HEPA or High Efficiency Filtration is NOT the Complete Answer
HEPA filter has very limited airflow capacity, and it can not be used for the filtration of the main airstream for any regular forced air systems serving buildings due to its high resistance to the airflow. Regular MERV 13 & pleated filter has very limited capacity to intercept SARS-Cov-2 with a size range of 60nm ~ 140nm (0.06 ~ 0.14 microns). The regular filter may intercept large droplets containing the virus, but the virus will eventualy break-off and escape the filter as RH humidity drops and temperature rises near the heating equippment.
Ventilation Airflow Rate is limited by HVAC Systems' Equipment Capacity
The FDA do NOT authorize the use of Ozone " in any medical condition for which there is no proof of safety and effectiveness". In any cases, the business reopening guidelines and restrictions from local authority, health departments must be followed. Increase outdoor air Ventilation, espercially the replacement ventilation, is the most effective means to control the indoor air quality. However, outdoor air ventilation comes with high energy cost, and almost any HVAC system will not have sufficient heating / cooling capacity for the increased outdoor air ventilation in both Summer and Winter seasons. We only have limited HVAC systems that are designed to handle 100% outdoor air, such as HVAC system serving O/R rooms in the hopitals. As weather gets cold, the HVAC system capacity will soon be maxed out if outdoor airflow rate is increased. Furthermore, the relative humidity will drop significantly when the O/A flowrate is increased for HVAC system serving building in cold climate zones. The lower RH level in the building, the easier the virus will spread.
Controlled Ozone (O3) is the key to disinfect indoor space, and turning indoor space to outdoor space while maintaining comfortable Temperature, RH value in the occupied indoor space. WH Engineering has developed an unique approach to disinfect whole indoor space with ultravoilet (UV) light and controlled ozone (O3) content in the air for specific duration in specific time. It provides proofing result by comparing the Ct value (before and after of the RT-PCR test) for suspended airborne virus content in the indoor space.
Reminder UV light and controlled Ozone treatment for the building must be carried out by the professionals with extensive knowledge about building HVAC system, and Indoor air Quality, and the nature of the infectious coronavirus disease _Covid-19. The treatment process may involve in air system and air flow control, building automation system override, time frame planning, airflow purging after the Ozone (O3) treatment...etc. The remaining O3 content in the air must drop to the safe level prior to the space occupancy.
UV light & controlled ozone content solutions must NOT replacement other required pandemic control measures: such as physical distancing, face masks protection, hands washing, occupancy limit...etc.

WH Engineering will monitor the Ozone (O3) content in the whole process very closely, and ensure Ozone (O3) guidelines, standards from following organizations are strictly followed: EPA, WHO, NOISH, ASHRAE, Health Canada and Ontario's Ambient Air Quality Criteria (AAQC)... As a mater of the fact: The actual outdoor air O3 contents is always higher than the indoor ozone content in the guidelines, expercially the eight hour exposure guidelines.

O3 is the most effective ingredient to inactivate virus in the air and on surfaces (maybe on the surface of human lungs as well). Outdoor O3 is produced by the sunlight, when the Vacuum UV (100~200nm wave length) light knocks off the single O from O2, NOx, VoC etc... NOx and VoC contribute smog, but not O3. O3 is the byproduct from the process when sunlight breaks down the NOx & VoC etc...

Important FACT

O3 in the air will oxidize lots of materials, including virus it collides with. It will turn into O2 and dissipate within 1/2 hour to maximum 4 hours. Excessive ground-level O3 in the air will cause chest pain, throat irritation & air way inflammation, bronchitis, emphysema etc...
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