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• 51.
Instituto Superior Técnico, Universidade de Lisboa, Portugal .
Instituto Superior Técnico, Universidade de Lisboa, Portugal . University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Instituto Superior Técnico, Universidade de Lisboa, Portugal .
Stationary solar concentrating photovoltaic-thermal collector - Cell string layout2016In: Proceedings - 2016 IEEE International Power Electronics and Motion Control Conference, PEMC 2016, IEEE, 2016, p. 1275-1282, article id 7752179Conference paper (Refereed)

The aim of this work is to design the cell string layout in stationary concentrating photovoltaic (PV) or hybrid systems (PVT) in order to minimize the effects of both the longitudinal and transversal shading inherent to concentrating collectors. In this paper it is determined the best configuration of a PV string of cells, composed by several modules, by using a simple mathematical model based on the current vs. voltage of the PV cell. The model calculates the power vs. voltage curves of different possible configurations, in order to identify the optimal one according to efficiency and reliability. The company SOLARUS manufactures PVT collectors with cell strings of 38 solar cells connected in series. Solar cells in the concentrated side of the collector are shaded due to the presence of the aluminium frame of the PVT collector. The effects of shading and non-uniform illumination are minimized by including bypass diodes. Each string has 4 modules of bridged cells, each one associated to a bypass diode. In this work, different combinations of string cells in the collector receiver have been simulated using the free circuit simulation package from Linear Technology Corporation (LTSPICE). Test results are provided by SOLARUS to validate the proposed approach. A comparative analysis is presented at the end, showing that the simulation model is an important tool to define the module configurations that achieve the best energy efficiencies of the PVT panel.

• 52.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Zaragoza.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
The impact of shading in the performance of three different solar PV systems2017In: PROCEEDINGS OF THE 11TH ISES EUROSUN 2016 CONFERENCE, INTL SOLAR ENERGY SOC , 2017, p. 1168-1179Conference paper (Refereed)

Partial shading decreases the performance of PV modules due to the series connection between the solar cells. In the recent years, several new technologies have emerged within the photovoltaics field to mitigate the effect of shading in the performance of the PV modules. For an accurate assessment of the performance of these devices, it is required to evaluate them comparatively in different circumstances. Three systems with six series-connected PV modules (each containing 60 cells) have been installed at the University of Gavle. System One comprises a string inverter system with 6 PV modules; System Two features a DC-DC optimizer per panel and a string inverter; System Three incorporates three micro inverters for six modules. A major conclusion of this study was that under partial shading of one (or more) modules both System Two (DC-DC optimizers) and System Three (micro inverters) perform considerably better than System One (string inverter), as long as the Impp of the shadowed module is lower than the Impp of the unshaded string It is also important that the Vmpp in the shaded module is higher than the lowest allowed voltage of the DC-DC optimizer or module inverter. The economic implications of the usage of these devices were also analyzed.

• 53.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Energibalans av två glödgningsugnar inom ett integrerat stålverk2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

The steel industry occupies the whole 7 % of the global carbon dioxide emissions caused by human factors and 5 % of the global energy usage. The steel industry is an energy intense industry and it’s therefore important to analyze its energy use for its future sustainability. Furnaces are driven on non-renewable fuels and are one of the devoting components to the high energy consumption, so studies of this are of high relevance.  Regarding modern techniques of furnaces in today’s mode are much concentrated on the combustion, which means the combustion of the fuel that supplies the furnaces with heat.  Oxy-fuel technology means that the fuel is combusted with pure oxygen instead of air, and its purpose is to increase the combustion efficiency. A second modern technology is the usage of burners that are able to recycle flue gases as an increase of energy efficiency.  Outokumpu is a world leading company in the manufacture of stainless steel and the plant in Avesta is an integrated steel mill, which means the steel production cover the entire process from scrap and raw material to finished product. The plant consists of three main works called the steel mill, hot rolling mill and KBR L76 which is the department for these annealing furnaces.  The main objective of this report is to present an energy balance of two annealing furnaces at the Outokumpu plant in Avesta. The boundary of the study is clear, the energy balance will take part from the inlet of the first furnace to the outlet of the second one. It’s the thermal energy efficiency that has been studied, that is to say how much energy you get from the fuel that is added. Information has been collected using historical data on the operation of the furnaces during a three month period of time, also manual temperature measurements has been carried out.  By calculations an efficiency has been developed for each furnace and the furnaces together. This has been carried out by weighing the proportion of the amount of heat that all material have accumulated, with the amount of oil used during the same time.  The results of this study mainly indicate that the furnaces are effective in heating the steel, and its heat losses from the surrounding areas are small. On the other hand, there is potential for recycling more heat regarding the use of flue gases in the exhaust-boiler.

• 54.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Universidad de Valladolid (UVa), School of Forestry, Agronomic and Bioenergy Industry Engineering (EIFAB), Department of Agricultural and Forestry Engineering, Campus Duques de Soria, Soria, Spain.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Simulation, validation and analysis of shading effects on a PV system2018In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 170, p. 828-839Article in journal (Refereed)

A simulation program for calculating the IV-curve for series connected PV-modules during partial shadowing has been developed and experimentally validated. The software used for modelling the modules is LTspice IV. The validation has been done by means of a comparative analysis using the experimental results obtained in a set of tests performed on the mono-crystalline modules of the Gävle University's laboratory in Sweden. Experimental measurements were carried out in two groups. The first group is a string of six modules with bypass diodes while the second one corresponds to a single PV module. The simulation results of both groups demonstrated a remarkable agreement with the experimental data, which means that the designed model can be used for simulating the influence of shading on the power of a string. The model has been used for analysing the performance of strings of PV modules with shadows and the benefits of installing DC-DC optimizers or module inverters, that minimise the impact of shading, have been investigated.

• 55.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem.
Near-Field Study of Multiple Interacting Jets: Confluent Jets2015Doctoral thesis, comprehensive summary (Other academic)

This thesis deals with the near-field of confluent jets, which can be of interest in many engineering applications such as design of a ventilation supply device. The physical effect of interaction between multiple closely spaced jets is studied using experimental and numerical methods. The primary aim of this study is to explore a better understanding of flow and turbulence behavior of multiple interacting jets. The main goal is to gain an insight into the confluence of jets occurring in the near-field of multiple interacting jets.

The array of multiple interacting jets is studied when they are placed on a flat and a curved surface. To obtain the boundary conditions at the nozzle exits of the confluent jets on a curved surface, the results of numerical prediction of a cylindrical air supply device using two turbulence models (realizable $\kappa$$\epsilon$ and Reynolds stress model) are validated with hot-wire anemometry (HWA) near different nozzles discharge in the array. A single round jet is then studied to find the appropriate turbulence models for the prediction of the three-dimensional flow field and to gain an understanding of the effect of the boundary conditions predicted at the nozzle inlet. In comparison with HWA measurements, the turbulence models with low Reynolds correction ($\kappa$ − $\epsilon$ and shear stress transport [SST] $\kappa$ − $\omega$) give reasonable flow predictions for the single round jet with the prescribed inlet boundary conditions, while the transition models ($\kappa$$\kappa$$\iota$ − $\omega$ and transition SST $\kappa$$\omega$) are unable to predict the flow in the turbulent region. The results of numerical prediction (low Reynolds SST $\kappa$$\omega$model) using the prescribed inlet boundary conditions agree well with the HWA measurement in the nearfield of confluent jets on a curved surface, except in the merging region.

Instantaneous velocity measurements are performed by laser Doppler anemometry (LDA) and particle image velocimetry (PIV) in two different configurations, a single row of parallel coplanar jets and an inline array of jets on a flat surface. The results of LDA and PIV are compared, which exhibit good agreement except near the nozzle exits.

The streamwise velocity profile of the jets in the initial region shows a saddle back shape with attenuated turbulence in the core region and two off-centered narrow peaks. When confluent jets issue from an array of closely spaced nozzles, they may converge, merge, and combine after a certain distance downstream of the nozzle edge. The deflection plays a salient role for the multiple interacting jets (except in the single row configuration), where all the jets are converged towards the center of the array. The jet position, such as central, side and corner jets, significantly influences the development features of the jets, such as velocity decay and lateral displacement. The flow field of confluent jets exhibits asymmetrical distributions of Reynolds stresses around the axis of the jets and highly anisotropic turbulence. The velocity decays slower in the combined regio  of confluent jets than a single jet. Using the response surface methodology, the correlations between characteristic points (merging and combined points) and the statistically significant terms of the three design factors (inlet velocity, spacing between the nozzles and diameter of the nozzles) are determined for the single row of coplanar parallel jets. The computational parametric study of the single row configuration shows that spacing has the greatest impact on the near-field characteristics.

