| 1. |
- Hagentoft, Carl-Eric, 1958, et al.
(author)
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Impact of Variable Air Flow Rate in Energy Smart Window Curtains, on the Total Net Heat Gain- Analytical Solutions
- 2019
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In: Building Simulation Conference Proceedings. - : IBPSA. - 2522-2708. ; 16:1, s. 494-499
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Conference paper (peer-reviewed)abstract
- In this paper, the impact of variable air flow rate on the performance of the solar collector function of the Climate Curtain is evaluated. Climate Curtain is a new type of window curtain developed by the company Climate Curtains AB in Sweden. This curtain consists of several layers of stagnant air, and the solar collector function of this curtain captures some part of solar radiation striking the window; warmer air is forced into the room by fans mounted inside the curtain. The paper presents general and handy formulas which can be used to determine the impact of the curtain and its solar collector function, on the total net heat gain in the room. The solution presented is applicable on similar vertical air gaps to evaluate energy performance.
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| 2. |
- Hagentoft, Carl-Eric, 1958, et al.
(author)
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Mathematical Expressions for Prediction of the Effective Thermal Conductivity of Perfectly Packed Two-phase Mixtures
- 2023
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In: Environmental Science and Engineering (Subseries: Environmental Science). - 1863-5520. ; , s. 767-774
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Conference paper (peer-reviewed)abstract
- This paper introduces new and handy mathematical expressions for predicting and understanding the effective thermal conductivity of two-phase homogeneous mixtures. In a two-phase mixture, particles of the dispersed phase are mixed in the matrix of the second phase. A primary purpose of the proposed model is to predict and understand the effective thermal conductivity of high porous thermal insulation materials, for which many other similar analytical models offer less accuracy. The presented expressions assume a perfectly packed mixture and consider the thermal conductivity of the two phases, the proportion and the particle size of the dispersed phase. The proposed model includes non-dimensional heat loss factors, calculated by two and three-dimensional numerical simulations. In the continuation of the work presented, an experimental study is planned to evaluate the accuracy of the model, compared to other existing analytical solutions, and the validity of the assumptions made.
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| 3. |
- Johansson, Pär, 1986, et al.
(author)
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Aerogelbaserad puts för energieffektivisering av äldre och kulturhistoriskt värdefulla byggnader (webinar)
- 2021
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Other publication (other academic/artistic)abstract
- I denna webinar i samarbete med Energimyndighetens program Spara och Bevara introduceras aerogelbaserad puts och vi beskriver hur materialet kan bidra till renovering och energieffektivisering. I webinariet presenteras också helt färska forskningsresultat. Många äldre byggnader är svåra att renovera för att uppnå en god energibesparing. Detta gäller speciellt för kulturhistoriska byggnader där det finns begränsningar i möjliga praktiska och tekniska lösningar. Byggnadernas karaktärsdrag, begränsningar i tillåten väggtjocklek i bygglov och risker for fuktrelaterade skador är bara några exempel. I ett forskningsprojekt på Chalmers studeras en ny typ av isolerande puts. Denna puts är baserad på aerogelpartiklar som möjliggör fler tekniska lösningar vid renovering och energieffektivisering än konventionell puts. Aerogelbaserad puts är kalk- eller cementbaserad och innehåller aerogel som är ett superisolerande material. Dess värmekonduktivitet är under 0,020 W/m·K, ungefär hälften av mineralullsisolering. Aerogelpartiklarna ger den aerogelbaserade putsen isolerande egenskaper jämförbara med konventionella isoleringsmaterial. Förutom bättre isolerande egenskaper jämfört med vanlig puts är den aerogelbaserade putsen fuktdiffusionsöppen och har en hög fuktkapacitet. Detta är fördelaktiga egenskaper för att uppnå en fuktsäker konstruktion. Aerogelbaserad puts kan vara en del av lösningen på utmaningarna för att renovera kulturhistoriska byggnader, utan att förvanska utseendet, samtidigt som tjockleken på isoleringen kan minska. Nu utvärderas materialet ur värme- och fuktsynpunkt för användning i svenska byggnader och klimatförhållanden.
