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| Essay:HAM: Lund-Gothenburg Group for Computational Building PhysicsLund-Gothenburg Group for Computational Building Physicshttp://www.blocon.se/lggroup.htm The research group studies heat, moisture and air flow processes in buildings and building components. The aim is to develop computer models and other tools of analysis in order to understand, describe and compute in sufficient detail temperatures, moisture levels, and so on. Numerical and analytical methods are often used in combination. An important goal is to establish simplified, practically useful methods of analysis, and in particular well-documented, handy PC-programs.
The mathematical, physical and computational methods to handle the multifarious processes of building physics have many common features. The same numerical technique may be used in quite different situations. This is the main rationale to have a group for computational building physics.
The diffusion and application of the developed models and other tools of analysis are an overall goal for the group. Hence, the group endeavors to work closely together with other researchers and research groups in various applications. This interaction is a main stimulus for the model development.
The group is mainly financed by the Swedish Council for Building Research (BFR). The group consists of the following members:
Dept. of Building Physics, University of Lund:
Tekn. Dr Jesper Arfvidsson Tekn. Dr Thomas Blomberg Dept. of Building Technology, Chalmers, Gothenburg: Prof Johan Claesson Prof Carl-Eric Hagentoft
Main fields of study and main results
The main results from the group during the last ten years are briefly indicated below.
Heat loss to the ground. Freezing in the ground
Essential parts of the research have been implemented in the standardization work of CEN (TC89/WG5). Hagentoft has been the Swedish delegate in the working group since 1989. As an example, the working group has produced a standard on frost heave. Freezing of the ground under a foundation can cause severe problems if the foundation is not properly designed.
Basic building physics. Course
The mathematical, physical and computational descriptions of building physics processes have many common features. The same or similar numerical techniques may be used in quite different situations. An endeavour to compile such knowledge in a systematic way is presented in a report by Claesson and Hagentoft, 1994, BASIC BUILDING PHYSICS. Mathematical Modelling. The mathematical, physical and computational descriptions of building physics processes have many common features. The same or similar numerical techniques may be used in quite different situations. This mathematical basis is expounded in an advanced course (194 pages, 180 figures). This material is used as an advanced course for graduate students.
HAMTIE. IEA cooperation
The IEA-Annex 24, Heat-Air-Moisture Transport in highly Insulated, new and retrofitted Envelope parts (HAMTIE) started its work in April 1991. Combined heat, air and moisture transport in and through highly insulated envelope parts is dealt with. Hagentoft has been the Swedish delegate from 1991. In total, 14 countries are represented in the annex. Hagentoft is the leader of Subtask 5, Performance and Practice. In this subtask the results from the annex will be transformed into design rules for engineers.
Numerical heat transfer
Quite complex heat transfer problems within the field of buildings physics may today be analysed using an ordinary PC because of the remarkable increase of computer capacity. Our heat transfer programs have been developed further in order to make them as easy to use as possible (e.g. within the Microsoft Windows environment). The PC-programs HEAT2 and HEAT3 are now used by researchers and consultant engineers in more than twenty countries.
These programs may solve many thermal problems, see Blomberg, 1996, Heat conduction in two and three dimensions. Computer modelling of building physics applications. This doctoral thesis presents the numerical modelling techniques used in the computer programs. Studies of numerical accuracy and methods to improve the accuracy by combining simulations with different meshes are reported. A number of particular applications are presented: Metal thermal bridges in thermal insulations, glass-encapsulated evacuated powder panels, rock caverns used for heat storage, thermal shielding of rock caverns, U-value for a window taking the wall into account, temperature and moisture conditions in attics, and insulated walls with slotted U-girders.
Convective-diffusive heat flow
The thermal problem of coupled heat conduction in nonpermeable materials with air flow in cracks is dealt with. A combination of numerically calculated temperatures in the solid material and analytical solutions for the interaction with the air flow in the air channels is used.
A semi-analytical solution for air flow through a straight crack in a wall is developed which is used to test the accuracy in the numerical solutions.
A new analytical technique to assess heat losses due to air leakage through thermal insulation is presented. A simple formula is presented for the case with air leakage through a slit into the insulation.
Moisture processes
The problems how to represent mathematically the moisture flow in porous materials are discussed. A major result is the systematic use of so called Kirchhoff potentials, which considerably facilitates analyses, numerical computations, and evaluations of moisture flow properties from experiments. See Arfvidsson, 1994, Isoterma fuktf?rlopp i por?sa material. Ber?kning och utv?rdering av m?tdata. (Isothermal moisture flow in porous materials. Calculation and evaluation of measured data.) Written in Swedish. The doctoral thesis presents the concept of Kirchhoff potentials, which facilitates analyses, calculations and evaluation of moisture flow properties considerably. The main program JAM2 is presented. An analytical solution for nonlinear step response at a boundary is derived. Nonlinear periodic penetration at a boundary is also dealt with. Numerical results are given. Finally, the method using Kirchhoff flow potential is extended to the anisotropic case of wood.
Computer model library
An important result from the group is the library of computer models. Most of the programs are shown in Complete list of PC-programs.
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