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  • 1.
    Anderson, Jan-Olof
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Analysis of the heat demand in batch kilns2012Conference paper (Other academic)
    Abstract [en]

    During the production of lumber more than half of the entering timber to the sawmill becomes biomass. About 12 %wt of the entering timber is combusted to supply heat for the sawmill. Major part of the heat is supply the kilns. Due to the high evacuation losses the energy efficiency in a traditional drying kiln is only 13 %. This makes the lumber drying to a low and ineffective process in an energy point of view.Forced drying technologies are a compromise between high lumber quality, low lead time and decreased energy use. Often is the quality and lead time prioritised. This paper advises an appropriate method to simulate the energy efficiency when drying lumber in a batch kiln. To ensure real life drying conditions, with sufficient quality and lead time the initial conditions were made from simulated drying schemes, from simulation program called Torksim. By combine thermodynamics and psychrometric relationship, the energy streams and losses during the drying scheme were established. The program can be used to compare several drying conditions and clarify the magnitude of losses. Different types of technologies affecting the kiln energy efficiency and to compare drying conditions to each other. For instance heat exchanger, heat pumps, condense walls, absorption system etc.The used drying conditions are suitable for north European lumber and climate, but the initial conditions can be changed for analyses of other types of drying conditions. The program is a usable tool to analyses different types of technologies effect on the kiln energy efficiency and to compare drying conditions and different drying scheme to each other.

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  • 2.
    Andersson, Jan-Olof
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Elfgren, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Improved energy efficiency in juice production through waste heat recycling2014In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 130, no S1, p. 757-763Article in journal (Refereed)
    Abstract [en]

    Berry juice concentrate is produced by pressing berries and heating up the juice. The by-products are berry skins and seeds in a press cake. Traditionally, these by-products have been composted, but due to their valuable nutrients, it could be profitable to sell them instead. The skins and seeds need to be separated and dried to a moisture content of less than 10 %wt (on dry basis) in order to avoid fermentation. A berry juice plant in the north of Sweden has been studied in order to increase the energy and resource efficiency, with special focus on the drying system. This was done by means of process integration with mass and energy balance, theory from thermodynamics and psychrometry along with measurements of the juice plant. Our study indicates that the drying system could be operated at full capacity without any external heat supply using waste heat supplied from the juice plant. This would be achieved by increasing the efficiency of the dryer by recirculation of the drying air and by heat supply from the flue gases of the industrial boiler. The recirculation would decrease the need of heat in the dryer with about 52%. The total heat use for the plant could thereby be decreased from 1262 kW to 1145 kW. The improvements could be done without compromising the production quality.

  • 3.
    Andersson, Jan-Olof
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Improved energy efficiency in sawmill drying system2014In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 113, p. 891-901Article in journal (Refereed)
    Abstract [en]

    The worldwide use of biomass has increased drastically during the last decade. At Swedish sawmills about half of the entering timber becomes lumber, with the remainder considered as by-product (biomass). A significant part of this biomass is used for internal heat production, mainly for forced drying of lumber in drying kilns. Large heat losses in kilns arise due to difficulties in recovering evaporative heat in moist air at low temperatures. This paper addresses the impact of available state-of-the-art technologies of heat recycling on the most common drying schemes used in Swedish sawmills. Simulations of different technologies were performed on an hourly basis to compare the heat and electricity demand with the different technologies. This was executed for a total sawmill and finally to the national level to assess the potential effects upon energy efficiency and biomass consumption. Since some techniques produce a surplus of heat the comparison has to include the whole sawmill. The impact on a national level shows the potential of the different investigated techniques. The results show that if air heat exchangers were introduced across all sawmills in Sweden, the heat demand would decrease by 0.3 TWh/year. The mechanical heat pump technology would decrease the heat demand by 5.6 TWh/year and would also produce a surplus for external heat sinks, though electricity demand would increase by 1 TWh/year. The open absorption system decreases the heat demand by 3.4 TWh/year on a national level, though at the same time there is a moderate increase in electricity demand of 0.05 TWh/year. Introducing actual energy prices in Sweden gives an annual profit (investment cost excluded) on national level for the open absorption system of almost 580 million SEK. For the mechanical heat pump technology the profit is 204 million SEK and for the traditional heat exchanger the profit is significant lower. It has been found that a widespread implementation of available energy recovery technologies across Swedish sawmills would result in substantial savings of biomass for other purposes in the society

  • 4.
    Andersson, Jan-Olof
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    MIND based optimisation and energy analysis of a sawmill production line2010In: PRES 2010: 13th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction, 28 August - 1 September 2010, Prague, Czech Republic, 2010, p. 1-5Conference paper (Refereed)
    Abstract [en]

    The lumber drying process uses about 80 % of the total heat consumption in sawmills. Efforts to increase energy efficiency in lumber kilns were very restricted due to the low biomass prices between the 80th and 90th. Today with higher production and biomass prices, companies want to decrease their own use of biomass and increase the heating system efficiency. The study proposes alternative ways to reduce the heat consumption at batch kilns by recirculation of the evacuation air and addresses particular problem encountered in sawmills. Which produce their own heat and suffer from bottlenecks in the heating system due to high heat load from the dryers and increased production. The study shows the possibility to recycle the evacuation air from each kiln which reduces the overall heat consumption of the kilns by 12 %. At nationally basis this corresponds to a decrease of heat consumption of 440 GWh annually, among Swedish sawmill. This will decrease the individual heat consumption of the kilns, heat load in the heating system and the bottleneck effect in the drying process. The decreased own use of biomass brings benefits of more available biomass to the market and increased profits for the sawmill.

