules still need to be developed further since BIPV elements behave differently to the building elements they substitute. The optical properties of BIPV modules, such as light transmittance or color rendering, also play a role in the search for a good balance between energy saving, electricity generation, aesthetics and visual comfort. However, architecturally adapted BIPV design may affect the electrical performance also, by reducing the efficiency of BIPV modules and systems compared to standard photovoltaic (PV) ones. This is not the sole challenge for the electrical designers, as the special operating conditions of BIPV systems such as non-homogeneous irradiance complicate the electrical design and the forecasting of BIPV performance. The aim of this review is to present the current state of knowledge of the aspects mentioned above, to promote continued progress in BIPV and to inform suitable standardization efforts.
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•Ideal U-values for 2050 climate projection in the Mediterranean region are determined.•Current well insulated buildings are not prone to overheating in the future.•In the future, ideal U-values are ...similar or even lower than current ones.•Casablanca is the only location presenting an overheating risk.•The increase of cooling demand will overcome the heating demand decrease.
One of the effects of climate change is global warming, which will increase cooling demand in buildings. However, scientific literature does not show consensus on the risk of highly insulated buildings being prone to overheating. This paper presents a statistical comparison of two synthetic datasets for current and future climates in sixteen Mediterranean locations. The weather data for the 2050 climate projection was generated by ‘morphing’ current weather data. The buildings were created using a generative design method to produce random geometries and random U-values for the envelope elements. Energy performance was evaluated using dynamic simulation. In addition to the expected general increase in cooling demand (up to 137 %) and a smaller reduction in heating demand (up to 63 %), the results demonstrate that the ideal U-values used in the current climate in almost all of the locations will not cause overheating. In several cases, the decrease of the U-values is even recommended for Podgorica, Valencia, Tunis, Malaga, Larnaca, and Alexandria, as the reduction of heating demand compensates the increase of cooling demand. Casablanca was the only location showing an increase in the ideal U-values, thus presenting risk of overheating if using current ideal U-values.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
► The paper studies the performance of innovative aerogel glazings. ► The monolithic is better than granular one for light transmittance, thermal insulation. ► High solar factor values are kept in ...aerogels windows. ► Monolithic aerogel glazings can achieve U-values lower than 0.5Wm−2K−1. ► Aerogels are suitable in daylighting also thanks to good colour rendering.
Innovative glazing systems with silica aerogel in interspace were investigated for energy saving in buildings. Aerogel is a promising transparent insulating material, due to its low thermal conductivity (down to 0.010Wm−1K−1), high solar factor, high daylight transmittance and remarkable lightweight. Four samples were constructed with float and low-e glasses and granular or monolithic aerogel in interspace (14mm thickness). The main optical characteristics of the samples were measured, in order to estimate the light transmittance τv, the solar factor g and the colour rendering index Ra, in compliance with EN 410/2011. Finally, the thermal transmittance was calculated. The monolithic aerogel glazings showed the best performance with respect to granular systems, both for light transmittance (0.62 between two 4mm float glasses) and thermal insulation (0.6Wm−2K−1). The solar factor was 0.74. Results showed a very promising behaviour of aerogel windows when compared to the windows normally used in Italy and in EU countries: monolithic aerogel between two 4mm float glasses gave a 62% reduction in heat losses, with a 17% reduction in light transmittance when compared to a double glazing with a low-e layer; a high solar factor and colour rendering were also assured.
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•Estimation of U-value by means of artificial neural network.•The model developed does not need a data post-processing.•Representative results for all the building periods considered.
Most of the ...existing building stock has a deficient energy behaviour. The thermal transmittance of façades is among those aspects which most affect this situation. In this paper, the calculation procedure with correction for storage effects from ISO 9869-1 was applied to the thermometric method to determine the U-value. Due to the need for determining the number and type of layers that compose the wall to apply the calculation, a multilayer perceptron has been developed to estimate the U-value. From the different model configurations suggested, the most adequate architecture was the one with 14 nodes in the hidden layer without making transformations in the input variables. Valid results have been obtained by the multilayer perceptron for the case studies analysed from different building periods, with deviations lower than 20% between the measured value and the expected one, varying the test duration according to the thermal resistance of the wall and the temperature variations. Furthermore, it is not necessary to carry out a data post-processing for the model, so this fact simplifies and hastens the calculation procedure.
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Reducing the energy requirements of buildings is essential in order to address anthropogenic global warming. Among the various factors affecting the energy requirements of buildings, the thermal ...transmittance of the walls is critical in understanding heat loss. It is therefore necessary to assess the thermal transmittances carefully in order to develop effective means of energy conservation. Although various theoretical methods and methods using in situ measurements are available for this purpose, the correct use of such methods depends on many factors. In a detailed review of more than 150 publications (scientific papers, congress reports, books, and other documents), the best-developed methods in use by researchers and professionals are analysed. These methods are as follows: the theoretical method, the heat flow meter method, the simple hot box-heat flow meter method, the thermometric method, and the quantitative infrared thermography method. This review is intended to be a useful resource for researchers and professionals in that it covers the fundamental theoretical background, the equipment and material required for in situ measurements, the criteria for installing the equipment, the errors caused by metrological and environmental aspects, data acquisition, data processing, and data analysis.
•Theoretical fundamentals of assessment methods of thermal transmittance.•Analysis of the benefits and limitations of the different assessment methods.•Acquisition, post-processing and data analysis for the different methods.
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•Robust procedure for the use of quantitative thermography to evaluate thermal transmittance on site.•Comparison between walls with different thermal capacity and mass per unit area.•Sensitivity ...analysis to define parameters of significance for the results accuracy.•Influence of weather conditions during and prior to the monitoring on expected outputs.•Comparison between values achieved through ITT, international standard approach and HFM method.
Quantitative thermography is now mostly accepted as a reliable method to measure energy performance of existing buildings, in particular the thermal transmittance U-values of opaque elements. Some researches have been conducted in this field, each presenting a different procedure verified by the application on simple case studies. Anyway, a comprehensive approach, based on a parametric analysis of walls with different typologies and exposure, but same boundary conditions, is still missing. This study proposes a systematic approach to the problem, based on a three years research activity carried on an experimental building where timber (light) and brick (heavy) structures were tested simultaneously with Infrared Thermovision Technique (ITT), also equipped with heat flow meter (HFM) sensors and a nearby meteo station. Standard deviation of U-values measured with ITT is given as well as absolute deviation against values calculated following international standards and measured with HFM method. Parameters having high significance for the achievement of good results compared to the expected U-values are assessed through a sensitivity analysis. Influence of weather conditions during the survey are also considered and a repeatable procedure is finally set up. The findings presented in the study show that the method gives good results for heavy constructions, while further studies are still needed for light and super-insulated walls.
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