Dario Ambrosini received his degree in electronic engineering in 1993 from the Sapienza University of Rome (Italy). His research interests include flow visualization, heat and mass transfer, NDT, optical metrology, thermography, and building physics. He is a member of UIT (Italian Union of Thermal-Fluid Dynamics), OPTICA (The Optical Society), Sigma Xi, and SPIE (The International Society for Optics and Photonics). In 2013 he was designated a Senior Member of both OSA and SPIE. He was named a Fellow Member of SPIE in 2019 and of OPTICA in 2023. He is an Associate Editor of the journal Optics and Lasers in Engineering (Elsevier).
This work contains an overview of infrared thermography (IRT) method and its applications relatin... more This work contains an overview of infrared thermography (IRT) method and its applications relating to the investigation of architectural structures. In this method, the passive approach is usually used in civil engineering, since it provides a panoramic view of the thermal anomalies to be interpreted also thanks to the use of photographs focused on the region of interest (ROI). The active approach, is more suitable for laboratory or indoor inspections, as well as for objects having a small size. The external stress to be applied is thermal, coming from non-natural apparatus such as lamps or hot / cold air jets. In addition, the latter permits to obtain quantitative information related to defects not detectable to the naked eyes. Very recently, the hybrid thermography (HIRT) approach has been introduced to the attention of the scientific panorama. It can be applied when the radiation coming from the sun, directly arrives (i.e., possibly without the shadow cast effect) on a surface exposed to the air. A large number of thermograms must be collected and a post-processing analysis is subsequently applied via advanced algorithms. Therefore, an appraisal of the defect depth can be obtained passing through the calculation of the combined thermal diffusivity of the materials above the defect. The approach is validated herein by working, in a first stage, on a mosaic sample having known defects while, in a second stage, on a Church built in L’Aquila (Italy) and covered with a particular masonry structure called apparecchio aquilano. The results obtained appear promising.
Several studies and correlations for the convective heat transfer coefficient (CHTC) are availabl... more Several studies and correlations for the convective heat transfer coefficient (CHTC) are available in literature and in handbooks, depending on type of convection, wind speed range or on the test rigs from which they are derived. The importance of accurate evaluation of CHTC, especially at the building façades, has been highlighted in the recent years, due to the need for reliable measurement of buildings’ heat transfer capability. This study aims at underlining the importance of proper CHTC values for the determination of the building envelope thermal transmittance (U-value) via infrared thermography (IRT). To this scope, firstly an overview on convective heat transfer coefficient is given; then, some CHTC models, chosen from literature, are analyzed at different wind speed classes. Subsequently, such models are employed in two formulas proposed in literature for the U-value measurement via IRT, by using data from previous experimental campaign carried out in controlled environment. Results were compared, and significant deviations were found: one of the employed approaches and formulation is less sensitive to the correlation adopted for the convection expression, amongst those considered and in the wind speed range analyzed. This constitutes an advantage, since one of the weak points of the IRT method is the convection expression itself.
Physical access to historic and artistic manufactures can be limited by a lot of factors. In part... more Physical access to historic and artistic manufactures can be limited by a lot of factors. In particular, the access to the collection of the ancient coins is difficult, especially for students. Indeed, for coins digital archive of high quality three-dimensional model and remote fruition is of great interest. In this work we propose 3D acquisition and digitizing techniques for the virtualized reality of ancient coins (virtual gallery). The system used for creating 3D shape of coins is based on conoscopic holography. This technique is a non-contact three-dimensional measuring technique that makes possible to produce holograms, even with incoherent light, with fringe periods that can be measured precisely to determine the exact distance to the point measured. It is suitable to obtain 3D profile with high resolution also on surface with unevenness reflectivity (this situation is usual on the surface of the ancient coins). By conoscopic holography, high-resolution 3D model can be obtained. However, accurate representation and high-quality display are fundamental requirements to avoid misinterpretation of the data. Therefore, virtual galleries can be obtained through a procedure involving 3D acquisition, 3D model and visualization. In conclusion, we propose an optoelectronic application, integrated with multimedia techniques, in order to improve the access to collection of ancient coins belonging to museums or privates.