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  • 5.
    Andersson, Jan-Olof
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Surplus biomass through energy efficient kilns2011In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 88, no 12, p. 4848-4853Article in journal (Refereed)
    Abstract [en]

    The use of biomass in the European Union has increased since the middle of the 1990s, mostly because of high subsidies and CO2 emission regulation through the Kyoto protocol. The sawmills are huge biomass suppliers to the market; out of the Swedish annual lumber production of 16.4 Mm3, 95% is produced by medium to large-volume sawmills with a lumber quotient of 47%. The remaining part is produced as biomass. An essential part (12%) of the entering timber is used for supply of heat in their production processes, mostly in the substantial drying process. The drying process is the most time and heat consuming process in the sawmill. This study was undertaken to determine the sawmills’ national use of energy and potential magnitude of improvements. If the drying process can be made more effective, sawmills’ own use of biomass can be decreased and allow a considerably larger supply to the biomass market through processed or unprocessed biomass, heat or electricity production. The national electricity and heat usage when drying the lumber have been analysed by theoretical evaluation and experimental validation at a batch kiln. The main conclusion is that the heat consumption for drying lumber among the Swedish sawmills is 4.9 TW h/year, and with available state-of-the-art techniques it is possible to decrease the national heat consumption by approximately 2.9 TW h. This additional amount of energy corresponds to the market’s desire for larger energy supply.

  • 6.
    Chen, Jingjing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. State Key Laboratory of Material-Oriented Chemical Engineering, Nanjing Tech University, 210009 Nanjing, PR China.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Jansson, Urban
    Boden Biogas Plant, 96138, Smidesvägen 3, Boden, Sweden.
    Lu, Xiaohua
    State Key Laboratory of Material-Oriented Chemical Engineering, Nanjing Tech University, 210009 Nanjing, PR China.
    Wang, Changsong
    State Key Laboratory of Material-Oriented Chemical Engineering, Nanjing Tech University, 210009 Nanjing, PR China.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    A high efficient heat exchanger with twisted geometries for biogas process with manure slurry2020In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 279, article id 115871Article in journal (Refereed)
    Abstract [en]

    Heat-transfer enhancement in manure slurry is crucial for increasing the efficiency and production of biogas during anaerobic digestion in biogas plants. In this study, a novel heat exchanger with an optimal twisted geometry was developed based on the numerical screening of the twisted tubes with equilateral polygons, and experiments were conducted to validate the numerical results. It was observed that the SST k-ω model is more efficient than other turbulence models in representing the heat transfer performance of the twisted tubes, and the numerical model with a thermostatic wall can be used to reliably screen the twisted geometries. The twisted hexagonal tube has the optimal geometry, with enhancement capability of up to 1.4 times compared to that of the circular tube. The formation of high continuity regions with relatively strong heat-transfer rates along the heat-exchange wall is the main reason for the high performance during heat transfer. The external heating process was integrated in a full-scale biogas plant, and the model and algorithm were developed and validated with additional experiments to describe the overall performance of both conventional and screened optimal geometries under different conditions. It was observed that a profit equivalent to 39% of total production for a large-scale biogas plant can be achieved owing to energy conservation in external heating with the twisted hexagonal tubes.

  • 7.
    Chen, Jingjing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. State Key Laboratory of Material-Oriented Chemical Engineering, Nanjing Tech University, 210009, Nanjing, People’s Republic of China.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Jansson, Urban
    Boden Biogas Plant, Smidesvägen 3, 96138, Boden, Sweden.
    Wang, Changsong
    State Key Laboratory of Material-Oriented Chemical Engineering, Nanjing Tech University, 210009, Nanjing, People’s Republic of China.
    Lu, Xiaohua
    State Key Laboratory of Material-Oriented Chemical Engineering, Nanjing Tech University, 210009, Nanjing, People’s Republic of China.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Heat-transfer performance of twisted tubes for highly viscous food waste slurry from biogas plants2022In: Biotechnology for Biofuels and Bioproducts, E-ISSN 2731-3654, Vol. 15, article id 74Article in journal (Refereed)
    Abstract [en]

    Background: The use of food waste as feedstock shows high production of biogas via anaerobic digestion, but requires efficient heat transfer in food waste slurry at heating and cooling processes. The lack of rheological properties hampered the research on the heat-transfer process for food waste slurry. Referentially, the twisted hexagonal and elliptical rubes have been proved as the optimal enhanced geometry for heat transfer of medium viscous slurries with non-Newtonian behavior and Newtonian fluids, respectively. It remains unknown whether improvements can be achieved by using twisted geometries in combination with food waste slurry in processes including heating and cooling.

    Results: Food waste slurry was observed to exhibit highly viscous, significant temperature-dependence, and strongly shear-thinning rheological characteristics. Experiments confirmed the heat-transfer enhancement of twisted hexagonal tubes for food waste slurry and validated the computational fluid dynamics-based simulations with an average deviation of 14.2%. Twisted hexagonal tubes were observed to be more effective at low-temperature differences and possess an enhancement factor of up to 2.75; while twisted elliptical tubes only exhibited limited heat-transfer enhancement at high Reynolds numbers. The heat-transfer enhancement achieved by twisted hexagonal tubes was attributed to the low dynamic viscosity in the boundary layer induced by the strong and continuous shear effect near the walls of the tube.

    Conclusions: This study determined the rheological properties of food waste slurry, confirmed the heat-transfer enhancement of the twisted hexagonal tubes experimentally and numerically, and revealed the mechanism of heat-transfer enhancement based on shear rate distributions.

