Air purifiers with HEPA filters protect against flu

Breathing clean, healthy air free of airborne pathogens is an achievable goal. Modern commercial air purification systems can effectively eliminate or reduce airborne viruses, allergens, and pollutants. They have therefore become a practical solution for nursing homes and hospitals, where vulnerable people need special protection, or in schools and workplaces, where flu season can significantly affect productivity.

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What does air purification help with?

Depending on capacity and filter type, air purification helps to reduce or eliminate the following:

• Airborne viruses (including COVID-19)
• Bacteria and germs
• Pollen and allergens
• Mold spores
• Unpleasant odors
• Smoke and VOCs (volatile organic compounds)
• Dust and fine dust

Air purifiers are ideal for environments where people spend a lot of time and clean air is crucial – for example, in hospitals, schools, offices, or catering establishments.

During flu season, older people are particularly at risk, and businesses suffer from absenteeism and loss of productivity because employees or their children are sick. For this reason, many companies and public institutions offer vaccinations and provide hand sanitizers. The use of air purifiers can also help to curb the spread of airborne diseases and protect general health. During the COVID-19 pandemic, air purifiers became very popular as an additional measure to contain the spread of the virus:

Even if the coronavirus no longer poses an acute public danger today, we can use the knowledge gained during the pandemic to prepare ourselves for similar viruses. By focusing on viruses, we set the bar high – because they are among the smallest particles in the air and are much smaller than bacteria or mold spores.

Air purifiers help keep the room warm

The usually recommended method to remove viruses from indoor air is regular ventilation by opening windows. However, since flu season coincides with the cold season, this is not always an energy-efficient solution.

Air purifiers draw in contaminated or polluted air and release purified, warm air back into the room. This helps to save heating energy. Modern air purifiers for home use can be very energy-efficient – with a power consumption of less than 0.2 kW at an air volume of over 1000 m³/h.

How does air purification work?

Professional air purifiers continuously draw in stale air, filter it through several filter stages, and release it as clean air back into the room. Key components include:

• Pre-filters trap coarse particles such as dust and hair.
• HEPA filters retain microscopic particles such as viruses, bacteria, and allergens.
• Optional activated carbon filters absorb odors and chemical pollutants.
• UV light or thermal disinfection inactivates infectious organisms.

Unlike ventilation systems that supply outside air, air purifiers circulate and clean the existing indoor air. This is a very energy-efficient method – especially in the colder months, when ventilation through open windows leads to heat loss and higher energy costs.

Note: It is still advisable to ventilate the house regularly and let in fresh air, especially in winter, to remove excess moisture. However, with an air purifier in the room, you don't have to exchange the air because of particles.

Is the effectiveness of HEPA filters proven?

HEPA is an abbreviation for “High Efficiency Particulate Air”. According to the US Environmental Protection Agency (EPA), HEPA filters can theoretically remove at least 99.97% of all dust, pollen, mold, bacteria, and other particles 0.3 micrometers (µm) in size from the air. The coronavirus is 0.1–0.5 µm in size, while a bacterium is 1–3 µm.

The higher the HEPA number, the smaller the particles it traps.

Example of an air purifier: AirgoClean One from Trotec – a brand of the Dantherm Group

Removing the top of the air purifier:

Air outlet:

Carbon filter:

HEPA filter:

The filter traps particles and must be replaced regularly. To inactivate trapped viruses, bacteria, and other pathogens, the air purifier should be equipped with a special hot air disinfection program or UV light.

How does thermal disinfection work?

According to a study published in The Lancet in 2020, the SARS-CoV-2 virus remains stable at low temperatures. However, as the temperature rises, the time until it is no longer detectable shortens significantly:

• At 22 °C, it is no longer detectable on a surface after 14 days.
• At 37 °C, it is no longer detectable after 2 days.
• At 56 °C, it is no longer detectable after 30 minutes.
• At 70 °C, it is no longer detectable after 5 minutes.

Air purifiers exploit this weakness of microorganisms by using heat: aerosols containing viruses and bacteria are filtered out. The heat-resistant filter is then periodically heated to approximately 100 °C for about 15 minutes. This denatures the viruses, rendering them harmless. This process runs fully automatically at a desired time – for example, once a week at night, outside of office or school hours.

Thanks to the short heating intervals, energy consumption is low and the room temperature remains unchanged. In addition, this process also prevents the formation of bacteria, biofilms, and unpleasant filter odors – without any chemical additives or UV-C radiation.

Why UV light should be avoided

Although microorganisms are also sensitive to UV light and some air purifiers have this function, there are certain challenges when integrating UV light into mobile devices. UV light can cause eye and skin damage and must therefore be completely shielded – which is difficult to ensure in practice.

In addition, the air must be exposed to sufficient UV intensity and for a long enough period for microorganisms to be reliably inactivated. However, in mobile air purifiers, the fans usually move the air too quickly for the UV light to have an effective germicidal effect.

How ozone generators disinfect

Viruses and bacteria are not always present in the air – they can also settle on surfaces and be transmitted through touch. Ozone generators are therefore a useful addition to air filter devices, as they reliably inactivate pathogenic microorganisms throughout the room.

