When undertaking a survey, consideration needs to be given to the environmental conditions present at the time and before the survey is carried out, also what the most appropriate thermographic technique is for carrying out the task.
Thermal anomalies only present themselves where temperature differences exist and environmental conditions are accounted for. As a minimum, the following conditions are required to be met.
- Temperature difference across the building fabric to be greater than 10°C.
- Internal air to ambient air temperature difference to be greater than 5°C for the last twenty four hours before survey.
- External air temperature to be within +/- 3°C for duration of survey and for the previous hour.
- External air temperature to be within +/- 10°C for the preceding twenty-four hours.
External surveys should also comply with the following:
- Surfaces free from direct solar radiation for at least one hour.
- No precipitation either just prior to or during the survey.
- Ensure all building surfaces to be inspected are dry.
- Wind speed to be less than 10 metres / second.
External inspection may be influenced by radiation emissions and reflections from adjacent buildings, a cold clear sky, or even the sun will have an influence on surface temperatures.
In order achieve the best results a minimum temperature differential between the inside and outside of the building of at least 10°C must be achieved. This can usually be done by leaving the heating system on inside the building for 12–24 hours prior to the survey.
External surveys should also be carried out after dark or early in the morning, to ensure problems
with sunlight warming up external surfaces can be ignored. |