  • 8.
    Dahl, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hermansson, Roger
    Westerlund, Lars
    Egenskaper hos gaser, vätskor och fasta ämnen2001In: VVS 2000 Tabeller och diagram, Stockholm: Förlags AB VVS , 2001Chapter in book (Other (popular science, discussion, etc.))
  • 9.
    Dahl, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hermansson, Roger
    Westerlund, Lars
    Abel, Enno
    Värmeströmning2008In: VVS 2000 Tabeller och diagram, Stockholm: Förlags AB VVS , 2008Chapter in book (Other (popular science, discussion, etc.))
  • 10.
    Darbandi, Tayebeh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CFD modeling of the forces in the wet scrubber acting on particulate matter released from biomass combustion2021In: Thermal Science and Engineering Progress, ISSN 2451-9049, Vol. 25, article id 100997Article in journal (Refereed)
    Abstract [en]

    The flue gas from biomass combustion contains particulate matter, which is a considerable precarious constituent cause of serious health issues. The wet flue gas cleaning method is one of the most efficient solutions for small-scale boilers (≈100 kW) and small particles. In this study, the forces on particulate matter in a wet flue gas cleaning process using an absorption solution have been studied with the implementation of compiled user-defined function code in Ansys Fluent 19.2®. The forces governing the wet cleaning process as well as the corresponding conditions of the system have also been studied. Drag, buoyancy, diffusiophoresis, and thermophoresis forces have been analyzed as the most important forces acting on particulate matters. Simulations have been conducted for velocities, particle sizes, temperatures, and water vapor mass fractions within the same range as experiments in order to acquire trends for particle collection for these variables.

    Moreover, the influence of diffusiophoresis force was compared to that of the thermophoresis force under different conditions. It was unveiled that the diffusiophoresis force had a significant effect on nanoparticle collection. The impact of diffusiophoresis is increased by the ascending gradient of temperature as well as water vapor mass fraction. Simulations declare that the thermophoresis force effect is small compared to the diffusiophoresis force effect in the particle collection process. Thereby, one could conclude that the diffusiophoresis force governs the collection of particulate matter in the wet scrubber method. The model validation is confirmed by comparing the results with previous empirical models.

  • 11.
    Darbandi, Tayebeh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Effect of operation conditions on particulate matter removal by a packed-bed wet scrubber for a small-scale biofuel boiler2024In: Thermal Science and Engineering Progress, ISSN 2451-9049, Vol. 47, article id 102290Article in journal (Refereed)
    Abstract [en]

    In 2013 the EU’s Clean Air Policy Package was established, aiming to reduce air pollution to half by 2030 compared to the level in 2005. Small-scale (<500 kW)biofuel boilers play a key role in particulate matter emission, and exposure to particulate matter even in the short term can cause different diseases. With the aim of reducing particulate matter emission in Europe, this study presents an approach to improve the removal of particulate matter emitted by small-scale boilers. A biofuel combustion boiler was equipped with a packed-bed wet scrubber, and the flue gas emitted through combustion was cleaned through the wet scrubber using a saltwater mixture. The performance of a packed-bed wet scrubber was investigated under different operating conditions. The effect of the salt concentration of the absorption solution, the temperature of the absorption solution fed to the absorber, and the height of the packed-bed material on the particle collection efficiency were measured. The operating conditions were selected based on the results obtained in a previous computational fluid dynamic simulation study. The results obtained in the present study show that an absorption solution temperature of 30 °C and an absorption solution concentration of 75 % with a full height of the packed-bed material lead to the best performance in the system. Totally keeping the absorption solution temperature as low as possible, increasing the absorption solution concentration, and raising the packed-bed material height could improve the particle collection efficiency by enhancing the effect of the diffusiophoresis and thermophoresis forces and the contact time between the flue gas and solution.

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  • 12.
    Darbandi, Tayebeh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Efficient Cleaning and Heat Recovery of Flue Gas from a Small-Scale Boiler2021In: Chemical Engineering & Technology, ISSN 0930-7516, E-ISSN 1521-4125, Vol. 44, no 11, p. 2116-2125Article in journal (Refereed)
    Abstract [en]

    Small-scale biomass boilers contribute to the emission of particulate matter (PM) to the environment. In this study, the performance of a wet scrubber purification system for flue gas was experimentally investigated. The experimental setup consisted of a boiler, a wet scrubber, a generator, and heat exchangers. The results show an average particulate collection efficiency of around 42% for a particulate matter size range of 0.08-10 µm, within a testing period of 5 months. Furthermore, the results show an improvement in the heat recovery of about18%. Focusing only on the heat losses through exhaust flue gases, the losses were shown to have decreased by 72%. During the total testing period (8.5 months), no decrease could be noticed in the absorption solution ability.  

  • 13.
    Gustafsson, Anna-Maria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Heat extraction thermal response test in groundwater-filled borehole heat exchanger: Investigation of the borehole thermal resistance2011In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 36, no 9, p. 2388-2394Article in journal (Refereed)
    Abstract [en]

    In groundwater-filled borehole heat exchangers (BHEs) convective flow influences the heat transfer in the borehole. During heat extraction thermal response tests (TRTs) the effect of the changing convective flow is more dominant than during heat injection tests. Water is heaviest around 4 °C and when exceeding this temperature during the test, the convective flow is stopped and restarted in the opposite direction resulting in a higher borehole thermal resistance during that time. Just before 0 °C the convective flow is the largest resulting in a much lower borehole thermal resistance. Finally, during the freezing period phase change energy is released and material parameters change as water is transformed into ice, resulting in a slightly higher borehole resistance than at a borehole water temperature of 0 °C. The changes in borehole thermal resistance are too large for ordinary analysis methods of thermal response tests to work. Instead another method is introduced where the borehole thermal resistance is allowed to change between different time intervals. A simple 1D model of the borehole is used, which is matched to give a similar mean fluid temperature curve as the measured one while keeping the bedrock thermal conductivity constant during the whole test. This method is more time-consuming than ordinary TRT analyses but gives a good result in showing how the borehole thermal resistance changes. Also, a CFD-model with a section of a simplified borehole was used to further study the effect of convection and phase change while the temperature was decreased below freezing point. The test and the model show similar results with large variations in the borehole thermal resistance. If the knowledge of changing borehole thermal resistance was used together with a design program including the heat pump and its efficiency, a better BHE system design would be possible.

