# Is there a way to convert ZoneInfiltration:DesignFlowRate to an equivalent AFN object?

In EnergyPlus, the ZoneInfiltration objects are not calculated when using the AirflowNetwork (AFN) for the MultiZoneWithoutDistribution control (amongst others). In a previous post[1] it's been suggested that the way to model infiltration in the AFN method, based on the ZoneInfiltration object, is to replace the infiltration objects with enough AFN leakage to get the equivalent infiltration amount of the ZoneInfiltration object. Is there a calculation to figure out this type of conversion out mathematically?

For context, I'm working on a software project where our zones all contain ZoneInfiltration:DesignFlowRate objects, using the Flow/ExteriorWallArea calculation method[2]. So we have the volumetric flow rate m3/s-m2, schedule, constant, temperature and velocity coefficients already defined. We want to include an option to use the AFN for mixed-mode, or purely passive cooling. When this translation is done, we'd like the infiltration rates to be equivalent (or somehow logically translated) from our ZoneInfiltration objects.

Does a formula/look-up table exist to convert the DesignFlowRate to an AFN leakage component, like the AFN:MultiZone:Surface:Crack or AFN:MultiZone:EffectiveLeakageArea objects?

Assuming constant value for exterior air infiltration is already a way to model the phenomenon. I guess that the values you are using are derived from an "airtightness indicator" such as N50 (Vol/h @50Pa) or Q4Pa (m3/h.m²@4Pa) for example. If yes, you could use it to compute and create EffectiveLeakageArea objects.

Good to know, thank you. At this point I'm trying to derive the Crack factor, but maybe in the future things might change to the ELA.