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  • 201.
    Torres, João Paulo N.
    et al.
    Instituto de Telecomunicações, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal.
    Fernandes, Carlos A. F.
    Instituto de Telecomunicações, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal.
    Gomes, João
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Luc, Bonfiglio
    Ecole Polytechnique Universitaire de Montpellier, Montpellier, France.
    Carine, Giovinazzo
    Ecole Polytechnique Universitaire de Montpellier, Montpellier, France.
    Olsson, Olle
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Branco, P. J. Costa
    Associated Laboratory for Energy, Transports and Aeronautics, Institute of Mechanical Engineering (LAETA, IDMEC), Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal.
    Effect of reflector geometry in the annual received radiation of low concentration photovoltaic systems2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 7, article id 1878Article in journal (Refereed)
    Abstract [en]

    Solar concentrator photovoltaic collectors are able to deliver energy at higher temperatures for the same irradiances, since they are related to smaller areas for which heat losses occur. However, to ensure the system reliability, adequate collector geometry and appropriate choice of the materials used in these systems will be crucial. The present work focuses on the re-design of the Concentrating Photovoltaic system (C-PV) collector reflector presently manufactured by the company Solarus, together with an analysis based on the annual assessment of the solar irradiance in the collector. An open-source ray tracing code (Soltrace) is used to accomplish the modelling of optical systems in concentrating solar power applications. Symmetric parabolic reflector configurations are seen to improve the PV system performance when compared to the conventional structures currently used by Solarus. The parabolic geometries, using either symmetrically or asymmetrically placed receivers inside the collector, accomplished both the performance and cost-effectiveness goals: for almost the same area or costs, the new proposals for the PV system may be in some cases 70% more effective as far as energy output is concerned.

  • 202.
    Torres, João Paulo N.
    et al.
    University of Lisbon, Lisbon, Portugal.
    Nashih, Samuel K.
    University of Lisbon, Lisbon, Portugal.
    Fernandes, Carlos A. F.
    University of Lisbon, Lisbon, Portugal.
    Leite, João C.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    The effect of shading on photovoltaic solar panels2018In: Energy Systems, Springer Verlag, ISSN 1868-3967, E-ISSN 1868-3975, Vol. 9, no 1, p. 195-208Article in journal (Refereed)
    Abstract [en]

    A modelling description of photovoltaic (PV) modules in a PSPICE environment is presented. To validate the simulation model, a lab prototype is used to create similar conditions as those existing in real photovoltaic systems. The effects of partial shading of solar cell strings and temperature on the performance of various PV modules are analyzed. The simulation results show a very good agreement with those obtained experimentally in similar conditions, either in lab, at Lisbon University, and under outdoor testing in Sweden, using PV solar collectors manufactured by Solarus Sunpower AB. The potential of the simulation analysis is highlighted as a flexible and powerful tool for the design of new and more competitive PV module configurations for the collectors in solar panels.

  • 203.
    Vaarama Danielsson, Adam
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Ahmedi, Omed
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Energikartläggning av kvarteret Bordsgossen i Gävle.Undersökning av energieffektiviseringsåtgärder passande flerbostadshus.2016Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
  • 204.
    Vachaparambil, Kurian Jory
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Karimipanah, Taghi
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Comparative Numerical Study of the Indoor Climate for Mixing and Confluent Jet Ventilation Systems in an Open-plan Office2018In: Proceedings of the 4th international Conference on Building Energy & Environment, Melbourne: Conference On Building Energy & Environment - COBEE2018, Melbourne Australia , 2018, p. 73-78Conference paper (Refereed)
  • 205.
    Vergés Gil, Albert
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Application of the hot-box technique to test the insulation effect of low-emissivity film on old windowsIndependent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
  • 206.
    Vicente Pina, Alejandro
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Analysis and consumption troubleshooting in a heat pump2016Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    One of the European Union priorities is the promotion of electricity generated from renewable energy sources. This is due to reasons of security and diversification of energy supply, environmental protection, reducing external dependence of the European Union (EU) in its energy supply and economic and social cohesion.

