FAQ

The selection of the appropriate filter depends on several factors.

These include the type of air pollutants, the required level of air cleanliness, the intended use of the space, and the characteristics of the ventilation system.

In many cases, one filter is not enough.

Modern ventilation systems often use multi-stage filtration.

In this approach, engineers arrange different filters in sequence.

Each filter removes a specific group of particles or pollutants.

For example, coarse and fine filters usually serve as the first filtration stage.

They capture larger dust particles.

At the same time, they protect high-efficiency filters from rapid contamination.

After that, HEPA filters remove very fine particles.

In addition to particle filtration, some systems also need molecular filters.

These filters remove gases and unpleasant odours.

CONFIRMATION

A properly designed filtration system often includes several types of filters working together.

Each filter has a specific role in removing different types of air pollutants.

See an example of multi-stage filtration in our Mini Case Study on verifying the performance of a central ventilation system in an apartment.

MPPS, or Most Penetrating Particle Size, refers to the particle size that passes through a filter most easily.

For this reason, it represents the most demanding filtration condition.

During standard laboratory testing, the filter faces a test aerosol.

This aerosol contains particles of different sizes.

Then, technicians measure particle penetration through the filter.

Based on these measurements, they identify the particle size that passes through most easily.

For HEPA filters, this size is typically around 0.2 µm, or 200 nm.

CONFIRMATION

Standards classify filters according to their efficiency in removing particles at this size.

This makes sense because MPPS represents the most challenging condition for filtration.

Air filters are tested according to different standards.

The applicable standard depends on the intended use of the filter.

For most HVAC filters, engineers use the EN ISO 16890 standard.

This standard determines filtration efficiency for three particle size fractions:

• PM1 – all particles sized 0–1 µm
• PM2.5 – all particles sized 0–2.5 µm
• PM10 – all particles sized 0–10 µm

The result shows the percentage of particle removal within each fraction.

For high-efficiency filters, such as EPA, HEPA, and ULPA filters, engineers use the EN 1822 standard.

This standard defines filtration efficiency based on MPPS, or Most Penetrating Particle Size.

CONFIRMATION

Different testing standards use different methods.

Therefore, when comparing filter performance, it is important to check which standard defines the filter classification.

Yes. HEPA filter certification is important.

It confirms that the filter meets the requirements of the EN 1822 standard.

It also confirms that the filter achieves the declared filtration efficiency.

Without certification, a filter cannot be considered a true HEPA filter.

During testing, technicians verify:

• overall filtration efficiency,
• local particle penetration through the filter media,
• potential leakage points through the filter or at its seals.

For high-efficiency filters, individual testing is especially important.

Even small irregularities in the filter structure can significantly reduce filtration efficiency.

Poor sealing can also reduce performance.

In addition, real-life performance depends on more than the filter itself.

Proper installation and sealing also play a critical role.

CONFIRMATION

The declared efficiency of a HEPA filter refers to its ability to remove particles.

However, actual performance in practice also depends on installation quality, sealing, and system validation.

Proper installation and sealing are very important for all air filters.

They are especially important for high-efficiency filters such as HEPA filters.

These factors have a major impact on the actual performance of the filtration system.

If someone installs a filter incorrectly, part of the air can bypass the filter media.

The same problem can occur if the filter does not seal properly within the housing.

In that case, unfiltered air can pass through the system.

For this reason, HEPA filtration systems require special attention.

Engineers must carefully design the filter housing.

They must also select high-quality sealing elements.

Finally, qualified personnel should install the filter correctly.

CONFIRMATION

Proper installation and sealing are critically important for all filters.

This is particularly true for HEPA filters.

In practice, a poorly installed or insufficiently sealed HEPA filter may perform worse than a correctly installed filter of a lower class.

Therefore, replacing a HEPA filter should not be treated as a simple do-it-yourself task in systems where filtration performance matters.

No. HEPA filters remove particles from the air.

However, they do not effectively remove gases, odours, or volatile organic compounds, known as VOCs.

The reason is simple.

Gas and odour molecules are much smaller than the particles captured by mechanical filtration.

Therefore, they can pass through the filter structure without being captured.

To remove gases and odours, engineers use other technologies, such as:

• molecular filters, such as activated carbon filters,
• chemisorption filters,
• other specialized air treatment systems.

However, airborne particles are not perfectly spherical, although people often imagine them that way.

They have irregular shapes.

They may also have a porous or sponge-like structure.

Because of this, a small amount of gases, odours, or oxides may adsorb onto the particle surface.

Then, the filtration process may remove them together with the particles.

However, these quantities remain very small.

Therefore, this does not represent an effective method for gas removal in practice.

CONFIRMATION

The declared efficiency of HEPA filters refers to particle removal.

