Correctly positioned air purifiers complement regular airing

Shock and cross ventilation are ideal for a good exchange of air

Regular ventilation reduces the contamination of the room air with pathogens such as coronaviruses, creating a more hygienic atmosphere for the people in the room. Tilted windows, however, are not suitable for a sufficient air exchange between indoor and outdoor air. Shock ventilation is a better idea, i.e. opening the windows wide for a short time. Cross ventilation is especially effective: Opening windows or doors on opposite sides of the room creates a draught that exchanges indoor air particularly effectively. When the outside temperature is cold, the room temperature drops only slightly with shock and cross ventilation. It rises again quickly after the windows are closed.

In windowless rooms and crane cabins, however, no fresh air exchange is possible in this way, and ventilation through an open door can even be detrimental to room air hygiene. This is because it swirls up the aerosols and germs and spreads them within the building. For the same reason, circulating air mode should be switched off in air handling units (AHUs) that do not have virus filters. Adequate indoor hygiene cannot be ensured without regular ventilation. This means that windowless rooms are not suitable for larger groups such as school classes. Air filter devices are often the only way to remove virus-containing aerosols and other contaminants from the air.

Air purifiers complement active ventilation

As a complement to active ventilation, we recommend the Bundesumweltamt (German Environment Agency) mobile air purifying units. They can additionally reduce the viral load in a room's air and are useful, for example, if the occupants cannot maintain sufficient minimum distances, or if there are many people present. At the same time, the Federal Environment Agency points out that only devices with adequate performance data are adequately effective. The effectiveness of an air purifying unit depends both on the unit itself (e.g. air flow rate, installed filters) and on the conditions in the room where it has been installed.

The required air flow rate can be easily calculated by multiplying length, width, and height of the room where the unit is installed. The room volume is then multiplied by 6. This is because the filter device should circulate the air 6 times per hour for adequate reduction of the viral load. The result is the minimum flow rate per hour that the air filter device must provide. Depending on the installation location and transport requirements, features such as castors or handles can also be useful.

Fewer air obstructions ensure efficient air flow

Air filter devices should preferably be positioned in the centre of the room. If this is impractical or impossible, the device can also be placed near walls. A minimum distance from obstructions such as walls and large pieces of furniture should ensure that the intake air can flow into the air purifier unhindered. If the device draws in the room air from only one side due to its design, we advise a minimum distance of 30 - 50 cm from the nearest wall.

Air is slowed down easily and can only flow far into a room if no obstacles, such as beams, ceiling lamps, furniture and appliances, are blocking its way. Otherwise, it accumulates around the device and the outflow air is directly sucked in again. The air that is blown out is distributed most evenly in rooms with few corners. The outflow jet should never be directed at people, as this exposes them to unpleasant draughts. A high outflow opening or a diffuser is suitable to avoid draughts. In addition, the outflow jet should not cross any other air streams, such as those that may arise between the window and the door. Taking these requirements into account, an appropriately equipped air filter device reduces the viral load in every part of the room without restricting the comfort of the room occupants.