What is the purpose of the International Organization for Standardization (ISO) 9972?

The purpose of ISO 9972 is specifically to provide a standardized method for determining the airflow characteristics of buildings using the fan depressurization method. This standard outlines the procedures for measuring the airtightness of buildings, which is crucial for assessing energy efficiency, indoor air quality, and the performance of HVAC systems. By using the fan depressurization method, practitioners can quantify how much air leaks into or out of a building, which directly impacts its energy consumption and comfort levels.

Understanding airflow in relation to building performance is essential for ensuring that buildings are energy efficient and meet ventilation requirements, thus emphasizing the significance of ISO 9972 in the realm of whole-building airtightness testing. The other options, while relevant to different aspects of building assessment and performance, do not pertain specifically to the method outlined by ISO 9972. This makes option A the correct and relevant answer in the context of whole-building airtightness testing practices.