NRVUs must be tested and calculated in accordance with Annex IX of Regulation (EU)1253/2014. In the case of BVUs, filter correction factors are given for cases in which either the filter on the inlet side or the one on the exhaust side (or both) are missing.
In the case of UVUs intended to be used with a filter, such correction factors are not given; therefore, compliance with the SFPint requirement shall only be assessed in the reference configuration.
In principle, the tests could be performed with a filter different from the ones foreseen in the reference configurations (see definitions 3 and 4 in Annex I, Part 2), e.g. using an F9 filter instead of an F7 filter. In this case, an appropriate (calculation) method must be used to infer (and declare) performance using the filter foreseen in the reference configurations.
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