  • 14.
    Gustafsson, Anna-Maria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Multi-injection rate thermal response test in groundwater filled borehole heat exchanger2010In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 35, no 5, p. 1061-1070Article in journal (Refereed)
    Abstract [en]

    During a thermal response test (TRT) or during operation of a borehole heat exchanger (BHE) system, a temperature gradient in and around the borehole is achieved. This causes convective flow in the groundwater due to density differences. In groundwater filled BHE the convective heat flow influences the heat transport in the borehole system. The size of the influence depends on the injection rate used, which changes during the year for normal BHE systems. Multi-injection rate TRT (MIR TRT) may be used as a method to detect the convective heat influence and to examine the effect on the BHE thermal transport parameters. It was shown that MIR TRT constitutes a valuable method to detect fractured bedrock and to examine the effect of different heat injection rates. For boreholes located in solid bedrock only the borehole thermal resistance was influenced by the convective flow. An increase in heat injection rate resulted in a decrease in resistance. It was shown that the length of the collector did not affect the result. For the fractured bedrock the effective bedrock conductivity was also affected, an increase in heat injection rate resulted in a higher effective bedrock thermal conductivity.

  • 15.
    Gustafsson, Anna-Maria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Simulation of the thermal borehole resistance in groundwater filled borehole heat exchanger using CFD technique2010In: International Journal of Energy and Environment, ISSN 2076-2895, E-ISSN 2076-2909, Vol. 1, no 3, p. 399-410Article in journal (Refereed)
    Abstract [en]

    The thermal borehole resistance in a groundwater-filled borehole heat exchanger (BHE) is affected of both conductive and convective heat transfer through the borehole water. To calculate this heat transport, different models are required compared to calculation of only conductive heat transfer in a back-filled BHE. In this paper some modelling approximations for groundwater-filled, single U-pipe BHEs were investigated using a 3D CFD model. The purpose is to find approximations that enable to construct a fast, simple model including the convective heat transfer that may be used in thermal response test analyses and BHE design programs. Both total heat transfer calculations (including convective and conductive heat transport) and only conductive heat transfer calculations were performed for comparison purposes. The approximations that are investigated are the choice of boundary condition at the U-pipe wall and using a single pipe in the middle of the borehole instead of the U-pipe. For the total heat transfer case, it is shown that the choice of boundary condition hardly affects the calculated borehole thermal resistance. For the only conductive heat transfer case, the choice of boundary condition at the pipe wall gives large differences in the result. It is also shown that using an annulus model (single pipe in the middle of the borehole) results in similar heat transfer as the U-pipe model provided that the equivalent radius is chosen appropriately. This approximation can radically decrease the number of calculation cells needed.

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  • 16.
    Gustafsson, Anna-Maria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hellström, Göran
    CFD-modelling of natural convection in a groundwater-filled borehole heat exchanger2010In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 30, no 6-7, p. 683-691Article in journal (Refereed)
    Abstract [en]

    In design of ground-source energy systems the thermal erformance of the borehole heat exchangers is important. In Scandinavia, boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a three meter long borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the borehole. The density gradient in the borehole is a result of the heat transfer rate and the mean temperature level in the borehole water. Therefore in calculations of the thermal resistance in groundwater filled boreholes convective heat flow should be included and the actual injection heat transfer rate and mean borehole temperature should be considered.

  • 17. Johansson, Lars
    et al.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    An open absorption system installed at a sawmill: Description of pilot plant used for timber and bio-fuel drying2000In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 25, no 11, p. 1067-1079Article in journal (Refereed)
    Abstract [en]

    This work describes a pilot plant and its different parts in a system used for bio-fuel drying and timber drying with an open absorption process. This technique has not been used previously in Sweden in this application. The open absorption system has been installed on four timber dryers and one bio-fuel dryer at a sawmill located in the northern part of Sweden. The annual energy demand for the dryers has decreased considerably. The specific heat demand for a conventional drying system is about 5970 kJ/kg of evaporated water. For the open absorption system, the corresponding value is a heat demand of approximately 1400 kJ/kg of evaporated water. At the same time, an additional 360 kJ/kg of electricity has to be supplied. Here, 45,000 m3 per year of dried bio-fuel has been sold on the market as a result of the decreased heat demand in the wood dryers at the sawmill. The plant has been working well and has had a high availability. The pay-off time for the investment will be approximately 3 years for nondiscounted cash-flows

  • 18. Johansson, Lars
    et al.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CFD modeling of the quench in a pressurized entrained flow black liquor gasification reactor2006In: CHISA 2004: 16th International Congress of Chemical and Process Engineering, 22 - 26 August 2004, Prague, Czech Republic, Prague, 2006, p. 11399-11409Conference paper (Refereed)
    Abstract [en]

    Black liquor, a biomass-based fuel formed in the papermaking process has traditionally been burned in recovery boilers to generate steam and electricity and recover the inorganic chemicals. Pressurized black liquor gasification offers an attractive alternative to the recovery boiler that has the potential to add a net electrical power of the order of 1000 MW to the Swedish power grid at full integration. Chemrec AB, one of the leading actors has developed an entrained down flow reactor. A development plant has been designed and is to be taken into operation during 2004, At the laboratory of Energy Technology Centre (ETC) in Pitea, Sweden. The plant will operate at 30 bar (a) and 30 tons/day black liquor will be gasified. The entrained flow reactor consists of two parts. In the gasification reactor black liquor is supplied together with an oxidant. Combustible fuel gases and inorganic smelt is formed. The smelt and fuel gases are transported to the quench cooler in the lower part where it is rapidly cooled by spray nozzles. The smelt is separated from the fuel gases by gravitation. At LTU a CFD model of the quench has been developed using the commercial code FLUENT 6. The simulations were performed in steady state using the segregated solver. A non structured mesh with approximately 48000 cells was used in the study. The results show that the model is predicting the flow pattern, velocity field and temperature field. The separation of smelt from the gas flow shows that droplets larger then 100 μm will be collected in the bottom of the quench but smaller droplets will travel with the gas flow to the quench outlet. Further work is required in order to make the model more complete. Radiation needs to be included as well as important chemical reactions. The model also needs to be validated against measurement data when the development plant is in operation.

