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  • 51.
    La Fleur, Lina
    et al.
    Division of Energy Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Rohdin, Patrik
    Division of Energy Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Moshfegh, Bahram
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Division of Energy Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Energy renovation versus demolition and construction of a new building—a comparative analysis of a Swedish multi-family building2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 11, artikel-id 2218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study addresses the life cycle costs (LCC) of energy renovation, and the demolition and construction of a new building. A comparison is made between LCC optimal energy renovations of four different building types with thermal performance, representing Swedish constructions from the 1940s, 1950s, 1960s, and 1970s, as well as the demolition of the building and construction of a new building that complies with the Swedish building code. A Swedish multi-family building from the 1960s is used as a reference building. LCC optimal energy renovations are identified with energy saving targets ranging between 10% and 70%, in addition to the lowest possible life cycle cost. The analyses show that an ambitious energy renovation is not cost-optimal in any of the studied buildings, if achieving the lowest LCC is the objective function. The cost of the demolition and construction of a new building is higher compared to energy renovation to the same energy performance. The higher rent in new buildings does not compensate for the higher cost of new construction. A more ambitious renovation is required in buildings that have a shape factor with a high internal volume to heated floor area ratio. © 2019 by the authors.

  • 52.
    La Fleur, Lina
    et al.
    Linköpings universitet.
    Rohdin, Patrik
    Linköpings universitet.
    Moshfegh, Bahram
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Linköpings universitet.
    Investigating cost-optimal energy renovation of a multifamily building in Sweden2019Ingår i: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 203, artikel-id 109438Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A significant reduction in energy use in the building stock is a major challenge for the future, and doing this in a cost-effective manner is important. This study uses an optimization approach to identify life cycle cost (LCC) optimal energy efficiency measures (EEMs) to implement as part of a renovation of a multifamily building in Sweden. The studied building is a multifamily building with a lightweight concrete construction and an exhaust air ventilation system, built in 1961. The optimization tool OPERA-MILP is used. The energy renovation approaches are compared to both the performed energy renovation of the building and a validated dynamic energy simulation model in IDA ICE 4.8. The results show that under the given framework conditions and assumptions it is not cost-optimal to improve the thermal performance of the building envelope or to implement heat recovery ventilation measures to reduce the space heating demand in the building when considering a life cycle of 40 years. Balanced mechanical ventilation system with heat recovery is cost-effective when an energy saving target of 40% is introduced. The energy renovation of the building has a slightly higher LCC than the cost-optimal level, and it would have been more cost-effective to add more insulation to the façade instead of the attic to achieve the same level of energy saving. A sensitivity analysis has been performed to reveal the effect of the discount rate, energy price, cost of EEMs, thermal properties of the building envelope and windows’ solar heat gain factors on the LCC.

  • 53.
    Lanca, Miguel
    et al.
    Instituto Superior Técnico, Lisbon University, Portugal.
    Gomes, João
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Hayati, Abolfazl
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Numerical Simulation of the Thermal Performance of Four Concentrating Collectors with Bifacial PV Cells2018Ingår i: PROCEEDINGS OF THE ISES EUROSUN 2018 CONFERENCE - 12TH INTERNATIONAL CONFERENCE ON SOLAR ENERGY FOR BUILDINGS AND INDUSTRY / [ed] Haberle, A., INTL SOLAR ENERGY SOC , 2018, s. 810-821Konferensbidrag (Refereegranskat)
    Abstract [en]

    Bifacial photovoltaic cells can produce electricity from the incoming solar radiation on both sides. Used in combination with concentrating solar technology, bifacial photovoltaic cells can see its electrical output further augmented, thus decreasing the cost per kWh. It is known, however, that the efficiency reduction when these cells are exposed to increased temperatures is a relevant factor. This can happen, for example, when they are mounted on a glassed collector or receiver. In this study, a thermal analysis is carried out on four prototypes of concentrating collectors with bifacial PV cells. Results show that, as expected, when glass and gables are removed from the collector, much better heat dissipation is achieved, thus resulting in favorable cell operation conditions.

  • 54.
    Lane, Anna-Lena
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. RISE Research Institutes of Sweden.
    Boork, Magdalena
    RISE Research Institutes of Sweden.
    Thollander, Patrik
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Barriers, driving forces and non-energy benefits for battery storage in photovoltaic (PV) systems in modern agriculture2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 18, artikel-id 3568Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Battery storage has been highlighted as one way to increase the share of renewables in energy systems. The use of local battery storage is also beneficial when reducing power variations in the grid, thereby contributing to more robust and cost-effective energy systems. The purpose of this paper is to investigate barriers, drivers and non-energy benefits (NEB) for investments in battery storage in photovoltaic systems (PV) in the context of farmers with PV systems in Sweden. The study is based on a questionnaire about barriers, driving forces and NEB for investment in battery storage connected to PV. The questionnaire was sent to farmers in Sweden who already have photovoltaics installed and about 100 persons answered, a response rate of 59%. The major barriers found are related to the technical and economic risks of investing in battery storage. One of the main conclusions is that the highest-ranked driver, i.e., to use a larger part of the produced electricity oneself, turns out to be the highest priority for the grid-owner seeking to reduce the need for extensive investments in the grid. The primary NEBs found were the possibility of becoming independent from grid electricity.

  • 55.
    Larsson, Erik
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Småskalig kraftvärmeproduktion för ett medelstort svenskt industriföretag: Potentialen för konventionell Rankinecykel2019Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Utsläppen av växthusgaser måste minska snabbt under de kommande åren. Sveriges mål är att uppnå nettonollutsläpp till år 2045. Industrisektorn spelar en avgörande roll i omställningsarbetet genom att minska sitt energibehov och fasa ut sin användning av fossila bränslen, teknikutvecklingen måste gå mot mer klimatsmarta och hållbara produkter och produktionsmetoder. Omställningen kommer att kräva ett mer robust och tillförlitligt energisystem där dagens centraliserade system kompletteras med mindre decentraliserade produktionsanläggningar så att effekt- och energibehov kan tillgodoses i alla lägen. Att producera el och värme närmare användaren bidrar till minskade överföringsförluster. Småskalig kraftvärmeproduktion (CHP) baserad på biobränslen eller restvärmeresurser kan vara en del av lösningen för att minska utsläppen av växthusgaser.

    Syftet med det här examensarbetet är att undersöka möjligheten för ett medelstort svenskt industriföretag att producera sitt eget basbehov av värme och el med hjälp av den konventionella Rankinecykeln. Samt att undersöka hur produktionskostnaderna av el och värme förändras beroende på anläggningens storlek.

    Arbetet har bestått av datainsamling från olika tillverkare av turbiner och pannor, en beräkningsmodell skapades i Excel där anläggningar av olika storlek har jämförts vid olika driftscenarion. Ekonomiska kalkyler har gjorts med hjälp av Pay-off metoden och Nuvärdesmetoden.

    Resultatet visar att produktionskostnaderna för anläggningar med turbiner i storleksordningen 10 – 100 kWel ligger på en relativt jämn nivå och betydligt lägre än priserna på köpt el och fjärrvärme. Den ekonomiska bedömningen visar generellt på positiva resultat med korta pay-offtider och positiva nuvärden.

    En jämförelse av anläggningarna visar att elverkningsgraden är låg och att totalverkningsgraden i vissa fall blir lägre än för företagets befintliga värmeleverantör. Detta visar att trots att det ur ett ekonomiskt perspektiv kan vara en lönsam investering kan det ur ett systemperspektiv vara ett sämre alternativ då en lägre verkningsgrad leder till en ökad primärenergianvändning.

    Det är många parametrar som påverkar en CHP-anläggnings prestanda och ekonomiska lönsamhet, men en av de viktigaste är drifttiden. Att ha en kontinuerlig drift under större delen av året har stor påverkan på anläggningens ekonomiska prestanda. Anläggningens låga elverkningsgrad gör också att största besparingen hamnar på värmeproduktionen vilket gör att anläggningen bör dimensioneras så att den ersätter så stor del som möjligt av företagets värmebehov.

  • 56.
    Lim, Eunsu
    et al.
    Toyo university, Tokyo, Japan.
    Chung, Juyeon
    Fukuoka Woman's University, Fukuoka, Japan.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Ito, Kazuhide
    Kyushu University, Fukuoka, Japan.
    Influence of chemical reactions and turbulent diffusion on the formation of local pollutant concentration distributions2020Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 168, artikel-id 106487Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanism of structure formation of non-uniform pollutant concentration distributions in indoor environments have been investigated over the past several decades to determine effective ventilation designs. In this study, numerical analyses of local pollutant concentration distributions in indoor environments are performed based on computational fluid dynamics techniques. In particular, the influence of gas phase chemical reactions and turbulent diffusion on the formation of the local pollutant concentration is parametrically analyzed, and the structures are quantitatively investigated using the index for ventilation efficiency, namely the net escape velocity (NEV) concept. The NEV concept represents the substantive velocity scale, combining advection and diffusion velocity of pollutant at a point, and functions as an index to determine the pollutant concentration at that point. Sensitivity analyses as functions of the first Damköhler number (Da) and the turbulent Schmidt number (Sct) were performed, and the influence of Sct on pollutant concentration distributions was more significant compared with that of Da. When Sct was changed from 0.5 to 1.0, the significant NEV increase, especially that in the stagnant flow region, could be attributed to the enhanced pollutant discharge efficiency due to turbulent diffusion in addition to convective flow. Thus, NEV could be used to quantitatively assess the changes in pollutant concentrations accompanying the change in Da or Sct. 