• 56.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University.
A study on proximal region of low reynolds confluent jets: Part 1: Evaluation of turbulence models in prediction of inlet boundary conditions2014In: ASHRAE Transactions, 2014, no PART 1, p. 256-270Conference paper (Refereed)

Conventional ventilation systems (mixing and displacement) produce low air quality in industrial premises. A new air supply system (confluent jets system) may improve the ventilation efficiency and the energy efficiency. When round jets issue from co-planar nozzles with enough spacing, they converge, merge, and combine at certain downstream distances, which are called confluent jets. In order to numerically predict confluent jets, it is crucial to provide inlet boundary conditions for these jets at the nozzles' exit. Numerical prediction of inlet boundary conditions of confluent jets was chosen due to two reasons: the difficulty of measurement at the nozzles' exit, and lack of information about the shape of the employed nozzles to make artificial inlet profiles. Numerical predictions by two turbulence models (Realizable k - ε and RSM) of the supply device producing the confluent jets was verified by hot-wire measurements at 0.26 d0 downstream of the nozzles' exit in both lateral and vertical direction. The verification was carried out for different nozzles in an array by measuring axial velocity and its turbulence intensity. The axial velocity profile at the nozzles exit has a saddle-back shape with two distinct off-centered overshoots. The convergence of the velocity profile shows the existence of Vena contracta phenomena. Low turbulence intensity at the central part of nozzles was found with narrow shear layer upstream of confluent jet flow. Differences of velocity components, turbulent kinetic energy (TKE), and turbulent dissipation rate (TDR) of the studied contraction nozzle were examined with a flow issuing from a typical long pipe. Reynolds number dependency in the studied range has been carried out and Re effects were observed on TKE but not on TDR.

• 57.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Division of Energy Systems, Department of Management and Engineering, Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Division of Energy Systems, Department of Management and Engineering, Linköping University.
A study on proximal region of low reynolds confluent jets: Part 2: Numerical prediction of the flow field2014In: ASHRAE Transactions, 2014, no PART 1, p. 271-285Conference paper (Refereed)

Conventional ventilation systems (mixing and displacement) produce low air quality in industrial premises. A new air supply system (confluent jet system) may improve both ventilation and energy efficiency. When round jets are issued from coplanar nozzles with enough spacing, they converge, merge, and combine at a certain downstream distance, which are called "confluent jets." In this study, the velocity field of the proximal region of confluent jets was recorded by traversing a hot-wire probe across the jets in one column at selected distances from the nozzles' exit in order to examine the performance of SST k - ω turbulence model. The experimental and numerical results from this work are summarized in a set of mapping fields of mean velocity for the confluent jet zones, which are presented in a generalized non-dimensional form. The existence of an initial, a converging, a merging, and a combined region in the confluent jets has been found for three low Reynolds numbers. Three different confluent jets can be seen in the array of jets studied placed six by six symmetrically on the long side of a cylindrical supply device. The streamwise velocity of the geometrical centerline of side jets and corner jets decays faster than that for the fully confluent jets, due to deflection towards their adjacent neighboring jets. Side jets and corner jets deflect to their adjacent jets and finally merge and combine with them, while fully confluent jets normally spread and amalgamate with each other. Low local pressure is responsible for the amalgamation of confluent jets, but the static pressure reaches a minimum value between side jets and their neighboring jets, which results in the deflection of the side jets.

• 58.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University.
Evaluation of RANS models in predicting low reynolds, free, turbulent round jet2014In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 136, no 1, article id 011201Article in journal (Refereed)

In order to study the flow behavior of multiple jets, numerical prediction of the three-dimensional domain of round jets from the nozzle edge up to the turbulent region is essential. The previous numerical studies on the round jet are limited to either two-dimensional investigation with Reynolds-averaged Navier-Stokes (RANS) models or three-dimensional prediction with higher turbulence models such as large eddy simulation (LES) or direct numerical simulation (DNS). The present study tries to evaluate different RANS turbulence models in the three-dimensional simulation of the whole domain of an isothermal, low Re (Re = 2125, 3461, and 4555), free, turbulent round jet. For this evaluation the simulation results from two two-equation (low Re k-ε and low Re shear stress transport (SST) k-ω), a transition three-equation (k-kl-ω), and a transition four-equation (SST) eddy-viscosity turbulence models are compared with hot-wire anemometry measurements. Due to the importance of providing correct inlet boundary conditions, the inlet velocity profile, the turbulent kinetic energy (k), and its specific dissipation rate (ω) at the nozzle exit have been employed from an earlier verified numerical simulation. Two-equation RANS models with low Reynolds correction can predict the whole domain (initial, transition, and fully developed regions) of the round jet with prescribed inlet boundary conditions. The transition models could only reach to a good agreement with the measured mean axial velocities and its rms in the initial region. It worth mentioning that the round jet anomaly is still present in the turbulent region of the round jet predicted by the low Re k-ε. By comparing the k and the ω predicted by different turbulence models, the blending functions in the cross-diffusion term is found one of the reasons behind the more consistent prediction by the low Re SST k-ω.

• 59.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Division of Energy Systems, Department of Management and Engineering, Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Division of Energy Systems, Department of Management and Engineering, Linköping University.
Investigation in the near-field of a row of interacting jets2015In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 137, no 12, article id 121202Article in journal (Refereed)

Multiple interacting jets (confluent jets) are employed in many engineering applications, and the significant design factors must be investigated. Computational fluid dynamics (CFD) is used to numerically predict the flow field in the proximal region of a single row of round jets. The numerical results that are obtained when using the low Reynolds k-∈ are validated with the experimental data that are acquired by particle image velocimetry (PIV). PIV was used to measure mean velocity and turbulence properties in the proximal region of a row of six parallel coplanar round air jets with equidistant spacing at low Reynolds number (Re = 3290). The low Reynolds k-∈ underpredicts the streamwise velocity in the onset of the jets' decay. The characteristic points are determined for various regions between two neighboring jets. The comparison of the merging point (MP) and the combined point (CP) computed from measurements and simulations shows good agreement in the different regions between the jets. In this study, a computational parametric study is also conducted to determine the main effects of three design factors and the interactions between them on the flow field development using response surface method (RSM). The influences of the inlet velocity, the spacing between the nozzles, and the diameter of the nozzles on the locations of the characteristic points are presented in the form of correlations (regression equations). CFD is used to numerically predict the characteristic points for a set of required studies, for which the design values of the simulation cases are determined by the Box-Behnken method. The results indicate that the spacing between the nozzles has a major impact on the flow characteristics in the near-field region of multiple interacting jets. The RSM shows that the inlet velocity has a marginal effect on the merging and CPs. All of the square terms are removed from the response equations of MP, and only one two-way interaction term between inlet velocity and spacing remains in the regression model with a marginal effect. The square of the nozzle diameter contributes in the regression equations of CP in some regions between the jets.

• 60.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Linköping University.
Near-field development of a row of round jets at low Reynolds numbers2014In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 55, no 8, p. 1789-Article in journal (Refereed)

This article reports on an experimental investigation of the near-field behavior of interacting jets at low Reynolds numbers (Re = 2125, 3290 and 4555). Two measurement techniques, particle image velocimetry (PIV) and laser Doppler anemometry (LDA), were employed to measure mean velocity and turbulence statistics in the near field of a row of six parallel coplanar round jets with equidistant spacing. The overall results from PIV and LDA measurements show good agreement, although LDA enabled more accurate measurements in the thin shear layers very close to the nozzle exit. The evolution of all six coplanar jets showed initial, merging, and combined regions. While the length of the potential core and the maximum velocity in the merging region are Reynolds number-dependent, the location of the merging points and the minimum velocity between jets were found to be independent of Reynolds number. Side jets at the edges of the coplanar row showed a constant decay rate of maximum velocity after their core region, which is comparable to a single round jet. Jets closer to the center of the row showed reducing velocity decay in the merging region, which led to a higher maximum velocity compared to a single round jet. A comparison with the flow for an in-line array of 6 x 6 round jets showed that the inward bending of streamwise velocity, which exists in the near field of the 6 x 6 jet array, does not occur in the single row of coplanar jets, although both setups have identical nozzle shape, spacing, and Reynolds number.

• 61.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Near-field mixing of jets issuing from an array of round nozzles2014In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 47, p. 84-100Article in journal (Refereed)

This article presents results of an experimental study of the confluence of low Reynolds number jets in the near field of a 6 x 6 in-line array of round nozzles. Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) were employed to measure mean velocities and turbulence statistics. The comparison of the results from PIV and LDA measurements along different cross-sectional profiles and geometrical centerlines showed good agreement. However, LDA enabled more accurate results very close to the nozzle exits. The evolution of all the individual jets in the array into a single jet showed flow regions similar to twin jets (i.e., initial, converging including mixing transition, merging and combined regions). The lateral displacements play an important role for a confluent jet, where all jets to some degree are deflected towards the center of the nozzle plate. The jet development in terms of velocity decay, length of potential core and lateral displacement varies significantly with the position of the jet in the array. A comparison with single jet and twin jets flow showed considerable differences in velocity decay as well as location and velocity in the combined point. The flow field of confluent jets showed asymmetrical distributions of Reynolds stresses around the axis of the jets and highly anisotropic turbulence. Additionally, the lateral displacement as well as the turbulence development in the proximal region of the studied confluent jet was shown to be dependent on Reynolds number.