The aim of this work is to create an automatic monitoring system for photovoltaic plant using an ... more The aim of this work is to create an automatic monitoring system for photovoltaic plant using an active load. This system is able to monitor photovoltaic panels connected in a string thanks to a switching circuit that disconnects and reconnects them. With the MOSFET active load, it is possible to reconstruct the IV characteristic of the panel concerned through current and voltage measurements. Furthermore, the system is powered by an energy harvesting circuit, making it autonomous. The proposed system is based on a SamD21G microcontroller that manages switching circuits, current and voltage measurement and generates the control signal for the MOSFET via a 12-bit DAC. The complete system is described in its parts and simulated with Spice.
In the last years, the importance of integrating the production of electricity with the productio... more In the last years, the importance of integrating the production of electricity with the production of sanitary hot water led to the development of new solutions, i.e. PV/T systems. It is well known that hybrid photovoltaic-thermal systems, able to produce electricity and thermal energy at the same time with better energetic performance in comparison with two separate systems, present many advantages for application in a residential building. A PV/T is constituted generally by a common PV panel with a metallic pipe, in which fluid flows. Pipe accomplishes two roles: it absorbs the heat from the PV panel, thus increasing, or at least maintaining its efficiency; furthermore, it stores the heat for sanitary uses. In this work, the thermal and electrical efficiencies of a commercial PV/T panel have been evaluated during the summer season in different days, to assess the effect of environmental conditions on the system total efficiency. Moreover, infrared thermographic diagnosis in real time has been effected during the operating mode in two conditions: with cooling and without cooling; cooling was obtained by natural flowing water. This analysis gave information about the impact of a non-uniform temperature distribution on the thermal and electrical performance. Furthermore, measurements have been performed in two different operating modes: 1) production of solely electrical energy and 2) simultaneous production of thermal and electrical energy. Finally, total efficiency is largely increased by using a simple solar concentrator nearby the panel.
Energy saving plays a key role in the reduction of energy consumption and carbon emission, and th... more Energy saving plays a key role in the reduction of energy consumption and carbon emission, and therefore it is essential for reaching the goal of the 20-20-2020 policy.In particular, buildings are responsible of about 30% of the total amount of Europe energy consumption; the increase of their energy efficiency with the reduction of the thermal transmittance of the envelope is a point of strength with the actions and strategies of the policy makers.Currently, the study of energy performance of buildings is based on international standards, in particular the Italian one allows to calculate the U-value according the ISO 6946 or by in-situ measurements, using a heat flow meter (HFM), following recommendations provided in ISO 9869.In the last few years, a new technique, based on Infrared Thermography (IRT) (also referred to as Infrared Thermovision Technique - ITT), has been proposed for in situ determination of the thermal transmittance of opaque building elements. Some case studies have been reported.This method has already been applied on existing buildings, providing reliable results, but also revealing some weaknesses.In order to overcome such weak points and to assess a systematic procedure for the application of IRT, a validation of the method has been performed in a monitored environment.Infrared camera, the heat flow meter sensors and a nearby meteorological station have been used for thermal transmittance measurement. Comparison between the U-values measured in a hot box with IRT as well as values calculated following international standards and HFM results has been effected. Results give a good description of the advantages, as well as of the open problems, of IR Thermography for estimating the U-value.Further studies will help to refine the technique, and to identify the best operative conditions.
In this paper, we present a new BOS (Background Oriented Schlieren), based on a hidden grid, for ... more In this paper, we present a new BOS (Background Oriented Schlieren), based on a hidden grid, for studying heat flows. In the setup, we record a grid-based intensity pattern whose phase map carries information about the temperature gradient. The background (undistorted) pattern is hidden in the light source. Quantitative analysis is obtained by a windowed Fourier transform approach. Some experimental results are given to demonstrate the feasibility of the technique.