  • 57.
    Lindqvist, Simon
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Energikartläggning och förbättringsförslag för lättbetonghus i Mellansverige2019Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Energieffektivisering inom bostäder är viktigt för att nå bestämda mål inom den Europeiska unionen, däremot kommer inte en bostadsägare att investera i energieffektiva åtgärder om de inte är lönsamma. Detta arbete kommer att undersöka energibesparingen och lönsamheten av att införa olika förbättringsåtgärder på ett lättbetonghus i Söderhamn vilket är studieobjektet i arbetet. Syftet är att undersöka byggnadens energibalans och hur olika åtgärder påverkar energianvändningen, upplevelsen av inomhusklimatet och driftkostnaden.

    Studieobjektet genomgick en energikartläggning för att sedan undersöka olika förbättringsåtgärder. Kartläggningen var utförd med simuleringsverktyget IDA Indoor Climate and Energy för att konstruera en referensmodell som inkluderade alla insamlade data från studieobjektet. Tidigare forskningsstudier inom området användes som vägledning till val av förbättringsåtgärder på studieobjektet. Energiförändring utav åtgärderna användes sedan i en kostnadskalkyl som var utförd med annuitetsmetoden för att åstadkomma den årliga kostnadsbesparingen vid installation för var och en av åtgärderna. Koldioxidhalten mättes i början av projektet för att undersöka luftkvalitén i byggnaden och om den behöver åtgärdas.

    Studieobjektets primärenergital blev 148 kWh/(m2·år) vilket var 43 % högre än Boverkets byggreglers energikrav för småhus. Byggnadens värmebehov var 18 209 kWh/år och kunde minskas med 42,7 % vid installation av ett åtgärdspaket och då var primärenergitalet 109 kWh/(m2·år). De tre mest energieffektiva åtgärder var att tilläggsisolera ytterväggar, isolera taket och minskning av inomhustemperaturen. Den mest kostnadseffektiva av enskilda åtgärder var att isolera taket ifall övervåningsutrymmet utnyttjades och att isolera källaren var den minst lönsamma av besparingsåtgärderna. Ventilationsproblemet i byggnaden kunde åtgärdas med installation av ett FTX-system som använder luftflödet 0,35 l/(s·m2) och 0,1 l/(s·m2) när inga personer är i byggnaden. Att komplettera uppvärmningen med en värmepump var en lönsam investering men ökade primärenergianvändningen och gör byggnadens energisystem mer komplext. Det rekommenderas att isolera klart taket ifall boende har intresse av att utnyttja övervåningsutrymmet.

  • 58.
    Lundström, Hans
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Mattsson, Magnus
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Radiation influence on indoor air temperature sensors: Experimental evaluation of measurement errors and improvement methods2020Ingår i: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 115, artikel-id 110082Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Radiation influence on commonly used temperature sensors for measuring indoor air temperatures can be significant, especially at the typically low air velocities occurring indoors. Conceptually, a physical sensor may not read the true air temperature, it only reads its own temperature, and, being a solid body, it will exchange energy with the surrounding surfaces (walls, windows etc.) through radiation. In the present study, radiation influence on indoor air temperature measurements was investigated experimentally and errors were quantified in simple terms. Measures to reduce the impact on some common temperature sensors were explored. A special test rig was built to simulate typical airflow and radiation environments indoors. It is suggested that the radiation impact on a temperature sensor is quantified by a radiation sensitivity factor defined as RSF = hrad/hconv, where hrad and hconv are heat transfer coefficients for radiation and convection, respectively. As this definition infers, the radiation sensitivity is dependent on size, geometry and emissivity of the temperature sensor. The radiation sensitivity factor, thus being unique for each type of sensor, was measured for some common types of thermistors and thermocouples. It is demonstrated that radiation errors may be reduced by 60 – 80 % on thermistors by reducing their emissivity through gold sputtering, and on thermocouples by stripping the insulation at the outermost part of their sensor leads.

  • 59.
    Lundström, Lukas
    et al.
    Mälardalens högskola.
    Akander, Jan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Bayesian calibration with augmented stochastic state-space models of district-heated multifamily buildings2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 13, nr 1, artikel-id 76Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reliable energy models are needed to determine building energy performance. Relatively detailed energy models can be auto-generated based on 3D shape representations of existing buildings. However, parameters describing thermal performance of the building fabric, the technical systems, and occupant behavior are usually not readily available. Calibration with on-site measurements is needed to obtain reliable energy models that can offer insight into buildings' actual energy performances. Here, we present an energy model that is suitable for district-heated multifamily buildings, based on a 14-node thermal network implementation of the ISO 52016-1:2017 standard. To better account for modeling approximations and noisy inputs, the model is converted to a stochastic state-space model and augmented with four additional disturbance state variables. Uncertainty models are developed for the inputs solar heat gains, internal heat gains, and domestic hot water use. An iterated extended Kalman filtering algorithm is employed to enable nonlinear state estimation. A Bayesian calibration procedure is employed to enable assessment of parameter uncertainty and incorporation of regulating prior knowledge. A case study is presented to evaluate the performance of the developed framework: parameter estimation with both dynamic Hamiltonian Monte Carlo sampling and penalized maximum likelihood estimation, the behavior of the filtering algorithm, the impact of different commonly occurring data sources for domestic hot water use, and the impact of indoor air temperature readings.

  • 60.
    Lundström, Lukas
    et al.
    Mälardalens högskola, Framtidens energi, Västerås, Sweden; Eskilstuna Kommunfastighet AB, Eskilstuna, Sweden.
    Akander, Jan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Zambrano, Jesus
    Mälardalens högskola, Framtidens energi, Västerås, Sweden.
    Development of a space heating model suitable for the automated model generation of existing multifamily buildings: a case study in Nordic climate2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 3, artikel-id 485Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Building energy performance modeling is essential for energy planning, management, and efficiency. This paper presents a space heating model suitable for auto-generating baseline models of existing multifamily buildings. Required data and parameter input are kept within such a level of detail that baseline models can be auto-generated from, and calibrated by, publicly accessible data sources. The proposed modeling framework consists of a thermal network, a typical hydronic radiator heating system, a simulation procedure, and data handling procedures. The thermal network is a lumped and simplified version of the ISO 52016-1:2017 standard. The data handling consists of procedures to acquire and make use of satellite-based solar radiation data, meteorological reanalysis data (air temperature, ground temperature, wind, albedo, and thermal radiation), and pre-processing procedures of boundary conditions to account for impact from shading objects, window blinds, wind- and stack-driven air leakage, and variable exterior surface heat transfer coefficients. The proposed model was compared with simulations conducted with the detailed building energy simulation software IDA ICE. The results show that the proposed model is able to accurately reproduce hourly energy use for space heating, indoor temperature, and operative temperature patterns obtained from the IDA ICE simulations. Thus, the proposed model can be expected to be able to model space heating, provided by hydronic heating systems, of existing buildings to a similar degree of confidence as established simulation software. Compared to IDA ICE, the developed model required one-thousandth of computation time for a full-year simulation of building model consisting of a single thermal zone. The fast computation time enables the use of the developed model for computation time sensitive applications, such as Monte-Carlo-based calibration methods. 

  • 61.
    Ma, Ding
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för datavetenskap och samhällsbyggnad, Samhällsbyggnad.
    Omer, Itzhak
    Tel-Aviv University, Tel-Aviv, Israel.
    Osaragi, Toshihiro
    Tokyo Institute of Technology, Tokyo, Japan.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Jiang, Bin
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för datavetenskap och samhällsbyggnad, Samhällsbyggnad.
    Why Topology Matters in Predicting Human Activities2019Ingår i: Environment and Planning B: Urban Analytics and City Science, ISSN 2399-8083, Vol. 46, nr 7, s. 1297-1313Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Geographic space is best understood through the topological relationship of the underlying streets (note: entire streets rather than street segments), which enabales us to see scaling or fractal or living structure of far more less-connected streets than well-connected ones. It is this underlying scaling structure that makes human activities or urban traffic predictable, albeit in the sense of collective rather than individual human moving behavior. This power of topological analysis has not yet received its deserved attention in the literature, as many researchers continue to rely on segment analysis for predicting urban traffic. The segment-analysis-based methods are essentially geometric, with a focus on geometric details such as locations, lengths, and directions, and are unable to reveal the scaling property, which means they cannot be used for human activities prediction. We conducted a series of case studies using London streets and tweet location data, based on related concepts such as natural streets, and natural street segments (or street segments for short), axial lines, and axial line segments (or line segments for short). We found that natural streets are the best representation in terms of traffic prediction, followed by axial lines, and that neither street segments nor line segments bear a good correlation between network parameters and tweet locations. These findings point to the fact that the reason why axial lines-based space syntax, or the kind of topological analysis in general, works has little to do with individual human travel behavior or ways that human conceptualize distances or spaces. Instead, it is the underlying scaling hierarchy of streets – numerous least-connected, a very few most-connected, and some in between the least- and most-connected – that makes human activities or urban traffic predictable.