    The members of the EU as a whole, constitute the major world power in what concerns the development and application of renewable energy. The Maastricht Treaty assigned the EU's objectives of promoting sustainable growth respecting the environment. Meanwhile the Treaty of Amsterdam incorporated the principle of sustainable development in the objectives of the EU.

    The price support system for renewable energy currently prevailing in the EU is the system Renewable Energy Feed-in Tariffs (REFIT). The geothermal energy is considered as one of these renewable energies, so, it gets benefits from this system.

    In the concrete case of Sweden, almost 40% of the energy used is represented by the residential and services sector. So, to maximize the usage of renewable energy in these sectors is a priority for the country. In this way, low enthalpy geothermal energy is the easiest way of using geothermal energy in residential buildings.

    In this project it is studied a block of flats in N. Kungsgatan 37-43 (Gävle), whose heating and tap hot water system are handled by a geothermal heat pump combined with district heating. The system has been analysed because the consumption of electricity was higher than expected and this is a problem when the energy saving is the objective.

    For the analysis, different elements of the installation have been checked to verify if they are working correctly. For example, if the temperature sensors are giving properly information to the controlling system and the effectiveness of heat exchangers is the correct. The whole installation has also been carefully inspected with a thermal camera to check possible liquid or heat leakages in the machines room.

    Finally, after study the heat pump, the conclusion is that the problem is in the geothermal part of the heat pump, because the probes are not able to supply the required heat to the system. This is due to the geothermal installation was designed for another heat pump which was installed in the building some years ago. However, when the new installation was done in 2010, the geothermal installation was not changed for the new heat pump installation.

  • 207.
    Wanasinghe, Buddhika Hasantha
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Steam driven boiler feed pumps for Lakvijaya Power Station, Sri Lanka2017Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Energy saving in coal power plants is a popular topic in present days with the global energy crisis. Internal electricity demand or auxiliary power consumption is an energy portion related with equipment supportive to the main equipment, which is unavoidable but with a proper investigation, some amount of this energy can be saved either by introducing thermally efficient auxiliary equipment or improving efficiencies of available equipment.

    Out of the various auxiliary equipment, the driving motor of boiler feed pump is the largest power consumer of internal electricity demand in 3x300 MW sub-critical Lakvijaya Power Station in Sri Lanka. So it is obvious that prime movers of feed pumps could be contributed for a large percentage of the losses. So it was decided to find out how to minimize the losses related to Boiler Feed Pump (BFP) system using small steam turbine to drive the BFP.

    The widely used alternatives for the BFP drivers are condensing type and back pressure type steam turbines. Eleven (11) different configurations of Condensing type, back pressure type and also extraction back pressure type turbines were considered and software programs for each configuration were implemented using Engineering Equation Solver (EES) software. The considered configurations are different to each other by inlet steam thermodynamic parameters, steam flow rate, exhaust thermodynamic steam parameters and intermediate extraction parameters etc.

    Thermodynamic analysis ended up with interesting solutions while all the configurations are giving improved efficiencies than existing electrical motor driven mode. But some of them had not improved their net output and hence there were no gain in net generator power output although the efficiencies are higher. Out of other configurations with improved net output and efficiency, the case with back pressure turbine arranged parallel to the HP turbine had the highest net output gain with better improvement in efficiency without changing the input power to the boiler. Considering the CO2 , SOx and NOx emissions, it was cleared that power plant with suggested BFP modes will give more clean energy than existing power plant.

    Considering the partial loads behavior it was observed that power plant with Back pressure turbine, steam extracted from HP turbines inlet for prime movers of boiler feed pumps is more thermodynamically economical than existing power plant.

    Annual financial saving with BFP configurations with positive net output gain and zero boiler input gain were calculated and it will be in between 0.46 and 2.72 UDS million / Year.

