The VE offers several mechanisms for implementing thermal bridging in a dynamic thermal model:
Clear field or repeating transmittances (construction layers).
Linear non-repeating transmittances (coefficient).
Linear non-repeating transmittances (Psi).
Random transmittances (area, linear, point).
The VE implementation is based on the methods and data contained in the following key references:
ISO 14683: 2017 – Thermal bridges in building construction.
UK BR 443: 2019 – Conventions for U-value calculations & BR 497 (2nd ed.) 2016 Conventions for calculating linear thermal transmittance and temperature factors.
ASHRAE 90.1: 2019 Energy Standard for Buildings except low-Rise Buildings with addendum av (2022).
Building Envelope Thermal Bridging Guide v1.5 2020 (Morrison Hershfield Limited).
As referenced in the following compliance standards:
UK Approved document L2: 2021 / UK NCM Modelling Guide 2021.
ASHRAE 90.1: 2019.
NECB 2020.
The implementation of thermal bridging in the VE offers a flexible tool with automated aspects:
A choice in resolution for linear non-repeating transmittances for early and detail design stage assessment (coefficient or Psi values).
For linear non-repeating transmittances Psi quick look-up values from key thermal bridging reference details.
For linear non-repeating transmittances and random transmittances, the VE automatically ‘takes-off’ the dimensional or count information from the model geometry using a rules-based approach.
All transmittances are automatically included in the existing VE VistaPro conduction gain variables - room total conduction gains (and optional detailed conduction gains) (see figure 22) and included in existing reportage.
Clear field, linear non-repeating and random transmittances (see section 5) are also optionally reported (see figure 21) as separate detailed room variables in VE Vistapro so the user can quickly investigate the contribution that they make to the model energy balance and thus identify where action maybe required.
