Sohrab Mofid | University of Colorado, Boulder (original) (raw)

Papers by Sohrab Mofid

ACS applied materials & interfaces, 2022

Various near-atom-thickness two-dimensional (2D) van der Waals (vdW) crystals with unparalleled e... more Various near-atom-thickness two-dimensional (2D) van der Waals (vdW) crystals with unparalleled electromechanical properties have been explored for transformative devices. Currently, the availability of 2D vdW crystals is rather limited in nature as they are only obtained from certain mother crystals with intrinsically possessed layered crystallinity and anisotropic molecular bonding. Recent efforts to transform conventionally non-vdW three-dimensional (3D) crystals into ultrathin 2D-like structures have seen rapid developments to explore device building blocks of unique form factors. Herein, we explore a "peel-and-stick" approach, where a nonlayered 3D platinum sulfide (PtS) crystal, traditionally known as a cooperate mineral material, is transformed into a freestanding 2D-like membrane for electromechanical applications. The ultrathin (∼10 nm) 3D PtS films grown on large-area (>cm2) silicon dioxide/silicon (SiO2/Si) wafers are precisely "peeled" inside water...

Proceeding of 5-6th Thermal and Fluids Engineering Conference (TFEC), 2021

International Journal of Heat and Mass Transfer, 2022

Advanced Electronic Materials, 2021

ACKNOWLEDGEMENTS. This work has been supported by the Research Council of Norway and several part... more ACKNOWLEDGEMENTS. This work has been supported by the Research Council of Norway and several partners through the research projects ”Building Integrated Photovoltaics for Norway” (BIPV Norway) and ”The Research Centre on Zero Emission Buildings” (ZEB).

High-performance nano insulation materials (Hi-Per NIM) may be developed by exploiting the Knudse... more High-performance nano insulation materials (Hi-Per NIM) may be developed by exploiting the Knudsen effect for reduced thermal conductivity and thus making air-filled nanoporous thermal insulation materials with a nanoporous air-filled structure. NIMs with very low thermal conductivity values will enable the use of normal or thin wall thicknesses in energy-efficient buildings. Especially for energy renovation of existing buildings, the reduced insulation thickness is of high interest. This study will present an exploration of attempting to achieve NIMs through experimental laboratory development of hollow silica nanospheres (HSNS), hollow silica nanofibres (HSNF) and hollow silica integrated nanospheres and nanofibres, alongside theoretical modelling and sustainability investigations.

Initiatives to incorporate energy efficiency measures and strategies in the building sector have ... more Initiatives to incorporate energy efficiency measures and strategies in the building sector have gained attention for several decades, and with increased focus on zero energy and zero emission buildings, such initiatives will probably still continue to emerge for several more decades to come. Development of new high-performance thermal insulation materials and super insulation materials (SIM) for the advanced building envelopes of tomorrow may play an essential role in this regard. Very thick building envelopes are not desirable due to several reasons, e.g. considering space issues with respect to both economy, floor area, transport volumes, architectural restrictions and other limitations, material usage and existing building techniques. Hence, the stage is set for the development of new thermal insulation materials with a very low thermal conductivity, thus allowing the usage of relatively thin building envelopes with a very high thermal resistance and thereby substantially reduced heat loss. In porous materials, when the mean free path of the gas molecules becomes larger than the pore diameter, there will be a decrease in the gas thermal conductivity including the gas and pore wall interaction, which is referred to as the Knudsen effect. This study will present our on-going efforts utilizing the Knudsen effect attempting to make SIMs with a nanoporous air-filled structure at atmospheric pressure, i.e. nano insulation materials (NIM). Some possible pathways to NIMs and SIMs like e.g. the template foaming method and the internal gas release method are promising with respect to their high potential, however, so far large experimental challenges have made us abandon these methods for the moment. That is, currently we are pursuing to make NIMs by the sacrificial template method, more specifically by the synthesis of hollow silica nanospheres (HSNS), where both the inner sphere diameter and shell thickness may be tailor-made and thereby determining the thermal conductivity

ACKNOWLEDGEMENTS. This work has been supported by the Research Council of Norway and several part... more ACKNOWLEDGEMENTS. This work has been supported by the Research Council of Norway and several partners through the research projects ”Building Integrated Photovoltaics for Norway” (BIPV Norway) and ”The Research Centre on Zero Emission Buildings” (ZEB).

