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Industry bodies around the globe have made it clear that air movement is key when managing commercial buildings during the COVID-19 pandemic.

ASHRAE said disabling HVAC systems is not a recommended measure to reduce the transmission of the virus. What is needed is air control and proper ventilation.

The Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA) which represents a network of more than 120.000 engineers from 27 European countries, warned infection risk can be high in poorly ventilated spaces.

REHVA research and technology committee chair, professor Jarek Kurnitski, said the size of a coronavirus particle is 80-160 nanometres.

He said the particle remains active up to 3 hours in indoor air and 2-3 days on room surfaces.

“It is recommended to switch on ventilation systems a couple of hours earlier and also to extend operation,” Kurnitski said.

“A better solution is to keep the ventilation on 24/7, possibly with lowered (but not switched off) ventilation rates when people are absent in order to remove virus particles out of the building.

“In buildings with mechanical ventilation, window airing can be used to further boost ventilation.”

REHVA has warned against recirculation because virus particles in return ducts can re-enter a building in recirculation sectors of centralized air handling units. Thus, recirculation dampers have to be closed via the Building Management System or manually.

Kurnitski said decentralized systems such as fan coil units that use local recirculation should also be turned off to avoid resuspension of virus particles at room level.

Similarly, he said heat recovery devices may carry over virus attached to particles from the exhaust air side to the supply air side.

In rotary heat exchangers particles deposit on the return air side of the heat exchanger surface after which they might be resuspended when the heat exchanger turns to the supply air side. Therefore it is recommended to (temporarily) turn off rotary heat exchangers during SARS-CoV-2 episodes.

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