  • 208.
    Wang, Q.
    et al.
    Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China .
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Hang, J.
    Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China .
    Assessment of air change rate and contribution ratio in idealized urban canopy layers by tracer gas simulations2014In: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate, 2014, p. 470-477Conference paper (Refereed)
  • 209.
    Wang, Qun
    et al.
    School of Atmospheric Sciences, Sun Yat-Sen University, Guangzhou, China.
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Lin, Yuanyuan
    School of Atmospheric Sciences, Sun Yat-Sen University, Guangzhou, China.
    Yin, Shi
    Department of Mechanical Engineering, The University of Hong Kong, PokFuLam Road, Hong Kong, China.
    Hang, Jian
    School of Atmospheric Sciences, Sun Yat-Sen University, Guangzhou, China.
    Impacts of Urban Layouts and Open Space on Urban Ventilation Evaluated by Concentration Decay Method2017In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 8, no 9, article id 169Article in journal (Refereed)
    Abstract [en]

    Previous researchers calculated air change rate per hour (ACH) in the urban canopy layers (UCL) by integrating the normal component of air mean velocity (convection) and fluctuation velocity (turbulent diffusions) across UCL boundaries. However they are usually greater than the actual ACH induced by flow rates flushing UCL and never returning again. As a novelty, this paper aims to verify the exponential concentration decay history occurring in UCL models and applies the concentration decay method to assess the actual UCL ACH and predict the urban age of air at various points. Computational fluid dynamic (CFD) simulations with the standard k-ε models are successfully validated by wind tunnel data. The typical street-scale UCL models are studied under neutral atmospheric conditions. Larger urban size attains smaller ACH. For square overall urban form (Lx = Ly = 390 m), the parallel wind (θ = 0°) attains greater ACH than non-parallel wind (θ = 15°, 30°, 45°), but it experiences smaller ACH than the rectangular urban form (Lx = 570 m, Ly = 270 m) under most wind directions (θ = 30° to 90°). Open space increases ACH more effectively under oblique wind (θ = 15°, 30°, 45°) than parallel wind. Although further investigations are still required, this paper provides an effective approach to quantify the actual ACH in urban-like geometries.

  • 210.
    Weinberger, Gottfried
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Amiri, Shahnaz
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Division of Energy Systems, Linköping University, Linköping, Sweden.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Division of Energy Systems, Linköping University, Linköping, Sweden.
    On the benefit of integration of a district heating system with industrial excess heat: an economic and environmental analysis2017In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 191, p. 454-468Article in journal (Refereed)
    Abstract [en]

    Energy-related cooperation using industrial excess heat (IEH) in district heating (DH) networks shows economic and environmental benefits. A rarely investigated approach is the energy cooperation which incorporates a jointly operated CHP plant also producing process steam for nearby industry. The present study aims to evaluate economic and environmental effects on the Hofors DH system with jointly operated CHP plant when the nearby steel mill extends the supply of recovered IEH. Various IEH supply opportunities with different capacities of hot water and steam were designed and compared with existing IEH utilization, plant heat and electricity production and DH system performance. The energy system model MODEST is used for cost-optimization. A parametric study is used to analyze influences of increasing IEH cost and fluctuating electricity prices. The results show advantages for the DH system to utilize IEH for deliveries of DH and process steam and the cogeneration of electricity. Economic and environmental benefits are decreased total system cost (-1.67 MEUR/a), less use of fuels and electricity, and reduced CO2 emissions with a maximal reachable amount of 28,200 ton/a when the use of biofuel is assumed as limited resource and the substituted marginal electricity production is based on coal condensing power plants. The results also show that industrial steam is a preferred heat supply source as long as the steam cost is below the alternative heat production cost, irrespective of the electricity price. While the cost-effective utilization of industrial hot water for DH is more sensitive and affected by a beneficial CHP production based on higher electricity price segments, it is also shown that utilization of continuously supplied industrial hot water is limited during seasons of low DH demand.

  • 211.
    Weinberger, Gottfried
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Investigating influential techno-economic factors for combined heat and power production using optimization and metamodeling2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 232, p. 555-571Article in journal (Refereed)
    Abstract [en]

    This paper investigates the interaction of a wide range of electricity and fuel prices and technical factors of combined heat and power production in a district heating system. A linear programming-based optimization model with the objective to minimize system cost was used to study the energy systems in the cities of Gävle and Sandviken in Sweden. The comprehensive outcomes from optimization and parametric studies have been analyzed using a polynomial-based metamodel. System costs include variable costs for the production and revenues for sale of heat and electricity. The metamodel is used as an analytical and explanatory tool to interpret input-output relationships. Municipal district heating systems of Gävle and Sandviken in Sweden are studied as an interconnected regional system with improved and new combined heat and power plants. The results show that effects from electricity and fuel prices are important, but that variations in energy system cost may also be caused by many cross-factor interactions with technical factors. A comparative system performance analysis with defined cases and optimal factor setting shows a substantial increase in the electricity production, here by up to 650 GWh annually. The profitability of investing in a new plant depends highly on the considered investment risk and electricity and fuel market prices. CO2 emission savings by up to 466 kton annually can be accomplished if marginal electricity production from coal-condensing power plants is avoided and biofuel is released at the same time.