  • 62.
    Maritz, Kerry-Leigh
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Feasibility Study of Chemical Energy Storage for an Energy Efficient Commercial Office Space2019Självständigt arbete på avancerad nivå (magisterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Shifting the load demand of a commercial office space to utilise off peak tariffs would lead to cost savings as power is cheaper at this time. To achieve this shift, chemical energy storage was considered using Lead Acid batteries, Lithium-ion batteries and Advance Lead Acid batteries. The output of these storage types is electricity.

    Current costs of storage do not support the option of reducing peak demand by adding chemical storage, as electricity from the grid is cheaper over the storage project life. A levelised cost analysis was completed and lithium-ion batteries proved to be the outright best choice for chemical storage in commercial office spaces.

    Town buildings were analysed and assessed for energy savings in order to reduce overall load demand. Incorporating chemical storage as a viable option was assessed based on cost. Heating, Cooling and lighting proved to be the highest load demands in the buildings. Cost savings in buildings can be better met by increasing the efficiency in buildings, rather than by reducing the cost by shifting the purchase of electricity from peak to off-peak tariffs.

    More suitable options to chemical energy storage would be to replace standard lights with energy efficient variations, installing an air heat pump to heat the space and ice thermal storage to cool the space. The use of a solar thermosyphon will meet the demand for heated water.

    Solar energy generation was assessed as an alternative as off-peak electricity stored using chemical storage proved to be too costly. A 50kW system would be suitably sized when peak sun hours were above the local areas average. Net metering could be used to offset costs during the winter months, when the peak sun hours fall below the average.

  • 63.
    Martinez, Pablo
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Quenching a steel plate by water - impinging jets and different simultaneous flow rates2019Självständigt arbete på avancerad nivå (magisterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Regarding the great importance of fast cooling in steel industry for the production processes, a deep understanding of heat transfer and fluid dynamics must be held. A steel plate is heated up until a maximum temperature of 700 ⁰ C to be the n cooled down seconds later by a configuration of multi ple impinging water jets. Different flow rates are used simultaneously by different adjacent jets to perform quenching over the sample, so different hardness is obtained in the material over a small area . Temperature drop in time i s measured and monitored by embedded thermocouples and LabVIEW program. To achieve greater understanding of the quenching performance with different flow rates , several parameters are selected to be varied in order to achieve the best working conditions. Jet diameter takes values between 4 and 10 mm, initial temperature of quenching varies from 400 to 700 ⁰ C , subcooling temperature is tested for 65 and 75 K, and jet velocity varies between 1.9 and 3.9 m/s. The result of total number of 9 expe riments shown that v ariation of jet diam eter does not influence substantially on the cooling rate if flow rate is kept constant. High initial quenching temperature (600 - 700 ⁰ C ) led to slightly higher cooling rate in the stagnation region of water jets. The peak value of heat transfer rate in the upwash flow zone was more highlighted for initial quenching temperature 600 ⁰ C and below it. High er values of subcooling and jet velocity produce better cooling rates. The result shown higher jet velocity at one column of water jets changes position of upw ash flow slightly toward the adjacent column of jets with lower jet velocity. In general, the result shown that all the studied parameters did not have negative effect on obtaining various cooling rates over the steel plate.

  • 64.
    Milić, Vlatko
    et al.
    Linköpings universitet.
    Amiri, Shahnaz
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Linköpings universitet.
    Moshfegh, Bahram
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Linköpings universitet.
    A systematic approach to predict the economic and environmental effects of the cost-optimal energy renovation of a historic building district on the district heating system2020Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 13, nr 1, artikel-id 276Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The economic and environmental performance of a district heating (DH) system is to a great extent affected by the size and dynamic behavior of the DH load. By implementing energy efficiency measures (EEMs) to increase a building’s thermal performance and by performing cost-optimal energy renovation, the operation of the DH system will be altered. This study presents a systematic approach consisting of building categorization, life cycle cost (LCC) optimization, building energy simulation and energy system optimization procedures, investigating the profitability and environmental performance of cost-optimal energy renovation of a historic building district on the DH system. The results show that the proposed approach can successfully be used to predict the economic and environmental effects of cost-optimal energy renovation of a building district on the local DH system. The results revealed that the financial gains of the district are between 186 MSEK (23%) and 218 MSEK (27%) and the financial losses for the DH system vary between 117–194 MSEK (5–8%). However, the suggested renovation measures decrease the local and global CO2 emissions by 71–75 metric ton of CO2eq./year (4%) and 3545–3727 metric ton of CO2eq./year (41–43%), respectively. Total primary energy use was decreased from 57.2 GWh/year to 52.0–52.2 GWh/year.

  • 65.
    Milić, Vlatko
    et al.
    Division of Energy Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Ekelöw, Klas
    Division of Energy Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Andersson, Maria
    Division of Energy Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Moshfegh, Bahram
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Division of Energy Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Evaluation of energy renovation strategies for 12 historic building types using LCC optimization2019Ingår i: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 197, s. 156-170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The life cycle cost (LCC)optimization is a vital method when performing building energy renovation. The present paper provides an evaluation of cost-optimal energy renovation strategies for historic buildings using LCC optimization software OPERA-MILP. The evaluation is performed based on preset targets depending on LCC (LCC optimum)and energy use (decrease by 50%), where the environmental performance is also addressed. Twelve building types, which are typical of the historic building stock in Visby, Sweden, are used as the study object. The results show possible decreases of 12–38% in LCC when targeting LCC optimum. When targeting a 50% decrease in energy use, the LCC is decreased in 21 of 26 cases compared to before energy renovation. Cost-efficient EEMs on the building envelope are characterized by low renovation costs and additional insulation of building components with poor thermal properties. Furthermore, the environmental performance from the energy renovations is highly dependent on the chosen energy system boundary. 

  • 66.
    Monjurul Hasan, A. S. M.
    et al.
    Department of Electrical and Electronic Engineering, Bangladesh Army International University of Science and Technology, Cumilla, Bangladesh.
    Rokonuzzaman, M.
    Institute for Intelligent Systems Research and Innovation, Deakin University, Victoria, Australia.
    Tuhin, R. A.
    Department of Computer Science and Engineering, East West University, Dhaka, Bangladesh.
    Salimullah, S. Md.
    Department of Electrical and Electronic Engineering, Bangladesh Army International University of Science and Technology, Cumilla, Bangladesh.
    Ullah, M.
    Department of Electrical and Electronic Engineering, Bangladesh Army International University of Science and Technology, Cumilla, Bangladesh.
    Sakib, T. H.
    Department of Electrical and Electronic Engineering, Bangladesh Army International University of Science and Technology, Cumilla, Bangladesh.
    Thollander, Patrik
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Division of Energy Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Drivers and barriers to industrial energy efficiency in textile industries of Bangladesh2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 9, artikel-id 1775Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bangladesh faced a substantial growth in primary energy demand in the last few years. According to several studies, energy generation is not the only means to address energy demand; efficient energy management practices are also very critical. A pertinent contribution in the energy management at the industrial sector ensures the proper utilization of energy. Energy management and its efficiency in the textile industries of Bangladesh are studied in this paper. The outcomes demonstrate several barriers to energy management practices which are inadequate technical cost-effective measures, inadequate capital expenditure, and poor research and development. However, this study also demonstrates that the risk of high energy prices in the future, assistance from energy professionals, and an energy management scheme constitute the important drivers for the implementation of energy efficiency measures in the studied textile mills. The studied textile industries seem unaccustomed to the dedicated energy service company concept, and insufficient information regarding energy service companies (ESCOs) and the shortage of trained professionals in energy management seem to be the reasons behind this. This paper likewise finds that 3–4% energy efficiency improvements can be gained with the help of energy management practices in these industries. 

  • 67.
    Olausson, Jesper
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Energy efficiency in a renovated modern office with activity-based work style2019Självständigt arbete på avancerad nivå (masterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    During renovation Ljusåret 2 was converted to a modern office with an activity based work style (ABW) with a Demand Controlled Volume (DCV) ventilation system connected to a closed-loop duct. Cooling is provided through air handling units and active water based beams, the underfloor heating system was kept.

    Written instruction and specification have been studied for the two different control systems Schneider EcoStructure and Lindinspect. Both control systems have been analyzed according to time schedule, set-point and process value by using different functions in software.

