Why aggregation rules matter
In practice, operators often assess each technology separately: one paint booth, one filter, one crushing line, one joinery section, one exhaust, or one handling area. From an air protection perspective, that may not be enough.
The Air Protection Act works with threshold values for many sources. What may be decisive is for example total rated thermal input, total designed capacity, consumption of organic solvents, quantity of processed material, or area of deposits. If multiple partial sources are aggregated under statutory rules, the entire operation may exceed a threshold that individual parts would not exceed on their own.
Aggregation can change the legal regime of a source. What might separately look like smaller technology without a permit can become a listed stationary source after inclusion of other parts of the operation.
This is important especially at plants with multiple similar technologies: paint shops, wood-processing plants, recycling lines, plastic processing, handling of bulk materials, welding shops, filtration systems, dryers, crushers, screens, or sets of technological exhausts.
What is actually aggregated
Aggregation rules do not create one new "super-source". Their purpose is to determine the total parameter by which individual sources are classified under Annex 2 to the Air Protection Act or by which certain operating conditions apply.
In other words: individual stationary sources remain individual sources, but their capacities may be assessed jointly for legal classification.
| What may be aggregated | Typical example |
|---|---|
| rated thermal inputs | multiple boilers or combustion sources in one boiler plant |
| designed capacities of technological sources | multiple lines of the same type in one plant |
| consumption of organic solvents | multiple paint or adhesive workplaces |
| quantity of processed material | multiple parts of wood-processing or recycling plant |
| area of deposits | multiple related areas with bulk materials |
| operating capacities under the same code | multiple sources typologically falling under the same Annex 2 code |
Practically important: aggregation rules are not an accounting sum for records. They are a legal and technical assessment for source classification, operating permit, and air protection conditions.
Three basic questions: same code, same plant, common exhaust
For technological sources, three basic conditions must especially be considered. Put simply, we ask whether sources typologically fall under the same Annex 2 code, whether they are in the same plant, and whether they pollute through a common exhaust or stack, or could do so given technical arrangement.
| Question | Practical significance |
|---|---|
| Do sources typologically fall under the same code? | technologies from different codes are not aggregated unless law or methodology leads to a different conclusion |
| Are they in the same plant? | typically one site or operational whole |
| Do they have a common exhaust or could they technically have one? | the so-called "virtual stack" principle is also important |
The third question is often the most complex in practice. It is not only about whether one common stack physically exists today. It is also assessed whether, given source arrangement, common discharge of emissions could occur. Methodological interpretations call this the "virtual stack".
Virtual stack: why it is not enough to say each exhaust is separate
The virtual stack principle is important mainly in plants where multiple similar technologies are located in one hall, in closely adjacent buildings, or in one site. If their emissions could technically be routed to one exhaust, an aggregation rule may apply even if exhausts are physically separate today.
That does not mean everything in the entire site should theoretically be aggregated. Real technical and operational connection decides. If sources are in different buildings, separated by large distance, without realistic possibility of common discharge, or involve different types of activity, the conclusion may differ.
| Situation | Possible interpretation |
|---|---|
| multiple similar workplaces in one hall | often relevant for aggregation |
| multiple exhausts from the same technology | technological whole must be assessed |
| separate buildings in close proximity | virtual stack may be relevant |
| distant operations in one site | depends on technical possibility of common discharge |
| different technologies under different codes | usually not aggregated with each other |
| separate plants | generally not assessed as one plant |
The practical impact is significant. An operator cannot automatically claim that sources are not aggregated just because they have separate ducting or separate fans.
Why aggregation can change operator obligations
If capacities are aggregated, the operation may exceed a threshold value in Annex 2 to the Air Protection Act. That can change the entire permitting regime.
| Result of aggregation | Possible impact |
|---|---|
| exceeding threshold capacity | source may become a listed stationary source |
| change of Annex 2 code | different emission limits or technical conditions |
| higher total capacity | need for operating permit change |
| new permitting regime | expert opinion, dispersion study, operating rules |
| different measurement obligation | emission measurement or operating records |
| impact on fees or records | change in emission calculation and reporting |
The greatest risk is at plants that grew gradually. Another booth, line, filter, storage area, or exhaust was added. Each individual change may have seemed small, but after inclusion of the whole, the legal regime of the source may differ from the beginning.
Practical examples
For a paint shop, total designed consumption of organic solvents may be decisive. If the plant has multiple paint booths, gun cleaner, paint preparation area, and other workplaces with solvents, each part cannot always be assessed separately. What matters is whether it is a related technological whole and what total designed VOC consumption is.
For a wood-processing plant, total designed consumption of processed material may be decisive. Individual machines may look like smaller partial technologies, but saw, planer, CNC centre, grinding workplace, and extraction may form one operational whole.
For a recycling centre, capacity of crushing, sorting, storage, and handling may be addressed. It is especially important whether individual parts fall under the same code or whether a more specific code for the particular activity applies.
For bulk materials, total designed area of open deposits may be decisive. If there are multiple stockpiles on one active handling area, this may be one source from the perspective of area, not several isolated piles.
Same code does not always mean a simple conclusion
MoE methodology notes that for classification, the Annex 2 code must first be correctly determined. Only then does aggregation make sense. General or "catch-all" codes are not used if the source can be classified under a more specific code.
This is important for example for activities that might at first glance fall under several categories. Where a general and a more specific code overlap, the more precise code takes precedence. If a technology typologically corresponds to a specific Annex 2 item, it should not be moved to a more general code just because that is simpler.
Put practically: first determine correctly what the source is and which code it belongs to. Only then address what its capacity is aggregated with.