  • 212.
    Yang, Bin
    et al.
    Department of Applied Physics and Electronics, Umeå University, Umeå, Sweden.
    Olofsson, Thomas
    Department of Applied Physics and Electronics, Umeå University, Umeå, Sweden.
    Nair, Gireesh
    Department of Applied Physics and Electronics, Umeå University, Umeå, Sweden.
    Kabanshi, Alan
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Outdoor thermal comfort under subarctic climate of north Sweden – A pilot study in Umeå2017In: Sustainable cities and society, ISSN 2210-6707, Vol. 28, p. 387-397Article in journal (Refereed)
    Abstract [en]

    Outdoor microclimate is important to determine the quality of outdoor spaces. Swedish people cherish summer period and prefer more outdoor activities in summer because of long winter with harsh outdoor environments. People in urban areas use parks for recreation and outdoor activities frequently in summer. Under subarctic climate, limited studies have been performed to explore the effect of microclimate environments on usage of outdoor spaces such as parks. The study explored the relationship of microclimate environments, park use and human behavioral patterns in urban area of Umeå, Sweden, which is under subarctic climate. Observations of naturally occurring behavior were recorded. Structured interviews, based on specially designed questionnaires, were performed during July to August in 2015. Measurements of objective parameters for microclimate environments, including air dry bulb temperature, relative humidity, wind speed, solar radiation and globe temperature, were performed. Human subjective responses from the questionnaire survey were compared with objectively measured results. 49% of local persons still prefer higher solar radiation even under “slightly warm” Thermal Sensation Vote (TSV), which reflects their high expectation to solar radiation. Local persons in Umeå, who expose themselves to a wider climate, are more adapted to subarctic climate than non-local persons.

  • 213.
    Yin, S.
    et al.
    Department of Mechanical Engineering, University of Hong Kong.
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Li, Y.
    Department of Mechanical Engineering, University of Hong Kong.
    Water tank investigation of single and multiple buoyant plumes from squared blocks in calm environment2014In: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate, 2014, p. 295-297Conference paper (Refereed)
  • 214.
    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
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Experimental investigation of near-field stream-wise flow development and spatial structure in triple buoyant plumes2019In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 149, p. 79-89Article in journal (Refereed)
    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.

  • 215.
    Yin, Shi
    et al.
    Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong.
    Li, Yuguo
    Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong.
    Fan, Yifan
    Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong.
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Unsteady large-scale flow patterns and dynamic vortex movement in near-field triple buoyant plumes2018In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 142, p. 288-300Article in journal (Refereed)
    Abstract [en]

    Unsteady flow patterns of interacting buoyant plumes are important for buoyant ventilation and particularly influence pollutant and heat transports in indoor and outdoor environments. This study reveals fundamental large-scale flow patterns in triple building plumes, investigates vortex moving trends during the pattern transition processes, and explores possible mechanisms of pattern diversity by two-dimensional (2-D) Particle Image Velocimetry (PIV). Total five tests are studied, including three different heat strengths Q (180, 90, and 30 W) and three source layouts characterized by the ratios of source spacing S to source width W (0.2, 0.5, and 1.0). Streamline distributions and axial velocity profiles clearly reveal three fundamental global flow patterns: a right-slanting asymmetrical flow pattern, a left-slanting asymmetrical flow pattern, and an axisymmetric flow pattern. Correspondingly, it indicates four basic transition processes, i.e., right-to-center, left-to-center, center-to-right, and center-to-left transitions (“center” represents the axisymmetric pattern). A novel vortex tracking method, based on lambda-2 (λ2) criterion and principles of the PIV technique, is developed and successfully applied to qualitatively track the vortex moving trends during the transition processes. The regular vortex moving trends are found to be reasonably consistent with the global pattern transition trends. The flow pattern diversity is speculated to be mainly driven by unstable heat source wall flows and downstream swaying motions in this study. These critical unstable motions are considered to probably relate to unstable lateral entrainment and vortex interaction, particularly beside the central plume. Consistently, the regular vortex moving trends are usually observed in and around the central plume.

