I am working on a CI project which is a factory/office space. The AHU provides fresh air only in certain spaces. The fresh air via the AHU is pretreated by F7 filters. Rest of the spaces are provided only with FCU without supply of fresh air. So, for minimum IAQ calculations can I consider infiltration through doors etc. as the reason for providing fresh air to these spaces? Or is it mandatory that these spaces must be supplied with separate fresh air duct?.