One of the key parameters that "meter" the energy performance of the whole structure of... more One of the key parameters that "meter" the energy performance of the whole structure of buildings is the thermal transmittance.This parameter can be evaluated with a theoretical approach, regulated by standard ISO 6946, once the stratigraphy of the envelope and the properties of the constituent materials are known, or by using a heat flow meter (HFM), following the recommendations provided in standard ISO 9869.Recently, the use of quantitative IR Thermography (IRT) has been proposed by several researchers; this method allows to determine the overall transmittance of an envelope in a short time (especially in comparison with HFM method). However, the theoretical or experimental transmittance, measured on real buildings having walls composed by different materials, can be rather distant from those calculated or measured with different procedures.For this reason, for a correct certification of the thermal performance of a building envelope, it is necessary the availability of experimental procedures for a direct and reliable evaluation of the thermal transmittance, suitable for different walls.Research has found that, especially in historical constructions, faults in the building envelope and the age of the materials can greatly affect the HFM measurements.The aim of this work is to analyze in situ the thermal performance of three different walls which have been selected according to: different materials, different age, and different construction. On each envelope, a comparison between U-values, measured by HFM and IRT, and computed according the standard procedure, has been effected.
Tecnica Italiana-Italian Journal of Engineering Science, 2021
The thermal characterization of building envelope materials is a crucial phase in understanding t... more The thermal characterization of building envelope materials is a crucial phase in understanding the building energy performance, and it is commonly evaluated through the thermal transmittance, often synthetically indicated as U-value. There are several ways to experimentally assess the U-value of insulating materials and multi-layers systems, usually defined by means of experimental in-situ heat flux measurements, where, however, a considerable variation of the boundary conditions may occur, making the measurement difficult. In this work, the experimental thermal characterization of different insulating materials applied to an X-lam wall is presented. The analysis is carried out using a Guarded Hot Box, which allowed to reproduce real, repeatable, and controlled operating conditions. Two different insulating materials were selected: expanded polystyrene (EPS) with graphite and hemp. The experimental tests were carried out by imposing a temperature difference reproducing the common o...
Dual mode imaging in the mid infrared band, a joint use of thermography and quasi-thermal reflect... more Dual mode imaging in the mid infrared band, a joint use of thermography and quasi-thermal reflectography, was recently proposed as a full field diagnostic tool in cultural heritage. Here we discuss for the first time, to the best of our knowledge, a detailed application of such non destructive technique to the diagnostics of frescoes, with an emphasis on the location of detachments. We also investigate the use of a thermographic method based on TSR (thermal signal reconstruction), in a long pulse stimulus scheme, as well as the spatial registration of thermal images after post-processing analysis to their visible counterpart, so as to obtain a fine resolution diagnostic map. As an exemplar case study, we report about the application of dual mode imaging with a 500 $${\upmu }\hbox {m}$$ μ m pixel size at object plane on the “Monocromo”, a fresco by Leonardo da Vinci located in the Sforza Castle (Milan, Italy). Our technique was used to guide the conservators during the restoration wo...
Optics for Arts, Architecture, and Archaeology VIII, 2021
In this paper, a method for artworks monitoring is proposed, able to perform simultaneously speck... more In this paper, a method for artworks monitoring is proposed, able to perform simultaneously speckle interferometry and speckle photography, thus the system can map both out-of-plane and in-plane displacements. The aim is to keep it as simple as possible to increase its possibilities to be routinely used in restoration laboratories. Though simple, the proposed method is tailored to some specific needs of artwork diagnostics.
In this study, convective heat transfer phenomena were investigated by means of a Guarded Hot Box... more In this study, convective heat transfer phenomena were investigated by means of a Guarded Hot Box (GHB) apparatus. An experimental setup characterized by air and surface temperature probes, and a hot-wire anemometer was used. Five small fans were installed in the metering chamber to generate a forced air flow characterized by different velocity values. So, the GHB was used for investigating the influence of different air speed values on internal convective coefficients. Considering horizontal heat fluxes, an internal convective coefficient values of 2.5 W/m2K is reported in the Standard ISO 6946. However, no exhaustive description about this value is provided. The aim of this work is to experimentally determine the internal thermal surface resistance, quantifying how the convective heat transfer coefficient varies as air velocity changes.
In this paper, the main results obtained for the identification of energy efficiency measures (EE... more In this paper, the main results obtained for the identification of energy efficiency measures (EEMs) in archetype public buildings selected by the Abruzzo Region within the European Project SHERPA (SHared knowledge for Energy Renovation in buildings by Public Administration), a three-year project involving 12 partners from the Mediterranean area, are presented.The analysis presented in this work was carried out on 12 public buildings, with different intended use, located in the four provinces of the Abruzzo Region characterized by different climate conditions. For each building, a complex work of documents acquisition has been carried out together with the regional coordinators of the Project. These documents have allowed the energy assessment of the selected buildings in their current condition. The second phase of the study has instead focused on the effects resulting from the application of EEMs on both passive and active components, in terms of energy savings and greenhouse gas ...