  • 216.
    Yin, Shi
    et al.
    Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China.
    Li, Yuguo
    Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China.
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Lam, Kitming
    Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China.
    The effect of building spacing on near-field temporal evolution of triple building plumes2017In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 122, p. 35-49Article in journal (Refereed)
    Abstract [en]

    Building plume is important for ventilation and pollutants dispersion along and above buildings in an urban canopy layer. This study fundamentally explores the merging process and temporal penetration of triple uniformly distributed starting building plumes, with a focus of the spacing effect on near-field flow dynamics. Instantaneous velocity and vorticity distributions, penetrating velocities, and stream-wise penetrated heights are quantitatively examined using 2-D particle image velocimetry (PIV) measurements at spacing ratios S/W (building spacing/building width) of 0.2, 0.5, and 1.0. We identified a four-stage merging progress and captured three main spacing-induced merging features. A compact layout at S/W = 0.2 introduces a strong upward channel flow. The wall flows beside the channel tend to draw together first and the unstable channel flow determines the flow pattern transition. In contrast, wider layouts at S/W = 0.5 and 1.0 exhibit intensive downward flow. The wall flows tend to exhibit self-merging initially and the downstream natural swaying motion dominates the merged pattern variations. Merging effect and buoyancy force jointly determine the temporal penetrating velocities. Temporal series of maximum axial velocities above the middle source fits into a power law profile at S/W = 0.2 but a linear function of time at S/W = 0.5 and 1.0. The normalized penetrated heights at S/W = 1.0 are notably faster than in the other two cases before the normalized time is at 3.00 probably because the weaker entrainment and interaction with neighbors lead to less energy and momentum dissipation, quicker self-merging, and faster penetration.

  • 217.
    Yin, Shi
    et al.
    Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong Special Administrative Region.
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Lam, Kit-Ming
    Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong Special Administrative Region.
    Li, Yuguo
    Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong Special Administrative Region.
    Near-field merging and penetration of triple starting plumes from volumetric heat sources in a calm environment2017In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 115, no Part B, p. 1321-1333Article in journal (Refereed)
    Abstract [en]

    This paper investigates the buoyancy effect on near-field evolution of triple equal starting thermal plumes from volumetric heat sources, with a focus on merging process, velocity evolution, and stream-wise penetration. Instantaneous velocity fields and corresponding vorticity distribution, temporal evolution of centerline axial velocities, temporal penetrating rates and heights are examined by 2-D particle image velocimetry (PIV) at three different source heat strengths of 180 W, 90 W, and 30 W. A four-stage merging process is demonstrated to be independent of heat strength. Normalized starting and terminating times of each developing stage are also unified regardless of the heat strength, i.e., t/t∗ = 1.7–2.5 for stage i (relatively isolated development), t/t∗ = 2.5–3.3 for stage ii (bending wall flows), t/t∗ = 3.3–3.9 for stage iii (development after a self-merged state), and t/t∗ > 3.9 for stage iv (evolution with global merging). The axial velocity at a specific centerline point usually involves three distinct developing periods: a “centerline-silent” period ending at a normalized transportation time tt_n when heat is just transported to the measuring points, a fast rising period, and a fluctuating period starting at a normalized endurance time te_n. The buoyancy-independent tt_n is approximately 1.5, 2.2, 3.0, and 3.2 at a normalized downstream distance of 1.5, 2.5, 3.5, and 4.5, respectively. The time te_n, independent of buoyancy and axial height, is about 3.6 for all measuring points in this study. The maximum axial velocity above the middle heat source exhibits three linearly developing periods with different acceleration rates successively: a quicker rate as the wall flow develops, a slower rate due to enhanced lateral interaction, and the fastest rate as the global merging happens. In different periods, the proportional coefficients of linear fitted functions vary from 0.48 to 2.98. The downstream distance where axial velocity is maximum shows similar power-law increasing during t/t∗ = 1.5–3.2 at Q = 180 and 90 W, but exhibits significant fluctuations at Q = 30 W. Normalized overall penetration based on global velocity fields is notably faster and higher at the lowest buoyancy (Q = 30 W) than that at the higher buoyancy (Q = 180 and 90 W), probably due to the weaker lateral interaction and turbulent mixing together with the more dedicated vertical rise at Q = 30 W.

