Validation is an extensive exercise
Qualification of the HVAC system is one component in the overall approach that covers premises, systems/utilities, equipment, processes, etc.
See also full guidelines on "Validation" in WHO TRS No 937, 2005, Annex 4.
Risk-based approach for HVAC qualification
8.2.1 Validation is a many-faceted and extensive activity and is beyond the scope of these guidelines. Qualification and validation guidelines are included in: Expert Committee on Specifications for Pharmaceutical Preparations.
Fortieth report. Geneva, World Health Organization, 2005 (WHO Technical Report Series, No. 937), Annex 4 (see also Fig. 28).