Outdoor Air Transfer in Zone air heat balance

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Hi,

Like a number of persons before me, I am trying to understand the zone air energy balance. I have some trouble to understand the Zone Air Heat Balance Outdoor Air Transfer Rate output.

According to the documentation : "It is the sum, in watts, of heat transferred to the zone air from all the transfers of air from the out side, such as infiltration"

The output is 0 when no "Zone Airflow" objects are declared

When I add "ZoneInfiltration:DesignFlowrate" or "ZoneVentilation:DesignFlowRate" (or both), the output is not null.

I was expecting :

Zone Air Heat Balance Outdoor Air Transfer Rate = Infiltration Total Heat Gain - Infiltration Total Heat Loss + Ventilation Total Heat Gain - Ventilation Total Heat Loss

(With Infiltration and Ventialtion converted in the appropriate unit and timestep)

However, I get variable and sometime strong difference that I can't explain :

• I cannot relate it to anything (schedule, temperature, etc.)
• The mean difference is not null
• The relative difference seems to be smaller with large ventilation flowrate

Do you know what I am missing ?

Thank you !