Basics and Some Theory of AnTherm
Weighting Factors
The air temperatures set in the spaces adjacent to a building component all
contribute to the temperature distribution resulting within the component.
Therefore, the specific temperature, T, at any given point in a model can
also be described as the result of all the space temperatures, T0
through Tn, weighted for the specific position and summed:
T = g0•T0 + g1•T1 + … gn•Tn
g-values |
The set of weighting factors, g0 through
gn, must be determined for each point of the model to be
considered more closely. These so-called g-values are normalised such
that their sum is equal to one. If all the interior spaces are set at the
same temperature (Ti for T1 through Tn),
and T0 is defined as the exterior temperature (Te),
then the equation above can be simplified to
T = g0•Te + (1 − g0)•Ti
and re-written as
T = Ti
− g0• ( Ti − Te )
In this case, g0 represents a generalised version of
the f-value familiar from the evaluation of surface temperatures for
one-dimensional heat flow (based on U-values). Contrary to a
conventional f-value, which applies to the entire interior surface
plane, the g-value above is only valid for a specific point of a
thermal bridge.
Once g-values have been characterised for the coldest points of
all interior surfaces, however, the temperatures resulting at these points
can be evaluated as simply as with the one-dimensional method.
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