One of the challenges when using VRF is integrating ventilation or outside air. There are different ways to bring in outside air.
The most straightforward way to bring in outside air through a dedicated outside air system, or DOAS. As the name implies, these are basically specialized rooftop packaged units whose only job is to bring in and temper fresh outside air. The main downside to this is that it will require its own ducting system and you’ll have to find a way to integrate it into the space; either mixing with the comfort cooling system, or by dumping it directly into the space.
Another way to do this is to do what I took of picture of here. Many cassette fan coils have a small perforated hole on the chassis that you can punch out and bring in a duct to introduce outside air.
I always have to preface this by saying it is a SMALL amount of outside air, typically 3–5% of the nominal airflow of the cassette and it will be untempered and unfiltered. But in some cases, it makes sense. I saw this in a brewery in Oakland and it was close to an outside wall and in the Bay Area, the climate is generally mild.
I had to take a picture while enjoying a beer since it was the first time I saw the OA knockout being used.