| 1. |
- Adl-Zarrabi, Bijan, 1959, et al.
(author)
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Högpresterande fjärrvärmerör
- 2012
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Reports (other academic/artistic)abstract
- I ett fjärrvärmesystem är det viktigt att den producerade värmen levereras tillkonsumenterna med minsta möjliga förluster. Distributionssystemet ger upphov tillden enskilt största delen av värmeförlusterna under rörsystemets livslängd. Frågan omstorleken på värmeförlusterna har studerats alltsedan det första fjärrvärmesystemetbyggdes.Syftet med projektet är att undersöka nya material med avseende på deraslämplighet som isoleringsmaterial för rörsystemet. Det finns idag kommersiellttillgängliga produkter baserade på aerogel-kompositer och vakuumisoleringsteknikmed omkring två till fyra gånger så bra isoleringsprestanda som polyuretanisolering.Det finns dock i dagsläget inga material som är speciellt anpassade för rörsystemetPrototyper av hybridisolerade fjärrvärmerör med aerogel-filtar och vakuumisoleringspanelerhar tillverkats. Prototyperna har utvärderats i laboratoriemiljö ochmed hjälp av fältmätningar.Resultaten från undersökningen visade att aerogel-filtar och vakuumisoleringspanelervar kompatibla med polyuretanisolering och att det går att använda materialeni hybridisolering av fjärrvärmerör. En 10 mm aerogel-filt eller en 5 mm vakuumisoleringspanelförbättrar värmekonduktiviten hos röret (DN 100/225) med 15 %.En 10 mm tjock vakuumisoleringspanel ger en förbättring så stor som 30 %.Resultaten från fältmätningar med dubbelrör isolerade med vakuumpaneler ärännu inte kompletta men de befintliga temperaturmätningarna indikerar en klarminskning av värmeförlusterna.Projektet fokuserade på förbättring av rörsystemets termiska egenskaper. Detbehövs ytterligare forskning och utveckling för att kunna använda dessa material påett säkert sätt i ett fjärrvärmenät. Exempel på saker som måste undersökas ärlivslängden för de nya produkterna och ekologiska och ekonomiska aspekterrelaterade till de nya materialen.
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| 2. |
- Berge, Axel, 1983, et al.
(author)
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Assessing the Thermal Performance of District Heating Twin Pipes with Vacuum Insulation Panels
- 2015
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In: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 78, s. 382-387
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Conference paper (peer-reviewed)abstract
- In Sweden, around 10% of the energy supplied to the district heating networks are lost through heat losses from the distribution pipes. In cylindrical geometries it is preferable to improve the insulation as close to the center as possible. This has resulted in a hybrid insulation district heating pipe concept with a combination of vacuum insulation panels at the center, held in place bypolyurethane foam. In the twin pipe concept, the vacuum insulation panel cover the supply pipe. This creates a complex temperature profile over the section and measured results on single pipes might not be applicable. Therefore, there is a need for a method to evaluate the improvement of hybrid insulation twin pipes in the laboratory. This paper presents a method where two guarded hot pipe apparatuses is used, one heating rod for each pipe, to measure the heat losses from hybrid pipes and compare to a conventional polyurethane pipe. The measurements indicate an improvement in thermal performance by 12%-18% for the total losses and by 29% -39% for the supply pipe losses.
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| 3. |
- Berge, Axel, 1983
(author)
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Assessment of novel applications for nano-porous thermal insulation in district heating pipes and building walls
- 2016
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Doctoral thesis (other academic/artistic)abstract
- In nano-porous thermal insulation there is a strong relation between the pressure and the thermal conductivity, even at pressures close to atmospheric pressure. This thesis presents research on applications of nano-porous insulation in hybrid insulation district heating pipes and in building walls.A concept of hybrid insulation district heating pipes has been investigated where the innermost layers of insulation consists of nano-porous insulation and the outer layers consists of polyurethane foam insulation. The concept has been investigated through a mix of laboratory measurements, field measurements and simulations. The presented research indicates that vacuum insulation panels (VIPs) can be used in district heating pipes to reduce the heat losses. For the evaluated configurations the heat losses were reduced by a magnitude of 30%. The heat losses from the supply pipe in a twin pipe were reduced by 50%. The two main considerations with using vacuum panels in district heating pipes are the thermal bridges and the long term performance. It is shown that the position of the thermal bridges in the panels has a large effect on the thermal performance of the twin pipes and the results indicate a preferred configuration to minimize heat loss. The thesis presents a model to evaluate the long term performance of the VIPs through temperature measurements. After three years of field measurements on pipes connected to a district heating network with temperatures up to 90C, there is no sign of any uncontrolled deterioration of the VIPs. Results from the investigation show that the use of aerogel can reduce the thickness of a load bearing stud wall with 40% compared to the use of conventional insulation. If done wrong, this can lead to some new consideration regarding mold growth risk. The fact that the thermal conductivity of nano-porous insulation is strongly influenced by the pressure in the pore gas can be used to create variable insulation, where the thermal properties of the insulation is changed to match the current circumstances. By putting the insulation in a diffusion tight bag, connected to a vacuum pump, the pressure in the material can be changed and thereby the thermal conductivity. The pressure was varied in a fumed silica and an aerogel blanket sample between 1 kPa and atmospheric pressure, which gave a variation in the thermal conductivity of 1.5 for the aerogel blanket and 3 for the fumed silica. Transient measurements during evacuation and refilling show that the thermal performance will be influenced by some transient effects, such as influence from the temperature of the inserted air, but the time scale is too small to have any large effect on the energy performance. When the variation is used in simulations of the energy use for an office building, an interesting result is that a variable construction gave a higher optimum U-value, corresponding to thinner walls.