This work contains an overview of infrared thermography (IRT) method and its applications relatin... more This work contains an overview of infrared thermography (IRT) method and its applications relating to the investigation of architectural structures. In this method, the passive approach is usually used in civil engineering, since it provides a panoramic view of the thermal anomalies to be interpreted also thanks to the use of photographs focused on the region of interest (ROI). The active approach, is more suitable for laboratory or indoor inspections, as well as for objects having a small size. The external stress to be applied is thermal, coming from non-natural apparatus such as lamps or hot / cold air jets. In addition, the latter permits to obtain quantitative information related to defects not detectable to the naked eyes. Very recently, the hybrid thermography (HIRT) approach has been introduced to the attention of the scientific panorama. It can be applied when the radiation coming from the sun, directly arrives (i.e., possibly without the shadow cast effect) on a surface exposed to the air. A large number of thermograms must be collected and a post-processing analysis is subsequently applied via advanced algorithms. Therefore, an appraisal of the defect depth can be obtained passing through the calculation of the combined thermal diffusivity of the materials above the defect. The approach is validated herein by working, in a first stage, on a mosaic sample having known defects while, in a second stage, on a Church built in L’Aquila (Italy) and covered with a particular masonry structure called apparecchio aquilano. The results obtained appear promising.
Several studies and correlations for the convective heat transfer coefficient (CHTC) are availabl... more Several studies and correlations for the convective heat transfer coefficient (CHTC) are available in literature and in handbooks, depending on type of convection, wind speed range or on the test rigs from which they are derived. The importance of accurate evaluation of CHTC, especially at the building façades, has been highlighted in the recent years, due to the need for reliable measurement of buildings’ heat transfer capability. This study aims at underlining the importance of proper CHTC values for the determination of the building envelope thermal transmittance (U-value) via infrared thermography (IRT). To this scope, firstly an overview on convective heat transfer coefficient is given; then, some CHTC models, chosen from literature, are analyzed at different wind speed classes. Subsequently, such models are employed in two formulas proposed in literature for the U-value measurement via IRT, by using data from previous experimental campaign carried out in controlled environment. Results were compared, and significant deviations were found: one of the employed approaches and formulation is less sensitive to the correlation adopted for the convection expression, amongst those considered and in the wind speed range analyzed. This constitutes an advantage, since one of the weak points of the IRT method is the convection expression itself.
Physical access to historic and artistic manufactures can be limited by a lot of factors. In part... more Physical access to historic and artistic manufactures can be limited by a lot of factors. In particular, the access to the collection of the ancient coins is difficult, especially for students. Indeed, for coins digital archive of high quality three-dimensional model and remote fruition is of great interest. In this work we propose 3D acquisition and digitizing techniques for the virtualized reality of ancient coins (virtual gallery). The system used for creating 3D shape of coins is based on conoscopic holography. This technique is a non-contact three-dimensional measuring technique that makes possible to produce holograms, even with incoherent light, with fringe periods that can be measured precisely to determine the exact distance to the point measured. It is suitable to obtain 3D profile with high resolution also on surface with unevenness reflectivity (this situation is usual on the surface of the ancient coins). By conoscopic holography, high-resolution 3D model can be obtained. However, accurate representation and high-quality display are fundamental requirements to avoid misinterpretation of the data. Therefore, virtual galleries can be obtained through a procedure involving 3D acquisition, 3D model and visualization. In conclusion, we propose an optoelectronic application, integrated with multimedia techniques, in order to improve the access to collection of ancient coins belonging to museums or privates.
The aim of this work is to create an automatic monitoring system for photovoltaic plant using an ... more The aim of this work is to create an automatic monitoring system for photovoltaic plant using an active load. This system is able to monitor photovoltaic panels connected in a string thanks to a switching circuit that disconnects and reconnects them. With the MOSFET active load, it is possible to reconstruct the IV characteristic of the panel concerned through current and voltage measurements. Furthermore, the system is powered by an energy harvesting circuit, making it autonomous. The proposed system is based on a SamD21G microcontroller that manages switching circuits, current and voltage measurement and generates the control signal for the MOSFET via a 12-bit DAC. The complete system is described in its parts and simulated with Spice.