• 62.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
A New Power Storage, Cooling Storage, and Water Production Combined Cycle (PCWCC)2016Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis

Fresh water shortage and hot weather are common challenges in many countries of the world. In the other hand, the air conditioning systems which are used for indoor cooling cause peak electricity demand during high temperatures hours. This peak hour demand is very important since it is more expensive and mainly is supplied by fossil fuel power plants with lower efficiencies compare to base load fossil fuel or renewable owe plants. Moreover, these peak electricity load fossil fuel power plants cause higher green house gas emission and other environmental effects. So, all these show that any solution for these problems could make life better in those countries and all over the world.In this thesis, a new idea for a Power storage, Cooling storage, and Water production Combined Cycle (PCWCC) is introduced and reviewed. PCWCC is combination of two thermal cycles, Ice Thermal Energy Storage (ITES) and desalination by freezing cycle, which are merged together to make a total solution for fresh water shortage, required cooling, and high peak power demand. ITES is a well known technology for shifting the electricity demand of cooling systems from peak hours to off-peak hours and desalination by freezing is a less known desalination system which is based on the fact that the ice crystals are pure and by freezing raw water and melting resulted ice crystals, pure water will be produced. These two systems have some common processes and equations and this thesis shows that by combining them the resulted PCWCC could be more efficient than each of them. In this thesis, the thermodynamic equations and efficiencies of each PCWCC sub-systems are analyzed and the resulted data are used in finding thermodynamics of PCWCC itself. Also, by using reMIND software, which uses Cplex to find the best combinations of input/output and related processes, the cost of produced fresh water and cooling from PCWCC is compared with total cost of fresh water and cooling produced by each sub-systems of PCWCC in three sample cities all over the world, Kerman, Dubai, and Texas. These cities are chosen since they have similar ambient temperature trend with different electricity and fresh water tariff's. The results show that, the PCWCC is economical where there is a significant electricity price difference between ice charging and ice melting hours, off-peak and peak hours, of the day or when the fresh water price is high compare to electricity price. The results also show that how the revenue from fresh water could cover the used electricity cost and make some income as well.

• 63. Giovinazzo, Carine
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Ray Tracing Modelling of an Asymmetric Concentrating PVT2014In: EuroSun 2014 Proceedings, 2014Conference paper (Refereed)

• 64.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Instituto Politécnico de Castelo Branco, Portugal. Instituto Politécnico de Castelo Branco, Portugal. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. olle@solarus.com.
Evaluation of the impact of stagnation temperatures in different prototypes of low concentration PVT solar panels2015In: ISES Solar World Congress 2015, Conference Proceedings, 2015, p. 993-1004Conference paper (Refereed)

• 65.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Instituto Superior Tecnico, Av. Rovisco Pais, Lisboa, Portugal . Energy and Building Design, Lund University, Lund, Sweden . University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Minimizing the impact of shading at oblique solar angles in a fully enclosed asymmetric concentrating PVT collector2014In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 57, p. 2176-2185Article in journal (Refereed)

PVT collectors produce both electricity and heat from the same area. PVT collectors with low concentration factor allow both stationary and tracking configurations. For stationary or single axis tracking, the daily variation in the solar incidence angle can cause significant shading in concentrating collectors. Shading has a larger impact on PV than on thermal collectors and thus the evaluations was more focused on the electrical part. Several prototype versions of a novel design for a concentrating asymmetric PVT collector have been tested and compared. One tested improvement was replacing the reflective end gables with transparent end gables. Another improvement was to use different cell sizes. These actions were expected to minimize the impact of the shading at oblique solar incidence angles. The second action was found to be more beneficial than the first. Measurements were also performed in the solar simulator to fully understand the impact of shading in cell strings with 1/6 the size of standard cells. The latest version of the PVT was found to have, at 25 °C and 1000w/m2, a collector efficiency of 13,7%, a cell area efficiency of 20,3% and an electrical power output of 237W. Lower side of the receiver was producing 58% of the total power.

• 66.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Solarus Sunpower Sweden AB.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Defining an annual energy output ratio between PV and solar thermal2014In: EuroSun 2014 Proceedings, 2014Conference paper (Refereed)

Photovoltaics (PV) and solar thermal (ST) collectors are often competing between themselves not only because the investment capacity is limited but also because the energy demand and roof space is limited and both types of panel provide energy which can be converted to a different type of energy under a certain efficiency. Therefore, it makes sense to develop a ratio that quantifies the difference in annual energy output between standard ST and PV for different locations. This ratio is useful, for example, to support the decision between installing ST or PV, when combined with other local specific information such as the value of heat and electricity for a specific location and application, the system complexity and efficiency, and others.A market survey was conducted for assessing the average performance specifications of the panels. Simulations were conducted and several ratios were plotted in the world map. Despite the large variations occurring due to local climate, the ratio increases at lower latitudes due to two factors: a) the efficiency of a PV panel is reduced with the increase of air temperature while, in solar thermal, the effect is the opposite; b) Under low intensity solar irradiance, the efficiency of a PV panel is maintained while a solar thermal collector can have its efficiency reduced to zero. For latitudes lower than 66º, the ratio flat plate at 50ºC to PV is ranging from 1,85 to 4,46 while in the ration between vacuum tube at 50ºC and PV from 3,05 to 4,76.

• 67.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Ecole Polytechnique Universitaire de Montpellier, France . Ecole Polytechnique Universitaire de Montpellier, France . Instituto Superior Técnico, Universidade de Lisboa, Portugal . Instituto Superior Técnico, Universidade de Lisboa, Portugal . University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Instituto Superior Técnico, Universidade de Lisboa, Portugal .
Analysis of different C-PVT reflector geometries2016In: Proceedings - 2016 IEEE International Power Electronics and Motion Control Conference, PEMC 2016, IEEE, 2016, p. 1248-1255, article id 7752175Conference paper (Refereed)

One of the main advantages of solar concentrating photovoltaic-thermal collectors (C-PVT) is that these systems are all-in-one module type. For this reason, they are associated to less area and material requirements. Nevertheless, these systems require a more complex analysis in order to improve their performances, since the two types of energy conversion are related to the different demands and their cross effects. In the overall analysis, the collector geometry and the used materials for all their components will be crucial to ensure the system reliability. This study presents preliminary work about re-designing the reflector of C-PVT collectors currently produced in the Swedish SME Solarus Sunpower AB with a comparative analysis on an annual basis of the solar radiation that reaches the collector. For the work accomplished, an open-source advanced object-oriented Monte Carlo ray tracing program (Tonatiuh) is used. For low latitudes, two reflector shapes have been selected since they ensure better performances than the current Solarus reflector. These two new designs achieve both the performance and cost-effectiveness objectives: for the same aperture area and for a thinner box, the collector is 7% to 10% more effective and 18% cheaper.

• 68.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Energy audit of a bakery in Sweden2017Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis

In order to reach the European aim for a sustainable growth, the “Triple 20 by 2020”, the energy audit in every sector is one of the keys of the success. In order to carry on with the energetical development, sustainability and future energy efficient systems, the energy efficiency in the industry is one of the most important matters. The Swedish industry uses 147 TWh of energy per year, which represents the 39% of the total final energy use and also the biggest energy user of the three sectors. The food processing industry only uses a 3% of the total Swedish industrial energy use, however this is 4410 GWh per year, what still has high possibilities to reduce the use of energy through different energy efficiency measures.The present study consists on an energy audit of a small-medium industrial bakery in Ockelbo, Sweden, by starting with the compilation of a few energy efficiency measures that are usually carried out on the energy audits. Then those measures have been tried to implement in the bakery in order to reduce the energy use and therefore the costs, which are the principal aims of the study, together with the approach to future energy efficiency ideas. However, the lack of electrical measure equipment has been a big limitation for the study. The method, that has been the guideline for the energy audit, is the Energy management procedure, which is a widely used method on different energy audits. The main measures that have been proposed are regarding the auxiliary processes like lighting and the compressed air system, additionaly, changes regarding the power contract and the installed power of they bakery are presented. Also different future possibilities for the heat recovery are analyzed and discussed like using the waste heat for preheating tap water for the dough processes. Additionally this study contains a wide explanation of the Swedish electrical bills that every company has to pay and probably many of them do not understand.If the presented energy efficiency measures are implemented the electrical energy use can be reduced with at least 23109 kWh per year. In terms of money, the cost savings are at least 57781 SEK per year with an investment of 106300 SEK.

• 69.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Bomhus Energi.
Identification and evaluation of internal leakages of a BFB Boiler integrated within a pulp and paper mill.2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Alternative fuels like biomass have become really popular in the last decades as a substitute to fossil fuels. One of the most used technologies in Sweden for the obtention of the energy from the biomass is its direct combustion in a boiler. Bomhus Energi is a company with the purpose of creating steam and district heating for Billerudkorsnäs pulp and paper mill in Gävle and district heating for the city by operating a biomass BFB boiler. Despite being a quite new boiler, there are many sources of errors, losses and unnecessary costs. Between huge number of different losses that can happen in this kind of industrial boilers, the concern about internal leakages is not usually popular among plant designers and operators. This often leads to forget about them or not giving the importance that they could have.This study consists on, firstly, an analysis of different boiler equipment that have potential possibilities of internal leakages by mass and energy balances and by the tracking of possible mass losses. The second point of this thesis is to evaluate the cost of internal leakages that could have happen before, in order to be aware of how important they are. Additionally, measures are proposed in order to avoid or reduce the duration of the internal leakages, where the most common problem is the ignorance of their existence. This study focuses partially on the valve condition and maintenance. It is highly important to carry out valve maintenance procedures at least once per year during the general stop of the plant. Checking and verifying valve perfect conditions, can avoid a waste of a huge quantity of money just by replacing some internal elements that are possibly damaged due to the extreme working conditions. This small damages in valve can lead to a non-proper water tightening, which will be increasing its leakage over time. In the present paper, possible internal leakages through the valves belonging to the feedwater, steam drum, preheater and pressure vessel in general have been the principal aim. The key of this study was to take into account that biggest part of the draining system and valves that are supposed to be closed end in the Bottom blowdown tank. By then a deep study was done regarding this tank. The results show that there is a clear relationship between mass that is getting loss from feedwater tank and pressure vessel and the necessary cooling flow in the bottom blowdown tank. This means that if the cooling flow increases at the same rate as a possible leakage in mass and energy balance, there is an internal leakage somewhere in the system. The author proposes add an alarm to the DCS system in order to alert the plant operations of possible internal leakages. On the other hand, this paper also recommends to carry out a general valve maintenance per year and check which of them could be leaking, a general stop is the perfect time for carrying it out.In conclusion, the study finds that internal leakages can be even automatically detected if the system is provided with the necessary tools for it. The study concludes that internal leakages are not impossible to detect and their cost is non-negligible: the latest two internal leakages in the boiler, happened in the last two years, were from the feedwater draining system and from the steam drum heating loop with a total cost of 200,000 SEK (4240 SEK/day during 47 days) and 263,000 SEK (2120 SEK/day during 124 days) respectively. Additionally, days after the study, the plant general stop was carried out, finding that 12 valves were leaking due to internal damage. The cost of repairing the broken or damaged elements were almost negligible compared with the expected savings estimated in 2 Million SEK per year.

