The problem

The recent COVID-19 pandemic has highlighted the risk of transmission of airborne pathogens and the requirement to be able to mitigate the risk within the workplace or public spaces using existing air handling and filtration units.

The SARS-COV-2 virus is now considered to spread primarily through the breathing of infected droplets and aerosols in the air. Although there has been limited evidence on the minimum infectious viral load for the COVID-19 pandemic.

Data suggests that over 94 percent of COVID-19 ‘superspreading’ events occurred in limited ventilation areas, supporting aerosolised transmission as a strong contributor to COVID-19 infections. Aerosols containing a virus can remain suspended in the air for an hour or more and the level of exposure to the SARS-COVID-2 virus affects both the likelihood of infection and the severity of illness.

The risk of transmission from an individual with SARS-CoV-2 infection varies by the type and duration of exposure and appears highest with prolonged contact in indoor settings. Despite proper Personal Protective Equipment (PPE) such as face masks, the virus has been reported to spread in hospitals and non-hospital congregate settings.

Increased demand necessitates newer methods to reduce the risk of spread through circulating air. UVC is highly effective, relatively inexpensive, and can be adapted to the current HVAC systems (Heating, Ventilation, and Air Conditioning). We describe the important role and effectiveness of Sanuvent™ which uses UVC.

Sick Building syndrome (SBS) is estimated to cost the British economy 24.6 million lost working days every year.

A report by the World Health Organisation determined that as much as 30 percent of new re-modelled building around the world could cause sick building syndrome symptoms. The ineffectiveness of current technology will only increase the threat of pathogen transmission. Today we are dealing with COVID-19, but what is next? Some existing air handling units (AHUs) re-circulate up to 85% of the returned air from the building to reduce the heating/cooling load of the fresh air coming in. Modern AHU systems use either plate to plate of thermal wheel heat recovery to extract the heat from the exhausted air.

Here lies the problem: Even with new modern AHUs under Health Technical Memoranda (HTM) guidance, with air leakage rates being less than 4%, cross contamination of the exhaust to fresh air is still possible! However according to BESA heat recovery units could typically have internal leakage rates of 8-10% thus making the risk greater.

Guidance as recommended by BESA for occupied buildings, larger dilution rates of fresh air are required to help mitigate COVID-19 and flush out buildings, this can be up to 2-3 times the normal rate. This will significantly affect the building efficiency increasing AHU running costs in energy, wear and tear, and further energy consumption costs of up to 45% could be required to heat and cool the fresh air.

Alternative uses of transmittance prevention like HEPA filtration to reduce odour and bacteria, down to 0.3 microns, in principle is a good idea. However, it is ineffective with COVID-19 particles as these are much smaller, these filters also create additional resistance to the system potentially reducing the airflow and fresh air dilution effectiveness.