In the last years, the importance of integrating the production of electricity with the productio... more In the last years, the importance of integrating the production of electricity with the production of sanitary hot water led to the development of new solutions, i.e. PV/T systems. It is well known that hybrid photovoltaic-thermal systems, able to produce electricity and thermal energy at the same time with better energetic performance in comparison with two separate systems, present many advantages for application in a residential building. A PV/T is constituted generally by a common PV panel with a metallic pipe, in which fluid flows. Pipe accomplishes two roles: it absorbs the heat from the PV panel, thus increasing, or at least maintaining its efficiency; furthermore, it stores the heat for sanitary uses. In this work, the thermal and electrical efficiencies of a commercial PV/T panel have been evaluated during the summer season in different days, to assess the effect of environmental conditions on the system total efficiency. Moreover, infrared thermographic diagnosis in real time has been effected during the operating mode in two conditions: with cooling and without cooling; cooling was obtained by natural flowing water. This analysis gave information about the impact of a non-uniform temperature distribution on the thermal and electrical performance. Furthermore, measurements have been performed in two different operating modes: 1) production of solely electrical energy and 2) simultaneous production of thermal and electrical energy. Finally, total efficiency is largely increased by using a simple solar concentrator nearby the panel.
Energy saving plays a key role in the reduction of energy consumption and carbon emission, and th... more Energy saving plays a key role in the reduction of energy consumption and carbon emission, and therefore it is essential for reaching the goal of the 20-20-2020 policy.In particular, buildings are responsible of about 30% of the total amount of Europe energy consumption; the increase of their energy efficiency with the reduction of the thermal transmittance of the envelope is a point of strength with the actions and strategies of the policy makers.Currently, the study of energy performance of buildings is based on international standards, in particular the Italian one allows to calculate the U-value according the ISO 6946 or by in-situ measurements, using a heat flow meter (HFM), following recommendations provided in ISO 9869.In the last few years, a new technique, based on Infrared Thermography (IRT) (also referred to as Infrared Thermovision Technique - ITT), has been proposed for in situ determination of the thermal transmittance of opaque building elements. Some case studies have been reported.This method has already been applied on existing buildings, providing reliable results, but also revealing some weaknesses.In order to overcome such weak points and to assess a systematic procedure for the application of IRT, a validation of the method has been performed in a monitored environment.Infrared camera, the heat flow meter sensors and a nearby meteorological station have been used for thermal transmittance measurement. Comparison between the U-values measured in a hot box with IRT as well as values calculated following international standards and HFM results has been effected. Results give a good description of the advantages, as well as of the open problems, of IR Thermography for estimating the U-value.Further studies will help to refine the technique, and to identify the best operative conditions.
In this paper, we present a new BOS (Background Oriented Schlieren), based on a hidden grid, for ... more In this paper, we present a new BOS (Background Oriented Schlieren), based on a hidden grid, for studying heat flows. In the setup, we record a grid-based intensity pattern whose phase map carries information about the temperature gradient. The background (undistorted) pattern is hidden in the light source. Quantitative analysis is obtained by a windowed Fourier transform approach. Some experimental results are given to demonstrate the feasibility of the technique.
One of the key parameters that "meter" the energy performance of the whole structure of... more One of the key parameters that "meter" the energy performance of the whole structure of buildings is the thermal transmittance.This parameter can be evaluated with a theoretical approach, regulated by standard ISO 6946, once the stratigraphy of the envelope and the properties of the constituent materials are known, or by using a heat flow meter (HFM), following the recommendations provided in standard ISO 9869.Recently, the use of quantitative IR Thermography (IRT) has been proposed by several researchers; this method allows to determine the overall transmittance of an envelope in a short time (especially in comparison with HFM method). However, the theoretical or experimental transmittance, measured on real buildings having walls composed by different materials, can be rather distant from those calculated or measured with different procedures.For this reason, for a correct certification of the thermal performance of a building envelope, it is necessary the availability of experimental procedures for a direct and reliable evaluation of the thermal transmittance, suitable for different walls.Research has found that, especially in historical constructions, faults in the building envelope and the age of the materials can greatly affect the HFM measurements.The aim of this work is to analyze in situ the thermal performance of three different walls which have been selected according to: different materials, different age, and different construction. On each envelope, a comparison between U-values, measured by HFM and IRT, and computed according the standard procedure, has been effected.