A great deal of attention has been paid to thermal insulation as it plays a significant role in i... more A great deal of attention has been paid to thermal insulation as it plays a significant role in improving the energy efficiency within the building and construction sector. There is an ever-increasing demand for advanced thermal insulation materials that show superior performance to that of the conventional ones. The state-ofthe-art thermal insulation materials and solutions, such as vacuum insulation panels (VIP) and silica aerogels, and the emerging ones like nano insulation materials (NIM), are under rapid development and show a promising potential. Hollow silica nanospheres (HSNS) may be a promising candidate for achieving high performance super insulation materials (SIM). This study investigates synthesis parameters and properties of HSNS with the aim of reaching low thermal conductivity by exploiting the Knudsen effect. The experiments are carried out to optimize thermal performance based on variation of structural parameters like e.g. HSNS shell thickness and inner diameter.

Materials Today Nano, 2021

Abstract VO2 nanoparticle–based thermochromic films have shown great promise for applications in ... more Abstract VO2 nanoparticle–based thermochromic films have shown great promise for applications in smart windows because of their relatively high luminous transmittance and solar modulation ability. To improve the lifetime of VO2 nanoparticles, environmentally stable oxide materials such as TiO2, SiO2, and ZnO have been utilized as protecting shells. However, the shell material changes the optical performance of the thermochromic films because of the variation of the dielectric environment of the VO2 nanoparticles. In this work, the effective medium theory is coupled with the transfer matrix method to study the influence of the optical constants of the shell materials and the shell thickness on the luminous transmittance and solar modulation ability of the VO2 core–shell nanoparticle–based thermochromic films. The calculation results showed that it is challenging to simultaneously improve both the luminous transmittance and the solar modulation ability of core–shell structures. With the refractive index of the shell material being between 1.6 and 2.3 (e.g. ZnO and Cr2O3), there exists an optimal shell thickness to obtain the maximum solar modulation ability. The results reported in this study can be exploited to guide the design and development of high-performance VO2 core–shell nanoparticle–based thermochromic smart window films.

Materials Today Physics, 2020

Vanadium dioxide (VO 2)ebased thermochromic films are of great interest for energy-saving smart w... more Vanadium dioxide (VO 2)ebased thermochromic films are of great interest for energy-saving smart windows as they can dynamically change the solar transmittance as the ambient temperature changes. However, VO 2 is thermodynamically unstable and could be easily oxidized by the oxygen and moisture in the ambient air. In this work, a durability-enhanced VO 2 nanoparticle-polymer thermochromic film was proposed and fabricated using the blade coating method where the cross-linked and highly entangled poly(methyl methacrylate) (PMMA) chains with a molecular weight (~950,000) was adopted to block gas diffusion in the polymer matrix. It was shown that the developed VO 2 nanoparticle film kept~30% of its solar modulation ability after~900 h of accelerated durability test in the aging environment with a temperature at 60 C and~95% relative humidity. This is~4 times of the lifetime of the VO 2 nanoparticles which are embedded in the nonecross-linked PMMA matrix with low molecular weight (~15,000). The cross-linked PMMA-VO 2 film also showed a high luminous transmittance of~50%, a high solar modulation ability of~17%, and a low haze of~11%. Our method provides an easy and effective strategy to improve the lifetime of VO 2 nanoparticles, showing a promising pathway toward environmentally stable and easily scalable thermochromic films for energy-efficient smart windows.

