Do HVAC systems help to spread the COVID-19 virus? Ever since the pandemic first emerged, questions have been asked. In part, that is because of the two main ways virus particles are transmitted. Close contact transmission through large droplets released in coughs and sneezes is one common risk. The droplets do not have to fall directly onto a healthy person. The infection can be passed on simply by a healthy person touching a surface on which droplets have fallen, then touching their eyes, nose or mouth. The other is an airborne transmission. It occurs when smaller particles, emitted during coughs and sneezes, stay in the air for several hours. Research into a COVID-19 outbreak at a restaurant in Guangzhou, China, was evident in its conclusions. It found that droplet transmission was prompted by air-conditioned ventilation. But opinion is far from settled. Dr Maher Balkis, an associate staff physician of infectious diseases at Cleveland Clinic Abu Dhabi, has reservations. He concedes that air currents caused by AC could potentially carry droplets further than they might naturally travel. But he insists there is not yet a firm link between the spread of COVID-19 and air conditioning systems.
What does this all mean for HVAC operators trying to provide the best and safest service to their clients in the Middle East?
There are several factors to consider. In hot regions like the Middle East, air conditioning is critical. Yet it consumes enormous amounts of energy, so traditionally focus has been placed on heat recovery in ventilation systems. Significant results can be achieved by recovering energy from exhaust air and using it to cool the incoming air. That is why heat recovery wheels have been so popular across the region. This ‘green’ approach to air conditioning has several benefits. Apart from lowering energy bills and carbon emissions, it also reduces installation and running costs. It can also result in smaller sizes of chillers and fresh air handling units. Energy efficiency becomes even more critical under COVID-19 guidance issued in April 2020 by REHVA, the Federation of European Heating, Ventilation and Air Conditioning Associations. The organization confirms that virus particles are best removed through continuous circulation. Therefore, REHVA urges operators to replace recirculation with increased air supply and exhaust ventilation. So while the wheel remains one of the most efficient methods of heat recovery, the most pressing issue today is whether it also promotes the spread of virus above other HVAC systems.
Do heat recovery wheels recirculate COVID-19 particles?
- In general, no. When installed and maintained correctly, heat wheels with purge sectors prevent the transfer of almost all virus particles.
- Leakage rates on well set-up rotary heat exchangers are similar to plate heat exchangers (1-2 percent). The most significant risk is from air leakage in older equipment, which is why proper maintenance is crucial.
- A heat wheel can remain in operation if it serves only one space, according to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).
- If the unit serves more than one space, more caution and careful assessment are necessary. The risks of the device continuing to operate should be carefully weighed against the benefits of shutting it down.
Best practices for using heat recovery wheels.
REHVA makes it clear in its guidance that there is no need to switch off rotors. No proven case exists of virus particles being transferred in carry-over leakage. The Federation outlines three broad principles to using a heat recovery wheel during COVID-19. These are:
- Keeping leakage rates below 5% and compensating with an increase of outdoor air ventilation according to EN 16798-3:2017.
- Ensuring wheels are correctly mounted. There should not be higher pressure on the exhaust airside.
- Correcting any pressure difference with dampers. Maintenance personnel should follow standard safety procedures of dusty work.
There are some common features in a quality heat recovery wheel. These typically boast REHVA-recommended purge sections, but also 3A molecular coating for anti-microbial properties, and a selection of independent hygiene certificates (VDI 6022, SWKI VA104-01). Or at least, that’s how we approach safety in wheels at Swiss Rotors.
About the author: Lech Lakomy, almost 30 years of experience in the HVAC industry. He’s worked at all organisational levels–from a specialist to a COO of an AHU manufacturer. At Swiss Rotors, he is in charge of business development in the EMEA region, focusing on forging strategic alliances in the UAE and Europe.