Airtight ductwork as the basis of the German Building Energy Act (GEG)

In Germany, the building sector currently accounts for around 35 to 40 % of energy consumption and around 30 % of CO2emissions. And that despite the fact that the law regulating energy savings in buildings (the Energy Saving Act (EnEG)) was passed in 2005, followed by the Energy Saving Ordinance (EnEV, ordinance on energy-saving thermal insulation and energy-saving systems technology in buildings) in 2007. In October 2013, the Federal Ministry of Construction published the guidelines on sustainable construction (BNB), which are mandatory for federal buildings. Together with an evaluation system, these aim at defining the requirements for fully optimised buildings. Based on these guidelines, a revision of the Energy Performance of Buildings Directive (EPBD) that regulates the overall energy efficiency of buildings followed at the end of May 2018. At almost the same time, in 2017, the first draft of the Building Energy Act (GEG) was submitted with the aim of summarising, standardising and simplifying essential aspects and requirements of the Energy Saving Act (EnEG), the Energy Saving Ordinance (EnEV) and the Renewable Energies Heat Act (EEWärmeG). Following positive reactions by the German Federal Association of Building Services Engineering (Bundesindustrieverband Technische Gebäudeausrüstung (BTGA)) even before it was passed, the German Building Climate Control Association (Fachverband Gebäude Klima (FGK)) and the German Association of HVAC Manufacturers (RLT-Herstellerverband), the GEG was passed into law by the German Bundestag on 19 June and is expected to come into force in November of this year. In addition to the goal of significantly reducing energy consumption and CO2 emissions, all of the above guidelines, ordinances and laws aim to increase the overall efficiency of buildings. Against this background, the German government has declared the goal of clearly reducing the heat requirement of buildings and to achieve a nearly climate-neutral building stock by 2050 – an ambitious goal, which requires a reduction in the demand for primary energy by around 80 % as well as new initiatives and approaches in the building sector.

Airtight ductwork as the cornerstone for energy savings and increased efficiency

One of the key factors are the ventilation and air conditioning systems, whose ductwork has been shown in numerous studies to have average leakage rates of 15 % or more throughout most of Europe. According to EN 16798-3, this corresponds to airtightness class ATC 6 – 2.5 times the worst airtightness class A (according to the former EN 13779). Almost a sixth of the total air volume conveyed is lost in suspended ceilings, shafts and elsewhere instead of arriving in the rooms that it is intended to reach. In addition to the loss of valuable air, the leaks mean a loss of efficiency and consequently unnecessarily high costs. Citing a study by Mc Kinsey & Company, The New York Times, for example, wrote that airtight ductwork offers the greatest energy-saving potential when modernising systems with a view on energy savings in the USA. According to the ICEE report "Energy savings estimates of duct sealing applications", eliminating leaks can yield energy savings of about 46 % and cut electricity bills by about 50 %. These findings are also confirmed by Marcel Riethmüller, managing director of ecogreen Energie GmbH & Co. KG: "A reduction of the air flow rate by about 20 %, for example, can reduce the energy input by about 50 %. It follows that adjusting the actual air flow rate to the demand that would result without leakage is the basis for an energy-efficient ventilation system. And this, in turn, requires reliably airtight ductwork." Ductwork thus offers enormous potential for energy savings, higher efficiency and reduced costs. They are also a fundamental prerequisite for truly exploiting the effectiveness of the measures proclaimed by politicians, such as BIM, smart building services, neighbourhood concepts, efficient and energy-saving fans and/or mandatory heat recovery. And also in terms of air purification and the associated fire and building protection, airtight duct systems are an essential basic requirement. Sven Rentschler, CEO of Reven GmbH, explains: "Air purification, typically used in food processing and engineering companies, involves the extraction of aerosols of coolants and lubricants emitted by machinery or of frying and baking oils. These then deposit on the ductwork and condense. If the ductwork shows leaks – and this is the case in almost all systems – the oil literally rains down from the overhead ducts. This often results in unavoidable damage to control cabinets and expensive production equipment. Also worth remembering is that the liquids dripping from the ductwork are often pure and highly flammable oils. They therefore present a significant additional fire hazard that goes mostly unnoticed until there's a fire."

In view of these diverse aspects, it seems almost logical to finally attribute to ductwork airtightness the importance it deserves according to the German Building Climate Control Association (FGK) as well as researchers, scientists and experts, not least as it contributes to fulfilling the specifications of VDI 2067 Part 1 (economical operation) and VDI 6022 (hygienic operation). After all, reliably airtight ductwork is a prerequisite for operating duct systems at minimum cost, maximum efficiency and minimum energy consumption as well as ensuring the provision of clean, hygienic air.