Designed capacity is not actual production last year
A common mistake is confusing designed capacity with actual annual utilisation. For source classification, designed capacity is usually important, not how much was actually produced or processed in the last year.
Actual operation may be lower due to orders, outage, seasonality, or economic situation. That does not automatically mean the source's designed capacity is lower. If equipment is designed for higher capacity and the permit or project counts on it, this value may be decisive for classification.
| Data | How it is used |
|---|---|
| designed capacity | decides source classification and obligations |
| actual production | important for records, emissions, and operating balances |
| maximum operating regime | important for conservative assessment |
| permitted capacity | must be consistent with decision and documentation |
| annual utilisation | may be lower than designed capacity |
For permitting and permit changes, it is therefore advisable to work with clear, technically substantiated designed capacity. Uncertainties in capacity often lead to supplementation of applications or differing interpretation between operator and authority.
Aggregation and operating records are not the same thing
MoE in its methodology explicitly notes that aggregation rules do not concern aggregation of data in summary operating records. That is important for practice.
Aggregation under Section 4b serves to determine total designed capacity for source classification and application of legal requirements. Operating records, by contrast, describe actual operation, consumptions, emissions, measurements, operating hours, and other data for a specific period.
The difference is this:
| Area | What it addresses |
|---|---|
| aggregation rules | legal classification of source according to designed parameters |
| operating permit | conditions, capacities, exhausts, limits, measurement |
| operating records | actual operation and data for a given year |
| summary operating records | reporting of data under record rules |
| emission calculation | actual or methodologically determined emissions for a period |
If an operator aggregates capacities for source classification, that does not automatically mean all data must be aggregated the same way in records. Conversely, clear records do not replace correct classification assessment.
What the operator should check
For every plant with multiple technologies, a basic check of aggregation rules is advisable. This is not an academic question. The outcome can decide whether an operating permit, permit change, expert opinion, dispersion study, or emission measurement is needed.
Checklist:
| Check question | Why it matters |
|---|---|
| Which technologies in the plant are stationary sources? | without defining sources, correct aggregation is impossible |
| Which Annex 2 code do they typologically fall under? | capacities of sources typologically under the same code are aggregated |
| Are they in the same plant? | typically same site or operational whole |
| Do they have a common exhaust or could they have one? | physical or virtual stack decides |
| What is the designed capacity of each part? | decides on exceeding threshold values |
| Is there overlap with a more specific code? | more specific code takes precedence over general |
| Does the permit match actual state? | older permit may not cover today's operation |
| Was technology added without permit change? | gradual expansion can change obligations |
This overview is advisable especially before production expansion, addition of technology, installation of new extraction, change of exhausts, or update of operating permit.
Impact on expert opinions and dispersion studies
Aggregation rules have a direct impact on expert documentation. If after inclusion of capacities a source enters a different regime, an expert opinion may be needed. If capacity or emissions increase, a dispersion study may also be required.
An expert opinion must correctly describe which parts of the operation are included, which code they fall under, and what total designed capacity is. A dispersion study must in turn be based on the real technical whole: exhausts, operating hours, emission parameters, and possible area or fugitive emissions.
An error in aggregation can therefore carry through the entire documentation. If source classification is wrongly determined, emission limits, measurement, records, and operating conditions may be wrongly set.
Most common mistakes
The most common mistake is assessing each device separately just because it has its own fan or exhaust. A second mistake is confusing designed capacity with actual annual operation. A third is omitting the virtual stack for sources located in one building or in a technically related part of the site.
The opposite problem is also common: unnecessary aggregation of technologies that are not typologically related or fall under different codes. Such an approach can burden the operator with stricter obligations than actually follow from the law.
For more complex sites, aggregation should therefore not be addressed by estimate alone. It is better to prepare a short technical-legislative assessment describing sources, codes, capacities, exhausts, and the conclusion on what should and should not be aggregated.
Summary
Aggregation rules for air pollution sources can fundamentally change operator obligations. If multiple technologies typologically falling under the same code are in the same plant and have a common or technically possible common exhaust, their designed capacities may be aggregated for classification purposes. The outcome can decide whether it is a listed stationary source and whether an operating permit, expert opinion, dispersion study, emission measurement, or operating rules are needed.
The key is to correctly determine sources, codes, designed capacities, and technical connection of exhausts. It is not enough to assess only an individual machine or current actual production. For plants that expanded gradually, it is advisable to verify whether the existing permit matches today's technical and legal state.
Send us a description of technologies, valid operating permit, exhaust schematic, designed capacities of individual parts of the operation, and site layout drawing. We will verify whether aggregation rules apply to your operation and whether they may affect operating permit, expert opinion, dispersion study, or operating records.
Factual basis of the article
The article is based mainly on these sources:
- MoE methodological guideline on aggregation of designed capacities of other technological stationary sources and their classification under the Air Protection Act,
- Act No. 201/2012 Coll., on air protection,
- Section 4a of Act No. 201/2012 Coll. – stationary sources and their classification,
- Section 4b of Act No. 201/2012 Coll. – aggregation rules,
- Decree No. 415/2012 Coll., on permissible pollution levels and their determination.
The MoE methodological guideline explains application of Sections 4a and 4b of the Air Protection Act for technological stationary sources. It states that total designed capacity is decisive for classification of sources under Annex 2 to the Act and for application of certain operating conditions and specific emission limits under Decree No. 415/2012 Coll. It also emphasises that capacities are aggregated only for sources typologically falling under the same code, in the same plant, and when the condition of common or technically possible common discharge of emissions is met.