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| 4. |
- Karim, Ali Naman, 1992
(author)
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Aerogel-based plasters for renovation of buildings in Sweden: Identification of possibilities, information deficiencies and challenges
- 2021
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Licentiate thesis (other academic/artistic)abstract
- Aerogel-based plasters are a class of high energy efficient wall finishes with declared thermal conductivities around 30-50 mW/(m∙K). Aerogel-based plasters are promising alternatives to substitute conventional insulation materials when renovating uninsulated building envelopes. Aerogel-based plasters have been successfully used in several buildings in a number of European countries but seldom in regions with cold, wet, windy climates combined with freeze-thawing. The potentials for introduction of aerogel-based plasters in Swedish buildings are large as around 27 % of all multi-family residential buildings in Sweden have façades covered by plasters. By using aerogel-based plasters in the renovation of listed buildings, new possible alternatives for solving some of the existing challenges in the renovations of such buildings can be created. This thesis summarizes the work done on addressing the possibilities and challenges associated with the application of aerogel-based plasters in Sweden. The study is from a risk assessment point of view with focus on the hygrothermal performance, long-term durability and compatibility of aerogel-based plasters with other materials when installed in multilayer wall configurations. Literature review, semi-structured interviews, numerical energy simulations, study visits and laboratory measurements are the selected methods for the purpose of this study. The results of the study show that APs are promising materials to improve the energy efficiency in buildings when renovating existing buildings in Sweden. However, and despite the large research efforts on aerogel-based plasters, a complete and reliable set of hygrothermal and mechanical properties for aerogel-based plasters is still lacking. Information about these properties is necessary to perform advanced hygrothermal- and risk assessment analyses. To confirm the performance and to justify the higher investment cost of aerogel-based plasters, their long-term durability and compatibility with other building materials need to be further explored as well. For the future introduction of aerogel-based plasters in Sweden, reliable information and documentation are needed. These are needed to evaluate the economic aspects, service life and adaptability of the material to the Swedish building regulations.
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| 5. |
- Karim, Ali Naman, 1992, et al.
(author)
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Aerogelbaserad puts- Superisolering för framtiden
- 2020
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In: Husbyggaren. ; :6, s. 8-11
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Journal article (other academic/artistic)abstract
- I ett forskningsprojekt på Chalmers studeras en aerogelbaserad puts med mycket bra isolerande egenskaper. Förhoppningen är att användningen av den så kallade superisolerande putsen ska bidra till att minska byggsektorns energianvändning, både för existerande och nya byggnader. Superisolerande puts kan, förutom att spara energi, dessutom resultera i funktionella väggar med mindre tjocklek. Detta bidrar i sin tur till att öka mängden uthyrningsbar golvyta inomhus, yta som annars skulle tagits upp av väggens isolering. I denna artikel vill vi informera om vad vi planerar att göra i projektet och berätta om den superisolerande putsens egenskaper.
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| 6. |
- Karim, Ali Naman, 1992, et al.
(author)
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Determination of the anisotropic thermal conductivity of an aerogel-based plaster using transient plane source method
- 2021
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 2069:1
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Conference paper (peer-reviewed)abstract
- Aerogel-based plasters are composite materials with declared thermal conductivities in the range of traditional insulating materials, i.e. 30-50 mW/(m K). Based on the results from reported field measurements, aerogel-based plasters can significantly reduce the thermal transmittance of uninsulated walls. However, the in-situ measured thermal conductivities have sometimes been higher than the declared values measured in laboratory and in the main direction of the heat flow. Meanwhile, the anisotropic thermal performance of aerogel-based plasters, i.e., deviating thermal performance in the different directions of heat flow, has not been explored yet. The objective of this study is thus to evaluate the anisotropic thermal conductivity of an aerogel-based plaster. This is done in a set of laboratory measurements using the transient plane source method. Six identical and cubic samples with the dimensions of 10x10x10 cm3 were paired two and two, creating three identical sample sets. In total, 360 measurements of thermal conductivity and thermal diffusivity, and 130 measurements for specific heat capacity were conducted. The results indicate a weak anisotropy of less than 6.5 % between the three directions (x, y, z). Considering the accuracy of the selected measurement technique, better than 5 %, supplementary measurements using another technique are recommended.
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| 7. |
- Karim, Ali Naman, 1992, et al.
(author)
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Determination of the Effective Thermal Conductivity of Aerogel-based Coating Mortars Using Numerical Simulations- Random Packing
- 2023
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In: Environmental Science and Engineering (Subseries: Environmental Science). - 1863-5520. ; , s. 757-765
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Conference paper (peer-reviewed)abstract
- Aerogel-based coating mortars have declared thermal conductivities of 0.03-0.05 W/(m∙K), similar to those of conventional thermal insulation materials. Due to the high porosity and fragility of aerogel granules, the material obtains a reduced mechanical strength compared to conventional mortars. Recently, there has been a large research effort on developing new mixtures with improved thermal and mechanical properties. This paper presents and evaluates two-dimensional numerical simulations, based on the random packing technique, as an alternative method to laboratory measurements in predicting the effective thermal conductivity of these mortars. Experimental data from the literature, on thermal conductivity of aerogel-based coating mortars containing 50-90 vol- % aerogels were used to validate the simulation results. In this preliminary validation study, a relative error of 6-10 % was observed. Future work can focus on improving the accuracy and including the prediction of mechanical properties in the suggested model.
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| 8. |
- Karim, Ali Naman, 1992, et al.