Process chain with leakage losses

Ensuring ductwork airtightness would require two essential key additions to the current ductwork construction process chain: 

• a minimum airtightness of all ductwork (class C), to be verified by independent inspectors who have no vested commercial interests, and
• (in most cases) the mandatory subsequent sealing of the entire duct system

If the measured airtightness established in a mandatory functional test performed during the installation phase lies below the agreed airtightness class, rectification should be mandatory. To date, neither planning specifications nor ductwork production and installation based on standards and other regulations can guarantee good airtightness and thus energy efficiency of a ventilation or HVAC system. This is due to a gradual deterioration of airtightness along the entire process chain (tendering, engineering, production, transport, handling and installation), as outlined below, which contributes significantly to the leakage rates of 15 % and more that are commonly encountered in existing systems.

Tendering for an insufficient airtightness class 

Starting with tenders in the building sector, only the minimum requirement of EN 16798-3 or the EnEV for renovation and new buildings – airtightness class B – is often specified. This means that a leak of 2 % (i.e. airtightness class B or ATC 4) is tacitly accepted and permitted in standard buildings. If there are special requirements regarding hygiene or energy efficiency, airtightness class C (0.67 % leakage or ATC 3) is recommended and ideally also tendered in accordance with VDI 3803, VDI 6022, EnEV, DIN 16798-3 and DIN 15780. Reinhard Siegismund, publicly appointed and sworn expert and consulting engineer of the association of consultant engineers VBI, explains: "In planning and constructing ventilation and air conditioning systems, rules and standards are usually only just about fulfilled. In my role as an expert in the acceptance test, I am often told the measurement tolerance with which my readings are to be evaluated. As a rule, this corresponds to +/-20 %, whereby -20 % is almost always used to achieve a deviation of the target value from the actual value that is just acceptable. The goals of energy saving, environmental protection and personal health are all too often recklessly ignored due to usually negligible cost savings."Accordingly, the highest airtightness class D and thus a leakage rate of only 0.22 % in the entire system is rarely specified in any tender. This is despite the fact that the production of ductwork components to airtightness class D (corresponding to ATC 2) in compliance with DIN 1507 or HFL2002 (for square ducts), DIN 12237 or HFL2003 (for round ducts) as well as EN 15727 and EN 1751 is usually not a problem in practice.

Loss of airtightness through transport to the construction site 

The transport of the components from the manufacturer to the construction site and their subsequent handling also present a problem with regard to the airtightness class. The unavoidable handling of the components during transport – such as, for example, lifting into and out of the truck, loading and unloading, stacking in the truck or on site, etc. – usually results in a loss of sealing capability in the order of one airtightness class. This is, among other things, due to the unavoidable slight deformations as well as damage to seams and seals. Consequently, a system of airtightness class B, as is still frequently specified in tenders and used in planning and production, will often correspond at best to airtightness class A (or ATC 5) after transport and handling. "Converted" to the leakage rate, this means a threefold increase, from 2 % to about 6 % of the total air flow rate.

Assembly under time pressure

A further cause for the deterioration in airtightness is the assembly of the components. Even if the installation recommendations of ductwork manufacturers' association HFL are followed, leaks are unavoidable. The reasons for this include that ductwork components often no longer fully correspond to their original shape and therefore do not fit together exactly. The accessibility of some components is severely restricted and the trial-and-error approach leads to new leaks, especially where holes are left by screws, rivets and clamps. Wherever old holes that are no longer used are simply left unsealed, new leaks occur. A further cause of leaks are oversized parts and fitted lengths produced on site, often under adverse conditions, according to production standards to compensate for the differences between the planned system and the actual situation on site. To achieve an optimum installation, a sense of responsibility, technical knowledge, space, time and sound training are, furthermore, required on the construction site. In contrast to other countries, there is no such thing as a ventilation installer in Germany; only VDI 6022 stipulates that a technical qualification, which must be verified through training and professional experience, is mandatory for planning, construction and operation. Two further important aspects for airtight ductwork are sufficient time and space during installation. In practice these are often lacking, according to Christian Podeswa, training officer at Helios Ventilatoren GmbH & Co. KG: "Due to the constructional requirements, it is becoming increasingly difficult to design and install duct systems in the way that the building standard would require. Lack of space and ever shorter installation times lead to severe pressure. And this in a job that actually demands a high level of prudence and precision. This, unfortunately, has a negative impact on the system's airtightness."

