Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
It all depends on the zoning. If the toilets are part of a larger zone that includes exterior openings, then the makeup air is likely to come from outdoors due to additional infiltration. In that case, ZoneVentilation is fine to use.
If the building is zoned so that the makeup air is coming from adjacent zone(s), then use ZoneMixing to move air from one zone to another. For the receiving zone (toilet), an equal amount of air is assumed to leave the zone without any additional input. For the supplying zone, make sure there is enough infiltration (or HVAC outdoor air) specified to make up for the air going to the toilet zone.
And it gets a little more complicated when modeling the HVAC system.