  • 19. Johansson, Lars
    et al.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Energieffektiv biobränsletorkning med öppen absorptionsprocess: beskrivning av befintligt system samt parameterstudie som underlag till systemförbättringar1999Report (Other academic)
    Abstract [sv]

    Denna rapport beskriver ingående en befintlig torkanläggning vid ett sågverk, Martinsons Trä, beläget i Västerbotten. Anläggningen bygger på en teknik, sk öppet absorptionssystem, vilken ej tidigare i Sverige utnyttjats i torksammanhang.För att belysa möjligheterna att vidareutveckla tekniken har en parameterstudie genomförts. Variabler såsom torktemperatur, absorptionslösningens koncentration samt kylning vid absorption har undersökts. Som jämförelse utnyttjas dagens anläggning, ett lågtemperatursystem, (torktemperatur 78°C).Resultaten visar att lufttemperaturen i torksystemet skall vara så hög som möjligt för att minimera erforderlig luftmängd. Det är möjligt att reducera luftflödet med ca 30% vid bibehållen torkkapacitet genom att höja torktemperaturen till 140°C.En kylning av luften vid passage genom absorbatorn minskar även erforderlig luftmängd. För att detta skall vara ett alternativ måste det finnas avsättning för den bortförda värmemängden från luftkretsen. Detta avser såväl temperaturnivå som energimängd. En kylning med 5°C jämfört med dagens anläggning minskar luftflödet med ca 50% vid bibehållen avfuktnings-kapacitet.Hög saltkoncentration bör eftersträvas för att minimera biobränsletork och absorbator. En begränsade faktor utgör kristallisationsproblem för absorptionslösningen. En saltkoncentration på 85 viktsprocent för lösningen i absorbatorn reducerar luftflödet med ungefär 30% av referensfallet.Studien visar att det är möjligt att reducera den befintliga anläggningens

  • 20. Johansson, Lars
    et al.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Energy efficient bio fuel drying with an open absorption system1999In: Applied Modelling and Simulation, International conference, 1999Conference paper (Refereed)
  • 21. Johansson, Lars
    et al.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Energy efficient bio fuel drying with an open absorption system: parameter study in order to reduce investment costs2000In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 67, no 3, p. 231-244Article in journal (Refereed)
    Abstract [en]

    A pilot plant using the open absorption system for drying of timber and bio fuel has been realized at a sawmill located in the northern part of Sweden. The technique decreases the energy demand for the dryers considerably and the system has an availability of about 8000 h per year. Compared with other drying techniques, the investment cost is high due to large airflow and therefore large apparatus. The main part of the investment cost, i.e. about 70% originates from the bio fuel dryer and the absorbers. In order to decrease the initial cost a parameter study has been made to investigate the possibilities to reduce the airflow of the drying process, i.e. bio fuel dryer and absorber. Parameters studied are drying temperature, salt concentration and cooling of the airflow during the absorption process. Measured values from the pilot plant have been used as a reference case. The results show that it is possible to decreases the airflow by 31% when using a higher drying temperature. Higher salt concentration decreases the airflow by approximately 32% and cooling during absorption makes it possible to decrease the airflow by 50%. In order to minimize the airflow, the three parameters were combined. In this case it is possible to decrease the airflow by approximately 60%. The electrical input for the plant is also high due to large air and solution flows. By decreasing the airflow, the required electrical input will also decrease since the fan power is proportional to the volume airflow. The results clearly show that it is possible to reduce the airflow and therefore the investment costs compared with the pilot plant.

  • 22. Johansson, Lars
    et al.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Energy savings in indoor swimming-pools: comparison between different heat-recovery systems2001In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 70, no 4, p. 281-303Article in journal (Refereed)
    Abstract [en]

    In indoor swimming-pool facilities, the energy demand is large due to ventilation losses with the exhaust air. Since water is evaporated from the pool surface, the exhaust air has a high water content and specific enthalpy. Because of the low temperature, the heat from the evaporation is difficult to recover. In this paper, the energy demand for the conventional ventilation technique in indoor swimming pools is compared to two different heat-recovery techniques, the mechanical heat pump and the open absorption system. The mechanical heat-pump is the most widely used technique in Sweden today. The open absorption system is a new technique in this application. Calculations have been carried out on an hourly basis for the different techniques. Measurements from an absorption system pilot-plant installed in an indoor swimming pool in the northern part of Sweden have been used in the calculations. The results show that with the mechanical heat pump, the electrical input increases by 63 MWh/year and with the open absorption system 57 MWh/year. However, a mechanical heat-pump and an open absorption system decrease, the annual energy demand from 611 to 528 and 484 MWh respectively, which correspond to decreases of approximately 14 and 20% respectively. The electricity input will increase when using heat-recovery techniques. Changing the climate in the facility has also been investigated. An increased temperature decreases the energy demand when using the conventional ventilation technique. However, when either the mechanical heat-pump or the open absorption system is used, the energy demand is increased when the temperature is increased. Therefore increasing the temperature in the facility when using the conventional technique should be considered the first measure to reduce the energy demand.

  • 23.
    Johansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Modelling gas cooling in black liquor gasification2011In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 31, no 16, p. 3176-3181Article in journal (Refereed)
    Abstract [en]

    Pressurized Entrained Flow High Temperature Black Liquor Gasification (PEHT-BLG) is a new technology not yet commercialized. The technology has the potential to improve the efficiency of energy and chemical recovery in the pulping industry. It also enables new processes, i.e. production of renewable motor-fuels from the syngas. The technology is not yet fully developed and interest in computer models for scale-up and optimization of the process in combination with experiments is favourable in the development process. A demonstration plant has been in operation since late 2005, in Pitea, Sweden. At Lulea University of Technology (LTU), a CFD model of a vertical tube in the counter current condenser has been developed using the commercial code FLUENT 6. The geometry is consistent with the demonstration plant and input data of the design has been used as boundary conditions for the model. The objective is to create a CFD model that can be used as a designing tool for the technology developer in future scale-up and for commercialized units. The model predicts the condensation process very well and shows that the major part of the condensation takes place in the first quarter of the tube under the given conditions. The heat transfer through the tube wall has been modeled based on results from the literature. The results show the importance of accurate heat transfer coefficients. Compared to designing data, the heat transfer through the wall and the condensate rate show good agreement. However, these results need to be validated against experimental data for different conditions.