  • 218.
    Ying, Song
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Energy analysis for a snow-free surface: A technical analysis of the benefits of insulation under the heating pipes2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Snow-free surfaces is needed for parking place, platform, and playground and even in city center square. With energy prices rising, energy saving is becoming a hot topic. Meanwhile environmental problems are becoming more and more serious, thus, the ways to saving energy is becoming an eye-catcher. So burring heating pipes underground has been a popular way to get ice-free surfaces. Using heating pipes for melting snow is much more efficient and more benefit for the environment comparing with using other methods.

     

    In this project, an energy analysis of a football pitch with an area of 5000 m2 is carried out under a series of conditions between insulated and uninsulated construction. All calculations are done with the so-called finite element method (FEM), in the COMSOL. COMSOL is used for simulating and calculating the energy use with outdoor temperatures of -5 ºC and -10 ºC. Top layer materials concrete, grass and stone are also discussed. The ability of XPS and EPS insulation material is compared and noted. The models are divided into two parts, one is with snowfall and the other is without snowfall.

     

    The results in the report shows that adding insulation under the heating pipe has significant energy saving potential. The surface with concrete layer has the best insulated ability, which can prevent more heat losses. The EPS insulated construction has a better performance in keeping more heat in the soil. 

  • 219.
    Zabala Urrutia, Laura
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Measurements and simulations of the performance of the PV systems at the University of Gävle2017Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In the following years, the countries will have to face an increase in the energy demand. So far, the fossil fuels have been the main source to meet the energy demand, but they involve serious problems: they contribute to the climate change with high emissions of greenhouse gases, there is an uneven distribution of these resources and their reserves are finite. The renewable energies are the most reliable alternative, with a very low environmental impact in comparison. Among them, the photovoltaics seems to be the most promising emerging technology for the electricity generation. Its rapid growth in the last years has been due to the reduction achieved in the cost of the PV panels. When planning a PV installation, it is essential to be able to estimate the production. The power of a PV-module is given by the manufacturer at standard conditions (STC), which means that the irradiance is G=1000W/m2 at normal incidence and the temperature of the module is 25˚C. However, these conditions will never be reached in a real installation. Therefore, the measured power of the system has to be adjusted for the real conditions so that the real production and performance can be estimated. Today there exists no standard method for this procedure in Sweden. The main aim of this thesis is to develop a theoretical model for the four PV-systems installed at the laboratories (building 45) of the University of Gävle to estimate the performance and production, and prove its validity by comparing with real data measured with a short time resolution (second). This will also allow to know if the power generated by the modules is the promised one by the providers. Three of the studied systems have monocrystalline silicon modules, with different schemes: one system with bypass diodes, another with TIGO optimizers, and the third one with microinverters. The fourth system has thin film modules. The theoretical model considers correction factors for the cell temperature, the angle of incidence and the real irradiation reaching the modules’ surface; as all these aspects reduce the power obtained. When studying this model for clear sunny days, it can be observed that the theoretical model adjusts perfectly for the four systems in these conditions and almost a completely linear dependence is achieved between the measured and estimated power. The worse adjustment is obtained for the thin film system, for which the theoretical model gives lower values than the real ones. However, a better approximation can be obtained for this system by adjusting the value of the correction factor for the cell temperature. Moreover, the high values obtained for the maximum power during the clear days, very close to the peak power, indicates that the maximum power value provided by the manufacturers is in concordance with the real performance of the modules. In case of cloudy days, a small-time delay has been appreciated between the data recorded by both logger. The results have been studied with the raw data, obtained worse adjusting, and correcting this time discordance, getting again accurate results from the theoretical model.

