Thermal Bridge Calculations

Thermal bridge calculations

Thermal bridge calculations quantify heat loss that is not captured by the U-values of the surrounding building elements.

Psi- and Chi-value calculations

Psi (ψ)-values quantify linear thermal transmittance through junctions such as wall interfaces, window connections, slab edges and other continuous thermal bridges.

Chi (χ)-values quantify point thermal transmittance through discrete connections such as brackets, fixings and other three-dimensional penetrations through the building envelope.

The appropriate calculation method depends on the geometry and heat-flow path of the detail.

2D and 3D thermal modelling

Standard linear junctions are assessed using 2D thermal modelling in Flixo. Where the geometry cannot be represented accurately in two dimensions, a 3D finite-element model is developed in COMSOL.

Calculations use the applicable methodology, including BS EN ISO 10211 where relevant.

• Psi-value calculations
• Chi-value calculations
• Linear and point thermal transmittance
• Heat-flow analysis
• Internal surface temperature assessment
• Comparison of alternative details or configurations where required

Typical applications

• Wall, floor and roof junctions
• Curtain-wall and façade connections
• Window and frame interfaces
• Rainscreen brackets and fixings
• Balcony and slab connections
• Brise soleil and shading-system connections
• Other complex penetrations through the thermal envelope

What you receive

• Model geometry and assumptions
• Material properties and boundary conditions
• Temperature and heat-flow results
• Calculated Psi- or Chi-value
• Technical calculation report
• Individual junction assessments or a wider façade thermal-analysis package

What I need

• Construction details or drawings
• Material specifications
• Relevant dimensions
• Required calculation or performance criteria
• Project location and boundary conditions, where applicable
• If the required 2D or 3D approach is unclear, send the available information and we can determine it