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Description

With the Psi-Value tool kind Edge/Spacer you can calculate the Ψ-values of glazing spacers or edge influences of frames according to EN ISO 10077-2.

The Ψ-value, which quantifies additional energy, is a correction value that is caused by linear shaped thermal bridges, and is not taken into account in 1 dimensional energy calculations with U-values.

The magnitude of the Ψ-value depends on several values: the quality of the construction, the quality of the measurements, as well as the U-value which calculates the loss of heat of the undisturbed component. Hence, it is possible that a poorly insulating flat roof protection has a better Ψ-value than a well insulating window-wall junction, because in the case of the former, the calculation of the Ψ-value is done with exterior measurements through which part of the energy is already covered by thermal bridge energy losses by flat roof and wall measurements. Ψ-values can also be negative.

The calculation of Ψ-values is explained in detail in tutorial 5.

How do I activate it?

The Psi-Value tool can be activated with the menu command Psi-Value in the menu Results or by clicking on the icon in the  Toolbox flyout. Then select the kind Edge/Spacer in the tool properties (cf. figure 2).

How do i use it?

First select the result object for which the spacer Psi-value should be calculated. Second you have to define in the dialog window the file with the Uf-value of the same frame.

If you want to calculate the spacer Psi-value according to EN ISO 10077-2 using this tool, following preconditions have to be fulfilled (see Limitations):

 

If these conditions are not fulfilled, you can calculate the spacer Psi-value using the Psi-value tool kind 2 Constructions respectively 3 Constructions (for mullion or transom). Using these tools, you have to enter the frame U-value manually in the Properties flyout.

With the Select, Move, Scale tool  or Edit tool respectively, you can change the text positions of the help objects, of the U-values of the base construction and the dimensions distance.

You can adjust afterwards the file with the Uf-value calculation in the Properties flyout (cf. file 1). If the Psi-value couldn't get calculated you can see the according error message in the Properties flyout (cf. figure 1  see Psi-value entry) as well.

Figure 1: Properties flyout for the spacer Ψ-value object

Defining Styles

The presentation of a Psi-value object can be defined in the Style list in the Psi-Value tool properties (see figure 2). The list shows all styles for Psi-value objects that have previously been determined in the Styles flyout.

A new Psi-value object is always created with the styles currently marked in the Style drop down list. You can either change the selection of the styles in the Styles flyout or in the Style drop down list in the Psi-Value tool properties.

The styles can also be adjusted afterwards by using the Assign Properties tool or by using the Drag&Drop function (see tutorial 1).

 

Figure 2: Tool Properties

Physical Explanation

The Ψ-value according to EN ISO 10077-2 is calculated as follows:

Figure 4: Calculation of spacer Psi-value

if it is a mullion or a transom with 2 glazings and 2 spacers the formula is as follows:

with:

Φ: Total heat flow in to or out of the model [W/m]

ΔT: Temperature difference [K]

Ug: U-Value of the panel  [W/m2K]

bg: Width of the glazing or the panel  [m]

bf: Width of the frame  [m]

Limitations