What are the officially recognised ways of human-to-human transmission and what relation is there with HVAC systems?

The WHO officially recognised transmission routes are: 1) By close and direct contact with an infected person; 2) by contact with surfaces contaminated by the virus with hands that later unconsciously touch mouth, nose or eyes; and 3) By inhalation of liquid droplets produced by the infected person. According to these officially declare transmission routes, HVAC systems do not any direct relation with the COVID-19 pandemic. However, HVAC systems in ICU in hospitals play a vital role as an engineering control for any airborne contaminants, including virus in droplets.