In February this year – what seems like a lifetime ago in the fast-moving world of Covid-19 – Harvard University professor Joseph Allen wrote in the Financial Times that building ventilation systems could be either a blessing or a curse in the effort to contain the novel coronavirus.
Professor Allen, co-author of ‘Healthy Buildings’ – a seminal book outlining how to commission, design, manage and use buildings to maximise people’s well-being – said: “The 1918 Spanish flu pandemic, measles outbreaks in schools and Sars all show that living conditions can play a critical role in the spread of disease. But if buildings can make things worse, they can also make things better.
“We don’t fully understand how the new coronavirus is transmitted yet… Even with this uncertainty, it is clear that we can enlist buildings to help us in this fight.”
…Or can we? So far, there have been no proven cases of person-to-person transmission of Covid-19 virus from air passing through ducts, according to Peter Dyment, technical manager at air filtration giant Camfil. However, he adds: “Swab tests by scientists from the Singapore National Centre for Infectious Diseases have found traces of the virus in an hospital isolation room exhaust air duct. This shows the virus can be carried by particles in air.”
The recent reports of research from Singapore seem to suggest from finding traces of the virus in an air duct connected to the room of a patient who had tested positive for the virus, that the natural conclusion was that the virus was being transferred via the air flowing through the duct.
But Graeme Fox, head of the Register of Companies Competent to Manage Refrigerants (REFCOM) and BESA Technical, disagrees strongly. According to Fox, a chartered engineer with more than 30 years’ experience of building services engineering, such reports are unhelpful. “Not only is this unscientific because it does not consider the distinct probability that someone has touched the outlet grille and left the trace amount there, but the scaremongering this creates is also unhelpful to those trying to get to grips with the reality of the situation,” he contends.
He adds: “Having said that, any airborne contaminants can be minimised, if not eliminated, by proper and effective filtration and regular cleaning and maintenance of ventilation systems.
“A clean ventilation system is an essential part of a healthy building and it is essential that any ventilation system serving a building where confirmed cases have been diagnosed are sanitised in accordance with best practice, and that any buildings where no cases have been confirmed have their ventilation system cleaned to industry best practice as a preventative measure during this time and in future.”
Camfil’s Dyment points out that the Covid-19 virus is exceptionally small (about 0.16 micron diameter) and is transported inside aerosol droplets projected by an infected person into the air surrounding them via coughing or sneezing.
“These droplets travel widely and can carry the virus effectively when in the 0.5 micron to 15 micron diameter size range. Recirculated air in a confined space will give an increased risk of infection rather than supply air from outside. Risk of virus transmission in HVAC ventilation air systems can be reduced by use of air filters capable of removing these virus-ridden aerosols from the airstream," Peter Dyment, technical manager at air filtration giant Camfil
Effective particle filters can play a key role in capturing airborne aerosols, but they must meet certain standards. The recommended particle filters are efficiency class ‘ePM1 80%’ filters performance tested to BS EN ISO 16890:2016. This means using high capacity filters that separate at least 80% of particulate matter (PM) sizes of one micron in diameter or below.
These filters must be properly fitted into an air handling unit with mounting frames that have a low air leakage rate. Dyment adds: “Where air systems do not have a recirculation capability, then standalone air purifiers and air cleaners can be used clean the air at point of need.” He adds that air monitoring of particle concentrations is also important to check that air is being cleaned to the required level so that it can be inhaled without risk to health.
James Gafford, air handling unit (AHU) specialist contracts manager at multi-specialist engineering contractor ECEX, explains that the air in many commercial ventilation systems is recirculated to maintain temperature: “Luckily, coronavirus requires fairly close proximity to survive transfer, so even ventilation systems running on very high recirculation levels are unlikely to spread the virus throughout a building.
|“That being said, the rapid spread of coronavirus has raised awareness of the wider need for cleanliness and regular disinfecting of surfaces to ensure precautions are taken to limit the transfer of all types of virus, and airborne viruses like colds and flu can easily be spread through a building by a recirculating ventilation system," James Gafford, air handling unit (AHU) specialist contracts manager at ECEX|
Of course, the UK government has effectively locked down the country, banning people from attending non-essential work. However, key workers in hospitals and other facilities are still required.
