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  • 1.
    Risberg, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Analysis of the Thermal Indoor Climate with Computational Fluid Dynamics for Buildings in Sub-arctic Regions2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis aims to increase the knowledge of simulation of thermal indoor climate for nearly zero energy buildings in a sub-arctic climate. Air heating systems in cold climate generate temperature gradients, which negatively affects the thermal indoor climate. Stand-ard multi-zone modeling has problemswithpredicting these gradients.

    In this work, Computerized Fluid Dynamics (CFD) simulations are used to model the tem-perature gradients. The consequences of reducing the cell sizes for the simulation volume are estimated and case studies of different building and heating systems are presented. The CFD method is validated for a traditional underfloor heating system and also for an air heating system.

    Furthermore, the effects of snow on heat losses for common building foundations are in-vestigated, and snow is shown to be an important boundary for CFD simulations of a build-ing. The snow and ground freezing areshown to reduce the annual heat losses between 7-10%.

    The CFD method is shown to be a suitable method for predicting thermal indoor climate. The method can determine the temperature variations inside a building, for different rooms, floors and heating systems. The CFD method is most appropriate for local distributed sys-tems. For traditional hydronic systems the method may be overambitious,since a good indoor climate is usually achieved anyway.

    Heat transfer coefficients are inaccurate when calculated using standard wall functions used in many turbulence models (like the k-ε model) for surfaces with a high heat transfer rate and natural convection. Automatic wall functions have shown better accuracy for this type of problem, but they require more cells. In order to still use the k-εmodel, a user defined wall function is investigated. This method gave good results and a significant re-duction in the number of necessary cells in the simulation volume. The validation of the indoor climate shows that the wall boundary conditions are important for predicting the indoor temperaturevariations for steady state simulations.

    New buildings have a higher thermal inertia, which affects the heat losses. It is important to include this effect in the boundary condition calculations for a CFD model.

    The CFD simulations show that air heatingand local distributed heating systems have dif-ficulties infulfillinga good thermal comfort inside all rooms. This is especially true for rooms with exhaustair and closed doors and multi-storybuildings. Results from a CFD simulation can be used to improve the thermal comfort in these cases.

  • 2.
    Risberg, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CFD simulation of indoor climate in low energy buildings2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis computational fluid dynamics (CFD) was used for simulation of the indoor climate of low-energy buildings in cold climate. The heat consumption in newly built houses was reduced drastically. Along with the different classification systems for low-energy buildings the demand for the indoor climate has increased, which causes a need to investigate buildings even before they are built. Than CFD is of importance in studies of different heating systems and how new construction solutions can affect the indoor environment. The work focus was on investigating the computational setup, such as grid size and boundary conditions in order to solve the indoor climate problems in an accurate way and compare different heating systems. A limited number of grid elements and knowledge of boundary settings is therefore essential in order to obtain reasonable calculation time.The models show that radiation between building surfaces has a large impact on the temperature field inside the building, with the largest differences at the floor level. An accurate grid edge size of around 0.1 m was enough to predict the climate. Different turbulence models were compared with only small differences in the indoor air velocities and temperatures. To explore the viability of this approach, the indoor climate in a building was studied considering three different heating systems: an underfloor heating system, air heating through the ventilation system and an air heat pump installation. The underfloor heating system provided the most uniform operative temperature distribution and was the only heating system that fully satisfies the recommendations to achieve tolerable indoor climate set by the Swedish authorities. On the contrary, air heating and the air heat pump created a relatively uneven distribution of air velocities and temperatures, and none of them fulfils the specified recommendations. From an economic point of view, the air heat pump system is cheaper to be installed but produces a less pleasant indoor environment then distributed heating systems. The most widely used turbulence model for indoor CFD simulations, the k-ε model, has exhibited problems with treating natural convective heat transfer, while other turbulence models have shown to be too computationally demanding. One paper therefore studies how to deal with natural convective heat transfer for a radiator in order to simplify the simulations, reduce the numbers of cells and the simulation time. By adding user-defined wall functions, to the k-ε model the number of cells can be reduced considerably compared with the k-ω SST turbulence model. The user-defined wall function proposed can also be used with a correction factor for different radiator types without the need to resolve the radiator surface in detail. Compared to manufacturer data the error was less than 0.2% for the investigated radiator height and temperature.

  • 3.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CFD modelling of radiators in buildings with user defined wall functions2016In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 64, p. 266-273Article in journal (Refereed)
    Abstract [en]

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

  • 4.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Investigation of thermal indoor climate for a passive house in a sub-Arctic region using computational fluid dynamics2019In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 28, no 5, p. 677-692Article in journal (Refereed)
    Abstract [en]

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

  • 5.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    The impact of snow and soil freezing for commonly used foundation types in a subarctic climate2018In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 173, p. 268-280Article in journal (Refereed)
    Abstract [en]

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

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

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

  • 6.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vesterlund, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hållbara, integrerade energi- och VA-system2014Report (Other academic)
  • 7.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vesterlund, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CFD simulation and evaluation of different heating systems installed in low energy building located in sub-arctic climate2015In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 89, p. 160-169Article in journal (Refereed)
    Abstract [en]

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

  • 8.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vesterlund, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CFD simulations of the indoor climate of a low energy building in a sub-Arctic climate: an evaluation of different heating systems2013Conference paper (Refereed)
    Abstract [en]

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

  • 9.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Computational fluid dynamics simulation of indoor climate in low energy buildings computational set up2017In: Thermal Science, ISSN 0354-9836, E-ISSN 2334-7163, Vol. 21, no 5, p. 1985-1998Article in journal (Refereed)
    Abstract [en]

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

1 - 9 of 9
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