    To be able to perform a energy audit and look at indoor climate for Ljusåret 2 there have been studies according to underfloor heating, constructions of ventilation system, diversity factor for DCV, closed-loop-ducts, heat losses from ducts, cooling demand and energy certification.

    According to this audit, energy performance is calculated to 89.1 kWh/m2 according to building energy, activity energy is not audited or calculated. During design phase, an energy calculation was made by an energy consultant with the result of 81.3 kWh/m2. The estimated performance is a 9.6 % increase. This building is designed for Miljöbyggnad certification of level silver and should be ≤ 109 kWh/m2,year. According to audit and calculation for energy performance this level is possible to keep.

    The estimated energy performance have been calculated with only 4 month of statistics from January until April 2019 because Ljusåret 2 have just been renovated. District heating has been estimated through the energy signature by data from energy meter. Electrical components for the building have been measured and energy usage calculated. Energy produced by compression chiller have been estimated with calculated performance from design phase and adding heat transfer between rooms and supply ducts. Energy between rooms and supply ducts were not included in energy calculation during the design phase.

    According to the control system for the DCV system there have been some issues with high temperature in supply ducts even when they are supplied with 15 ºC from air- handling unit. There have been measurement to the ventilation system 5701-5704 that is connected to a close-loop duct with a result of temperatures between 15.2 ºC up to 21.4 ºC and the velocity has varied between 0.05-2.1 m/s in different measurement spots. This is an increase of 6.4 ºC.

    A heat transfer calculation have been made in Paroc Calculus to estimate heat transfer between room and supply ducts. The results of this calculation indicates the same level of temperature increases as when the system was measured. With no thermal insulation cooling capacity is lost to half after less than 5 m with a velocity of 0.2 m/s, after 15 m with a velocity of 1 m/s and 30 m with a velocity of 2 m/s . This should be compared with supply duct with 20 mm of thermal insulation that has lost its cooling capacity after less than 13 m with a velocity of 0.2 m/s, after 63 m with a velocity of 1 m/s and is increase with 4 ºC after 100 m with a velocity of 2 m/s.

    Using closed-loop ducts with velocity below 2.0 m/s and without thermal insulation combined with under tempered supply air is not a good combination. Even short length with low velocity and lack of thermal insulation is devastating because of heat transfer according to logarithmical temperature difference between room and supply ducts.

    A closed-loop duct is often designed as a pressure chamber and recommended when using DCV and/or VAV ventilation to avoid problems with noise and to be able to reduce the need of dampers. Problems with temperature increasing according to velocity in ducts must be taken in consideration.

    For Ljusåret 2 this will affect district heating usage where ducts are placed because underfloor heating must compensate heat transfer. Chilled water must be provided an extra time for rooms with both DCV and chilled beams and rooms with only DCV is less comfortable which they could been with a correct installation.

  • 68.
    Panchal, Rajan
    et al.
    University of Kassel, Germany.
    Gomes, João
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Cabral, Diogo
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Eleyele, Abideme
    Uppsala University.
    Lança, Miguel
    Instituto Superior Técnico, Lisboa, Portugal.
    Evaluation of Symmetric C-PVT Solar Collector Designs with Vertical Bifacial Receivers2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Photovoltaic thermal (PVT) solar collectors can be an effective solution for system output improvement. Photovoltaic thermal collectors naturally have a more expensive receiver than simpler photovoltaic or thermal only collectors, therefore making concentration a more appealing solution to achieve cost reduction. However, concentrating systems need careful analysis on the design phase in order to optimize the annual output. In addition, for stationary (non-tracking) collectors, it is critical to determine the incidence angle modifier (IAM).For this reason, a reflector study was carried out to determine suitable reflector designs for a stationary concentrating PVT collector. The reflectors were simulated using a Monte Carlo raytracing software called Tonatiuh. The two selected reflectors designs were named “pure parabola” (PP) and “compound parabolic concentrator” (CPC). The concentration ratio of 1.2 and 1.6 were selected for each reflector designs, which means a total of 4 collector troughs. The next step involved the construction of the two selected C-PVT collector designs, which were built and subsequently tested by the authors. The IAM was assessed and discussed by simulation and outdoor testing in detail.The IAM results show similar decreases in longitudinal IAM for both the PP and the CPC CPVT collector for the 1.2 concentration factor. For the transversal IAM with 1.2 of concentration factor, the CPC over performs. For the 1.6 concentration prototype collectors, the results are fairly similar. Lastly, the annual output was also simulated and presented.

  • 69.
    Panicker, Suresh Ambu
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Student.
    Investigation of the energy performance and renovation opportunities in a historic building.: using questionaire and assessment scale for decision making and improving energy performance.2019Självständigt arbete på avancerad nivå (masterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    On a global scale it is estimated that the building sector accounts for about 35% of the final energy use. The building sector accounts for nearly 40% of energy demand in European union (EU) and in Sweden too it is almost the same percentage demand. It is also known that more than 40% of the residential buildings in Europé were built before 1960 when the energy performance regulations for buildings were not so strict in view of the climate change objectives.

    Compared to other countries in the EU, Sweden has a large number of listed or historic buildings as almost 15% of multi-family buildings and 27% of all single-family houses in Sweden were built before 1945. However it also stated that research on listed buildings energy efficiency potential and indoor environment is very scarce in Sweden.

    Due to climate change and the need to reduce greenhouse gas emission

    (mainly CO2) associated with reduction in energy use in buildings is very evident. Some buildings are of heritage significance due to their historical, architectural or cultural values. The Swedish standard SS-EN 16883:2017 refers to them as listed or historic buildings. This standard does not presuppose that all historic buildings need energy performance improvements. The use of this standard is not limited to historic building with heritage values however it can also be applied to historic buildings of all ages and types.

    This study presents an assessment of a historic building built around 1945 where both the building owners energy use data and the building tenants or users indoor environment perceptions includes their expectations on daylight needs, illumination, temperature control or heating and ventilation are evaluated by the assessment scale methodology recommended in the Swedish Standard SS-EN 16883:2017.

    The results obtained have been presented on an assessment scale as per SS-EN 16883:2017 also considering the building users perceptions of the indoor work environment. This could be a basis for future decision making for the building owner considering the planned investments on prioritized and feasible energy effective measures. Thus this study is based on quantitative approach. This assessment scale decision making model can be a basis for future builing investigations and investments iii

    plans in building refurbishments leading to improvements in energy performance of this historic building.

    Keywords:

    english

    Listed building, Energy performance, Energy efficient measures, historic buildings, Energy use, Indoor environment, Building survey and accessment, Energy efficient measures.

    swedish

    Byggnadsminne, Energiprestanda, förbättring av energiförbrukning, historiska byggnader, energianvändning, inomhusmiljö, byggundersökning och bedömning, energieffektiva åtgärder.

  • 70.
    Ramirez Villegas, Ricardo
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. School of Technology and Business Studies, Dalarna University, Falun, Sweden.
    Eriksson, Ola
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Miljövetenskap.
    Olofsson, Thomas
    Department of Applied Physics and Electronics, Umeå University, 90187 Umeå, Sweden.
    Life Cycle Assessment of Building Renovation Measures: Trade-off between Building Materials and Energy2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 3, artikel-id 344Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The scope of this study is to assess how different energy efficient renovation strategies affect the environmental impacts of a multi-family house in a Nordic climate within district heating systems. The European Union has set ambitious targets to reduce energy use and greenhouse gas emissions by the year 2030. There is special attention on reducing the life cycle emissions in the buildings sector. However, the focus has often been on new buildings, although existing buildings represent great potential within the building stock in Europe. In this study, four different renovation scenarios were analyzed with the commercially available life cycle assessment software that follows the European Committee for Standardization (CEN) standard. This study covers all life cycle steps from the cradle to the grave for a residential building in Borlange, Sweden, where renewable energy dominates. The four scenarios included reduced indoor temperature, improved thermal properties of building material components and heat recovery for the ventilation system. One finding is that changing installations gives an environmental impact comparable to renovations that include both ventilation and building facilities. In addition, the life cycle steps that have the greatest environmental impact in all scenarios are the operational energy use and the building and installation processes. Renovation measures had a major impact on energy use due to the cold climate and low solar irradiation in the heating season. An interesting aspect, however, is that the building materials and the construction processes gave a significant amount of environmental impact.

  • 71.
    Röjerås, Anders
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Projektering av takkonstruktioner med förindustriella träförband: beräkning och provning av hophuggningar2019Självständigt arbete på grundnivå (högskoleexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    I äldre träbärverk var metoden för sammanfogning av virkesdelar hophuggningen. Det finns en mängd olika typer av hophuggningar. Vilken typ av hophuggning som användes berodde dels på byggnadstypen men även på lokala variationer i byggnadstradition. Industrialiseringen under slutet på 1800-talet bidrog till ny byggteknik med nya typer av förband. Det blev efter hand svårare för timmermännen att konkurrera med massproducerade standardförband med skruv och spik. Under senare halvan av 1900-talet började det åter bli populärt med hophuggningen. Ny teknik inom träindustrin började åter göra timmerförband konkurrenskraftiga. Modern teknik med modellering av geometrier har även gjort det möjligt att på ett nytt sätt analysera och optimera bärverk och förband. Verifiering genom tester har också lett till ökad förståelse av timmerförband. Beräkning av bärförmågan i hophuggningar är möjligt genom tillämpning av beräkningsregler i Eurokod.

