Saturday 26 November 2011

What is the "HARMONIC" Option of AnTherm

The HARMONIC option of AnTherm calculates “harmonic thermal conductivities” of component or building as indicators required for transient building energy simulations based on periodic (harmonic) approach. This also includes PHPP calculations.
Thermal Harmonic Conductivities and further dynamic indicators facilitating heat transport with heat capacity capabilities follow the ISO and EN standard EN ISO 13786.

The harmonic thermal conductivity is given by the amplitude and phase lag of the heat flow which follows periodically changing boundary conditions (either temperatures or heat sources or sinks). Lagging in time with damping of amplitude (attenuation) results from heat storage capability of materials.
Heat losses might lag many months, intermittent heat gains might result also. Cooling infrastructure might become obsolete or overheating can be practically resolved with the building own (heat) capacity.
Transient heat flows are heavily dependent on heat capacity of building components, especially massive, solid or brick walls, slab or ground structures.

The Harmonic option of AnTherm can be seen as a small brother of the much more extensive TRANSIENT-Option of AnTherm.
The purpose of the Harmonic option is to solve transient, periodic heat transmission equation for the 0-th and 1-st harmonic. The 0-th harmonic is the steady state solution of the equation corresponding to mean heat flows under periodic boundary conditions. The 1-st harmonic provides solutions of amplitude and phase lag for the main period, such as day or year.
When power sources are involved AnTherm’s Harmonic option reports Harmonic Heat Distribution Factors (additionally to Harmonic Thermal Conductivities reported for spaces) and are also given by their amplitude and phase lag of the heat flow following the oscillation of respective heat source or sink.

By using the harmonic indicators much better approximation of dynamic thermal behavior of the building can be obtained when compared to simplified steady state approach – even with only one first harmonic of the oscillation.

Exact indicators calculated with AnTherm for any 3 dimensional geometry and arbitrary combination of materials are indispensible replacement for approximations restricted to few simplified geometries only as those provided in ISO 13370.

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 – harmonic thermal conductances are output just following the steady state thermal conductances L2D, L3D in the respective report. There is also no need to specify or assume any starting boundary conditions as compared to time step based methods.

It is very important to emphasize, that harmonic thermal conductance are characteristic for the object concerned and by that are independent of any boundary conditions. The proper calculation of these harmonic periodic indicators does not need to know nor to apply any boundary conditions. Further evaluation of the behavior of a building component under certain and periodically changing boundary conditions is subject to the “TRANSIENT” Option of AnTherm (higher harmonics, periodic boundary conditions, animation in time and timeline outputs).

What is the "TRANSIENT" Option of AnTherm

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 modeling 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 tuning on and off electric heating appliance.

Respective boundary conditions, periodically variable in time, can be modeled as series of values at specific time points or as series of mean values valid for several intervals of equal or variable lengths. Modeling periodic boundary conditions is not limited to air temperature but also possible for volumetric heat sources or sinks. The later will often be modeled as step (switch) functions while the other will result from some long term data measurements. The set of tools provided for modeling 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/TRANSIENT 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 modeling 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).