Modeling zone internal air mass load in internal mass

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How do you model the load effects of a zones internal air mass? I would like the "Convection Heat Gain Rate" of the air mass within the zone. Is this done in the internal mass class like the physical internal mass objects?

To model furnishings and partitions in internal mass, you create an object in the internal mass class where the construction type is furnishings and partitions. How is this done for the air in the zone?