• 70.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Comparing air quality in a training facility: What effects do air balancing have for carbon dioxide reduction?2017Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis

The link between a good indoor climate and environmental impacts e.g. global warming and different pollution in the air is something that are important today and will certainly become more important in the future with increased energy prices and new laws.

Too keep the indoor air quality within limits is it important to have a good and competitive ventilationsystem.

The ventilations function is mainly to supply fresh air and to remove polluted air from the room. It’s important that the ventilation system works as it should so that the indoor air quality is as good as possible. The lack of good ventilation can create several symptoms such as headaches, nausea, fatigue, poor concentration etc.

In Sweden are ventilation control mandatory for every newly produced building and this control are repetitive usually every 3-6 years for some types of buildings.

The foundation of this thesis is from a previous degree project performed by a master’s student in 2013 named Ander Barroeta with supervision of Magnus Mattsson and Taghi Karimipanah.

The thesis was to improve and design a ventilation system in two rooms at a training facility named Friskis & Svettis in Gävle so that the CO2 level did not exceed 1000 ppm.

In this thesis was the main goal to do similar measurements as the previous thesis and compare the results to see what difference air balancing has done to the ventilation system. Field measurements were performed at the training facility were the focus was on carbon dioxide but also on other parameters such as temperature, humidity and air velocity so that air exchange rate could be calculated. With these parameters can evaluations be made to see if air balancing of the ventilation system made any difference in indoor air quality.

During measurements in one of the training rooms where spinning is exercised was carbon dioxide levels up to 3300 ppm measured which is above the recommended indoor limit at 1000 ppm. If that room should be design to not exceed 1000 ppm must the air exchange rate increase from 6.3 h-1 to 35.1 h-1.

• 71.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Challenges for decision makers when feed in tariffs or net metering schemes change to incentives dependent of a high share of self-consumed electricity2017In: 2017 IEEE 44th Photovoltaic Specialist Conference (PVSC), IEEE conference proceedings, 2017, p. 2025-2030Conference paper (Refereed)

When there are differences in economic value of self-consumed and exported electricity, profitable PV installations are dependent on accurate predictions of self-consumed electricity. In this study, minute-based data of PV production and electricity use were logged in a single-family house in Sweden. It is shown that when self-consumed electricity is measured, a low time resolution and different electric meter configurations can result in 60% lower registered self-consumed electricity than predicted. When feed-in tariffs or net metering schemes change to incentives dependent on the fraction of self-consumed electricity, the market and electric meter infrastructure must be prepared to avoid market disturbances.

• 72.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Gävle Energi, Gävle, Sweden.
Effects of different time resolution when self-consumed and produced excess electricity is predicted in a single family house: case study in cold climate, Sweden2016Conference paper (Refereed)
• 73.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Energy efficiency measures in the built environment - some aspects to consider in Sweden2018Doctoral thesis, comprehensive summary (Other academic)

The traditional energy system as we know it today will change in the future. There is a worldwide concern about the global warming situation and there are different actions implemented to limit the consequences from, mainly, the use of fossil fuels.

In this thesis, multi-unit apartment buildings have been simulated according to how the global CO2 emissions change when different energy efficiency measures are implemented. The simulated buildings have also been used to investigate how the calculated energy efficiency of a building according to Swedish building regulations varies depending on which technology for heating is used in the building and if the building has a solar PV installation or solar thermal system. When the energy efficiency of a building is calculated accord-ing to Swedish building regulations, this thesis shows that heat pumps are a favored technology compared to district heating. Another result is that electric-ity use/production within the investigated district heating system is the most important factor to consider when minimizing global CO2 emissions.

This thesis also investigates how the configuration of electric meters owned by the distribution system operator affects the monitored amount of self-consumed and produced excess electricity. Finally, four local low-voltage distri-bution networks were simulated when a future charging scenario of electric vehicles was implemented.

If a single-family house installs a solar PV installation, this thesis reveals that the configuration of the electric meter is important for the monitored amount of self-consumed electricity. This thesis also shows that the investigated low-voltage distribution networks can handle future power demand from electric vehicles and a high share of solar PV installations, but rural low-volt-age distribution networks will need to be reinforced or rebuilt to manage the investigated future scenarios.

• 74.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Evaluation of energy conserving measures in buildings connected to a district heating system: case studies in Gävle, Sweden2016Licentiate thesis, comprehensive summary (Other academic)

When different energy conserving measures are implemented for reducing energy use in buildings and the buildings are connected to district heating systems, it is important that an overall system analysis is made which takes into account the effects of total change of energy use due to the energy conserving measures.

The method applied in this thesis uses hourly production data for the different production units in the district heating system in Gävle, Sweden. The merit order of the different production units is dependent on the electricity spot market price. To calculate the merit order, hourly data for the electricity price is used. The marginal production unit can then be determined for each hour of the investigated year.

This thesis analyzes five different energy conserving measures in a multi-dwelling building regarding how they affect the marginal production units in the district heating system. For CO2 emission evaluations, two different combinations of heat and electricity conserving measures are compared to installation of an exhaust air heat pump. This thesis also analyzes how the configuration of the electric meter affects the measured amount of self-consumed and produced excess electricity for a single-family house and for two multi-dwelling buildings of different sizes.

The results show that the use of electricity is the most important objective to consider. The increased use of electricity for operation of the heat pump contributes to an increase of global CO2 emissions and the electricity produced by the solar photovoltaic installation contributes to a decrease of global CO2 emissions.

The results also show that the configuration of the electric meter is important for the single-family house but negligible for the multi-dwelling buildings. The amount of produced excess electricity is high for all buildings, which means that the economic value of produced excess electricity is important for a profitable installation.

• 75.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Impacts of different electric vehicle charging strategies on low voltage distribution networks, a case study for SwedenManuscript (preprint) (Other academic)
• 76.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Gävle Energi AB, Gävle, Sweden.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Högskolan Dalarna.
How the electric meter configuration affect the monitored amount of self-consumed and produced excess electricity from PV systems: case study in Sweden2017In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 138, p. 60-68Article in journal (Refereed)

This study evaluates how the principal function of bi-directional electric meters affects the monitored amount of self-consumed and produced excess electricity for dwelling buildings connected to the grid by three phases. The electric meters momentarily record the sum of the phases or the phases individually and then summarize the recorded values to a suitable time period and is then collected by the grid owner. In Sweden, both electric meter configurations fulfill laws and regulations.

The meter configuration affects the monitored distribution of self-consumed and produced excess electricity significantly for the investigated single-family house but is negligible for the investigated multi-dwelling buildings. The monitored self-consumed electricity produced by the PV installation for the single-family house varies between 24% and 55% depending on the configuration and how the inverter is installed for the investigated year. The difference in economic value for the produced electricity varies between 79.3 to 142 Euros.

Due to the electric meter configuration, the profitability of PV systems will be different for identical single-family houses with identical conditions. This should be corrected for a well-functioning market. It is also important to decide how the configuration should be designed to ensure that different incentives and enablers results in desired effects.

• 77.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Gävle Energi AB, Gävle, Sweden .
Energy Technology, Högskolan Dalarna, Falun, Sweden. Linköpings universitet. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
CO2 emission evaluation of energy conserving measures in buildings connected to a district heating system: case study of a multi-dwelling building in Sweden2016In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 111, p. 341-350Article in journal (Refereed)

When taking action to fulfill the directives from the European Union, energy conserving measures will be implemented in the building sector. If buildings are connected to district heating systems, a reduced heat demand will influence the electricity production if the reduced heat demand is covered by combined heat and power plants.

This study analyze five different energy conserving measures in a multi-dwelling building regarding how they affect the marginal production units in the district heating system in Gävle, Sweden. For CO2 emission evaluations, two different combinations of heat and electricity conserving measures are compared to an installation of an exhaust air heat pump.

The different energy conserving measures affect the district heating system in different ways. The results show that installing an exhaust air heat pump affects the use/production of electricity in the district heating system most and electricity conserving measures result in reduced use of electricity in the building, reduced use of electricity for production of heat in the district heating system and an increase of electricity production.