For Gafford, the simplest ‘fix’ for ventilation systems in these premises is to shut all recirculation dampers and run the systems on full fresh air/full exhaust, with all air being replaced in a building every 10 minutes (although he admits the increase in energy demand for maintaining comfortable temperatures would be unacceptable for most businesses, especially at this time of year).
“The remaining option,” he says, “is to disinfect the air and surfaces inside the ventilation systems, either through regular manual cleaning or through the use of automated UV-C lighting systems. These can be retrofitted into existing ventilation systems and constantly work to kill bacteria and virus growth on surfaces, especially on cooling coils where moisture is taken out of the air through condensation and collects on surfaces and in drain trays.”
Virologist Dr Rob Lambkin-Williams of consultancy VirologyConsult.com has developed and supervised multiple clinical studies for large pharma, biotechs, the US and UK governments. For him, the risk from HVAC systems is small because they circulate air.
“Airborne transmission is not the major issue… [The virus] is caught by somebody coughing or sneezing and that can spread out to about 2m. Most comes out in the first 0.5 to 1m in large droplets and then sticks to surfaces and people touch these and then touch their faces.”
However, he adds: “All companies should have in place a maintenance schedule as part of their standard operating procedures. If they have an opportunity to bring that forward, then they should.”
David Cook, technical product manager at Vent-Axia, agrees: “With the challenge we are currently facing with Coronavirus, now is the time to follow best practice guidelines when it comes to the maintenance of HVAC systems to help ensure buildings are as healthy as possible.
“Even though many people are now working from home, it’s essential that workplaces are in good shape for when everyone returns to work. This means keeping ventilation systems clean; checking that filters are clean and whether they need replacing; making sure ventilation systems are well-maintained and ensuring that a building is sufficiently ventilated to at least meet minimum ventilation levels.” (See large box out for more information).
|Box: Fighting the virus|
Experts at REHVA (the Federation of European Heating, Ventilation and Air Conditioning Associations) have drafted a guidance document on how to operate and use building services in areas with a Coronavirus outbreak to prevent the spread of Covid-19. The document considers the best available evidence and knowledge to date, using a Dutch literature review elaborated by Dr Francesco Franchimon, complemented by international REHVA experts as a joint effort. Because of the ever-changing information about the disease, the document will be updated as becomes available.
|Box: Maintaining a ventilation system|
Ventilation systems must be serviced regularly to ensure the system runs at optimum efficiency and provides good indoor air quality. Regular servicing also helps to avoid costly repairs and reduces running costs, as well as making a system last longer and operate more quietly and efficiently. Servicing includes cleaning the filters and replacing them when necessary; cleaning air valves and inside and outside the unit; product inspection and installation inspection.
Some ventilation systems, such as demand energy recovery ventilation and mechanical ventilation with heat recovery, not only extract harmful pollutants but also direct the air coming into the building through filters, removing harmful airborne bacteria and dangerous contaminants.
Vent-Axia’s David Cook says: “It is important to opt for higher-grade filters and to maintain them. Dirty filters will affect the efficiency of the ventilation system which reduces its effectiveness.”
Increasing ventilation rates can improve the healthiness of a building, Cook adds: “It makes sense that increasing the ventilation rates will improve the indoor air quality (IAQ) of a building. Increasing ventilation rates does seem to conflict with current energy efficiency targets; however, a healthy environment for occupants should be the most important factor, especially with the current risk of Covid-19.”
Contractors’ group the Building Engineering Services Association has an expert group looking at the expanding issue of health and wellbeing in buildings and the links between IAQ and health. David Frise, CEO of BESA, says: “The threat to human health posed by indoor pollution is immediate. This is not something that can wait for a policy change in 15 years’ time – and the present threat from Coronavirus should be the ultimate wake-up call.”
BESA group member Richard Greenwood of Radic8 adds: “Viruses attach to particulate matter in the air and when they hit a filter, they break up. Some stick to the filters, others get trapped in the membrane and some get through. Filters allow time for other technologies such as UV radiation to destroy the DNA of viruses.”