Transient (periodic) time dependant simulation

DRAFT

The TRANSIENT option of AnTherm calculates, evaluates and visualizes heat flows and temperature distributions in building components under boundary conditions changing in time periodically. By that it allows modelling and analysis of effects of heat storage in building construction and their response to changing conditions due to heat capacity of materials.

Such simulation approach is also known by “Transient periodic”, “Transient harmonic” or “quasi steady periodic”.
The efficiency and precision of this simulation approach results from the assumption of periodicity. By assuming periodicity of the processes the proper of periodic simulation does not need any starting distribution of temperature field. This is especially true for climatic boundary conditions (year, day), utilization scenarios (including the period of one week) or any other “repetitive” situation, e.g. periodically turning on and off electric heating appliance.

TRANSIENT-option: Solving and evaluating time dependant dynamic, periodic problems when heat capacity effects are concerned is only possible with an active TRANSIENT-Option of the program.

Respective boundary conditions, periodically variable in time, can be modelled as series of values at specific time points or as series of mean values valid for several intervals of equal or variable lengths. Modelling periodic boundary conditions is not limited to air temperature but also possible for volumetric heat sources or sinks. The later will often be modelled as step (switch) functions while the other will result from some long term data measurements. The set of tools provided for modelling periodic data includes for example: values at equidistant points (regular points), mean values at equally or irregularly distributed time intervals (regular means, irregular means), values in steps (switching) on irregularly tiled intervals (irregular steps). Furthermore any periodic distribution given by complex coefficients of Fourier series can be employed too.

Compared to HARMONIC option (this earlier option of AnTherm is available already for years) the TRANSIENT option adds higher precision of results, ability to evaluate higher harmonics of the main period requested (up to 1000 harmonics), evaluate timelines of temperatures at arbitrary probe points or visualize time dependant animations in 3D (by employing the already well known techniques of “standard” steady state AnTherm to chosen time series) and record them for movie reproduction.

The strength of the HARMONIC tool relies on the fact, that harmonic thermal conductances (complex number, amplitude and the phase lag) can be calculated without the need to enter nor to know any boundary conditions.
The TRANSIENT Option goes much further by adding the ability of modelling periodic boundary conditions (fully automated Fourier analysis) for the purpose of time dependant evaluations (either a 3D view at some point in time, then available to creating time series animation, or timelines of temperature changing in time at selected location of the 3D model).

See also: Theoretical background, European standards on thermal bridges, EN ISO 13786, EN ISO 13370