The conclusion is that electricity use in the building is the most important factor to consider when energy conserving measures are introduced in buildings within the district heating system in Gävle.

• 78.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Division of Energy Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden.
Rev-Changes in Primary Energy Use and CO2 Emissions: An Impact Assessment for a Building with Focus on the Swedish Proposal for Nearly Zero Energy Buildings2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 7, article id 978Article in journal (Refereed)

In the European Union's Energy Performance of Buildings Directive, the energy efficiency goal for buildings is set in terms of primary energy use. In the proposal from the National Board of Housing, Building, and Planning, for nearly zero energy buildings in Sweden, the use of primary energy is expressed as a primary energy number calculated with given primary energy factors. In this article, a multi-dwelling building is simulated and the difference in the primary energy number is investigated when the building uses heat from district heating systems or from heat pumps, alone or combined with solar thermal or solar photovoltaic systems. It is also investigated how the global CO2 emissions are influenced by the different energy system combinations and with different fuels used. It is concluded that the calculated primary energy number is lower for heat pump systems, but the global CO2 emissions are lowest when district heating uses mostly biofuels and is combined with solar PV systems. The difference is up to 140 tonnes/year. If the aim with the Swedish building code is to decrease the global CO2 emissions then the ratio between the primary energy factors for electricity and heat should be larger than three and considerably higher than today.

• 79.
School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran.
School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Multi-Objective Optimization of Impinging Jet Ventilation Systems: Taguchi Based CFD Method2018In: Building Simulation, ISSN 1996-3599, E-ISSN 1996-8744, Vol. 11, no 6, p. 1207-1214Article in journal (Refereed)

This paper presents a Taguchi method-based approach that can optimize the operating performance of impinging jet ventilation (IJV) systems with limited computational fluid dynamics (CFD) simulation results. The Taguchi optimization calculation finds the best operating design for the weighted overall objective function as a presenter of the multi-objective function problem. The method is used to optimize the operating characteristics of an IJV system considering the factors of supply air temperature, level of the return air vent and percentage of the air exhausted through the ceiling to achieve an overall best performance of thermal comfort, indoor air quality (IAQ) and system energy performance as the objective functions. The study indicates the contribution percentage for each factor in each objective function. The level of the return air vent, the supply air temperature, and the percentage of air exhausted through the ceiling have a contribution of 35.8%, 28.5%, and 35.8% in the objective functions, respectively. Based on the results, the best performance of the IJV system happens when the inlet air temperature is 18 °C, the height of the return air vent is 2 m above the floor, and the percentage of air exhausted through the ceiling is 22.5%.

• 80.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Förundersökning av möjligheten till modifiering av kylvattenintag: Undersökning av möjligheten till modifierat kylvattenintag vid Forsmarks kärnkraftsanläggning2016Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis

Elproduktion är en viktig del i dagens samhälle och hur man producerar elen har blivit en viktig fråga som diskuteras flitigt i Sverige och i omvärlden. I Sverige har elanvändningen och elproduktionen varit i närmaste oförändrad sedan 90-talet. Elanvändningen i Sverige är ca 140 TWh per år och drygt 40 % av detta produceras av kärnkraften. Detta medför att kärnkraften är en viktig del av den Svenska elproduktionen. Kärnkrafts-bolagen som äger kärnkraftverken i Sverige letar alltid efter sätt för att förbättra säkerheten på sina anläggningar samt att genomföra verkningsgradsförbättringar som minskar bränsleanvändningen. Det här arbetet inriktar sig på att öka produktionsförmågan genom att genomföra en verkningsgradsförbättring. Rapporten använder sig av en kvantitativmetod och behandlar vilka förutsättningar samt lösningar det finns till att sänka kylvattentemperaturen vid kärnkraftsanläggningen i Forsmark. Arbetet begränsar sig till att endast ge en överblick för vilka lösningar som finns. Ingen av lösningarna undersökas på djupet med undantag på mammutpumpar. Forsmark kärnkraftsanläggning består utav tre stycken reaktorer och använder tillsammans ca 145 m3/s kylvatten för att kyla ner ångan i turbinkondensatorerna. Att sänka temperaturen på kylvattnet med en grad innebär en verkningsgradsförbättring på 0,444 % vilket är utrett i rapporten. En sådan förbättring innebär att Forsmarks reaktor 3 ökar sin nettoeffekt med 5,25 MW. Att sänka kylvattentemperaturen kan göras på många sätt och i denna rapport ansågs det vara relevant att undersöka lösningar som lyfter upp bottenvatten eller blandar om vattnet ifrån olika nivåer i havet. De lösningarna som undersöktes var mammutpumpar, luftridå en vägg längst ytan, utgrävning av kylvattenkanal, förlängning av existerande kanal, djupvattenintag och strömbildare på botten. Den lösning som ansågs vara den mest attraktiva lösningen var luftridå och det var på grund utav att dess fördelar var många och dess nackdelar inte var alltför stora. De slutsatser som görs i denna rapport kan användas i andra reaktorer runtom i världen som har liknande förutsättningar.

• 81.
Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China.
Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China . Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China . University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China . Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Salento, Lecce, Italy. Department of Physics and Astronomy, University of Bologna, Bologna, Italy .
City breathability in medium density urban-like geometries evaluated through the pollutant transport rate and the net escape velocity2015In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 94, no P1, p. 166-182, article id 4213Article in journal (Refereed)

This paper investigates pollutant removal at pedestrian level in urban canopy layer (UCL) models of medium packing density (λ<inf>p</inf> = λ<inf>f</inf> = 0.25) using computational fluid dynamics (CFD) simulations. Urban size, building height variations, wind direction and uniform wall heating are investigated. The standard and RNG k-ε turbulence models, validated against wind tunnel data, are used. The contribution of mean flows and turbulent diffusion in removing pollutants at pedestrian level is quantified by three indicators: the net escape velocity (NEV), the pollutant transport rate (PTR) across UCL boundaries and their contribution ratios (CR).Results show that under parallel approaching wind, after a wind-adjustment region, a fully-developed region develops. Longer urban models attain smaller NEV due to pollutant accumulation. Specifically, for street-scale models (~100 m), most pollutants are removed out across leeward street openings and the dilution by horizontal mean flows contributes mostly to NEV. For neighbourhood-scale models (~1 km), both horizontal mean flows and turbulent diffusion contribute more to NEV than vertical mean flows which instead produce significant pollutant re-entry across street roofs. In contrast to uniform height, building height variations increase the contribution of vertical mean flows, but only slightly influence NEV. Finally, flow conditions with parallel wind and uniform wall heating attain larger NEV than oblique wind and isothermal condition.The paper proves that by analysing the values of the three indicators it is possible to form maps of urban breathability according to prevailing wind conditions and known urban morphology that can be of easy use for planning purposes.

• 82.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Measurements and modeling of airing through porches of a historical church2018In: Science and Technology for the Built Environment, ISSN 2374-4731, E-ISSN 2374-474X, Vol. 24, no 3, p. 270-280Article in journal (Refereed)

In churches, intentional airing may be a measure to evacuate temporarily high levels of contaminants, emitted during services. Crucial contaminants include moisture and other emissions that may deteriorate and/or soil painted surfaces and other precious artefacts. Most old churches do not have any mechanical ventilation system or any purpose provided openings for natural ventilation, but the ventilation is governed by air infiltration. Enhanced airing may be achieved by opening external windows or doors. Thus, models provided in energy simulation programs should predict this kind of airflows correctly, to get a proper estimation of the total energy use. IDA Indoor Climate and Energy (IDA-ICE) simulation program is examined here and its model for airflow through large vertical openings is investigated. Moreover, field measurements were performed for airing rate in a historical church including. The simulated single-sided flows were of the same magnitude of the measured ones, but the effect of wind direction was less considered by the simulation program. At cross flow, when wind is approaching the opening it has a choice; flow through the opening or around and above the building. This process is not considered in the IDA-ICE model, which can contribute to the discrepancy between measurements and predictions.

• 83. Buy this publication >>
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Natural Ventilation and Air Infiltration in Large Single‑Zone Buildings: Measurements and Modelling with Reference to Historical Churches2017Doctoral thesis, comprehensive summary (Other academic)

Natural ventilation is the dominating ventilation process in ancient buildings like churches, and also in most domestic buildings in Sweden and in the rest of the world. These buildings are naturally ventilated via air infiltration and airing. Air infiltration is the airflow through adventitious leakages in the building envelope, while airing is the intentional air exchange through large openings like windows and doors. Airing can in turn be performed either as single-sided (one opening) or as cross flow ventilation (two or more openings located on different walls). The total air exchange affects heating energy and indoor air quality. In churches, deposition of airborne particles causes gradual soiling of indoor surfaces, including paintings and other pieces of art. Significant amounts of particles are emitted from visitors and from candles, incense, etc. Temporary airing is likely to reduce this problem, and it can also be used to adjust the indoor temperature. The present study investigates mechanisms and prediction models regarding air infiltration and open-door airing by means of field measurements, experiments in wind tunnel and computer modelling.

