The ‘nominal flow rate’ for NRVUs is the ‘declared design flow rate’ under the conditions described in definition 6 of Annex I, Part 2. Therefore, the manufacturer has the freedom to determine such conditions in more detail, depending on specific design choices (e.g. including or excluding a pressure reserve for clogging).
As an indirect conclusion from definition 8 of Annex I, Part 2, it is deemed necessary that the ‘nominal flow rate’ is the one at which the maximum rated fan speed occurs.
Disclaimer: Please note that the European Commission cannot provide a legally binding interpretation of the EU legislation, as this is the sole competence of the European Court of Justice. Any remarks from the European Commission services are without prejudice to the position the Commission might take should related cases arise in a procedure before the Court of Justice.