Does Air-conditioning spread Covid-19?

A case study of a restaurant in China.


The truth of the matter is in the failure of the Air-conditioning systems (A/C) not ventilating and filtering the circulating indoor air.


In this case, ten seated at the back of the restaurant became sick, while those seated at the front were not affected. One infected person through respiration (normal breathing or sneezes) releases droplets in the air, carried along by the A/C stimulated air movements, re-circulated within the grey area at the back, and people seated in proximity were exposed.


There were four ductless split units without fresh air features, with only one (1) air inlet at the far front end of the premise and one (1) exhaust outlet but close-up inside the toilet.  So, there was no exhausting and fresh air to ventilate the indoor air.


The time-averaged ventilation rate per person in that restaurant was 0.9 L/s (less than 2CFM). Based on ASHRAE’s 62.2 standards, the suggested minimum per person is 7.5CFM which was way too low.



Sealed-up air-conditioned building traps pollutants indoors that needed to be diluted with outdoor fresh air, O2 while exhausting the high pollutant (PM2.5, CO2, VOC, Formaldehyde) indoor air to balance indoor air pressure and create air movements. Indoor air is normally more polluted than outdoor in a natural conditions, but not so in an urban industrialized environment. The rising concern is about whether the outdoor fresh air has lesser discrepancy i.e., particulate matter, germs, humidity, and temperature when brought into an air-conditioned sealed environment.


Fresh Air System is part of HVAC on ventilation, which is gaining attention from local authorities predominantly related to compliances for buildings and business premises related to ‘Sick Building Syndrome’ and COVID-19 precautions. It is an inevitable application for comfort and occupants’ health and safety. There are many applauded professionally written research out there that can be intimidating to the public and users. Hence, this presentation is a snippet overview of the Fresh Air System to assist in general decisions making.


Minimize the spread of Coronavirus. What can SMEs and Homeowners do?


  1. Can filters catch Airborne bacteria and viruses (Microorganisms)?

  2. Are UV lights effective in killing germs?

  3. What’s humidity control got to do with fresh air?

  4. What is a Fresh Air System and ERV?

  5. What other options do we have?