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To manage a highly transmissible disease such as Covid-19, medical facilities have used multiple methods to increase air exchanges in rooms and spaces.
One high-tech solution used in some hospitals in the US is converting rooms – or entire floors – into ‘negative pressure spaces’ with mechanical ventilation, run by a building management system, which maintains lower air pressure within the area than that in the rooms or hallways outside it. Air naturally flows from higher pressure areas to lower pressure areas, preventing contaminated air from the isolation room escaping outwards.
A less high-tech and cheaper method is to install a HEPA filtration system into HVAC systems. However, this can affect air distribution, so it’s important that HVAC systems are designed with enough fan power at the air handling units (AHUs) to support their use. Alternatively, HEPA filter racks can be installed that are only deployed in a pandemic situation, saving on operation and maintenance costs.
AHUs can be engineered to manage dual conditions for heating and cooling coils: minimum outside air intake for normal conditions, and 100% outside air for pandemic and emergency conditions.
High-intensity UV lights or similar air-treatment systems can also be used to help keep cooling coils clear of biomass. They can also be installed in the ducts to kill virus particles in the air flow.
Shock of the pandemic
Bill Anderson, director of Puravent, provider of UV air-purification systems, said: “This isn’t a new technology but, although it’s commonly used in humid countries in the Americas and Asia, it’s relatively uncommon in the UK.
“We were horribly unprepared for the Covid pandemic. Countries like Singapore learned lessons from SARS, for example, but the UK did not implement UVC treatment systems despite the technology being proven and mature.”
Advice from SAGE says that the UV in air purification is unproven and risks oxidising agents being released into the air. However, Anderson countered: “The efficacy of UVC air and surface purification has a research history measured in decades. If only SAGE officials could appreciate that UV splits into different bands which each have different characteristics.
“Before issuing incorrect advice, they should know that mercury vapour lamps made with quartz casing emit a tight output of germicidal UVC light at or near 254nm wavelength which doesn’t create ozone. Broad spectrum UV lamps, typically with glass casing, produce shorter wavelengths which create ozone. In small doses ozone can be useful in certain applications; however it’s a dangerous gas and should be avoided in occupied spaces.”
Official advice
Government advice states that in addition to opening windows and doors, it’s important to make sure mechanical ventilation works properly and that systems and does not recirculate indoor air. IMechE’s Covid taskforce believes HEPA and UV-C systems are good low-cost soluations in the short-term.
Jenny Smith, head of marketing at Vent-Axia, said: “There are some simple steps businesses can take to help minimise virus transmission risks. The first is to undergo a risk assessment to ensure their premises are adequately ventilated. Ventilating for longer and opting for ventilation with higher airflow volumes will also help reduce the risk.”
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.