The lowest bidder and piecemeal parts selection 

Another reason for the deteriorating airtightness class during installation is the common practice of selecting the cheapest, and therefore often a less experienced bidder – a selection criterion that should, says Reinhard Siegismund, be reconsidered: "Perhaps we should change the public procurement regulations and, in public tenders, eliminate the cheapest and the most expensive bidder from the comparison. Currently, the contract often goes to the cheapest bidder almost by default. The contractor then usually continues this trend under the motto 'the cheapest is good enough for our customers' with the inevitable impact on the installation's airtightness. It would make much more sense, instead, to award the contract to the most economically efficient bidder, as stipulated in the federal Regulation on the Award of Public Contracts. Admittedly, in the absence of prior experience with the bidders, it is often difficult or even impossible to assess this. It would, however, represent an opportunity for getting away from duct systems that are made from the cheapest components by the cheapest installer in such a way that they only just meet the minimum requirements of an already low sealing class at the highest possible measuring tolerance". Also coming into play is the fact that assembly involves joining a range of different components that would often have been certified according to different criteria so do not meet the exact same sealing standards. Often, individual components are used that do not correspond to the airtightness class of the overall system. Individual components with airtightness class A may, for example, be installed in duct systems that are intended to meet airtightness class B or C overall. The specified airtightness class for the entire system (B or C) cannot then be achieved without replacing the class A component or subsequently sealing the system. The same applies to already installed ductwork components of a high airtightness class that were deformed through misuse – for example as seating – in the course of the installation work and no longer comply with their original airtightness class, thereby compromising the system's overall airtightness.

Tightness inspection after installation 

Once a duct system – regardless of its airtightness class – is fully installed, it is usually inspected "as per specifications". This usually begins with a visual inspection of the system to identify potential leaks early on, which can then be sealed already before commissioning. However, a visual inspection is generally only possible in places that are easily accessible and, even when using spray mist or soapy water, will only yield usable results if the inspector is sufficiently experienced and conscientious. In addition to the visual inspection, a metrological test, which is usually carried out in accordance with EN 12599, offers the possibility of quantifying the leakage airflow rate, from which a system's airtightness class can be determined. The problem is that the metrological test is usually performed only on ductwork sections and is compulsory only if mandated in the specification. If it is not, as is often the case, the acceptance criteria are a matter of discretion and the system ends up in the hands of experts who, according to Reinhard Siegismund, are already drowning in work. "We are not only called in those cases where promises were not kept (e.g. airtightness class C) and the client then demands a new installation of the duct system, which can sometimes incur costs reaching six-figure numbers."

A lot of effort for a mostly low success rate 

If leaks have been identified in a duct system by visual or metrological inspection, they must be sealed. This process was often done manually and iteratively – i.e. one leak at a time, starting with the largest leaks and working towards the smaller ones. Depending on the type of leak, manual sealing is performed using sealing tape and cold shrink tape among many other methods. With effort, time and good accessibility of the system, and given an experienced, precise and diligent installer, it is possible to achieve airtightness class B or even C. This is the exception rather than the rule, however, and an airtightness class C guaranteed in advance would represent a great risk for installers and engineers.

Airtightness class C on paper, A in reality 

Once the duct system is "fully" sealed and the required airtightness class is achieved, sealing is completed and the installer confirms the system's airtightness. It is important to observe, however, which part of the ductwork has been tested to determine its airtightness class: 100 %, 50 % or only the 10 m² or 10 % of the ductwork surface specified as reference in EN 12599 with a representative cross-section of all components. If the latter is the case then no meaningful representative claims can be made in practice about the actual airtightness of the entire duct system. Even in ductwork with an overall airtightness class A or worse, there are often duct sections that correspond to airtightness class C. If the test is carried out along exactly one of these sections, a duct system with an airtightness at the lower end of class A – i.e. leakage rates of about 15 % and more – could be classified as being of airtightness class C (i.e. having a 0.67 % leakage rate). This airtightness class might look good to the building owner on paper but, in practice, unnecessarily high additional costs arise due to high leakage rates and the resulting losses in energy efficiency.

From C to A in a few steps

In summary, this means that almost every single step along the process chain in ductwork construction can have a negative impact on quality and thus the airtightness of the entire duct system (see Table 1). If, for example, airtightness class C (0.67 % leakage rate) is specified in the tender, the best one can hope for in practice without subsequent sealing is airtightness class A (6 % leakage rate). But since only the minimum requirement of airtightness class B is specified in the tenders of (public) clients or planners in many cases, the actual leakage rates are, on average, 15 % and higher. Consequently, duct systems are, in fact, operated at an undefined airtightness class with a leakage rate that is 2.5 times higher than the lowest airtightness class A, contrary to the self-imposed requirements. The result: considerable energy and efficiency losses as well as unnecessarily high costs, beside numerous other disadvantages.

Table 1: Theoretical specifications for duct systems and actually achievable airtightness

Detlef Malinowsky, auditor, instructor for building services technology, KfW- and BAFA-listed consultant as well as member of the board of the energy cooperative and the trade association, confirms this: "I would estimate that the airtightness of duct systems does not correspond to any airtightness class in about 50 % of cases. This means that the ductwork is very leaky, resulting in

• noise generation in suspended ceilings that is unpleasantly audible even in the rooms below.
  