  • 24.
    Lundqvist, Petter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Air heating system design for a sub-Arctic climate using a CFD technique2019In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 160, article id 106164Article in journal (Refereed)
    Abstract [en]

    The thermal comfort in a residential building equipped with an air heating system and located in a sub-Arctic region was investigated with computational fluid dynamics (CFD) software. The predicted percentage of dissatisfied (PPD) was used to identify flaws with the heating system during winter conditions. New scenarios were simulated and compared to each other to see potential improvements of the thermal indoor climate. Comparison was done by combining the discomfort spaces inside rooms, the level of the discomfort and the time spent in these spaces. The discomfort covered 8–38% of the interior volume depending on the test case. The results provide the necessary means to create a satisfactory thermal indoor climate if an air heating system is to be utilized in sub-Arctic regions during the winter. The correct heat demand for each floor and appropriate placement of the supply devices are required. Adding air transfer units or grilles in rooms from which exhaust air is removed further improves the comfort. The results also show the strength of using CFD technique when investigating the indoor discomfort with PPD, and how a fair assessment can be done by combining the PPD with time.

  • 25.
    Lundqvist, Petter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Indoor thermal climate after a renovation of a residential building in the sub-Arctic region: Comparing CFD and IDA ICE methodsManuscript (preprint) (Other academic)
  • 26.
    Lundqvist, Petter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Indoor thermal climate after energy efficiency measures of a residential building in a sub-Arctic region: Comparing ANSYS CFX and IDA ICE methods2022In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 31, no 3, p. 732-744Article in journal (Refereed)
    Abstract [en]

    A residential building which had been subjected to an energy efficiency measures study had its indoor thermal climate investigated using two software approaches to understand how each approach would predict the outcome, using the predicted percentage of dissatisfied (PPD). The computational fluid dynamics software (ANSYS CFX) and the building performance simulation (BPS) software (IDA ICE) were used to simulate the indoor thermal climate before and after the measures. The measures included additional insulation and changing the ventilation system. The results showed a difference in how the software packages handled the thermal radiation. The difference was also because CFX could calculate the indoor thermal climate of the whole interior. While the PPD values could remain similar between the CFX solutions, the area with dissatisfaction in the apartment was decreased when the building envelope was improved. These changes gave an improvement for the CFX solutions, which was not possible to predict with IDA ICE because only the central node was visible. The user should be aware of the shortcomings of BPS and building energy simulation software when evaluating the indoor thermal climate to predict changes. A coupling between BPS and CFX software should be considered when new measures or significant changes are planned.

  • 27.
    Lundqvist, Petter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    The importance of adjusting the heating system after an energy-retrofit of buildings in a sub-Arctic climate2020In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 217, article id 109969Article in journal (Refereed)
    Abstract [en]

    There is a need to improve the understanding and the knowledge of energy efficiency measures for residential buildings in sub-Arctic climate regions. This paper presents an investigation of two identical multi-family residential buildings in the sub-Arctic climate of northern Sweden, before and after renovation. During the renovation, additional insulation of the external walls and new windows were installed in one building, while the other building retained its original envelope.

    The energy usage data for the past four heating seasons were collected, including data from before and after the renovation. Detailed thermal indoor climate data were gathered for specific months. The data from the two separate buildings showed that the renovation did not result in a significant improvement in energy usage. Prior to the renovation, the energy usage data showed a difference of 2-3% in the heat supply between the two buildings, and this difference persisted after the renovation. On the other hand, the indoor air temperature was raised. The renovated building had an indoor air temperature which was 2°C higher than the not yet renovated building.

    IDA ICE models were constructed and validated with the measured data to investigate how a lower indoor air temperature would affect the energy usage and indoor thermal climate. The models showed that with a reduction in the indoor air temperature by 2°C after the renovation, the thermal climate would maintain an acceptable level according to PMV/PPD standards, and would result in a 13-14% reduction of the heat supply during the cold months. With an annual reduction of 15%, the heat supply could be reduced by 270 MWh per year for the whole area where the buildings are located. This clearly demonstrates the importance of adjusting the heating system after an energy efficiency measure has been performed.

  • 28.
    Mattsson, Jonathan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water. S-Group Solutions, Malmö.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ashley, Richard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Impacts on rural wastewater systems in subarctic regions due to changes in inputs from households2018In: Journal of cold regions engineering, ISSN 0887-381X, E-ISSN 1943-5495, Vol. 32, no 1, article id 04017019Article in journal (Refereed)
    Abstract [en]

    The use of water-saving appliances and heat exchangers is becoming increasingly popular to decrease water consumption and recover energy from preheated water. However, such in-household changes can bring particular implications for subarctic rural areas, in terms of solids deposition in sewers and drops in performance of wastewater treatment plants (WWTPs), because these are already experiencing diminishing wastewater flows due to depopulation and seasonal dips in wastewater temperature resulting from infiltration into sewers. Hence, this study has considered two communities in Sweden, postulating three different cases with various scales of retrofitting and usage. The results indicate that the decrease in in-pipe velocities when all households are retrofitted with water-saving appliances could be counteracted by sewer relining, but not by the inclusion of a conventional estimate of infiltration. However, for the case in which retrofitting was combined with decreased usage of the appliances, the decrease in self-cleansing capacity could not be counteracted. The retrofitting of heat exchangers under shower trays in all households did not have a significant effect on treatment processes at the WWTP.

