What is a thermal index?
The Thermal Index (TI) is a fixed value used for determining the risk of surface condensation or mould growth within an area. As an industry standard, a Thermal Index value of 0.75 is recommended to provide a consistent guideline for temperature assessment.
Thermal Indexing is used to define a quantitative pass/fail criteria that can be used to determine whether a thermal anomaly within a building fails to meet its design intent for thermal performance.
Thermal Index Calculation Example
The Thermal Index (TI) value is used when calculating the Minimum Internal Surface Temperature using the formulae below, and using it as a guideline for temperature measurement.
Minimal Internal Surface Temperature = (Thermal Index x (Internal Temperature – External Temperature)) + External Temperature
In practice, we know that the Thermal Index value will be 0.75, and the internal and external temperatures will be recorded during the survey.
For example, if during a building survey the internal temperature was 20ºC and the external temperature was 10ºC, the formulae would work as follows:
Minimal Internal Surface Temperature = ( 0.75 x ( 20 – 10 ) ) + 10
Minimal Internal Surface Temperature = 17.5 (ºC)
In this example, this would mean that if any area within the building measured less than 17.5ºC with a thermal imaging camera, it would “fail” according to this criteria.