In natural ventilation, both air infiltration and airing share the same driving forces, i.e. wind and buoyancy (indoor-outdoor temperature differences). Both forces turn out to be difficult to predict, especially wind induced flows and the combination of buoyancy and wind. In the first part of the present study, two of the most established models for predicting air infiltration rate in buildings were evaluated against measurements in three historical stone churches in Sweden. A correction factor of 0.8 is introduced to adjust one of the studied models (which yielded better predictions) for fitting the large single zones like churches. Based on field investigation and IR-thermography inspections, a detailed numerical model was developed for prediction of air infiltration, where input data included assessed level of the neutral pressure level (NPL). The model functionality was validated against measurements in one of the case studies, indicating reasonable prediction capability. It is suggested that this model is further developed by including a more systematic calibration system for more building types and with different weather conditions.

Regarding airing, both single-sided and cross flow rates through the porches of various church buildings were measured with tracer gas method, as well as through direct measurements of the air velocity in a porch opening. Measurement results were compared with predictions attained from four previously developed models for single‑sided ventilation. Models that include terms for wind turbulence were found to yield somewhat better predictions. According to the performed measurements, the magnitude of one hour single-sided open-door airing in a church typically yields around 50% air exchange, indicating that this is a workable ventilation method, also for such large building volumes. A practical kind of diagram to facilitate estimation of suitable airing period is presented.

The ability of the IDA Indoor Climate and Energy (IDA-ICE) computer program to predict airing rates was examined by comparing with field measurements in a church. The programs’ predictions of single-sided airflows through an open door of the church were of the same magnitude as the measured ones; however, the effect of wind direction was not well captured by the program, indicating a development potential.

Finally, wind driven air flows through porch type openings of a church model were studied in a wind tunnel, where the airing rates were measured by tracer gas. At single-sided airing, a higher flow rate was observed at higher wind turbulence and when the opening was on the windward side of the building, in agreement with field measurements. Further, the airing rate was on the order of 15 times higher at cross flow than at single-sided airing. Realization of cross flow thus seems highly recommendable for enhanced airing. Calibration constants for a simple equation for wind driven flow through porches are presented. The measurements also indicate that advection through turbulence is a more important airing mechanism than pumping.

The present work adds knowledge particularly to the issues of air infiltration and airing through doors, in large single zones. The results can be applicable also to other kinds of large single-zone buildings, like industry halls, atriums and sports halls.

• 84.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Development of a Numerical Air Infiltration Model Based On Pressurization Test Applied On a Church2016In: ASHRAE and AIVC IAQ 2016 — Defining Indoor Air Quality: Policy, Standards and Best Practices, 2016, ASHRAE, 2016, p. 224-231, article id C030Conference paper (Refereed)

Pressurization (blower door) test is a well-established standardized method, performed in order to quantify the total leakage in a building envelope. However, blower door results are not adequate to use when air leakage through the building envelope during natural conditions (non-pressurized) is to be estimated. A common assumption made when estimating air leakage during natural conditions, is that air leakage paths are evenly distributed in the areas of the building envelope. This assumption gives quite poor calculation results since different leakage configurations are often situated unevenly in the envelope. In order to improve the correspondence between Blower door and air leakage model results, more information on the types and locations of the leakage paths are required as input to simulation models.

This paper investigates if additional information from visual inspection and IR-thermography observations at site can increase the precision when simulating air change rates due to air leakage in natural conditions.  A numerical model is developed in this study by allocating leakage in various parts of the building envelope. The leakage allocation is based on visual inspection and IR-thermography observations at the site during the blower door test.

This procedure is tested in the case study of a large single zone church. Blower door, neutral pressure level measurement and leakage allocation results are used as input in the numerical model. Model results are compared with tracer gas measurements and result accuracy is compared with results from the Lawrence Berkeley Laboratory model (LBL) and the Alberta Air Infiltration Model (AIM-2) for the same church.

• 85.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Simulation of Ventilation Rates and Heat Losses during Airing in Large Single Zone Buildings in Cold Climates2019In: Cold Climate HVAC 2018: Sustainable Buildings in Cold Climates / [ed] Johansson, D., Bagge, H., Wahlström, Å., Springer, 2019Conference paper (Refereed)

Airing can be a solution to introduce extra ventilation in large single zone buildings, especially where there are large aggregations of people such as churches or atriums. In naturally ventilated domestic and ancient buildings, opening of a window or door can introduce extra fresh air and remove particles and other contaminants emitted from people and other sources such as lit candles in churches. However, the energy use might be an issue in cold climates, where airing might lead to waste of heated air, at the same time as indoor air temperatures can be uncomfortably low. In the present study, the energy loss and ventilation rate due to airing in a large single zone (church) building is investigated via IDA-ICE simulation on annual basis in cold weather conditions. The results can be used in order to prepare airing guidelines for large single zone buildings such as atriums, churches, industry halls and large sport halls. According to the results, one-hour of airing in the studied church building resulted in 40-50 % of exchanged room air and, if practiced once a week, an increase of around 1 % in heating energy.

• 86.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
A Study on Airing Through the Porches of a Historical Church – Measurements and IDA-ICE Modelling2016In: ASHRAE and AIVC IAQ 2016 - Defining Indoor Air Quality: Policy, Standards and Best Practices, 2016, ASHRAE, 2016, p. 216-223, article id C029Conference paper (Refereed)

In churches, intentional airing may be a measure to evacuate temporarily high levels of contaminants that are emitted during services and other occasions. Crucial contaminants include moisture and other emissions that may deteriorate and/or soil painted surfaces and other precious artefacts. Most old churches do not have any mechanical ventilation system or any purpose provided openings for natural ventilation, but the ventilation is governed by air infiltration. Enhanced airing may be achieved by opening external windows or doors. Thus, models provided in energy simulation programs should predict this kind of air flows correctly, also in order to get a proper estimation of the total energy use. IDA-ICE is examined here and the model for air flow through a large vertical opening used in the program is investigated. In the present study, field measurements were performed for airing rate in a historical church. In comparison with measured air flow rates, the simulated results were of the same magnitude, but the effect of wind direction was less considered by the simulation program.

• 87.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Evaluation of the LBL and AIM-2 air infiltration models on large single zones: three historical churches2014In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 81, p. 365-379Article in journal (Refereed)

Air infiltration in ancient churches and other historical and monumental buildings is of great importance considering moisture transfer, energy consumption, thermal comfort and air pollutants that induce surface soiling. Two of the most established models for predicting air infiltration rate in buildings are the Lawrence Berkeley Laboratory (LBL) model and the Alberta air Infiltration Model (AIM-2). Being originally developed mainly for dwellings, their applicability to large single zone buildings is evaluated in this study by comparing model predictions with field measurements in three historical stone churches that are naturally ventilated only through infiltration. The somewhat more developed AIM-2 model yielded slightly better predictions than the LBL model. However, an LBL version that allows inclusion of the Neutral Pressure Level (NPL) of the building envelope produced even better predictions and also proved less sensitive to assumptions on air leakage distribution at the building envelopes. All models yielded however significant overpredictions of the air infiltration rate. Since NPL may be difficult to attain in practice, the AIM-2 model was chosen for model modification to improve predictions. Tuning of this model by varying its original coefficients yielded however unrealistic model behaviors and the eventually suggested modification implied introducing a correction factor of 0.8. This reduced the median absolute prediction error from 25% to 11%. Thus, especially when the NPL is not at hand, this modification of the AIM-2 model may suit better for air infiltration assessment of churches and other buildings similar to the tested kind.

• 88.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Single-sided ventilation through external doors: measurements and model evaluation in five historical churches2017In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 141, p. 114-124Article in journal (Refereed)

Ventilation through open doors is a simple way to temporarily enhance ventilation of indoor spaces, with the purpose to evacuate indoor air pollutants or to adjust the indoor temperature. In churches and other historical buildings, which otherwise are ventilated only through air infiltration, temporarily enhanced ventilation through open doors or windows may be a prudent deed after e.g. services involving large congregations and burning of candles or incense. In the present study, the air exchange occurring at single-sided ventilation through the external doors of five historical churches is measured by tracer gas decay method. Further, air velocity measurements and smoke visualization in a doorway are performed. Measurement results are compared with predictions attained from four previously developed models for single‐sided ventilation. Models that include terms for wind turbulence yielded somewhat better predictions. According to the performed measurements, the magnitude of one hour single-sided open-door airing in a church is typically around 50% air exchange, indicating that this is a workable ventilation method, also for such large building volumes. A practical diagram to facilitate estimation of a suitable airing period is also presented. The study adds particularly knowledge to the issue of airing through doors, in large single zones.

• 89.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Utredning av undercentral i Brf. Bogården: En jämförelse mellan en ny och en gammal undercentral2017Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis

This paper takes its starting point from an old report named ”Samkörning mellan värmepumpar och fjärrvärme. – Bostadsrättsföreningen Bogården” from the year 2008. This report discusses a sub-station where there was a risk of proliferation of legionella bacteria. The 2008 report resulted in action proposals that were taken into account by tenant Bogården and thereafter efforts were implemented by SWECO in the form of a new projection of the entire sub-stationed facility. What happened next was that the sub- center was rebuilt completely in 2012 and a new management control settings were put into use.

