As the introduction of a vaccine in one form or another for COVID-19 is gradually introduced to populations around the world, restrictions will no doubt begin to ease and allow for working life to return to normal function.

The transition period in this process, however, means office workers will have to return to work with the virus still in circulation. The anxiety of whether working conditions are safe or not has caused a spike in interest in air filtration technologies to keep office spaces COVID-free. As a result, HVAC systems industries, which is short for Heating, Ventilation and Air Conditioning, face ten times their normal annual demand this year.

In a room which is confined with no office windows, a person who is sick can produce enough airborne virus particles to infect several others in the same room. The arrival of winter also means that opening a window, causing chilling conditions, holds little appeal. With the rise of modern thinking co-working space culture in both the East and West, packed shared work spaces mean effective ventilation with well thought-out passages of airflow are more important than ever. Getting this wrong can mean virus particles can be distributed throughout the building's AC system into other rooms full of unwitting recipients. This year, therefore, employers have had to step up their HVAC knowledge, whether it be in hospitals, schools or offices.

Raefer Wallis, a leading expert in the field, who also lived in China for many years working as an architect, stated "Most HVAC systems are designed to replace all the air in a building every 20-30 minutes, pumping used air outside and pulling in fresh. With COVID recommendations however, this is to increase to every 10 - 15 minutes." Air purifiers which can ventilate a room extremely quickly, alongside those that can filter out unwanted particles using absorbent materials, are called high-efficiency particulate air purifiers, or HEPA.

Experts admit that there is currently little research, however, clearly showing the link between filtration and ventilation and the transmission of novel coronavirus. However, they can infer what is known from similar viruses such as SARS. During the SARS epidemic, hospital authorities in Hong Kong recommended the use of HEPA filters to protect healthcare workers. In the United States, the Center for Disease Control also recommends the use of HEPAs if natural ventilation is not an option.

It is important to note that many of the same benefits achieved by air purifiers and filters can also be imitated by opening windows and doors, allowing natural fresh air currents to replace air with unwanted particles. The fact airborne droplets are the main way in which COVID seems to spread, rather than through surfaces, adds to the fact that just opening a few windows will do good, with very little effort.

In the meantime, those who are especially anxious or wish to pacify their employees have more expensive options in an industrial landscape which is constantly evolving. Ventilation and air conditioners now see China as their biggest market, and are yet another industry that is evolving to fit into the near post-pandemic world.

Barry He is a London-based columnist for China Daily