IOP Conference Series: Materials Science and Engineering, 2019

As the world’s focus is turned even stronger toward miscellaneous energy efficiency and saving as... more As the world’s focus is turned even stronger toward miscellaneous energy efficiency and saving aspects, the development of new high-performance thermal insulation materials for building applications will play an important role in this regard. The aim of the presented study is to develop an understanding for the governing thermal transport mechanisms and utilize the Knudsen effect in nanoporous insulation materials through theoretical concepts and experimental laboratory explorations, thus being able to synthesize nano insulation materials (NIM) with very low thermal conductivity values as a major goal. NIMs based on hollow silica nanospheres (HSNS) have been synthesized by a sacrificial template method, where the idea is that the heat transport by gas conductance and gas/solid state interactions decreases with decreasing pore diameters in the nano range as predicted by the Knudsen effect. HSNS with reduced thermal conductivity compared to their solid counterparts have been prepared ...

IOP Conference Series: Materials Science and Engineering, 2019

As the world’s focus is turned even stronger toward miscellaneous energy efficiency and saving as... more As the world’s focus is turned even stronger toward miscellaneous energy efficiency and saving aspects, the development of new high-performance thermal insulation materials for building applications will play an important role in this regard. The aim of the presented study is to develop an understanding for the governing thermal transport mechanisms and utilize the Knudsen effect in nanoporous insulation materials through theoretical concepts and experimental laboratory explorations, thus being able to synthesize nano insulation materials (NIM) with very low thermal conductivity values as a major goal. NIMs based on hollow silica nanospheres (HSNS) have been synthesized by a sacrificial template method, where the idea is that the heat transport by gas conductance and gas/solid state interactions decreases with decreasing pore diameters in the nano range as predicted by the Knudsen effect. HSNS with reduced thermal conductivity compared to their solid counterparts have been prepared ...

Applied Thermal Engineering, 2019

• A reduced-scale hot box is built to measure window insulation materials. • The built system can... more • A reduced-scale hot box is built to measure window insulation materials. • The built system can measure the specimens with sizes < 0.2 m × 0.2 m accurately. • The thermal conductivity and U-value of transparent porous aerogel are measured.

Proceeding of Second Thermal and Fluids Engineering Conference, 2017

Construction and Building Materials, 2018

Hollow silica nanospheres (HSNS) show a promising potential to become good thermal insulators wit... more Hollow silica nanospheres (HSNS) show a promising potential to become good thermal insulators with low thermal conductivity values for construction purposes. The thermal conductivity of HSNSs is dependent on their structural features such as sizes (inner diameter and shell thickness) and shell structures (porous or dense), which are affected by the synthetic methods and procedures including reaction medium, polystyrene template, and silica precursor.. Formation of thermally insulating HSNS was in general favoured by alkaline reaction, whereby highly porous silica shells were formed, promoting less silica per volume of material, thus a lower solid state thermal conductivity. The Knudsen effect is in general reducing the gas thermal conductivity including the gas and pore wall interaction for materials with pore diameters in the nanometer range, which is also valid for our HSNS reported here. Further decreasing the pore sizes would invoke a higher impact from the Knudsen effect. The additional insulating effect of the inter-silica voids (median diameter D50 ≈ 15 nm) within the shell coating contributed also to the insulating properties of HSNS. The synthesis route with tetraethyl orthosilicate 2 (TEOS) was more robust and produced more porous silica shells than the one with water glass (Na2SiO3, WG), although the latter might represent a greener synthetic method.

Energy Procedia, 2017

District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

Energy Procedia, 2017

District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

Procedia Engineering, 2016

Today energy-efficient and energy-harvesting buildings experience an ever-increasing interest and... more Today energy-efficient and energy-harvesting buildings experience an ever-increasing interest and demand. Building integrated photovoltaics (BIPV) may in this respect represent a powerful and versatile tool for reaching the goal of zero energy and zero emission buildings. The BIPV systems replace the outer building envelope skin, thus serving simultanously as both a climate screen and a power source generating electricity. However, snow and ice formation on the exterior solar cell surfaces reduce their performance and may also lead to faster deterioration. Hence, if one could find a way to develop solar cells which were able to avoid snow and ice formation on their surfaces, one would have moved a large step ahead. This work presents a review exploring miscellaneous pathways for avoiding snow and ice formation on solar cell surfaces including superhydrophobic and icephobic surfaces.