(author)
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Drying of an aerogel-based coating system in Swedish climates: Field tests and simulations
- 2024
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In: Journal of Building Engineering. - 2352-7102. ; 84
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Journal article (peer-reviewed)abstract
- Aerogel-based coating mortars (ACM-systems) introduce new solutions for energy-retrofit of uninsulated building envelopes, preserving their characteristics while minimizing the material thickness. However, when introducing new solutions, the long-term durability needs to be investigated. The hygrothermal (heat and moisture) performance is one aspect that needs to be secured. The aim of this study is to investigate the hygrothermal performance, with specific focus on moisture drying, of an ACM-system for external applications in Swedish climates. A field test was conducted where an ACM-system with 40 mm of ACM was applied on the exterior of a brick masonry wall partition. The temperature and relative humidity in the wall were monitored for 15 months. Furthermore, numerical hygrothermal simulations were used to predict the early stage drying and long-term performance of the ACM-system in four Swedish climates. The field mea- surements showed that the built-in moisture dried out after approximately 6 months, after which the ACM-system followed the variations in the surrounding climate for the remaining period. The simulations predicted that the early stage drying time ranged from 134 to 336 days, depending on climate and time of application. Furthermore, the elevated relative humidity in the ACM due to rainwater absorption resulted in an average thermal conductivity of up to 9 % above the rated value. Consequently, mitigating water absorption at the exterior is crucial for enhancing the long- term thermal performance in high rain load scenarios.
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| 9. |
- Karim, Ali Naman, 1992, et al.
(author)
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Duration of Early Stage Drying of Aerogel-based Renders: Field Tests and Simulations in Four Swedish Cities
- 2022
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In: Thermal Performance of the Exterior Envelopes of Whole Buildings. - 2166-8469. - 9781955516280 ; 2022
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Conference paper (peer-reviewed)abstract
- Aerogel-based renders are considered as suitable solutions for energy retrofitting of building envelopes due to their energy and space-saving potentials. Their thermal conductivity measured in laboratory and dry state is within 0.03-0.05 W/(m·K) (0.21-0.35 Btu·in/h·ft2·℉), around one tenth of conventional renders. However, previous research showed higher thermal conductivities measured in field than the declared values measured in laboratory. Aerogel-based renders are wet during the early stage of application until the initial built-in moisture is dried out. This higher initial moisture content is often given as an explanation for the higher values measured in field. To investigate the influence of the elevated initial moisture content further, the early stage drying performance of aerogel-based renders in Swedish climate conditions was studied experimentally and numerically. A section of a historical brick building in Gothenburg, Sweden, was renovated by applying a 30-40 mm (0.10-0.13 ft) thick layer of a commercial aerogel-based render. The construction was equipped with temperature and moisture sensors. Also, the exterior air temperature and relative humidity were measured. Numerical hygrothermal (heat and moisture) simulations were used to calculate the required drying time of the initial built-in moisture in aerogel-based renders. Several locations, representing different climates, and different application times of the aerogel-based render were considered in the simulations. The results of the field testing showed that a drying period longer than three months was required before the initial built-in moisture was completely dried out. According to the hygrothermal simulations conducted, a drying period of around 128-355 days could be expected for the built-in moisture in aerogel-based renders to dry out in four Swedish cities. The drying time depends on the time of application and the corresponding outdoor climate conditions during the early stage drying.
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| 10. |
- Karim, Ali Naman, 1992, et al.
(author)
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Experimental and Modelling Study of the Energy Performance of New Types of Energy Smart Window Curtains
- 2019
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In: Proceedings of the 14th International Conference on Buildings, Clearwater Beach, FL, USA, 9-12 December, 2019. ; , s. 276-
-
Conference paper (peer-reviewed)abstract
- New types of energy smart window curtains, with the aim to reduce the heat losses through windows have been studied. By covering windows with these curtains, for instance when buildings are not occupied, the energy performance can be improved and becomes more economical and sustainable. The paper aims to evaluate the energy performance of the curtains by in-situ measurements and simulations. In this paper, two different designs of these curtains have been studied. Curtain design (A) has the aim to increase the overall thermal resistances of window constructions and by that decrease the heat losses through windows. Curtain design (B) has an additional solar collector function which is aimed to capture some part of solar radiation striking windows and warm up the indoor environment. Warmer air is forced into the indoor environment by small fans inside the curtain. The paper investigates also the possibilities to optimize the design of the curtains regarding the emissivity of the material used in the design, using analytical models. During a 27 days measurement campaign, interior and exterior temperatures, intensity of solar radiation and energy consumptions in three identical test huts are continuously measured. The interior temperatures are kept constant using radiators. Results from the pilot study show that the total U-values of windows can be improved by using the curtains. For the case studied in this project, using the curtain design (A) improves the U-value of the window by approximately 50 %. For Curtain design (A) a surface to surface resistance of 0.65 m2K/W and for design (B) a resistance of 0.38 m2K/W is estimated.
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