    Syftet med detta arbete är att verifiera hållfasthetsberäkningar för ett traditionellt timmerförband. 

    En analys av en tänkt timmerram och takstol gjordes i ett beräkningsprogram för att på ett överslagsmässigt sätt bedöma vilka snittkrafter konstruktionen utsattes för. Ett laxförband i takstolen som visas i fig. 1 valdes ut för vidare analys. Manuell beräkning av bärförmågan i laxförbandet gjordes. Verifiering av beräkningarna gjordes därefter genom hållfasthetsprovning av förbandet i laborationslokal.

    Studien pekar mot att det går att med tillförlitlighet beräkna bärförmågan för ett traditionellt laxförband och att hänsyn skall tas till excentriciteter och varierande virkeskvalitet.

  • 72.
    Sanchez, Hector
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Testing of an innovative metal nanothread heat flux sensor2019Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Thermal sensors are currently highly used in building applications to assess losses and determine possible thermal bridges. However, in some cases they are not useful enough because of the field conditions or, sometimes, due to the dimensions of the sensor.This thesis aims to calibrate and test a new product developed by JonDeTech AB company; a tiny heat flux - temperature sensor based on metal nanothreads and a vertical or “out-of-the-plane” thread arrangement. It may have a bright future in measuring local heat flux through building and installation components owing to its tininess.Three methods have been applied. First, calibration with a specific device designed for this purpose in a controlled environment. Second, field test measurements within an ongoing project by Gävle University in Gävle city hall historical building. And third, finite element simulations where the experimental scenarios were replicated. By these methods it was possible to apply corrections on the experimental procedures and make this work more accurate. It was also determined, the calibration curve of the sensor and a slight temperature dependency. In the field measurements, the output of the new heat flux sensor (using the calibration curves) was compared with output from a heat flux sensor available on the market. There is a good correspondence in the dynamics of the two sensors output, but there are discrepancies in the order of magnitude. Finite element simulations indicate that differences in the incidental direction of heat through the sensor are different in-situ and calibration, thus affecting results. Larger deviations are obtained for lower heat flux values (< 10 W/m2). These differences suggest that the calibration procedure can yet be improved.Regarding the usefulness of the studied sensor, its tininess makes it a perfect measurement device in little spaces such as small cavities or narrow frames where other sensor cannot even be placed and also disturbs much less than the ones in the market. Nevertheless, it still can be further developed i.e. encapsulating it in a non-metal guard that would interfere less with the incidental heat.

  • 73.
    Sandberg, Mats
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Kabanshi, Alan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Is building ventilation a process of diluting contaminants or delivering clean air?2019Ingår i: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The purpose of this paper is to discuss the performance of air distribution systems intended for dilution of contaminants (e.g. mixing ventilation) and those intended for delivery of clean air to local regions within rooms (e.g. personalized ventilation). We first start by distinguishing the systems by their visiting frequency behaviour. Then, the performance of the systems with respect to their possibility to influence contaminant concentration in the room or regions within the room is dealt with. Dilution capacity concept for mixing systems is discussed, and delivery capacity concept for systems intended to deliver clean air locally is introduced. Various ways for supply of clean air to regions within the room are presented and their pros and cons are discussed. In delivery capacity systems, the most important single parameter is the entrainment of ambient air into the primary supply flow. Therefore, methods of determining entrainment in these systems need to be defined and the results should be included when describing the performance of the air terminal devices.

  • 74.
    Schweitz, Anders
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    The potential of grid energy storage: a case study of the Nordic countries and Germany2019Självständigt arbete på avancerad nivå (magisterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The increasing share of renewable electricity will make energy storage technologies indispensable in the future. In this study, the potential of grid energy storage technologies is discussed, focusing on the Nordic countries as well as Germany. It is challenging to balance the intermittency of wind power and solar power production in the energy system. In Norway and Sweden, and to some extent Finland, hydropower is a very important balancing resource. Compressed Air Energy Storage (CAES) is a technology that has not had a real breakthrough yet. There are ongoing projects at different locations where one of the targets is to achieve better round-trip efficiency by taking care of the heat generated at compression. Pumped hydroelectric storage (PHS) has advantages in being cost-efficient and has a high round-trip efficiency. There is probably a high theoretical potential of new generating capacity in Norway and Sweden, but the electricity cost does not vary enough for new developments to be profitable at the moment. The environmental and social impact of PHS plants is an important and difficult aspect to handle. Power-to-gas, power-to-power and hydrogen storage has been getting more attention recently but needs more research to increase the round-trip efficiency and to reduce the costs of electrolysers, storage and fuel cells. Batteries can be well suited as a minute reserve or for peak shaving but are currently not cost-efficient for long-time storage. With lower prices and the possibility of using more abundant metals with less environmental and social impact batteries could play a larger role in electric grids. There might be possibilities of integrating batteries in electric vehicles with power systems as well.To speed up the development of energy storage technologies, governmental subsidies might be necessary. In the future, a larger variation in electricity cost can be expected during different times of the day and the year, which will make energy storage facilities more profitable.

  • 75.
    Svedman, Mathias
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Förhindrande av frostbildning i plattvärmeväxlare via variabel förvärmd uteluft2019Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Denna studie har undersökt om förvärmning av luft är en bra metod för att undvika frostbildning i motströmsplattvärmeväxlare i luftbehandlingsaggregat. Frostbildning i värmeväxlare för ventilation är ett problem i kalla klimat och sänker den återvunna energimängden när potentialen för energiåtervinning är som högst.  

    Tidigare forskning i området har utförts för att bland annat: 1) Definiera säkra förhållanden utan frostbildning i värmeväxlare med laminär luftströmning.  2) Jämföra olika frostkontrollstrategier. 3) Analysera frostbildningens egenskaper och effekt på värmeväxlare i ventilation. Att forskningen inte är entydig för vilken frostkontrollstrategi som är bäst belyser vikten av detta arbete.  

    I en fallstudie kvantifieras empiriska värmeöverföringskoefficienter som används i en analytisk modell som förutspår energianvändningen för luftvärmning under olika driftfall för ett luftbehandlingsaggregat. Värmeöverföringskoefficienterna tas fram genom mätningar i ett luftbehandlingsaggregat lokaliserat i ett flerbostadshus. Mätobjektet har ett installerat värmebatteri före värmeväxlaren vilket värmer inkommande uteluft till konstant lufttemperatur.  Tillverkaren proklamerar att det sker turbulent luftströmning i den studerade värmeväxlaren. Vid olika lufthastigheter ändras värmeöverföringskoefficienten mer vid turbulent strömning än vid laminär strömning. Att olika lufthastigheter har betydlig inverkan på värmeöverföringskoefficienten överensstämmer med resultatet från mätningarna.

    Effektiviteten av den aktuella styrningen av förvärmaren har granskats och brister har upptäckts. En ny optimerad styrning föreslås för frostfri drift och minimerad energianvändning. Den optimerade styrningen jämförs sedan med en vanlig avfrostningsmetod och utförs med hjälp av flödesbalansstatistik från ett aggregat med sektionsavfrostningsstyrning. Resultatet visar att förvärmning av luft för frostfri drift använder mindre energi än vid sektionsavfrostningsstyrning.  Den föreslagna styrningen innebär att bypass-spjället öppnas då förvärmaren går på full effekt. Detta för att förhindra påfrostning vid extrema utetemperaturer, då förvärmaren inte ger tillräcklig effekt för att undvika påfrostning. Den föreslagna styrningen regleras utifrån daggpunkten, temperaturen på tilluften innan värmeväxlaren och temperaturen på avluften.

    Den framtagna värmeöverföringskoefficienten i studien tar inte i beaktning ökad koefficient under fuktiga förhållanden då daggpunkten i frånluften är över fryspunkten och det sker kondens. En framtida studie kan hitta värmeöverföringskoefficienter som förutspår yttemperaturen under kondensutfällning då daggpunkten är över 0°C vilket ger medel för att ta fram en ännu mera energieffektiv styrning. Detta kan utföras genom mätning i ett luftbehandlingsaggregat med hög temperaturverkningsgrad placerat i en fuktig miljö.