Journal of Water Process Engineering, 2022

ACS applied materials & interfaces, 2022

Various near-atom-thickness two-dimensional (2D) van der Waals (vdW) crystals with unparalleled e... more Various near-atom-thickness two-dimensional (2D) van der Waals (vdW) crystals with unparalleled electromechanical properties have been explored for transformative devices. Currently, the availability of 2D vdW crystals is rather limited in nature as they are only obtained from certain mother crystals with intrinsically possessed layered crystallinity and anisotropic molecular bonding. Recent efforts to transform conventionally non-vdW three-dimensional (3D) crystals into ultrathin 2D-like structures have seen rapid developments to explore device building blocks of unique form factors. Herein, we explore a "peel-and-stick" approach, where a nonlayered 3D platinum sulfide (PtS) crystal, traditionally known as a cooperate mineral material, is transformed into a freestanding 2D-like membrane for electromechanical applications. The ultrathin (∼10 nm) 3D PtS films grown on large-area (>cm2) silicon dioxide/silicon (SiO2/Si) wafers are precisely "peeled" inside water...

Proceeding of 5-6th Thermal and Fluids Engineering Conference (TFEC), 2021

International Journal of Heat and Mass Transfer, 2022

Advanced Electronic Materials, 2021

ACKNOWLEDGEMENTS. This work has been supported by the Research Council of Norway and several part... more ACKNOWLEDGEMENTS. This work has been supported by the Research Council of Norway and several partners through the research projects ”Building Integrated Photovoltaics for Norway” (BIPV Norway) and ”The Research Centre on Zero Emission Buildings” (ZEB).

High-performance nano insulation materials (Hi-Per NIM) may be developed by exploiting the Knudse... more High-performance nano insulation materials (Hi-Per NIM) may be developed by exploiting the Knudsen effect for reduced thermal conductivity and thus making air-filled nanoporous thermal insulation materials with a nanoporous air-filled structure. NIMs with very low thermal conductivity values will enable the use of normal or thin wall thicknesses in energy-efficient buildings. Especially for energy renovation of existing buildings, the reduced insulation thickness is of high interest. This study will present an exploration of attempting to achieve NIMs through experimental laboratory development of hollow silica nanospheres (HSNS), hollow silica nanofibres (HSNF) and hollow silica integrated nanospheres and nanofibres, alongside theoretical modelling and sustainability investigations.

Initiatives to incorporate energy efficiency measures and strategies in the building sector have ... more Initiatives to incorporate energy efficiency measures and strategies in the building sector have gained attention for several decades, and with increased focus on zero energy and zero emission buildings, such initiatives will probably still continue to emerge for several more decades to come. Development of new high-performance thermal insulation materials and super insulation materials (SIM) for the advanced building envelopes of tomorrow may play an essential role in this regard. Very thick building envelopes are not desirable due to several reasons, e.g. considering space issues with respect to both economy, floor area, transport volumes, architectural restrictions and other limitations, material usage and existing building techniques. Hence, the stage is set for the development of new thermal insulation materials with a very low thermal conductivity, thus allowing the usage of relatively thin building envelopes with a very high thermal resistance and thereby substantially reduced heat loss. In porous materials, when the mean free path of the gas molecules becomes larger than the pore diameter, there will be a decrease in the gas thermal conductivity including the gas and pore wall interaction, which is referred to as the Knudsen effect. This study will present our on-going efforts utilizing the Knudsen effect attempting to make SIMs with a nanoporous air-filled structure at atmospheric pressure, i.e. nano insulation materials (NIM). Some possible pathways to NIMs and SIMs like e.g. the template foaming method and the internal gas release method are promising with respect to their high potential, however, so far large experimental challenges have made us abandon these methods for the moment. That is, currently we are pursuing to make NIMs by the sacrificial template method, more specifically by the synthesis of hollow silica nanospheres (HSNS), where both the inner sphere diameter and shell thickness may be tailor-made and thereby determining the thermal conductivity

ACKNOWLEDGEMENTS. This work has been supported by the Research Council of Norway and several part... more ACKNOWLEDGEMENTS. This work has been supported by the Research Council of Norway and several partners through the research projects ”Building Integrated Photovoltaics for Norway” (BIPV Norway) and ”The Research Centre on Zero Emission Buildings” (ZEB).

