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Computational fluid dynamics simulation of indoor climate in low energy buildings computational set up
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0003-0225-711X
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
2017 (English)In: Thermal Science, ISSN 0354-9836, E-ISSN 2334-7163, Vol. 21, no 5, p. 1985-1998Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
2017. Vol. 21, no 5, p. 1985-1998
National Category
Energy Engineering Fluid Mechanics and Acoustics
Research subject
Energy Engineering; Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-66606DOI: 10.2298/TSCI150604167RISI: 000414237000010Scopus ID: 2-s2.0-85032913950OAI: oai:DiVA.org:ltu-66606DiVA, id: diva2:1157928
Note

Validerad;2017;Nivå 2;2017-11-17(inah)

Available from: 2017-11-17 Created: 2017-11-17 Last updated: 2018-05-17Bibliographically approved
In thesis
1. Analysis of the Thermal Indoor Climate with Computational Fluid Dynamics for Buildings in Sub-arctic Regions
Open this publication in new window or tab >>Analysis of the Thermal Indoor Climate with Computational Fluid Dynamics for Buildings in Sub-arctic Regions
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Analys av termiska inomhusklimatet med CFD för byggnader in subarktiskt klimat
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.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-68067 (URN)978-91-7790-086-3 (ISBN)978-91-7790-087-0 (ISBN)
Public defence
2018-05-24, E632, 971 87, Luleå Tekniska Universitet, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2018-04-04 Created: 2018-03-27 Last updated: 2018-05-17Bibliographically approved

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Risberg, DanielWesterlund, LarsHellström, J. Gunnar I.

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