  • 76.
    Thollander, Patrik
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Karlsson, Magnus
    Rohdin, Patrik
    Wollin, Johan
    Rosenqvist, Jakob
    Introduction to industrial energy effiiciency: Energy auditing, energy management, and policy issues2020Bok (Refereegranskat)
  • 77.
    Thollander, Patrik
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Linkoping Univ, Div Energy Syst, Dept Management & Engn, S-58183 Linkoping, Sweden..
    Palm, Jenny
    Lund Univ, Int Inst Ind Environm Econ, S-22350 Lund, Sweden..
    Hedbrant, Johan
    Linkoping Univ, Dept Management & Engn, Div Appl Thermodynam & Fluid Mech, S-58183 Linkoping, Sweden..
    Energy efficiency as a wicked problem2019Ingår i: Sustainability, ISSN 2071-1050, E-ISSN 2071-1050, Vol. 11, nr 6, artikel-id 1569Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Together with increased shares of renewable energy supply, improved energy efficiency is the foremost means of mitigating climate change. However, the energy efficiency potential is far from being realized, which is commonly explained by the existence of various barriers to energy efficiency. Initially mentioned by Churchman, the term wicked problems became established in the 1970s, meaning a kind of problem that has a resistance to resolution because of incomplete, contradictory, or changing requirements. In the academic literature, wicked problems have later served as a critical model in the understanding of various challenges related to society, such as for example climate change mitigation. This aim of this paper is to analyze how the perspective of wicked problems can contribute to an enhanced understanding of improved energy efficiency. The paper draws examples from the manufacturing sector. Results indicate that standalone technology improvements as well as energy management and energy policy programs giving emphasis to standalone technology improvements may not represent a stronger form of a wicked problem as such. Rather, it seems to be the actual decision-making process involving values among the decision makers as well as the level of needed knowledge involved in decision-making that give rise to the wickedness. The analysis shows that wicked problems arise in socio-technical settings involving several components such as technology, systems, institutions, and people, which make post-normal science a needed approach.

  • 78.
    Thollander, Patrik
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Rohde, Clemens
    Fraunhofer Institute for System and Innovation Research, ISI, Germany.
    Kimura, Osamu
    Central Research Institute of Electric Power Industry, Japan.
    Helgerud, Hans-Even
    Norsk Energi, Norway.
    Realini, Anna
    Ricerca sul Sistema Energetico, Italy.
    Maggiore, Simone
    Ricerca sul Sistema Energetico, Italy.
    Cosgrove, John
    Limerick Institute of Technology, Ireland.
    Johansson, Ida
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    A review of energy efficiency policies for small and medium-sized manufacturing enterprises from around the world2019Ingår i: 2019 ACEEE Summer Study on Energy Efficiency in Industry, Portland, August 12-14, 2019, 2019, s. 3-135-3-150Konferensbidrag (Refereegranskat)
    Abstract [en]

    In most countries, small and medium-sized manufacturing (industrial) enterprises (SMEs) represent more than 99% of the number of companies and 60% of employment. Thus, this sector, apart from using energy, is a major driver in the economy with regard to innovations, GDP, investments and export. Despite the importance of SMEs in the economy, they have not received much attention in most countries' energy policy activities. Energy management in its various forms is regarded as one of the key drivers of industrial energy efficiency. While the term "energy management" is often associated with the ISO 50001 standard, there is a broad variety of different programs and schemes in place that do not strictly abide by the framework of the standard. Especially for SMEs, the standardized protocols of ISO 50001 are often too complex for cost-efficient implementation. The aim of this paper is to provide an international overview of existing energy efficiency policies with a focus on energy management practices in selected EU member states as well as Norway and Japan. Results indicate that different countries apply a broad variety of policy contexts in which the energy management practices are embedded.

  • 79.
    Torre, Andoni
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Energy analysis of a house and proposals for improvements2019Självständigt arbete på avancerad nivå (magisterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
  • 80.
    Tsivras, Sotirios-Ilias
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Load Demand Forecasting: A case study for Greece2019Självständigt arbete på avancerad nivå (masterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    It is more than a fact that electrical energy is a main production factor of every economic activity. Since electrical power is not easy to store, it needs to be consumed as it is generated in order to keep a constant balance between supply and demand. As a result, for developing an efficient energy market it is significant to create a method for accurately forecasting the electricity consumption.

    This thesis describes a method for analyzing data provided by the ENTSO-E transparency platform. The ENTSO-E (European Network of Transmission System Operators) is a network of electricity operators from 36 countries across Europe. Its main objective is to provide transparency concerning data of electricity generation and consumption in Europe in order to promote the development of efficient and competitive electricity markets.

    By using the method described in this thesis, one may use historical data provided by ENTSO-E to forecast the electricity consumption of an EU country for the years to come. As an example, data of electricity consumption in Greece during the years 2015-2018 have been used in order to calculate the average load demand of a weekday during the year 2030.

    On the other hand, in order to correctly predict the electricity demand of a specific region over the next decade, one should take into account some crucial parameters that may influence not only the evolution of the load demand, but also the fuel mix that will be used in order to cover our future electricity needs. Advances in power generation technologies, evolution of fuel prices, expansion of electricity grid and economic growth are a subset of parameters that should be taken into account for an accurate forecast of the electricity consumption in the long run.

    Particularly for Greece, a set of parameters that may affect the electricity consumption are being computationally analyzed in order to evaluate their contribution to the load demand curve by the year 2030. These include the interconnection of Greek islands to the mainland, the development of Hellinikon Project and the increase of the share of electric vehicles.

    The author of this thesis has developed code in Python programming language that can be found in the Appendix. These scripts and functions that implement most of the calculations described in the following chapters can also be used for forecasting the load demand of other EU countries that are included in the ENTSO-E catalogue. The datasets used as input to these algorithms may also be used from the readers to identify more patterns for predicting the load demand for a specific region and time.

    A sustainable energy system is based on consumers with environmental awareness. As a result, citizens living inside the European Union should become a member of a community that promotes energy saving measures, investments in renewable energy sources and smart metering applications.

  • 81. Törnström, T.
    et al.
    Amiri, Shahnaz
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Tekniska Verken i Linköping.
    Moshfegh, Bahram
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Linköpings universitet.
    Flow and thermal characteristics of warm plane air jets (measurements and predictions using different k-ε models)2001Ingår i: Computational Engineering, 2001, s. 33-44Konferensbidrag (Refereegranskat)
    Abstract [en]

    Jets are often used for supplying air to buildings. For designing ventilation systems it is therefore of great importance to have a good understanding of air jets to avoid draught, which might lead to discomfort. At the same time as we want a good indoor climate, we also want to reduce energy consumption. The purpose of this study is to investigate the flow and thermal characteristics of warm air jets supplied under the ceiling, as a heating method, by means of numerical prediction and full-scale experiments. Together with the warm wall jet, an isothermal wall jet will also be examined. For the calculations, three different k-ε models have been used and evaluated, namely the standard k-ε, the Chen-Kim k-ε model and the Renormalization Group k-ε model. The experiments have been carried out in a full-scale room where the temperature and velocity within the air jet are conducted. For the isothermal wall jet, the Chen model gives best agreement for the growth rate, while the standard k-ε model gives the best result for the velocity decay of the jet. The evaluation of the warm jet provided best results for the Chen model regarding both the growth rate and the velocity decay. The velocity and temperature profiles for the warm jet provided similar results for all models, but also some differences between the predicted and measured temperatures.

  • 82.
    Wang, Chengju
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Energy use and energy saving in buildings and asthma, allergy and sick building syndrome (SBS): a literature review2019Självständigt arbete på avancerad nivå (magisterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Energy use in buildings is an important contribution to global CO2 emissions and contributes to global warming. In recent years, there has been concern about creating energy efficiency buildings, green buildings and healthy buildings but this development needs guidance by multidisciplinary scientists and experts. Since energy saving can influence the indoor environment in different ways, epidemiological research is needed in different climate zones to evaluate the health consequences of making the buildings more energy efficient. Epidemiological studies and modelling studies are available on health effects and indoor effects of energy conversation, improved thermal insulation, increased air tightness and creating green buildings. The health-related literature on this issue was reviewed, by searching scientific articles in the medical Database PubMed and in the general database Web of Science as well as Nature database. In this literature review, 53 relevant peer reviewed articles on health effects of energy use and energy saving were found. Most of the studies had investigated residential buildings. One main conclusion from the review is that combined energy efficiency improvements in buildings can be associated with improvement of general health, such as less asthma, allergies, sick building syndrome (SBS) symptoms, respiratory symptoms, and reduced cold-related and heat-related mortality. Moreover, combined energy efficiency improvements can improve indoor air quality, increase productivity and satisfaction and reduce work leave and school absence. Effective heating of buildings can reduce respiratory symptoms and reduce work leave and school absence. However, some potential health problems can occur if increased energy efficiency will reduce ventilation flow. Energy saving by increasing air tightness or reducing ventilation is associated with impaired indoor air quality and negative health effects. In contrast, improved ventilation may reduce SBS, respiratory symptoms and increase indoor air quality. Installation of mechanical ventilation can solve the negative effects of making the building construction in dwellings more air tight. In future research, more studies are needed on health impacts of single energy efficiency improvement methods. Existing studies have mostly used a combination of improvement methods. In addition, modelling software programs should more often be used, since they can take into account effects of different energy efficiency improvement methods on indoor air quality in different types of buildings and in different climates.