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| 4. |
- Berge, Axel, 1983, et al.
(author)
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Changing internal pressure to achieve variable thermal conductivity in thermal insulation
- 2015
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In: Advance building skins: Proceedings of the International Conference on Building Envelope Design and Technology. - 9783851253979 ; , s. 309-316
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Conference paper (peer-reviewed)abstract
- Cold climates might have a variable need for thermal insulation. When there are large heat loads a low Uvalueis preferable, and opposite when heat loads are low and it is cold outdoors. One way to adjust the Uvalueis to change the gas pressure within the insulation. This would be especially effective in nano-porousmaterials where the relation between pressure and thermal conductivity is stronger. Measurements have beenconducted on an aerogel blanket and a fumed silica material. The results show an almost linear dependencein thermal conductivity at pressures between 1 kPa and 100 kPA for both materials. In the measurements,the thermal conductivity increase by a factor between 1.5 and 2.6 (highest conductivity divided by lowestconductivity).
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| 5. |
- Berge, Axel, 1983, et al.
(author)
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Determination of specific heat capacity by Transient Plane Source
- 2012
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In: Proceedings of the 5th International Building Physics Conference. ; , s. 131-136
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Conference paper (peer-reviewed)abstract
- The specific heat capacity of a material is of importance for thermal storage. Transient Plane Source (TPS) is a measurement method with a sensor that works both as a heat source and as a resistance thermometer. The standard TPS measurement gives the thermal conductivity and thermal diffusivity of an isotropic material which can be used to calculate the heat capacity. The thermal properties of an anisotropic material can be measured if the heat capacity is known. A method for heat capacity measurement exists, where the TPS sensor is attached to a golden sample container which is surrounded by insulation. However, its results are based on an assumption of negligible heat losses which leads to uncertainties in the results. From that position, this paper aims to give an answer of how to model the heat losses from the specific heat measurements with TPS. A new set-up is introduced, where the sensor with the container hangs freely in a steel tube in order to get more predictable heat losses. The results show that the measurements can be modelled as a network of lumps connected by conductances which can be approximated as constant. Thereby, the conductances out from the system can be solved from a reference measurement and used as input data for a model of a measurement with a sample. The model seems to underestimate the heat capacity, which might be a consequence of temperature dependent effects on the conductances from convection. The tube in the set-up could be evacuated to minimize those losses.
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| 6. |
- Berge, Axel, 1983, et al.
(author)
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Determination of specific heat capacity by transient plane source
- 2013
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In: Frontiers of Architectural Research. - : Elsevier BV. - 2095-2635. ; 2:4, s. 476-482
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Journal article (peer-reviewed)abstract
- A standard TPS measurement gives the thermal conductivity and thermal diffusivity of an isotropic material which in turn gives the heat capacity. The thermal properties of an anisotropic material can be measured if the heat capacity is known. A method for heat capacity measurement exists, where the TPS sensor is attached to a sample container which is surrounded by insulation. However, it's based on an assumption of negligible heat losses which leads to uncertainties in the results. From that position, this work aims to model the heat losses from the specific heat measurements with TPS. A new set-up is introduced, where the sensor with the container hangs freely in a steel tube to get more predictable heat losses. The results show that the measurements can be modelled as a network of lumps connected by conductances approximated as constant. Thereby, the conductances out from the system can be solved from a reference measurement and used as input for a model of a measurement with a sample. The model seems to underestimate the heat capacity, which might be a consequence of temperature dependent effects on the conductances from convection. The tube in the set-up could be evacuated to minimize those losses.
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| 7. |
- Berge, Axel, 1983, et al.