  • 220.
    Zhang, Taoju
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Energy simulation for improved ventilation system in a collection of Swedish multi-family houses2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Building sector takes a large part of Swedish domestic energy use. Swedish government had set goal that required energy consumption should decrease by 20% in year 2020 compared to 1995. Public house companies will play an important role in the process.

     The work studies a typical Swedish Multi-family dwelling, built in 1960s and belonging to Älvkarlebyhus AB. These buildings were given enhanced air tightness in recent years which yielded a good result. This work focuses on improving the old ventilation system and decreasing energy consumption.

     Building energy simulation tool IDA ICE was used to model the object building and to examine the effectiveness of the new system. The tested energy efficiency measures include upgraded ventilation system with heat exchanger, and the installation of demand control (DCV) to the ventilation. Both energy, environmental and economic aspects are considered in the study.

    The result showed the total energy demand decreased 35% with renovation. Total investment for all buildings correspond to 5 760 000 SEK. New system could save 237 872 SEK/year and payback time will be 24 years.

  • 221.
    Åhman, Matilda
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Luftburen värme med ett centralaggregat i flerbostadshus2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The fact that the global warming is a major probelm in today´s society is no news and the climate change continues to take place at a very high rate. In order to create a sustainable society change requires where the potential is on energy efficiency and increased use of renewable energy. Energy efficiency can be changes in behavior, additional insulation of buildings or switching to more energy efficient installations. From a thermal comfort- and energyperspective today there are diffrent oppinions about airborne heat if it is a good heating system.

    This thesis is made for Ramböll, a consultant firm which focuse on technology and construction of society. The purpose of the study is to investigate whether a radiator system in an appartent buildning can be replaced by an airborne heating system with a central unit to get a more cost efficient system.

    This study is based on calculations for transmissions, airflow and directed operative temperature for the current building. Based on these data the ventilationsystem has been constructed and dimensioned. Also a proposal for the regulation of the indoor temperature for the system has been produced and also a economic comparison between the airborne heating system and the radiator heating system has been made.

    The resaults of the study shows that for the apartment building the airborne heating system is a cheaper alternative compared to the radiator system, based on prices of materials and work. The study shows that the thermal comfort with a airborne heating system is not affected in a bad way by the directed operative temparature in the occupied zone. Also larger ducts will be needed with airborne hating, which will require bigger and more space consuming shaft. The regulation of the indoor temperature is going to be with VAV-throttle in every appartmen, which means that the regulation can be done in each appartment but not in every single room. 

  • 222.
    Åsander, Henrik
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Tillvaratagande av värmeenergi ur gråvatten med värmepump i flerbostadshus2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Large amounts of energy leave homes with wastewater without any effort to return the heated water's thermal energy back to the building. With increased thermal envelope improvements of a traditional nature to meet the nearly zero-energy requirements for residential buildings that will come into effect by the end of 2020, energy losses in buildings can increasingly be allocated to the wastewater leaving the building.

    The aim of this work is to investigate whether significant energy savings in the mentioned area can be obtained, as well as to assess the economic opportunities and prospects for utilizing heat energy from grey water from multi-residential buildings connected to district heating networks with the help of a heat pump. And by that show which factors are shown to influence the operational savings and how sensitive the results are in relation to a selection of these factors. The work consists of and has been carried out in two parts: a literature study and a calculation study.

    Household wastewater can be divided into grey and black water. Grey water is the water that comes from bath, dishes and laundry and black water is the water that is flushed out of the toilets. Separated flows reveal the possibility of utilizing thermal energy directly from grey water, which is also the warmer, volume largest and more manageable fraction, both from a water purification and heat recovery standpoint. Studies on source separated systems show a wide range of benefits, largely by keeping household wastewater separated, such as increased resource efficiency of nitrogen and phosphorus at the wastewater treatment plants. The contamination of heat exchanger surfaces, especially biofilm, poses a challenge when wastewater is used as a heat source and is something that has to be taken into account even when using grey water as a heat source.