  • 83.
    Wennberg, Tim
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Fjärrvärme och frånluftsvärmepump: Systemets lönsamhet och primärenergitalets inverkan2019Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Kombinationen av fjärrvärme och frånluftsvärmepump (FVP) har blivit allt vanligare i Sverige. Detta kombinerade värmesystem är väl lämpat för att reducera energianvändningen i befintliga fastigheter med mekanisk frånluftventilation som saknar värmeåtervinning. Dock kan en FVP-installation leda till högre returtemperaturer i fjärrvärmenätet vilket det ofta finns avgifter för i dagsläget. För att främja fjärrvärmeanvändning sommartid använder fjärrvärmeleverantören sig av säsongsvarierande prismodeller i vilket fjärrvärmepriset varierar under en del av året. Genom att stänga av FVP sommartid och endast bruka fjärrvärme finns en potentiell kostnadsbesparing då fjärrvärmepriset är som lägst. Denna kostnadsbesparing undersöks utifrån olika typer av fjärrvärmetaxor, elnätsavgifter och elhandelspris. Det undersöks också hur Boverkets regler för beräkning av primärenergital påverkar denna värmesystemtyp. Typiska prismodeller för fjärrvärme har undersökts, samt så har energianvändning framräknats för sex fiktiva flerbostadshus runtom i landet. För varje byggnad beräknas energianvändningen utifrån tre fall. I referensfallet, Fall 1 används bara fjärrvärme och i Fall 2 används FVP till både uppvärmning och tappvarmvatten (TVV). Fall 3 är som Fall 2 fast FVP täcker inget TVV-behov och stängs av under sommar-perioden. Energianvändningen är framräknad över ett år och energikostnaden jämförs mellan fallen. I Fall 2 och Fall 3 är de totala energikostnaderna för byggnaderna mellan 61–75% respektive 67–78% av energikostnaderna i Fall 1. Mellan Fall 2- och 3 finns däremot ingen tydlig besparingstrend trots att alla fjärrvärmenät på orterna har ett säsongsvarierande fjärrvärmepris. Att ingen besparingstrend uppstår påvisar att kostnaden för varje levererad värmeenhet från FVP sommartid är ungefär lika stor som varje värmeenhet fjärrvärme. Detta beror på att en hög värmefaktor används vilket gör det väldigt kostnadseffektivt att köpa el. Med en lägre värmefaktor gynnas avstängning av FVP sommartid. Utifrån den framräknade energianvändningen beräknas primärenergitalet och den specifika energianvändningen för samtliga byggnader. Primärenergitalet är i de flesta fall större än den specifika energianvändningen för att elanvändningen räknas upp. I Luleå är däremot den specifika energianvändningen större än primärenergitalet, även vid användning av FVP.

  • 84.
    Yang, Bin
    et al.
    Department of Applied Physics and Electronics, Umeå University, Umeå, Sweden.
    Melikov, A.K.
    International Centre for Indoor Environment and Energy, Department of Civil Engineering, Technical University of Denmark, Denmark.
    Kabanshi, Alan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Zhang, C.
    Department of Civil Engineering, Aalborg University, Aalborg, Denmark.
    Bauman, F. S.
    Center for the Built Environment, University of California, Berkeley, CA, United States.
    Cao, G.
    Department of Energy and Process, Norwegian University of Science and Technology, KolbjørnHejesVei 1B, Trondheim, Norway.
    Awbi, H.
    School of Construction Management and Engineering, University of Reading, United Kingdom.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Niu, J.
    School of Architecture, Design and Planning, The University of Sydney, Australia.
    Cheong, K. W. D.
    Department of Building, School of Design and Environment, National University of Singapore, Singapore.
    Tham, K. W.
    Department of Building, School of Design and Environment, National University of Singapore, Singapore.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Nielsen, P. V.
    Department of Civil Engineering, Aalborg University, Aalborg, Denmark.
    Kosonen, R.
    Department of Mechanical Engineering, School of Engineering, Aalto University, Espoo, Finland; College of Urban Construction, Nanjing Tech University, Nanjing, China.
    Yao, R.
    School of Construction Management and Engineering, University of Reading, United Kingdom.
    Kato, S.
    Institute of Industrial Science, The University of Tokyo, Tokyo, Japan.
    Sekhar, S. C.
    Department of Building, School of Design and Environment, National University of Singapore, Singapore.
    Schiavon, Stefano
    Center for the Built Environment, University of California, Berkeley, CA, United States.
    Karimipanah, Taghi
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Li, X.
    Department of Building Science, School of Architecture, Tsinghua University, Beijing, China.
    Lin, Z.
    Division of Building Science and Technology, City University of Hong Kong, Hong Kong, Hong Kong.
    A review of advanced air distribution methods - theory, practice, limitations and solutions2019Ingår i: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 202, artikel-id 109359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ventilation and air distribution methods are important for indoor thermal environments and air quality. Effective distribution of airflow for indoor built environments with the aim of simultaneously offsetting thermal and ventilation loads in an energy efficient manner has been the research focus in the past several decades. Based on airflow characteristics, ventilation methods can be categorized as fully mixed or non-uniform. Non-uniform methods can be further divided into piston, stratified and task zone ventilation. In this paper, the theory, performance, practical applications, limitations and solutions pertaining to ventilation and air distribution methods are critically reviewed. Since many ventilation methods are buoyancy driving that confines their use for heating mode, some methods suitable for heating are discussed. Furthermore, measuring and evaluating methods for ventilation and air distribution are also discussed to give a comprehensive framework of the review.

  • 85.
    Yang, Hongyu
    et al.
    Sun Yat-sen University.
    Chen, Taihan
    Sun Yat-sen University.
    Lin, Yuanyuan
    Sun Yat-sen University.
    Buccolieri, Riccardo
    University of Salento.
    Mattsson, Magnus
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Zhang, Ming
    State Power Environmental Protection Research Institute, Nanjing.
    Hang, Jian
    Sun Yat-sen University.
    Wang, Qun
    University of Hong Kong.
    Integrated impacts of tree planting and street aspect ratios on CO dispersion and personal exposure in full-scale street canyons2020Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 169, artikel-id 106529Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Validated by experimental data, this paper performs computational fluid dynamics (CFD) simulations to investigate the influence of tree plantings on urban airflow and vehicular CO exposure in two-dimensional (2D) street canyons with various aspect ratios (building height/street width, AR = H/W = 0.5, 1, 3, 5) and ground-level source. The impacts of tree canopy bottom height (Htb = 2 m, 6 m), tree stand density (y-density = 0.33, 0.67, 1) and leaf area density (LAD = 0.5, 1, 2 m2/m3) are considered. Personal intake fraction (P_IF) and its spatial mean value in leeward and windward sides (&lt;P_IF&gt;lee, &lt;P_IF&gt;wind) and for entire streets (street intake fraction, &lt;P_IF&gt;) are adopted to assess overall pollutant exposure. For cases without trees, only one main vortex exists in shallow streets with AR = 0.5-3 and &lt;P_IF&gt; as AR = 3 (5.80 ppm) slightly exceeds AR = 0.5-1 (3.98-3.84 ppm). However, two counter-rotating vortexes appear in deep streets (AR = 5), inducing 1-2 orders smaller pedestrian-level velocity (U/Uref~10−4-10−3) and one-order greater &lt;P_IF&gt; (46.80 ppm) than shallow streets. Trees always weaken wind in streets and raise &lt;P_IF&gt; more in shallower streets by 46.0% as AR = 0.5 (3.98 ppm-5.81 ppm), 26.0-45.9% as AR = 1 (3.84 ppm to 4.84-5.60 ppm), 16.2-50.3% as AR = 3 (5.80 ppm to 6.74-8.72 ppm), but only 8.5-23.4% as AR = 5 (46.80 ppm to 50.78-57.73 ppm). Particularly, as AR = 1, trees raise &lt;P_IF&gt;lee (5.87 ppm) by 27.1-57.2%, while &lt;P_IF&gt;wind (1.80 ppm) only by 0%-23.3%. Higher Htb, smaller y-density or LAD produce less increase of &lt;P_IF&gt;. As AR = 3, vegetation increases &lt;P_IF&gt;lee (8.84 ppm) by 21.2%-66.4% but little affects &lt;P_IF&gt;wind (2.76 ppm). Lower Htb produces smaller &lt;P_IF&gt; differing from AR = 1. As AR = 5, vegetation increases &lt;P_IF&gt;wind (63.97 ppm) by 15.1-36.6% but reduces &lt;P_IF&gt;lee (29.63 ppm) by 5.2-8.5%. Although further investigations are still required for design purpose, this paper provides effective methodologies to quantify how vegetation influences street-scale pollutant exposure.