(author)
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Effect from a Variable U-Value in Adaptive Building Components with Controlled Internal Air Pressure
- 2015
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In: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 78, s. 376-381
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Conference paper (peer-reviewed)abstract
- A variable U-value would be beneficial for a buildings thermal performance. One way to switch the U-value of a wall, insulated with nano-porous material, is to change the internal pressure of the insulation This paper present thermal conductivity measurements showing a possible variation around of 3 times for a fumed silica and less than 2 times for an aerogel blanket when the pressure was varied between 1 and 100 kPa. The variation factor of 3 was used in building energy simulation of a Swedish office showing that a U-value which can be varied within that range can give a significant reduction energy demand. Especially when energy used for cooling is weighted as worse than energy used for heating.
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| 8. |
- Berge, Axel, 1983, et al.
(author)
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Evaluation of vacuum insulation panels used in hybrid insulation district heating pipes
- 2014
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In: Proccedings of The 14th international symposium on district heating and cooling. - 9789185775248 ; , s. 454-461
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Conference paper (other academic/artistic)abstract
- It is of interest to lower the energy losses from districtheating pipes both for economic and environmentalreasons. This paper evaluates a hybrid insulationsolution where Vacuum Insulation Panels (VIP) are putaround the supply pipe in a district heating pipe and therest of the casing pipe is filled with polyurethane foam(PUR).The apparatus for the “guarded hot pipe” method wasused to estimate the thermal properties of single pipes,which have been used as input in finite element modelsfor simulation of twin pipes in field. The simulationsindicate a total reduction in the energy loss between18% and 32% compared to pipes of the same size withpure PUR insulation. Furthermore, the losses from thesupply pipe decrease by up to 56%.To achieve the low energy losses, the vacuum in thepanels has to be preserved over the life span of theVIP. In field measurements, a hybrid pipe prototypewas connected to the district heating grid in Varberg(southwest Sweden). After almost two years, the pipeis still working without any detectable deterioration ofthe insulation performance. The panels have alsobeen tested at high temperatures in laboratory withpromising results.
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| 9. |
- Berge, Axel, 1983, et al.
(author)
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Field measurements on a district heating pipe with vacuum insulation panels
- 2016
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In: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 87:3, s. 1130-1138
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Journal article (peer-reviewed)abstract
- © 2015 Elsevier Ltd. In Swedish district heating networks, around 10% of the supplied thermal energy is lost in the distribution system. One solution to decrease the losses is to use hybrid insulation district heating pipes, a concept where the innermost part of the thermal insulation consists of vacuum insulation panels, held in place by polyurethane foam. One problem with vacuum insulation panels are their sensitivity to high temperatures. This paper presents field measurements on a hybrid insulation district heating pipe where the temperatures have been measured continuously at various positions of a pipe section. The measurements show consistency and a large difference between hybrid insulation parts and reference parts without vacuum insulation panels. A superposition model has been used to calculate the temperature in a point and compare it to the measurement. The results are compared to the same calculation on the results from finite element simulations. The results show clearly that the vacuum panels in the pipes have not collapsed. A slow deterioration of the panels is harder to find with this model. Changes in the system, such as a return temperature which decreases over time, can give a larger impact, concealing the change in the panel performance.
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| 10. |
- Berge, Axel, 1983, et al.
(author)
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Literature Review of High Performance Thermal Insulation
- 2012
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Reports (other academic/artistic)abstract
- The European Union has decided to decrease the energy use for heating of buildings with 50% in 2050. To reach the target the amount of insulation in the building envelope has to increase. With conventional insulation materials, such as mineral wool and expanded polystyrene (EPS), the required additional thickness of the building envelope leads to a larger share of the building area dedicated for structural elements. A number of high performance thermal insulation materials and components have been introduced to the building market during the last decades which can give the same thermal resistance using a thinner construction. This report presents how insulation materials work. The properties of aerogels and vacuum insulation panels (VIP) are described more in detail.Heat transfer in thermal insulation materials is generally divided in heat conduction through the solid material, conduction through the gas molecules and radiation through the pores. Gas convection in the material can be important on a larger material scale and in porous materials, such as mineral wool. Aerogel for building applications has a thermal conductivity of around 14-16 mW/(m•K) while VIP can reach down to 4 mW/(m•K). This can be compared to EPS and stagnant air with a thermal conductivity of 36 and 25 mW/(m•K) respectively. Aerogel and VIP have small pores in the range of 10-100 nm which means the gas conductivity is reduced at atmospheric pressure.Up till now aerogel has been used in space industry, chemical industry and in sport equipment but not that much in buildings. A limiting factor is the high cost of the aerogel. Since the end of the 1990s VIP has been used in buildings but originally they were developed for refrigerators and cold shipping boxes. To use VIP in buildings, the architects and engineers have to pay special attention to attachment details since the VIP cannot be adapted on the construction site. Nevertheless, novel high performance thermal insulation materials could be an important and feasible solution to decrease the thickness of the building envelope while maintaining the thermal resistance. These materials create new opportunities for architects and engineers to design energy efficient buildings.
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