A great deal of attention has been paid to thermal insulation as it plays a significant role in i... more A great deal of attention has been paid to thermal insulation as it plays a significant role in improving the energy efficiency within the building and construction sector. There is an ever-increasing demand for advanced thermal insulation materials that show superior performance to that of the conventional ones. The state-ofthe-art thermal insulation materials and solutions, such as vacuum insulation panels (VIP) and silica aerogels, and the emerging ones like nano insulation materials (NIM), are under rapid development and show a promising potential. Hollow silica nanospheres (HSNS) may be a promising candidate for achieving high performance super insulation materials (SIM). This study investigates synthesis parameters and properties of HSNS with the aim of reaching low thermal conductivity by exploiting the Knudsen effect. The experiments are carried out to optimize thermal performance based on variation of structural parameters like e.g. HSNS shell thickness and inner diameter.

Materials Today Nano, 2021

Abstract VO2 nanoparticle–based thermochromic films have shown great promise for applications in ... more Abstract VO2 nanoparticle–based thermochromic films have shown great promise for applications in smart windows because of their relatively high luminous transmittance and solar modulation ability. To improve the lifetime of VO2 nanoparticles, environmentally stable oxide materials such as TiO2, SiO2, and ZnO have been utilized as protecting shells. However, the shell material changes the optical performance of the thermochromic films because of the variation of the dielectric environment of the VO2 nanoparticles. In this work, the effective medium theory is coupled with the transfer matrix method to study the influence of the optical constants of the shell materials and the shell thickness on the luminous transmittance and solar modulation ability of the VO2 core–shell nanoparticle–based thermochromic films. The calculation results showed that it is challenging to simultaneously improve both the luminous transmittance and the solar modulation ability of core–shell structures. With the refractive index of the shell material being between 1.6 and 2.3 (e.g. ZnO and Cr2O3), there exists an optimal shell thickness to obtain the maximum solar modulation ability. The results reported in this study can be exploited to guide the design and development of high-performance VO2 core–shell nanoparticle–based thermochromic smart window films.

Materials Today Physics, 2020

Vanadium dioxide (VO 2)ebased thermochromic films are of great interest for energy-saving smart w... more Vanadium dioxide (VO 2)ebased thermochromic films are of great interest for energy-saving smart windows as they can dynamically change the solar transmittance as the ambient temperature changes. However, VO 2 is thermodynamically unstable and could be easily oxidized by the oxygen and moisture in the ambient air. In this work, a durability-enhanced VO 2 nanoparticle-polymer thermochromic film was proposed and fabricated using the blade coating method where the cross-linked and highly entangled poly(methyl methacrylate) (PMMA) chains with a molecular weight (~950,000) was adopted to block gas diffusion in the polymer matrix. It was shown that the developed VO 2 nanoparticle film kept~30% of its solar modulation ability after~900 h of accelerated durability test in the aging environment with a temperature at 60 C and~95% relative humidity. This is~4 times of the lifetime of the VO 2 nanoparticles which are embedded in the nonecross-linked PMMA matrix with low molecular weight (~15,000). The cross-linked PMMA-VO 2 film also showed a high luminous transmittance of~50%, a high solar modulation ability of~17%, and a low haze of~11%. Our method provides an easy and effective strategy to improve the lifetime of VO 2 nanoparticles, showing a promising pathway toward environmentally stable and easily scalable thermochromic films for energy-efficient smart windows.