Ozone is a toxic gas and, due to its gaseous form, has the great advantage over other disinfectants that it distributes evenly within a few minutes – even in hard-to-reach areas. This allows surfaces to be effectively and quickly decontaminated without the need for additional disinfectants.

Ozone generators mimic the natural formation of ozone during a thunderstorm. Using high-voltage current, oxygen molecules (O₂) are split into individual oxygen atoms. These then combine with other O₂ molecules to form ozone (O₃).

Areas of application include air purification and general disinfection in cars, homes, hotel rooms, or offices. However, since ozone is a toxic gas, it can cause respiratory problems. Therefore, ozone generators must never be used in occupied rooms. The room should be well ventilated, and people and pets must stay out until the ozone has dissipated (usually 30 minutes to several hours, depending on the concentration).

Ozone generators are available in different designs and sizes depending on the application – from handy devices for cars to powerful models for large rooms.

Trotec ozone disinfection device – a brand of the Dantherm Group

What is CADR?

Another metric frequently used for air purifiers is CADR, which stands for Clean Air Delivery Rate. This metric indicates how much filtered air is delivered per minute (CFM) or per hour ($\text{m}^3/\text{h}$). If the CADR value is too low relative to the room size, the air purifier will not be effective.

CADR is tested for three particle sizes:

• Smoke (~0.1–1 µm)
• Dust (~0.5–3 µm)
• Pollen (~5–11 µm)

A higher CADR value means faster and more effective air purification. The CADR value of an air purifier should be at least two-thirds of the room area. Example: For a room of 60 m², an air purifier with a CADR value for smoke of at least 40 is required.

For most users who don't want to do calculations, however, the recommended room size of the respective air purifier is the decisive metric.

Where are air purifiers used?

Thanks to their high efficiency, HEPA filters are used in particularly demanding environments – for example, in the pharmaceutical industry, in sensitive semiconductor manufacturing processes, or in hospitals to reduce the risk of virus transmission.

Today, air purifiers are widely used in many industries, for example:

• Healthcare – Hospitals and clinics use air purifiers in waiting rooms and patient rooms to reduce the risk of airborne infections and increase patient safety.
• Education – With over 76 million pupils and students in the EU, air purification can make an important contribution to public health by creating a safe learning environment – without losing heating energy through window ventilation.
• Workplaces – Offices benefit from virus-free air, leading to fewer sick days and higher productivity.
• Retail – Shops and supermarkets use air purifiers to protect customers and employees. A clean, safe atmosphere can also be an important argument for particularly vulnerable customer groups.
• Hospitality – Restaurants and hotels use quiet air purification systems to eliminate odors and create a pleasant, healthy environment.

By using air purifiers, catering establishments and workplaces can advertise clean air as an advantage for customers and employees, just as thermal disinfection devices can be advertised for insect-free rooms.

As a supplement to the air purifier, you can place a particle counter in the same room to monitor air quality.

Are air purifiers energy efficient?

Compared to alternatives such as ventilation through open windows in the cold season, air purifiers are very energy efficient. Air purifiers clean and recycle existing indoor air, thus reducing heating costs.

What types of air purifiers are there and which one should you buy?

Not all air purifiers are the same. With the wide range on the market, it is not always easy to find the right model for your purpose. Some rules of thumb can help with the decision:

• Is it portable? For businesses, a floor-standing model with sufficient airflow is recommended. Smaller devices are often not suitable for larger rooms. Portable air purifiers can be used flexibly where they are needed – for example, briefly in a meeting room and then back in the office. Look for sturdy castors and a practical handle.
• Know your particle sizes! Those who want to protect themselves from bacteria and viruses should look for a device with HEPA H14 filters – these have proven particularly effective against viruses.
• Enough power for your room size? The airflow should be 3 to 5 times the room volume per hour. Example: A classroom of 5 × 8 × 4 meters requires an air purifier with an airflow of at least 480–800 m³/h.
• Does the device have disinfection capabilities? Viruses are heat-sensitive. Some devices work with heat or UV light. Alternatively, an ozone generator can also be used.
• App control available? If you operate several air purifiers, you save a lot of time if they can be monitored and controlled centrally and remotely.
• How high is the noise level? In production areas, this plays a minor role. In bedrooms or catering establishments, a model with a silent mode of around 38–40 dB(A) is recommended. For comparison: Normal conversations are around 50–65 dB(A).

Design also plays a role. An air purifier should work quietly in the background without drawing attention to itself. Look for a design that harmoniously blends into the existing decor.

Maintenance of air purification systems

Air purifiers are a relatively simple technology – and so is their maintenance. However, regular care is essential to maintain continuous performance.

Filter replacement is done in a few steps:

1. Remove cover
2. Remove old pre-filter and main filter
3. Insert new filters according to manufacturer's instructions
4. Clean housing

The frequency depends on usage and air quality. As a rule, most filters should be replaced every 6 to 12 months. Modern models automatically indicate when a change is necessary.

Filter replacement is uncomplicated and involves no health risks.

Pre-filter replacement:

Clean air helps you stay fit during flu season

Air purification systems offer a practical, efficient, and scientifically proven solution to protect patients, students, and employees from airborne diseases. In addition to other protective measures such as hand sanitizers and flu vaccinations, air purifiers – supplemented by the occasional use of ozone generators – represent a reliable strategy to ensure efficiency in the workplace during flu season.

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