  • 86.
    Yang, Xia
    et al.
    Sun Yat-sen University, Guangzhou, PR China.
    Zhang, Yong
    Sun Yat-sen University, Guangzhou, PR China.
    Hang, Jian
    Sun Yat-sen University, Guangzhou, PR China.
    Lin, Yuanyuan
    Sun Yat-sen University, Guangzhou, PR China.
    Mattsson, Magnus
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Zhang, Ming
    State Power Environmental Protection Research Institute, Nanjing, China.
    Wang, Kai
    Department of Civil, Environmental and Geomatic Engineering, University College, London, UK.
    Integrated assessment of indoor and outdoor ventilation in street canyons with naturally-ventilated buildings by various ventilation indexes2020Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 169, artikel-id 106528Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The integrated assessments of indoor and outdoor ventilation are still rare so far. As a novelty, this paper aims to quantify the influence of street aspect ratios (building height/street width, H/W = 0.5–5) and window sizes (1 m × 1 m, 1.5 m × 1.5 m) on indoor-outdoor ventilation in two-dimensional streets with single-sided naturally-ventilated buildings. Numerical simulations with RNG k-ε model are validated against experimental data and the grid independence are tested as well. Air change rates per hour (ACH, h−1) are adopted for assessing indoor-outdoor ventilation by mean flows (ACHmean) and turbulent fluctuations (ACHturb) respectively. Age of air(τ), purging flow rate (PFR) and its corresponding ACHPFR are used to evaluate overall ventilation capacities.

    Shallower streets experience better indoor-outdoor ventilation. Outdoor ACHPFR drop from 14.69 to 17.55 h−1 to 3.96–3.97 h−1 as H/W rises from 0.5 to 3. In extremely deep canyon (H/W = 5), two-counter-rotating vortices produce much smaller velocity at low-level regions (U/Uref~10−3-10−5), resulting in small ACHPFR for outdoor (~0.76–0.91 h−1) and indoor in 1–13th floors (~0.03–0.61 h−1). When H/W = 0.5–1, leeward 5–6th floors experience smaller ACHPFR(e.g.~1.13–1.40 h−1 as H/W = 1) than the other floors (e.g. ~1.54–9.52 h−1 as H/W = 1). Particularly, as H/W = 2–3, leeward-side indoor ACHPFR in the middle floors (except the first and top two floors) are nearly constants (~1.02–1.69 h−1) and much smaller than windward-side ACHPFR(~1.41–4.35 h−1) which increase toward upper floors. Besides, the smaller window size reduces indoor ACHPFR by 19.38%~88.28%, but hardly influences outdoor ventilation. Moreover, both outdoor and indoor ACHPFR are greater than ACHmean but smaller than ACHmean + ACHturb. Although further investigations are still required, this paper provides an insight and scientific foundation on integrated indoor-outdoor ventilation evaluation with various effective ventilation indexes.

  • 87.
    Yin, Shi
    et al.
    Department of Mechanical Engineering, The University of Hong Kong, Hong Kong Special Administrative Region.
    Fan, Yifan
    Department of Mechanical Engineering, The University of Hong Kong, Hong Kong Special Administrative Region; College of Civil Engineering and Architecture, Zhejiang University, Yuhangtang Road, Hangzhou, China .
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Li, Yuguo
    Department of Mechanical Engineering, The University of Hong Kong, Hong Kong Special Administrative Region.
    PIV based POD analysis of coherent structures in flow patterns generated by triple interacting buoyant plumes2019Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 158, s. 165-181Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper performs an investigation on multi-scale coherent structures that exist in different flow patterns of triple interacting plumes. Time-averaged and turbulent flow characteristics are first obtained by the two-dimensional (2-D) particle image velocimetry (PIV) technique. Proper orthogonal decomposition (POD) method is then applied to extract the dominant coherent structures. Energy contributions, POD modes, and POD coefficients are systematically explored to understand the spatial-temporal characteristics of the coherent structures. The first three POD modes are most important in the turbulent kinetic energy (TKE). Mode 1, as the most dominant mode, can contain about 10% TKE in an average sense. In addition, the first 12–14 POD modes can totally contribute 50% TKE. Hierarchical four-scale flow structures, independent of the flow patterns, are clearly identified when mode number increases, which are successively characterized by main flows (the 1st scale), larger-scale outer-side vortex rings (the 2nd scale), shear-layer vortex shedding (the 3rd scale), and smaller-scale homogeneous turbulent vortices (the 4th scale). Frequency spectra analysis confirms the co-existence of lower-frequency and higher-frequency periodic cycles in one certain POD mode. Dominant frequencies of the first three POD coefficient series (a1–a3) fall into the range of 0.025–0.187 Hz. Probability density analysis has identified negative/positive peak probability densities of the series a1. Cumulative probabilities of negative and positive coefficients are approximately equivalent during the sampling period. 

  • 88.
    Yin, Shi
    et al.
    Department of Mechanical Engineering, The University of Hong Kong, Hong Kong SAR, China.
    Li, Yuguo
    Department of Mechanical Engineering, The University of Hong Kong, Hong Kong SAR, China.
    Fan, Yifan
    Department of Mechanical Engineering, The University of Hong Kong, Hong Kong SAR, China.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Experimental investigation of near-field stream-wise flow development and spatial structure in triple buoyant plumes2019Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 149, s. 79-89Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a systematic experimental study on stream-wise flow development and spatial structure of triple buoyant plumes. Two-dimensional Particle Image Velocimetry (2-D PIV) is employed to resolve velocity fields. Stream-wise axial velocity profiles, flow structure, flow region parameters, and self-similarity properties are analyzed at different configurations that are characterized by spacing ratios S/W (source spacing S divided by source width W). From velocity fields and axial velocity profiles, a similar stream-wise developing trend is identified in different source configurations. When near-field plumes travel downstream, axial velocities increase rapidly, off-center velocity peaks get merged with the central peak, and the number of velocity peaks reduces with the downstream distance. A compact source layout, comparing with the wide one, could enhance the near-field plumes interaction and promote the plumes deflection significantly. Fundamentally, the stream-wise spatial structure of the triple plumes initially consists of a converging region, followed by a merging region, and finally a combined region. By examining the averaged velocity fields, flow recirculation with negative axial velocities is found to scarcely exist in the converging region. Merging level Zm and quasi-combined level Zqc are analyzed quantitatively and statistically. Within the studied S/W range, the normalized Zm shows a linear increase with S/W in the formula of Zm/H=2.007(S/W)+1.173 and the normalized Zqc gives a power law increase with S/W in the formula of Zqc/H=6.035(S/W)0.4959. In addition, triple plumes are found to establish self-similarity approximately at Z = 3H with S/W of 0.2 and at Z = 4.5H with S/W of 0.5.

  • 89.
    Östlund, Christine
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Dimensionering och optimering av ett solcellssystem för en industribyggnad i Mellansverige: En simuleringsstudie2019Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Vid omställningen till förnybara energisystem är solkraften som energikälla ett möjligt alternativ, för att uppnå klimat och energimålet med 100% förnybar energiproduktion år 2040. Detta är något regeringen eftersträvar genom infört bidrag i form av subventioner och skattereduktion vid installation av solceller. I denna fallstudie undersöks vilken effekt två olika solcellssystem har för en industribyggnad i Mellansverige, där studien tar hänsyn till ekonomisk-, teknisk- och klimatrelaterade aspekter. Systemen dimensioneras i strävan av optimala förhållanden samt av byggnadens begränsningar, med kostnadsförslag från en lokal återförsäljare få en bild av om återbetalningstiden är motiverande i frågan. Den lokala klimatpåverkan analyseras med växthusgasutsläpp i fokus, detta genom resultat av litteraturstudie. Dimensioneringen av solcellssystemen baseras på empiriskt material av studieobjektet och simuleras i programmet Winsun PV. Studien resulterade i två storlekar på system med tillhörande kostnadsförslag som ligger till grund för återbetalningstiden. System fall 1 dimensionerades i syfte att hålla den nominella systemeffektens storlek till 255 kWp, detta för att undgå extra energiskatt. Systemet gav ett årligt utbyte av 228 MWh/år som gav återbetalningstid mellan 18 – 22,5 år. Systemet simulerades med optimal lutningsvinkel av 39° i 15° azimutriktning av modulerna. System fall 2 dimensionerades till 1200 kWp i syfte att täcka effektivt användbar takyta, med årligt utbyte på 886 MWh/år och återbetalningstiden blev mellan 22,5 – 25,1 år. Modulerna simulerades med takets lutning ±4,7° i -15° azimutriktning. För att solceller ska ge ett mer lönsamt utbyte i högre latituder krävs en vidare effektivitetsutveckling för solcellstekniken samt ett förlängt investeringsstöd från Länsstyrelsen för framtida installationer. Om solcellssystemet ger en positiv inverkan på det ekologiska fotavtrycket beror av vart solcellen är tillverkad samt vilken elmix som byts ut mot den producerade solenergin.

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