    The result of the calculations of an individual case with preheating of domestic hot water, given a series of assumptions, resulted in operational cost savings of approximately SEK 31,000 per year and a present value of these annual savings over 20 years of approximately SEK 355,000. Energy savings amounted to approximately 63,000 kWh per year, which means a reduction of the total need for purchased energy for domestic hot water production by 67 % with an assumption of a final domestic hot water temperature of 55 °C. The sensitivity analysis shows that crucial parameters in the calculation study such as electrical and district heating price, heat pump life and discount rate entail relatively large changes in profit if allowed to vary.

    It is obvious that there are large amounts of energy to potentially recycle. It is also obvious that difficulties cause grey water as a source of heat not be treated easily because, among other things, the long-term development of household water use and high pollution rates are factors that must be considered in addition to the factors brought up in the sensitivity analysis.

    District heating and heat pump combined imply a higher investment than a single heating system, but at the same time is something that can be seen as a tool for utilizing the assumed increasing energy price variations that an increasing proportion of intermittent renewable power generation implies simply by varying heating configuration with changes in energy prices and finding the optimal share. For a property owner, it would at this point be favorable to be able to choose what the cheapest option is currently.

  • 223.
    Åström, Frida
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Energieffektiviseringsanalys av ventilationssystemet för ett kraftvärmeverk: En fältstudie utförd i samarbete med Bomhus energi AB och ABB2017Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Detta arbeta kommer att utreda vilka det vanligaste energiförlusterna för ett kraftvärmeverk är, med fördjupning på förlusterna i deras ventilationssystem.  Kraftvärmeverket som har analyserats i detta arbete är Bomhus energi AB (BEAB) kraftvärmeverk och utredningen har skett i samråd med ABB Energy Efficiency team.    

    Världens energianvändning kan delas in i tre sektorer: industri, transport samt bostad- och servicesektorn. Industrisektorn kan sedan delas in i flera sektorer där massa och pappersindustrin står för majoriteten av energianvändningen i Sverige. Industrisektorn står för ca 64% utav världens el-energiförbrukning. Detta gör att det finns stort intresse i att se över de komponenter som har hög elförbrukning.     

    Fokuset har i detta arbete varit på ventilationssystemet och dess fläktrift. För att få information om vart det kan finnas komponenter som brukar mycket el så har styrsystemets loggar setts över. Besparingspotential har då identifierats i att installera frekvensomriktare till aggregatens fläktar istället för att använda den befintliga spjällregleringen. ABB har tidigare funnit besparingspotential i pumpdrifter för kraftvärmeverk och är därför nu intresserade av att se om det finns någon besparingspotential i ventilationssystemet.

    BEABs ventilation är uppdelad på process och allmänventilation, och genomlysning utav ventilationssystemet är i detta arbete begränsat till allmänventilationen i pannhuset. Detta då processventilationen anses vara korrekt dimensionerat.

    För att få insikt i hur energieffektivisering utav ventilationssystem kan gå tillväga har olika vetenskapliga artiklar rörande ämnet valts ut och analyserats. Som systemet är uppbyggt så sker regleringen utav ventilationen med spjällreglering. Spjällreglering innebär att fläktarna går på konstant flöde och för att uppnå önskad temperatur och tryck i byggnaden så sitter det tryckreglerande spjäll på taket som släpper ut luft ur byggnaden. Denna typ av styrning är inte särskilt energieffektiv, vilket har motiverat detta arbete till att rikta in sig på frekvensomriktare till aggregaten och hur mycket energi som då skulle kunna sparas.  För att få fram besparingspotentialen har hänsyn tagits till aggregatens: nominella volymflöde, fläktverkningsgrad, transmissionsverkningsgrad, flödesreglering, motoreffekt, motorns verkningsgradsklass, matningsspänning, fläkttyp, pumphjulstyp, varaktighetskurva, årgångstid, energipris samt multiplikatorn för Co2-utsläpp. Data har sedan matats in i ABB Energy Save kalkylatorn som då har tagit fram hur mycket energi och pengar som skulle kunna sparas genom att installera en frekvensomriktare.  Om de frekvensomriktare som då har tagits fram för de olika aggregaten skulle installeras så skulle uppskattningsvis ca 67 000 kr/år kunna sparas för kraftvärmeverket. 

2345 201 - 223 of 223
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