In contrast, the removal of gases and odours requires molecular filters or other adsorption technologies.

It may also require non-conventional air treatment methods, such as bipolar ionization.

Marquis Intelligence often applies bipolar ionization.

This technology can contribute to reducing the concentration of VOCs and odours generated within indoor spaces.

In principle, it should.

However, in practice, this is not always the case.

Higher-class filters have greater declared particle removal efficiency.

Still, this does not automatically mean they will provide better air quality in every system.

In real operating conditions, filtration efficiency depends on several factors, including:

• proper ventilation system design,
• airflow velocity through the filter,
• pressure drop across the filter,
• quality of installation and sealing,
• regular maintenance and filter replacement.

If a high-efficiency filter creates excessive pressure drop, it may reduce airflow through the ventilation system.

In such cases, indoor air quality can actually become worse.

This can happen even when the system uses a higher-class filter.

For this reason, engineers must always align filter selection with the ventilation system design and real operating conditions.

CONFIRMATION

In practice, engineers can sometimes increase the filtration class by changing the filter type or filter media construction.

This does not always increase pressure drop in the system.

Marquis Intelligence has identified such upgrade opportunities in multiple projects.

In these cases, the company upgraded filtration classes within HVAC units without structural modifications or fan replacement.

Also, the upgrade did not increase pressure drop. In some cases, the pressure drop remained the same or even decreased slightly.

With additional air treatment using bipolar ionization, the system can further improve particle removal efficiency. However, such results require proper system design.

They also require precise positioning of ionization devices within the ventilation system.

Example from practice: In one residential project, Marquis Intelligence used a dedicated filtration chamber with a HEPA H14 filter and a molecular filter. During the design process, the available fan static pressure and the effect of filtration on the overall airflow were checked. After commissioning, the achieved airflow was also measured. More details are available in our Mini Case Study on verifying the performance of a central ventilation system in an apartment.

There is no single universal time interval for all filters and all buildings.

Filter replacement depends on the pressure drop across the filter.

More precisely, it depends on the measured pressure drop in relation to the designed allowable pressure drop.

In other words, replacement frequency depends on several factors, such as:

• filter class and type,
• quality of outdoor air,
• concentration of pollutants in the space,
• system operating regime,
• airflow velocity through the filter,
• system maintenance conditions.

In buildings located in areas with increased outdoor pollution, filters may become contaminated much faster.

These areas include locations near roads, industrial zones, or airports.

Also, higher-class filters may clog more quickly if the system has no pre-filtration stage.

In addition, different filter types have different dust-holding capacities.

Therefore, filter replacement should not depend only on a calendar schedule.

It should also depend on the actual filter condition and the measured pressure drop.

CONFIRMATION

In practice, teams most often replace filters during planned preventive maintenance.

However, proper maintenance does not rely strictly on time intervals.

Instead, it considers the actual contamination level and system operating conditions.

Marquis Intelligence places special importance on maintaining the equipment it supplies and services under maintenance contracts.

When it comes to filter replacement, premature replacement increases operating costs.

On the other hand, delayed replacement can compromise air quality and system performance.

At the PROMENADA shopping center in Novi Sad, Marquis Intelligence applied the same filter configuration for exhaust air treatment in McDonald’s, a Chinese restaurant, and KFC.

The systems also had identical capacities.

However, replacement intervals differed. For:

• McDonald’s, the interval was one month.
• KFC, it was one and a half months.
• The Chinese restaurant, it was two months.

This example shows how operating conditions directly affect maintenance frequency.

In HVAC systems, engineers most often assess filter contamination by measuring the pressure drop across the filter.

As the filter collects particles during operation, it creates more resistance to airflow.

The pressure difference between the upstream and downstream sides of the filter then increases.

This difference is called the differential pressure drop.

Teams usually measure it with:

• differential manometers,
• pressure switches, or pressostats,
• differential pressure sensors connected to automation systems or a BMS, or Building Management System.

Based on the measured pressure drop, maintenance teams can determine when the filter has reached the replacement point.

However, increased pressure drop does not affect only the filter.

The entire ventilation system also feels its impact.

For example, airflow can decrease.

At the same time, fan load can increase.

CONFIRMATION

Monitoring the pressure drop across filters is the standard and most reliable method for assessing filter contamination in HVAC systems.

However, many users do not know that standards define the final recommended pressure drop up to which filters should remain in use.

For coarse filters, this value is around 250 Pa, and for HEPA filters, it can reach up to 850 Pa.

Pressure drop also has a direct impact on the energy consumption of the ventilation system.

Technical literature often uses a practical rule of thumb.

According to this rule, each additional 1 Pa of pressure drop can increase annual electricity costs by approximately 1 EUR, depending on system operation and airflow.