  • 29.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CFD modelling of radiators in buildings with user defined wall functions2016In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 64, p. 266-273Article in journal (Refereed)
    Abstract [en]

    The most widely used turbulence model for indoor CFD simulations, the k-ε model, has exhibited problems with treating natural convective heat transfer, while other turbulence models have shown to be too computationally demanding. This paper studies how to deal with natural convective heat transfer for a radiator in order to simplify the simulations, reduce the numbers of cells and the simulation time. By adding user-defined wall functions the number of cells can be reduced considerably compared with the k-ω SST turbulence model. The user-defined wall function proposed can also be used with a correction factor for different radiator types without the need to resolve the radiator surface in detail. Compared to manufacturer data the error is less than 0.2% for the investigated radiator height and temperature.

  • 30.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Investigation of thermal indoor climate for a passive house in a sub-Arctic region using computational fluid dynamics2019In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 28, no 5, p. 677-692Article in journal (Refereed)
    Abstract [en]

    There is currently an increasing trend in Europe to build passive houses. In order to reduce the cost of installation, an air-heating system may be an interesting alternative. Heat supplied through ventilation ducts located at the ceiling was studied with computational fluid dynamics technique. The purpose was to illustrate the thermal indoor climate of the building. To validate the performed simulations, measurements were carried out in several rooms of the building. Furthermore, this study investigated if a designed passive house located above the Arctic Circle could fulfil heat requirements for a Swedish passive house standard. Our results show a heat loss factor of 18.8 W/m2 floor area and an annual specific energy use of 67.9 kWh/m2 floor area, would fulfils the criteria. Validation of simulations through measurements shows good agreement with simulations if the thermal inertia of the building was considered. Calculation of heat losses from a building with a backward weighted moving average outdoor temperature produced correct prediction of the heat losses. To describe the indoor thermal climate correctly, the entire volume needs to be considered, not only one point, which normally is obtained with building simulation software. The supply airflow must carefully be considered to fulfil a good indoor climate.

  • 31.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    The impact of snow and soil freezing for commonly used foundation types in a subarctic climate2018In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 173, p. 268-280Article in journal (Refereed)
    Abstract [en]

    Heat losses from a building foundation are affected by both the surrounding conditions and the surrounding soil properties. These include many factors that complicate the analysis of heat loss, such as thermal storage, snow and soil freezing. The effect of snow and soil freezing was studied with a 3D simulation model in a subarctic climate.

    The heat losses from the most commonly used foundation types in Sweden were studied. This paper shows that it is possible to achieve a good thermal estimation of the air temperatures in a crawl space, with an average difference of 0.4°C compared with the validation data over a year. Snow and soil freezing reduce the annual heat losses through the different foundation types by 7-10% and the maximum heat loss rate by 13-25%. In order to describe the heat transfer correctly, snow must be included in the calculations, while soil freezing has only a minor impact. The 3D model implemented in this study shows a significant impact on the soil temperatures when these parameters are included.

    For a subarctic climate, the commonly used calculation methods based on the European standard ISO 13370 are not thorough enough to calculate the heat transfer through a foundation accurately.

  • 32.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vesterlund, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hållbara, integrerade energi- och VA-system2014Report (Other academic)
    Download full text (pdf)
    FULLTEXT01
  • 33.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vesterlund, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CFD simulation and evaluation of different heating systems installed in low energy building located in sub-arctic climate2015In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 89, p. 160-169Article in journal (Refereed)
    Abstract [en]

    Computational Fluid Dynamics (CFD) simulations were used to study the indoor climate in a low energy building in northern Sweden. The building’s low heat requirement raise the prospect of using a relatively simple and inexpensive heating system to maintain an acceptable indoor environment, even in the face of extremely low outdoor temperature. To explore the viability of this approach, the indoor climate in the building was studied considering three different heating systems: a floor heating system, air heating through the ventilation system and an air heat pump installation with one fan coil unit. The floor heating system provided the most uniform operative temperature distribution and was the only heating system that fully satisfied the recommendations to achieve tolerable indoor climate set by the Swedish authorities. On the contrary, air heating and the air heat pump created a relatively uneven distribution of air velocities and temperatures, and none of them fulfills the specified recommendations. From the economic point of view, the air heat pump system was cheaper to be installed but produced a less pleasant indoor environment than the other investigated heating systems.

  • 34.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vesterlund, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CFD simulations of the indoor climate of a low energy building in a sub-Arctic climate: an evaluationof different heating systems.2013Conference paper (Refereed)
    Abstract [en]

    Computational Fluid Dynamics (CFD) simulations were used to study the indoor climate in a low energy building in northern Sweden. The building’s low heat requirements raise the prospect of using relatively simple and inexpensive heating systems to maintain an acceptable indoor environment, even in the face of extremely low outdoor temperatures. To explore the viability of this approach, the indoor temperature and air velocity distribution inside the building were studied assuming that it was fitted with one of four different heating systems: radiators, an underfloor heating system, a pellet stove, and an air/air heat pump. The radiators produced a relatively uniform horizontal temperature distribution throughout the house. The underfloor system provided an even more uniform temperature distribution. In contrast, the heat pump created a relatively uneven internal temperature distribution. Several locations for the pump were considered, all of which had significant drawbacks. The pellet stove produced a more even temperature distribution than the pump but not to the same extent as the underfloor system or the radiators. Overall, point source heating systems cost less to fit and operate over a given period of time but produce a less clement indoor environment than distributed heating systems.

    Download full text (pdf)
    fulltext
  • 35.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Computational fluid dynamics simulation of indoor climate in low energy buildings computational set up2017In: Thermal Science, ISSN 0354-9836, E-ISSN 2334-7163, Vol. 21, no 5, p. 1985-1998Article in journal (Refereed)
    Abstract [en]

    In this paper CFD was used for simulation of the indoor climate in a part of a low energy building. The focus of the work was on investigating the computational set up, such as grid size and boundary conditions in order to solve the indoor climate problems in an accurate way. Future work is to model a complete building, with reasonable calculation time and accuracy. A limited number of grid elements and knowledge of boundary settings are therefore essential. An accurate grid edge size of around 0.1 m was enough to predict the climate according to a grid independency study. Different turbulence models were compared with only small differences in the indoor air velocities and temperatures. The models show that radiation between building surfaces has a large impact on the temperature field inside the building, with the largest differences at the floor level. Simpling the simulations by modelling the radiator as a surface in the outer wall of the room is appropriate for the calculations. The overall indoor climate is finally compared between three different cases for the outdoor air temperature. The results show a good indoor climate for a low energy building all around the year.

