What are the key differences between HVAC systems and in-room devices for air cleaning?

HVAC systems are designed to provide whole-building air cleaning, whereas in-room devices are typically smaller, portable units that clean the air in a specific room or area. HVAC systems often have higher airflow rates and can be more effective at removing airborne pathogens, but may require more complex installation and maintenance. In-room devices, on the other hand, are often easier to install and maintain, but may not be as effective at removing airborne pathogens from the entire building.