By comparison, bipolar ionization systems create a very low pressure drop.

This value is typically around 6 Pa.

In systems with mechanical filters, Marquis Intelligence always includes differential pressure monitoring as part of technical supervision and maintenance.

This approach enables timely filter replacement and stable system operation.

No. HVAC systems and compressed air treatment systems do not use the same filters.

Although both systems remove particles from the air, they operate under very different conditions.

Therefore, the filters differ in design, operating principle, and purpose.

In HVAC systems, filters improve indoor air quality.

They also protect ventilation equipment.

The most commonly used HVAC filter types include:

• panel filters,
• bag filters,
• fine filters,
• HEPA filters,
• molecular filters for gas removal.

In compressed air systems, filtration has a different role.

These systems remove:

• solid particles,
• oil aerosols,
• oil and water droplets,
• oil vapours.

For this reason, compressed air systems use specialized filters, such as:

• coalescing filters,
• oil vapour removal filters,
• adsorption filters.

These filters operate under significantly higher pressures.

They also work in conditions typical for pneumatic systems.

CONFIRMATION

Both HVAC systems and compressed air systems use filtration.

However, filter selection, testing standards, and design principles differ significantly.

This difference comes from different operating conditions and different air quality requirements.

Filtration in compressed air systems has a different purpose from filtration in HVAC systems.

The goal is not to improve indoor air quality.

Instead, compressed air filtration protects pneumatic equipment, production processes, and products from contamination.

Compressed air leaving a compressor may contain different impurities, such as:

• solid particles, including dust and rust,
• water droplets,
• oil aerosols,
• oil vapours,
• microorganisms and particles generated by system corrosion.

For this reason, compressed air systems use specialized filters.

These filters operate under high pressure and high gas velocities.

The most commonly used filter types include:

• coalescing filters, which remove fine oil and water droplets from compressed air,
• particulate filters, which capture dust and other mechanical impurities,
• adsorption filters with activated carbon, which remove oil vapours and odours.

Engineers often arrange these filters in several filtration stages.

This helps achieve the required compressed air quality for a specific industrial application.

CONFIRMATION

Unlike HVAC filtration, compressed air filtration does not usually define air quality by particle concentration in a space.

Instead, the international standard ISO 8573 defines compressed air quality.

This standard classifies allowable levels of:

• particles,
• water,
• oil.

Due to different industrial requirements, engineers must carefully select and arrange filters in compressed air systems.

This ensures the desired level of air purity.

Marquis Intelligence has supplied such filtration systems to several clients, including Šabac Dairy.

In HVAC systems, engineers sometimes use combined or hybrid filters.

These filters combine mechanical particle filtration with gas or odour removal in one filtration unit.

They usually perform two functions:

• mechanical filtration of particles, such as dust, pollen, and aerosols,
• adsorption of gases and odours using materials such as activated carbon.

From a construction standpoint, these filters can have different designs.

In practice, common types include:

• media filters with an activated carbon layer,
• filters with granular or impregnated carbon media,
• multi-layer filters that combine fibrous media and adsorption materials.

These solutions allow one filtration section to remove particles and certain gaseous pollutants at the same time.

CONFIRMATION

Combined filters can help reduce gas and odour concentrations.

However, their adsorption capacity remains limited compared to specialized molecular filters designed specifically for gas removal.

For this reason, buildings with higher levels of gaseous pollutants or odours often require separate molecular filtration sections.

They may also require other air treatment technologies.

When designing air quality systems, Marquis Intelligence selects the filtration type according to the type of pollution.

The company also considers the facility’s operating conditions and the available space within the ventilation system.

No. Although filtration is one of the most important and reliable methods for removing particles from the air, it cannot remove all types of pollutants.
Mechanical filters, including fine and HEPA filters, are highly effective in removing:

• dust
• pollen
• aerosols
• microorganisms
• other suspended particles

However, many air pollutants exist in a gaseous form and cannot be effectively removed by mechanical filtration. This group includes, for example:

• volatile organic compounds (VOCs)
• odours
• certain nitrogen and sulfur oxides
• other gaseous pollutants

For this reason, systems for improving air quality often combine different air treatment technologies, such as:

• molecular filters (activated carbon or chemisorption filters)
• electrostatic filters
• UV disinfection systems
• bipolar ionization
• other specialized air treatment technologies

CONFIRMATION
Modern indoor air quality control systems often use a combination of different technologies, as no single method can effectively remove all types of pollutants.
In designing such systems, Marquis Intelligence applies an approach that combines particle filtration, removal of gaseous pollutants, and additional air treatment technologies to achieve stable and long-term sustainable indoor air quality.