Tecnica Italiana-Italian Journal of Engineering Science, 2021
The thermal characterization of building envelope materials is a crucial phase in understanding t... more The thermal characterization of building envelope materials is a crucial phase in understanding the building energy performance, and it is commonly evaluated through the thermal transmittance, often synthetically indicated as U-value. There are several ways to experimentally assess the U-value of insulating materials and multi-layers systems, usually defined by means of experimental in-situ heat flux measurements, where, however, a considerable variation of the boundary conditions may occur, making the measurement difficult. In this work, the experimental thermal characterization of different insulating materials applied to an X-lam wall is presented. The analysis is carried out using a Guarded Hot Box, which allowed to reproduce real, repeatable, and controlled operating conditions. Two different insulating materials were selected: expanded polystyrene (EPS) with graphite and hemp. The experimental tests were carried out by imposing a temperature difference reproducing the common o...
Dual mode imaging in the mid infrared band, a joint use of thermography and quasi-thermal reflect... more Dual mode imaging in the mid infrared band, a joint use of thermography and quasi-thermal reflectography, was recently proposed as a full field diagnostic tool in cultural heritage. Here we discuss for the first time, to the best of our knowledge, a detailed application of such non destructive technique to the diagnostics of frescoes, with an emphasis on the location of detachments. We also investigate the use of a thermographic method based on TSR (thermal signal reconstruction), in a long pulse stimulus scheme, as well as the spatial registration of thermal images after post-processing analysis to their visible counterpart, so as to obtain a fine resolution diagnostic map. As an exemplar case study, we report about the application of dual mode imaging with a 500 $${\upmu }\hbox {m}$$ μ m pixel size at object plane on the “Monocromo”, a fresco by Leonardo da Vinci located in the Sforza Castle (Milan, Italy). Our technique was used to guide the conservators during the restoration wo...
Optics for Arts, Architecture, and Archaeology VIII, 2021
In this paper, a method for artworks monitoring is proposed, able to perform simultaneously speck... more In this paper, a method for artworks monitoring is proposed, able to perform simultaneously speckle interferometry and speckle photography, thus the system can map both out-of-plane and in-plane displacements. The aim is to keep it as simple as possible to increase its possibilities to be routinely used in restoration laboratories. Though simple, the proposed method is tailored to some specific needs of artwork diagnostics.
In this study, convective heat transfer phenomena were investigated by means of a Guarded Hot Box... more In this study, convective heat transfer phenomena were investigated by means of a Guarded Hot Box (GHB) apparatus. An experimental setup characterized by air and surface temperature probes, and a hot-wire anemometer was used. Five small fans were installed in the metering chamber to generate a forced air flow characterized by different velocity values. So, the GHB was used for investigating the influence of different air speed values on internal convective coefficients. Considering horizontal heat fluxes, an internal convective coefficient values of 2.5 W/m2K is reported in the Standard ISO 6946. However, no exhaustive description about this value is provided. The aim of this work is to experimentally determine the internal thermal surface resistance, quantifying how the convective heat transfer coefficient varies as air velocity changes.
In this paper, the main results obtained for the identification of energy efficiency measures (EE... more In this paper, the main results obtained for the identification of energy efficiency measures (EEMs) in archetype public buildings selected by the Abruzzo Region within the European Project SHERPA (SHared knowledge for Energy Renovation in buildings by Public Administration), a three-year project involving 12 partners from the Mediterranean area, are presented.The analysis presented in this work was carried out on 12 public buildings, with different intended use, located in the four provinces of the Abruzzo Region characterized by different climate conditions. For each building, a complex work of documents acquisition has been carried out together with the regional coordinators of the Project. These documents have allowed the energy assessment of the selected buildings in their current condition. The second phase of the study has instead focused on the effects resulting from the application of EEMs on both passive and active components, in terms of energy savings and greenhouse gas ...
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