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I choose to use air-flow ventilation systems, and I added the supply duct and air supply diffusers to my mechanical building model. Below is a overview 3D view of my HVAC system.
I added a mechanical room containing an air handler on every floor to supply the air needed for the HVAC system.
First, I ran the heating and cooling load analysis in Revit:
Each space's use was identified, for example, the “Space Type” of Level 1 Gift Shop is “Department Store Sales Area - Retail”. All the types of spaces were “Heated and Cooled”.
After running the load report, I now have a reference required air flow number for every space.
For example, the calculated supply airflow needed was 1206 CFM, and the default airflow of each air supply diffuser is 500 CFM. So, in total, 3 supply diffusers were required for this space.
After adding all the airflow supply diffusers, I then use duct systems to connect them. The ducts have a “Upper End Top Elevation” of 14 ft, and the diffusers have an elevation of 13 ft. Each level in this building has a height of 15 feet, so the ducts and diffusers will then have enough space.

Challenges:
My floor plans for every level are very different, and thus I have different HVAC plans for every level, which increased the workload and complexity.