Linear non-repeating transmittances

Linear non-repeating transmittances can be defined simply using an overall coefficient method or a detailed method where geometry is utilised. Either method can be used but not both in a model. The method is set on the Tools menu > Preferences dialog > Bridging tab.

 

Coefficient or Psi values are edited in the ApCDB editor thermal bridging tab.

 

For each ApCDB construction type external wall, roof, external windows, rooflights, external door thermal bridging appropriate Psi inputs are provided as shown in figure 9 as well as a thermal bridging coefficient input & checkbox.

 

 

Fig: ApCDB editor thermal bridging tab

 

Values for common reference details are also provided. Select the standard required from the Defaults combo-box then for each transmittance select the detail code provided in the standard for the detail that is required. The relevant Psi will be written to the Psi input box.

 

Selecting a standard resets the reference details to the first on the list for each transition type; however, any custom edited values will be retained.

If a transmittance is not required i.e. it does not exist enter zero for the Psi value.

Fig 13: ApCDB editor thermal bridging tab – common details interface

 

 

Fig: Extract from ISO 14683 - common corner details

 

Note that the default data provides values for both dimensional conventions; a suffix denotes the basis of the dimension used to derive the set of Psi values.

 

For Linear non-repeating transmittances, the Take off rules are utilised to automatically determine from the model geometry the length of each type of transmittance and whether it is shared or not between adjoining surfaces.

 

For adjoining surfaces with a shared junction but with dissimilar assigned constructions Psi values an average Psi value is applied.

 

An example take-off for external wall and roof transitions is provided below including notes for exceptions:

 

Fig: Example take-off model

 

 

Fig: Example take-off geometry

 

 

Fig: Example take-off external wall linear dimensions

 

 

 

Fig: Example take-off roof external linear dimensions

 

For external openings in the example the take-offs are straightforward i.e. the edge lengths for external window and door lintel, jamb and sill transitions and the perimeter for rooflight kerb transitions.