IOP Conference Series: Materials Science and Engineering, 2019

As the world’s focus is turned even stronger toward miscellaneous energy efficiency and saving as... more As the world’s focus is turned even stronger toward miscellaneous energy efficiency and saving aspects, the development of new high-performance thermal insulation materials for building applications will play an important role in this regard. The aim of the presented study is to develop an understanding for the governing thermal transport mechanisms and utilize the Knudsen effect in nanoporous insulation materials through theoretical concepts and experimental laboratory explorations, thus being able to synthesize nano insulation materials (NIM) with very low thermal conductivity values as a major goal. NIMs based on hollow silica nanospheres (HSNS) have been synthesized by a sacrificial template method, where the idea is that the heat transport by gas conductance and gas/solid state interactions decreases with decreasing pore diameters in the nano range as predicted by the Knudsen effect. HSNS with reduced thermal conductivity compared to their solid counterparts have been prepared ...

IOP Conference Series: Materials Science and Engineering, 2019

As the world’s focus is turned even stronger toward miscellaneous energy efficiency and saving as... more As the world’s focus is turned even stronger toward miscellaneous energy efficiency and saving aspects, the development of new high-performance thermal insulation materials for building applications will play an important role in this regard. The aim of the presented study is to develop an understanding for the governing thermal transport mechanisms and utilize the Knudsen effect in nanoporous insulation materials through theoretical concepts and experimental laboratory explorations, thus being able to synthesize nano insulation materials (NIM) with very low thermal conductivity values as a major goal. NIMs based on hollow silica nanospheres (HSNS) have been synthesized by a sacrificial template method, where the idea is that the heat transport by gas conductance and gas/solid state interactions decreases with decreasing pore diameters in the nano range as predicted by the Knudsen effect. HSNS with reduced thermal conductivity compared to their solid counterparts have been prepared ...

Applied Thermal Engineering, 2019

• A reduced-scale hot box is built to measure window insulation materials. • The built system can... more • A reduced-scale hot box is built to measure window insulation materials. • The built system can measure the specimens with sizes < 0.2 m × 0.2 m accurately. • The thermal conductivity and U-value of transparent porous aerogel are measured.

Proceeding of Second Thermal and Fluids Engineering Conference, 2017

Construction and Building Materials, 2018

Hollow silica nanospheres (HSNS) show a promising potential to become good thermal insulators wit... more Hollow silica nanospheres (HSNS) show a promising potential to become good thermal insulators with low thermal conductivity values for construction purposes. The thermal conductivity of HSNSs is dependent on their structural features such as sizes (inner diameter and shell thickness) and shell structures (porous or dense), which are affected by the synthetic methods and procedures including reaction medium, polystyrene template, and silica precursor.. Formation of thermally insulating HSNS was in general favoured by alkaline reaction, whereby highly porous silica shells were formed, promoting less silica per volume of material, thus a lower solid state thermal conductivity. The Knudsen effect is in general reducing the gas thermal conductivity including the gas and pore wall interaction for materials with pore diameters in the nanometer range, which is also valid for our HSNS reported here. Further decreasing the pore sizes would invoke a higher impact from the Knudsen effect. The additional insulating effect of the inter-silica voids (median diameter D50 ≈ 15 nm) within the shell coating contributed also to the insulating properties of HSNS. The synthesis route with tetraethyl orthosilicate 2 (TEOS) was more robust and produced more porous silica shells than the one with water glass (Na2SiO3, WG), although the latter might represent a greener synthetic method.

Energy Procedia, 2017

District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

Energy Procedia, 2017

District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

Procedia Engineering, 2016

Today energy-efficient and energy-harvesting buildings experience an ever-increasing interest and... more Today energy-efficient and energy-harvesting buildings experience an ever-increasing interest and demand. Building integrated photovoltaics (BIPV) may in this respect represent a powerful and versatile tool for reaching the goal of zero energy and zero emission buildings. The BIPV systems replace the outer building envelope skin, thus serving simultanously as both a climate screen and a power source generating electricity. However, snow and ice formation on the exterior solar cell surfaces reduce their performance and may also lead to faster deterioration. Hence, if one could find a way to develop solar cells which were able to avoid snow and ice formation on their surfaces, one would have moved a large step ahead. This work presents a review exploring miscellaneous pathways for avoiding snow and ice formation on solar cell surfaces including superhydrophobic and icephobic surfaces.

Journal of Water Process Engineering, 2022