Air Change Rate is a measure of the air volume added to or removed from a space divided by the volume of the space. The infiltration calculation assumptions are based on the EN 15242 standard. 

Cove.tool is referring to the EN 15242 Annex B Table B.1 for a pressure difference of 4 Pa. The Air Changes per Hour can be edited via 'Baseline Energy' > 'Building System'.

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