In this work, a broad picture of the energy situation in the world and in Sweden is presented, and after that the paper shifts focus on Gävle and the sub-center of tenant Bogården. In this study, many observation visits were made and during these notes were made to see how the plant and its control and regulatory flows occurred. The side effect of the visits consisted of discoveries that in one way or another affected the plant. What was discovered was that the sub-central did not control and regulate according to the design, the return and outflow temperatures in the radiator circuit were way too high and the heat pump operating hours were not at all according to the functional description that was provided to aid this report. These controls and regulate errors forces the tenant Bogården to buy more district heating than needed, which leads to more costs than necessary.

• 90.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Utvärdering av avfrostning med ackumulatortank för motströmsvärmeväxlare: En teoretisk forskningsstudie med fokus på effektiviserad avfrostning för motströmsvärmeväxlare i ventilationsaggregat2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

The energy consumption in the world continues to increase, which makes energy saving measures important. In Sweden, where buildings account for a large part of total energy use, heat exchangers in ventilation are important to reduce energy consumption. However, Sweden's winters are often cold over large parts of the country, causing frost in the heat exchanger and high and uneven heating power requirements for ventilation units.

The heating system in the building is required to manage the biggest power demand that may arise. From the ventilation unit, the greatest heating power requirement is arise in the event of frost conditions, as the power requirement from the heating coil increases during defrosting. By installing an accumulator tank together with the ventilation unit, the power requirement can be evened out.

Power requirement for three different scenarios where the storage tank is used has been calculated. By using thermodynamic equations and measurements from Swegon counter flow heat exchanger results were accomplished. Optimal defrosting cycle times were evaluated by theory and equations. Other defrosting methods have been calculated to be compared to the solution with the accumulator tank.

In a case with 600 litres per seconds supply and exhaust air flow, outdoor temperature at -10 ° C, the power requirement to the unit could be reduced by 67 % using an accumulator tank. An accumulator tank with a volume of 73 litres was required.

By using an accumulator tank with the ventilation unit, investment costs could decrease by approximately 18 000 SEK when district heating is used as energy source. However, the solution with the storage tank will not be able to reduce district heating costs more than reduced flow cost for the district heating. If a heat pump I used approximately 95 000 SEK in investment cost could be saved when using an accumulator tank. Electricity cost could also be reduced but not much.

Compared to other defrosting methods, the solution with accumulator tank will require the lowest power requirement for the ventilation unit, heat recover  most energy in the heat exchanger and at the same time create an even heat power requirement at frost conditions.

• 91.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Environmental psychology.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Environmental psychology. School of Psychology, University of Central Lancashire, Preston, United Kingdom. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Environmental psychology.
When A+B < A: Cognitive bias in experts' judgment of environmental impact2018In: Frontiers in Psychology, ISSN 1664-1078, E-ISSN 1664-1078, Vol. 9, article id 823Article in journal (Refereed)

When ‘environmentally friendly’ items are added to a set of conventional items, people report that the total set will have a lower environmental impact even though the actual impact increases. One hypothesis is that this “negative footprint illusion” arises because people, who are susceptible to the illusion, lack necessary knowledge of the item’s actual environmental impact, perhaps coupled with a lack of mathematical skills. The study reported here addressed this hypothesis by recruiting participants (‘experts’) from a master’s program in energy systems, who thus have bachelor degrees in energy-related fields including academic training in mathematics. They were asked to estimate the number of trees needed to compensate for the environmental burden of two sets of buildings: One set of 150 buildings with conventional energy ratings and one set including the same 150 buildings but also 50 ‘green’ (energy-efficient) buildings. The experts reported that less trees were needed to compensate for the set with 150 conventional and 50 ‘green’ buildings compared to the set with only the 150 conventional buildings. This negative footprint illusion was as large in magnitude for the experts as it was for a group of novices without academic training in energy-related fields. We conclude that people are not immune to the negative footprint illusion even when they have the knowledge necessary to make accurate judgments.

• 92.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Environmental psychology.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Environmental psychology. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Occupant perception of “green” buildings: Distinguishing physical and psychological factors2017In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 114, p. 140-147Article in journal (Refereed)

Studies have found a preference bias for “environmentally friendly” or “green” artifacts and buildings. For example, indoor environments are more favorably viewed when the building is labeled/certified “green”, in comparison with one that is not labeled/certified, even though the two environments are actually identical. The present study explored how physical properties of the indoor environment (high vs. low temperature) and labeling (“green” vs. “conventional”) interacts in their effect on environment perception. Participants performed a series of tasks in four indoor environments with different labels (low vs. high carbon footprint) and different temperatures (23°C vs. 28°C). Label and temperature were manipulated orthogonally. The participants’ environmental concern was also measured. The environmentally concerned participant assigned higher thermal acceptance and satisfaction scores to the environment labeled “low carbon footprint” (i.e., “green” certified) compared to the environment labeled “high carbon footprint” (i.e., not “green” certified), but only in the cooler thermal environment. Environmentally indifferent participants’ perception of the environment did not differ depending on label or room temperature. The results suggest that a “green” label positively influence the perception of the indoor environment for occupants, but only when the temperature is within the acceptable range as proposed in guidelines for “green” buildings.

• 93.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Hur kan värmeenergianvändningen i en fastighet med ett högt energiuttag och komplicerat energisystem sänkas och hur påverkar det uppvärmningskostnaden: En fallstudie gjord på Gävle Energi ABs huvudkontor 2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

Gävle Energi AB has put forward proposals for a new pricing model that is seasonal dependent and provides a better reflection of consumers' real energy outages. The new pricing model is divided into an power price and an energy price. The power price is based on the energy consumption of the property at an outdoor temperature of -10°C. The energy price varies over the year and is intended to reflect the cost of producing the heat energy, which is intended to be cost neutral for the producer. If the customer has a well-functioning heating system with low power output, the cost will be lower and vice versa. Customers who are at risk of getting an increased cost are those with more advanced energy systems.

In the case study, Gävle Energi AB's head office is being investigated. The head office is a property that has a complicated energy system and high energy output, which makes it possible to get an increased fee. In order to investigate how it can be avoided, an energy survey has mainly been carried out on the heating system in the property. The goal was to find ways to reduce both the energy demand and the capacity requirement.

In the property's energy system there are four ventilation units, underfloor heating, windows, air heaters, two cooling machines and free cooling. All added heat in the property comes from district heating. For the measurement data that are not available, reasonable assumptions are made, and then supporting the theories are supplemented by calculations.

The most uncomplicated way to reduce costs has been shown by lowering indoor temperatures. After lowering the indoor temperature by 1°C and a temperature reduction in the garage, a new capacity requirement of 4 720 kWh/day will be obtained. Compared to the original capacity requirement of 5 011 kWh/day. The total energy saving for these measures amounts to around 51 MWh. There are also some unexpected measures where excess heat from the refrigeration compressor can be reused. Changed airflows in the ventilation can also cause major cost reductions on both energy and power prices.

• 94.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Study of the ventilation system in a warehouse and a cooking school: Impact of the use of a heat exchanger system and a more optimised operating schedule2018Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis

The motivation of this project is found on the past trend of growing greenhouse gases emissions and, also growing, energy use over the world that still remains. This trend overlaps with a more recent increase in the awareness regarding the effects of human activities towards the Earth ecosystems. Thus, the upgrade of the already-in-use systems is necessary to move towards greener and more modern technologies that permit continue with the economic growth while building more sustainable societies.

Thereby, the research focuses on the improvement of the ventilation system of a warehouse building and a cooking school located in the same plot, in an industrial area in Gävle, Sweden. The current system conditions, even consisting in some cases in recirculating air handling units, doesn’t permit the utilisation of the waste heat by bringing it back to the system.

The strategy used during the project follows a case study scheme: looking the system, understanding it in a complete way and designing the proper solution that fulfils the requirements. The study was approached as an energy audit: with several meetings with the company, collecting airflows data with the thermo-anemometer device, sketching the required building drawings and designing the optimal solution for the company.

Finally, the project resulted in the selection of the proper air handling unit, equipped with a heat recovery system, and the design of its ventilation duct system that permit a heat energy savings derived of the heat demand used to heat the makeup air of about 67 %. Furthermore, the occupancy study helped design the new scheduling for the ventilation periods that reduce the electricity demand of the ventilation system by 30 %. Thus, was obtained a significant energy use reduction that results in a sizeable energy cost saving.

• 95.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Numerical analysis using simulations for a geothermal heat pump system.: Case study: modelling an energy efficient house2018Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis

The ground source resources are becoming more and more popular and now the ground source heat pumps are frequently used for heating and cooling different types of buildings. This thesis aims at giving a contribution in the development of the thermal modelling of borehole heat storage systems. Furthermore, its objective is to investigate the possibility of implementing of a GSHP (ground source heat pump) with vertical boreholes, in order to deliver the heating and cooling demand for a passive house and to emphasize some certain advantages of this equipment even in the case of a small building (e.g. residential house).

A case study is presented to a suitable modelling tool for the estimation of the thermal behaviour of these systems GSHP by combining the outcome from different modelling programs. In order to do that, a very efficient residential solar house (EFden House – a passive residential single-family house, which was projected and built in Bucharest with academic purposes) is being analysed.

The numerical results are produced using the software DesignBuilder, EED (Earth Energy Designer) and a sizing method for the length of the boreholes (ASHRAE method). The idea of using 2 different modelling programs and another sizing method for the borehole heat exchanger design (ASHRAE method) is to make sure that all the calculations and results are valid and reliable when analysing such a system theoretically (in the first phases of implementing a project), before performing a geotechnical study or a thermal response test in order to assess the feasibility of such a project beforehand.

