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).
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