  • 36.
    Risberg, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Sandberg, Marcus
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.
    Lidelöw, Sofia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Modulära och energieffektiva datacenters i trä2017Report (Other academic)
  • 37.
    Risberg, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Experimental investigation of a crawl space located in a sub-arctic climate2020In: Results in Engineering (RINENG), ISSN 2590-1230, Vol. 7, article id 100158Article in journal (Refereed)
    Abstract [en]

    A common type of foundation for family houses in Northern countries is crawl spaces, where mould and moisture are a common problem for a large share of these. In this study, measurement in a crawl space located in a subarctic climate has been performed for over a year. Calculation and prediction of the climate inside the crawl space are performed both for the experimental case with a dehumidifier and a theoretical case without a dehumidifier. The results show that it is not necessary to measure at several points in the crawl space since the difference between the measurement points is small. The relative humidity is below the critical in the investigated crawl space during the whole year when a dehumidifier is used and therefore is no risk for mould growth. Prediction for a naturally ventilated crawl space with ACR of 1.5 shows that mould index will reach almost four and very close not to reach zero between different years, which indicates that mould index could start to increase between the years and cause problems.

  • 38.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Absorptionsteknik: förstudie1988Report (Other academic)
  • 39.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Open absorption system for drying of moist air1995Doctoral thesis, comprehensive summary (Other academic)
    Download full text (pdf)
    FULLTEXT01
  • 40.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    The open absorption system: experimental study of the system and different absorbers1991Licentiate thesis, monograph (Other academic)
    Download full text (pdf)
    fulltext
  • 41.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öppna absorptionssystem: absorbatorers egenskaper1989Report (Other academic)
  • 42.
    Westerlund, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Absorbers in the open absorption system1994In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 48, no 1, p. 33-49Article in journal (Refereed)
    Abstract [en]

    This paper describes an experimental study of four different absorber designs in this type of system: cross-current and counter-current packed-absorbers, the spray absorber and fluid-bed absorber. In a laboratory pilot, plant, working lines for the absorbers were determined under adiabatic conditions. The influences of internal solution flow, gas flow, pressure drop and dissipation are discussed. The working lines represent the efficiency for each absorber. The highest performance occurs with the packed-bed absorbers, followed by the fluid-bed absorber and finally the spray absorber. For open absorption systems in air-conditioning applications (small scale) the fluid-bed absorber should be chosen

  • 43. Westerlund, Lars
    et al.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Application of an open absorption heat pump for energy conservation in public bath2002In: Proceedings of the International Sorption Heat Pump Conference: September 24 - 27, 2002, Shanghai / [ed] Ruzhu Wang, Beijing: American Science Press Inc., 2002Conference paper (Refereed)
  • 44. Westerlund, Lars
    et al.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Avfuktning av luft: Adiac-systemet, funktion och dimensioneringskriterier1983Report (Other academic)
  • 45. Westerlund, Lars
    et al.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Avfuktning av luft: Adiac-systemet, ny torkmetod1982Report (Other academic)
  • 46. Westerlund, Lars
    et al.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Multiphase flow in a packed bed absorber: comparison to experimental results1999In: Applied Modelling and Simulation, International conference, 1999Conference paper (Refereed)
  • 47.
    Westerlund, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahl, Jan
    Open absorption system: experimental study in a laboratory pilot plant1991In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 38, no 3, p. 215-229Article in journal (Refereed)
    Abstract [en]

    The open absorption system is specially fitted in drying processes using air for the transport of the water. Advantages of the system are that different types of energy supply can be used, and that direct contact between the working media and the solution gives an effective absorber. This experimental study concerns measurements of the capacity of the system when a cross-flow absorber is used. Experiments were done under adiabatic and non-adiabatic conditions, and the results show that non-adiabatic conditions give a considerable increase in the absorption capacity. The dissipation of solution media increases strongly for air velocities over 2m/s. However, a demister can be used to reduce these losses. Investigation of the packing depth shows that the absorption takes place mainly in the first quarter of the packing. Different types of plastic packings were studied, the Telpac packing giving the best results.

  • 48.
    Westerlund, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahl, Jan
    Use of an open absorption heat-pump for energy conservation in a public swimming-pool1994In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 49, no 3, p. 275-300Article in journal (Refereed)
    Abstract [en]

    A conventional climatization system at a public swimming-pool normally uses outdoor air to remove the moisture from the facility. This practice results in large heat losses. An open absorption heat-pump can dehumidify the outlet air from the building: this makes it possible to recirculate a larger amount of air and so reduce the heating requirement for the facility significantly. Measurements on two types of systems have been performed during approximately 4000 h in a bath house in northern Sweden. In 1990, the use of an open absorption heat-pump decreased the heat supply by 445 MWh (from 742 MWh), while the electricity supply was increased by 233 MWh. The uncertainty in the annual energy saving with the open system can be estimated to be in the range 10-15%. If the present electric energy supply to the generator is replaced by another energy source, for example natural gas, the electricity demand of the absorption system will decrease considerably. The results show that public baths are an interesting application area for the open absorption technique

  • 49.
    Westerlund, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öppet absorptionssystem i badhus: Resultat och utvärdering av långtidsförsök med avfuktningssystemet vid simhallen i Öjebyn1993Report (Other academic)
    Download full text (pdf)
    FULLTEXT01
  • 50.
    Westerlund, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hansson, Hans
    Luleå University of Technology.
    ADIAC-systemet: Egenskaper hos olika fyllbäddstyper1987Report (Other academic)
    Download full text (pdf)
    FULLTEXT01
12 1 - 50 of 58
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