One of my colleagues passed on some useful information from the Federation of European Heating, Ventilation and Air Conditioning Associations regarding HVAC and COVID-19.
It brings up valid questions regarding the use of typical split unit aircon systems, which simply refrigerate the air in a space, and do not introduce fresh air into it. Obviously more substantial fresh air systems do exist on the temporary market, but introduce a far greater level of infrastructure requirements, void sizes, and potential noise issues into otherwise quiet spaces such as meeting rooms.
The guidance also recommends turning systems on 2 hours before a room is occupied and keeping them on 2 hours after a room is vacated.
On large scale events we have a great deal of experience deploying "spilt" and "fresh air systems", fresh air systems generally are more environmentally natural and less noticeable extremes in the feeling of temperature. As you mention Alex the down side of any HVAC system on events is a clients being un willing to release real estate back of house and front of house to land and accommodate plant. This generally leads to a compromise in design. Comiting bigger air handling solutions could be a a way forward where budget permits.