The results highlight that the length of the borehole, which is the main design parameter and also a good index in estimating the cost of the system, is directly influenced by the other fundamental variables like thermal conductivity of the grout, of the soil and the heat carrier fluid. Also, some correlations between these parameters and the COP (coefficient of performance) of the system were made. The idea of sizing the length of boreholes using two different methods shows the reliability of the modelling tool. The results showed a difference of only 2.5%.  Moreover, the length of borehole is very important as it was calculated that can trigger a difference in electricity consumption of the GSHP up to 28%.

It also showed the fact that the design of the whole system can be done beforehand just using modelling tools, without performing tests in-situ. The method aims at being considered as an efficient tool to estimate the length of the borehole of a GSHP system using several modelling tools.

• 96.
Danish Building Research Institute, Aalborg University, Copenhagen, Denmark .
Danish Building Research Institute, Aalborg University, Copenhagen, Denmark . University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Indoor Environmental Engineering, Aalborg University, Aalborg, Denmark .
Discharge coefficient of centre-pivot roof windows2015In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 92, p. 635-643Article in journal (Refereed)

Use of centre-pivot roof windows is very common in single family houses in Nordic Europe. Unfortunately the wind-driven airflow characteristics of this kind of windows are missing in the scientific literature. In the present study, the airflow rate through the window was specified by using the discharge coefficient. Wind tunnel measurements using a modelled centre-pivot roof windowwas used in the present study. For smaller sash opening angles the value of discharge coefficientwas approaching unity and the discharge coefficient decreased with increase in the sash opening angle. The value of 0.6 was only obtained when the window was without sash. Hence, the inclusion of sash improved the airflow characteristics of the window due to increased value of the dischargecoefficient. The discharge coefficient also depended on turbulence in the flow. In the absence of external wind, the turbulence was described by the value of Re. Only for higher values of Re the still-air discharge coefficients became independent of the flow direction and the air velocity. Whereas for wind driven natural ventilation the ratio of average air speed within the opening and the reference wind speed (velocity ratio) was used to define the fully developed turbulent flow. Constant values of wind-driven discharge coefficients were obtained when the average air speed within the opening was equal to or greater than the reference wind speed i.e. the velocity ratio greater than unity. Moreover, when the velocity ratio was greater than unity, the still-air discharge coefficients became identical to the wind-driven discharge coefficients.

• 97.
Danish Building Research Institute, Aalborg University, Copenhagen, Denmark .
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Indoor Environmental Engineering, Aalborg University, Aalborg, Denmark. Danish Building Research Institute, Aalborg University, Copenhagen, Denmark .
Effect of opening the sash of a centre-pivot roof window on wind pressure coefficients2014In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 13, no 3, p. 273-284Article in journal (Refereed)

This paper describes the effect of outward opening the sash of a window on local and overall windpressures. Wind tunnel experiments were used for the purpose of evaluation. A centre-pivot roofwindow on a pitched roof in a modelled scaled building was used in the analysis of wind pressures.The wind pressures were defined in terms of wind pressure coefficients. Traditionally, wind pressurecoefficients are extracted from the analysis of a sealed plane surface. These wind pressurecoefficients are used to estimate the natural ventilation rate through windows/openings due to windeffect. Surface averaged wind pressure coefficients do not accurately estimate the airflow rates. Therefore, local wind pressure coefficients are needed, especially for dynamic calculation of airflow rates. From the wind tunnel experiments, it is concluded that outward opening the sash can significantly affect the wind pressure distribution near to the window. The use of wind pressurecoefficients from the analysis of a sealed plane surface may lead to erroneous estimation of airflow rate.

• 98.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Department of Mathematics, Linköping University, Linköping, Sweden. Department of Management and Engineering, Linköping University, Linköping, Sweden. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University, Linköping, Sweden.
Transient inverse heat conduction problem of quenching a hollow cylinder by one row of water jets2018In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 117, p. 748-756Article in journal (Refereed)

In this study, a two-dimensional linear transition inverse heat conduction problem (IHCP) was solved using the Generalized Minimal Residual Method (GMRES) in quenching process by water jets. The inverse solution method was validated by set of artificial data and solution sensitivity analysis was done on data noise level, regularization parameter, cell size, etc. An experimental study has been carried out on quenching a rotary hollow cylinder by one row of subcooled water jets. The inverse solution approach enabled prediction of surface temperature and heat flux distribution of test specimen in the quenching experiments by using measured internal specimen temperature. Three different boiling curves were defined in the quenching process of a rotary cylinder. Result obtained by the inverse solution showed clear footprint of rotation in surface temperature and heat flux on each revolution of cylinder and temperature variation damping from quenching surface toward interior of specimen.

• 99.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Division of Energy Systems, Department of Management and Engineering, Linköping University.
Experimental study of quenching process on a rotating hollow cylinder by one row of impinging jets2017In: 9th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 12-15 June, 2017, Iguazu Falls, Brazil, 2017Conference paper (Refereed)

Quenching cooling rate of rotary hollow cylinder by one row of water impinging jets has been experimentallystudied. Water jets (d = 8 mm) with sub-cooling 55 to 85°C and Reynolds number 8,006 to 36,738 impinged over rotaryhot hollow cylinder (rotation speed 10 to 70 rpm) with initial temperature 250 to 600°C. Impingement impact angle of row of jets varied between 0 to 135° and jet-to-jet spacing in row patten was 2 to 8d. The results revealed more uniformityon cooling rate of quenching in smaller jet-to-jet spacing (2 and 4d) where wetting front regions are located closer toneighbor jet’s region. By increasing spacing, footprint of annular transition region was highlighted in quenching coolingrate contour. A distinct quenching characteristic was obtained for impingement impact angle of 0° compare to otherangles. With initial temperature above the Leidenfrost temperature, low cooling rate was achieved in film and transitionboiling compare to a steep increase of cooling rate at start of quenching with higher maximum heat transfer for experimentswith initial temperatures less than Leidenfrost temperature. The effect of other parameters on quenching coolingrate was highlighted in film and transition boiling while no significant differences were observed in nucleate boiling.

• 100.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Linköpings universitet, Energisystem.
A Ventilation Strategy Based on Confluent Jets: An Experimental and Numerical Study2015Doctoral thesis, comprehensive summary (Other academic)

This study presents air distribution systems that are based on confluent jets; this system can be of interest for the establishment of indoor environments, to fulfill the goals of indoor climate and energy-efficient usage. The main objective of this study is to provide deeper understanding of the flow field development of a supply device that is designed based on wall confluent jets and to investigate the ventilation performance by experimental and numerical methods. In this study, the supply device can be described as an array of round jets on a flat surface attached to a side wall. Multiple round jets that issue from supply device apertures are combined at a certain distance downstream from the device and behave as a united jet or so-called confluent jets. Multiple round jets that are generated from the supply device move downward and are attached to the wall at the primary region, due to the Coanda effect, and then they become wall confluent jets until the floor wall is reached. A wall jet in a secondary region is formed along the floor after the stagnation region.

The characteristics of the flow field and the ventilation performance of conventional wall confluent jets and modified wall confluent jets supply devices are investigated experimentally in an office test room. The study of the modified wall confluent jets is intended to improve the efficiency of the conventional one while maintaining acceptable thermal comfort in an office environment. The results show that the modified wall confluent jets supply device can provide acceptable thermal comfort for the occupant with lower airflow rate compared to the conventional wall confluent jets supply device.

Numerical predictions using three turbulence models (renormalization group (RNG k– ε), realizable (Re k– ε), and shear stress transport (SST k– ω) are evaluated by measurement results. The computational box and nozzle plate models are used to model the inlet boundary conditions of the nozzle device. In the isothermal study, the wall confluent jets in the primary region and the wall jet in the secondary region, when predicted by the three turbulence models, are in good agreement with the measurements. The non-isothermal validation studies show that the SST k– ω model is slightly better at predicting the wall confluent jets than the other two models. The SST k– ω model is used to investigate the effects of the nozzle diameter, number of nozzles, nozzle array configuration, and inlet discharge height on the ventilation performance of the proposed wall confluent jets supply device. The nozzle diameter and number of nozzles play important roles in determining the airflow pattern, temperature field, and draught distribution. Increased temperature stratification and less draught distribution are achieved by increasing the nozzle diameter and number of nozzles. The supply device with smaller nozzle diameters and fewer nozzles yields rather uniform temperature distribution due to the dominant effect of mixing. The flow behavior is nearly independent of the inlet discharge height for the studied range.

The proposed wall confluent jets supply device is compared with a mixing supply device, impinging supply device and displacement supply device. The results show that the proposed wall confluent jets supply device has the combined behavior of both mixing and stratification principles. The proposed wall confluent jets supply device provides better overall ventilation performance than the mixing and displacement supply devices used in this study.

This study covers also another application of confluent jets that is based on impinging technology. The supply device under consideration has an array of round jets on a curve. Multiple jets issue from the supply device aperture, in which the supply device is positioned vertically and the jets are directed against a target wall. The flow behavior and ventilation performance of the impinging confluent jets supply device is studied experimentally in an industrial premise. The results show that the impinging confluent jets supply device maintains acceptable thermal comfort in the occupied zone by creating well-distributed airflow during cold and hot seasons.

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