ELEMENTS
Here you can define special elements that can be used to perform particular computations.
There are three kinds of special elements:
bridge section elements;
bridge areas;
10077-2 insulation panel.
Bridge section elements
Cross section elements let you subdivide thermal bridge in various parts; each one is considered homogeneous along its length. We'll show some examples to clarify main concepts of this computation method. From version 3 of the software it is possible to define two distinct lengths for each section element in order to calculate two different Ψ (see example 2).
These
elements can be used to perform perticular analysis (for example,
Glaser analysis) along a section. Through
button you'll access to each element's properties: specifically,
"affect heat flow" option, if disabled, makes it possible
to use the element just as an analysis tool, i.e. it won't affect Ψ
computation.
Glaser analysis
To
enable this feature, simply use the
tool to access the properties of the element and select the wanted
type of Glaser analysis. Particular attention should be paid in the
evaporation case: the layer containing the element's red central
vertex will be used as wet layer.
Example 1: T shaped thermal bridge
To compute the linear thermal transmittance Ψ in the common T shaped thermal bridge, it is necessary to compute the total heat flow through the cross section and the heat flow that would be if there wasn't the effect of the thermal bridge (see example2.mos).
The
former is easily obtainable with the standard simulation, while the
latter can be computed by marking the elements that make up the cross
section using the button
.
Referring
to the picture, the purpose is to tell Mold Simulator that there is a
vertical element where there is heat flow; the heat flow through the
element is computed as U * l * DT, where:
- U: is the thermal transmittance of the element, identified the green horizontal line;
- l: is the length of the element, identified by the green vertical line;
- DT: is the temperature difference between the two square boxes at the two ends of the green horizontal line.
Cross section elements automatically detect thermal transmittance by default; it is possible to manually define it, as shown in the next example.
Example 2: internel and external Ψ interno in a corner wall
As anticipated, you can define two different lengths of section elements. To activate this feature, you must enable the "double-length" in section elements' properties.
As shown in the figure, an additional length (blue) will appear in addition to the standard one (green),and this will generate two different linear thermal transmittances Ψ. This project is contained in example2.mos file in "/ Doc / samples / mold_simulator /" folder.
Example 3: window with wall
This case is slightly more complex than the one before, but it will be reduced to cross section elements identification as well.
Figure
is referred to example7.mos.
As shown, we identify three elements: wall, frame and insulation
panel. Before explaining why insulation panel is used, let's suppose
we've computed frame's transmittance with EN ISO 10077-2; its value
will be inserted in frame's section element, telling Mold Simulator
to not automatically detect U. You've to click
button to do so; once pressed, you've to select frame's section
element and disable automatic U detection on the new window and
insert the desired U value.
Having used insulation panel allows to compute Ψ in the same configuration used to compute Uf with EN ISO 10077-2, which needs an insulation panel, with conductivity set to 0.035 W/mK, placed instead of glazing; moreover, we've obtained a Ψ value not dependent on glazing type.
If we had the whole window Uw value (frame and glazing together), we should have used glazing instead of insulation panel and just one section element (for frame and glazing) with U set to Uw.
5.1- Area method
This method can be used to compute the exact heat flow exchanged between two parts of a section; the obtained Ψ value is simply this heat flow divided by internal / external environments temperature difference.
Example 1: windows
We want to compute heat exchange between window and wall of the same project of previous paragraph:
To perform the computation of the thermal bridge it's necessary to know the heat flow exchanged between wall and frame; this value can be computed as the difference between the heat flow through the entire cross-section, as it is shown, and the heat flow that would be if wall and frame were completely insulated one from the other.
It would be necessary to perform three different simulations:
- standard simulation, from which we get F1, the total heat flow;
- simulation of the wall alone, from which we get F2, where the frame and window are filled with adiabatic material;
- simulation with the frame and window alone, from which we get F3, were the wall is filled with adiabatic material.
F2 + F3 = FI, the heat flow if there wasn't thermal bridge between wall and frame. The sought heat flow is computed as FD = F1 – FI. By dividing this value by the temperature difference between internal and external environment we get the linear thermal transmittance.
Mold
Simulator makes this procedure completely automatic; it is indeed
enough to draw a closed polygon using the button
;
in the tab “Simulation” FI will be shown as “Flow,
no bridge” while F1 will be shown as “Flow, bridged”.
Example 2: discontinuous wall
The discontinuity in a wall (subdivided in two zones with different thermal transmittance) can be subject to a thermal bridge. The calculation method is identical to the previous one:
F1 = heat flow that goes through the entire wall;
F2 = heat flow through the left part of the wall with the right part made of adiabatic material;
F3 = heat flow through the right part of the wall with the left part made of adiabatic material.
In order to create closed paths (defining elements) you can use the following commands:
|
Move closed paths' points. |
|
Create a new closed path. |
|
Delete a closed path by clicking on it. |
Clicking on “Import from areas” button you'll be able to create closed paths from areas created in “Areas” tab.
10077-2 insulation panel
Since version 2.0 it is possible to tell the software where the insulation panel should replace glazing; in this way linear thermal transmittance (ψ) will be automatically computed, applying 10077-2 norm.
In order to use this feature, follow these simple steps:
create or import the lines of the project you wish to simulate;
go to "Elements" tab and create a closed path around the area where the glazing will be placed;
go to "Areas" tab and assign all the materials as usual; glazing area must be filled with proper materials (glass, gas etc...) and NOT with insulation panel materials.