Recent surveys show that infection risk increases when there are large amounts of aerosols, classified as PM10PM2,5 and nanoparticles PM1 with dimensions respectively lower than 10 mm, 2,5 µm and 1 µm. Particles with larger dimensions coming from outdoor or indoor air can be a means of transport for the virus.

Under ventilated, occupied spaces can increase the risk of infection

Items that can decrease infection risk within occupied spaces, are the air renewal rate and the air filtration efficiency. In confined spaces that do not have air conditioning systems, ventilation can be achieved by the opening of windows (if possible). This does not guarantee air filtration and can cause occupant discomfort and energy waste.

Without a constant rate of air renewal, there could also be an increased risk of infection. This demonstrates the important role of a mechanical ventilation system, with controlled inlet of external purified and handled air and the extraction and expulsion of used air, above all during such a difficult pandemic.

ASHRAE, REHVA and national association guidelines suggest to increase as much as possible the renewal air inlet in existing installations and to assure correct pressure differences to toilet extract systems.

Clivet has developed CMV (Controlled Mechanical Ventilation) and DOAS (Dedicated Outdoor Air Systems) particularly suitable for easy installation in bars, shops, large and medium-sized sales areas, and restaurants. These packaged high efficiency systems do not need to be fed with hot or chilled water or refrigerant gas. Available with air flow rates from 125m3/h to 14.000m3/h, they allow heating, cooling and dehumidification to the renewal air, to automatically control flow rates, and to expel used air.

They also utilise the energy contained in the exhaust air through a thermodynamic heat recovery system that can obtain thermo-frigorific powers much higher than those obtainable from conventional heat recovery systems, thus being able to satisfy the thermal loads of cooling and heating during the mid-season. They have electronic filters that capture particles through an electrostatic field with minimum losses than can reduce the energy used by the fans. They also perform an ionizing action to the treated air, with an effective microbicidal action on bacteria and viruses. These filters are washable and do not require replacement.

Aware that each building has different air conditioning needs, Clivet offers several renewal and purification systems for commercial and residential applications, air handling units for hospitals, process industry, data centres, full fresh air systems, air renewal and air conditioning systems for medium and high attendance for commercial centres, multiplex cinemas, restaurants and kitchens. For houses with nearly zero energy need, the company offers an innovative packaged unit that renews and purifies the air, heats, cools and produces sanitary hot water.

Electronic filters are an efficient way to avoid the diffusion of bacteria, but are they efficient to limit the propagation of viruses too?

Electronic filters capture particles from 0,01 µm to 100 µm with a variable efficiency that depends on the speed of air that passes through them. With an average speed of 2,5 m/s they are classified according to UNI EN 16890 PM1 90% (efficiency higher than 90% on particles with dimensions lower than 1 micron) or PM2,5 95% (efficiency higher than 95% on particles with dimension lower than 2,5 micron).

Electronic filters also have a high microbicide power thanks to their high efficiency on sub-microbial particles.This is due to the destruction of the external membrane of bacteria/virus caused by thermoelectric shock when the ionized particles come in contact with the bulk blade located within the uptake section. The concentration of some common bacterias were measured before and after the electronic filter and the efficiency, certified by ILH Institute of Berlin, is between 98 and 99%. It is important to point out that it's possible to reduce the risk of COVID-19 infection in confined spaces,where there is an air conditioning system, an efficient air filtration system with a high air renewal rate, all combined with abiding by accepted rules of social distancing, hand and surface hygiene.