• undesirable air flow and therefore odour nuisance, for example because the air flows from an odour-intensive room, such as a cafeteria, into an office area.
• a lack of air distribution in a branched duct system, so that the airflow in the system cannot be adjusted.
• rooms that receive insufficient air through the ventilation system and thus experience poor 
  air quality with excessive CO2 values.
• unavoidable malfunctions of air flow rate controllers due to an insufficient charge pressure.
• an unnecessarily high energy consumption at the fan, which must compensate for the leakage air flow.
• a lack of reserves to overcome rising filter pressures caused by contamination during operation (as a rule, most new HVAC systems already run at maximum capacity after acceptance).

This means that most HVAC systems should not actually pass their acceptance test at all, as none of them can fulfil their specified function." Marcel Riethmüller agrees: "When I see and hear some of the installed ducts, I would be happy if we were to achieve even airtightness class B in practice." 
Valerie Leprince, managing director of PLEIAQ, has come to the same conclusion, stating that "a recent survey conducted by the Tightvent Airtightness Association Committee (TAAC) working group shows that, except in Sweden, awareness of the airtightness of duct systems is very low throughout Europe. In addition, recent measurements carried out in France under the Effinergie+ label have shown that almost 50 % of duct systems have an airtightness of 2.5 times airtightness class A or even worse, even though they were designed to meet the minimum airtightness class A required by the Effinergie+ label.

50 % additional costs due to leaky ductwork

It follows that a change in construction habits that focuses on the importance of airtight ductwork makes sense not only from an energy point of view; airtight systems can also help avoid additional financial costs due to the loss of heat and cooled air that often go unnoticed. As Jens Amberg, inventor of the air energy meter and CEO of Luftmeister GmbH, Kirchzarten, explains: "Regarding ductwork airtightness, in most cases only the loss of air volume is considered, i.e. the cubic metres of air that escape and cannot be used. Equally important, however, is the loss of expensive heating or cooling energy conveyed by the air." Using the example of a partial air conditioning system (ventilation, filtering, heating, cooling), Wolf Rienhardt, a freelance engineer, trainer, HVAC systems consultant and member of the German Association for Air and Water Hygiene (DFLW), has calculated the additional costs resulting from leaks for air delivery and heating in a winter period (based on statistical weather data for Mühldorf am Inn) at around 370 euros (air conditioning) and 385 euros (air conditioning and delivery). Valerie Leprince confirms these figures, adding that "various calculations, investigations and studies have shown that by eliminating leaks in ductwork, heating loads can be reduced between 5 and 18 % and cooling loads between 10 and 29 %. In addition, ductwork leakage increases the required fan power by around 30 to 75 % and the required cooling capacity in HVAC systems by up to 48 %. By reliably eliminating leaks, up to 50 % of the energy costs for the fans can be saved."

Moreover, the ductwork leakages have a negative impact on construction costs as ventilation, partial air conditioning and HVAC systems are oversized at the planning stage, with flow rates specified 15 to 20 % higher to ensure that the actual required minimum air exchange rate can be achieved. This results in unnecessarily high costs as well as oversized air handling units, more space needed for the larger pipes and components as well as additional expenditure for sound insulation and building fabric. While building owners and operators tend to turn a blind eye to energy efficiency, according to 
Christian Podeswa, the ever more pronounced additional costs caused by leaking ductwork is slowly but surely leading to a rethink. "In addition to the legal requirements and standardisation principles, which are increasingly aimed at boosting the efficiency of ventilation systems, more and more operators are becoming aware of the issue of economic efficiency of a ventilation system. Airtightness plays a decisive role in this. Put simply: What do I pay for and what good is conditioned air to me in the suspended ceiling when it should actually be down in the rooms?" Detlef Malinowsky agrees, adding that, in practice, "the areas in an office building with the best air quality are the shafts and false ceilings!"

A paradigm shift and rethink in ductwork construction

Changing this situation, saving costs and increasing energy efficiency while at the same time ensuring that the valuable conditioned air – complete with the heating or cooling energy it carries – arrives where it is needed, is basically not difficult nowadays. It does, however, require a fundamental paradigm shift, as increasingly demanded by associations and experts: away from the previous practice of a tacit acceptance of leakage rates of 15 % and more towards specified and mandatory reliably sealed ductwork; away from ignoring or disregarding the significance of high leakage rates towards an awareness among engineers, installers and operators that airtight ductwork is the cornerstone of higher efficiency, lower energy consumption and enormous cost savings; away from a process chain without verification of airtightness towards a mandatory metrologically proven good airtightness 
class (C) that is accepted as part of the process chain together with subsequent sealing of the entire duct system.

Wolf Rienhardt formulates the necessary rethink, which also represents a return to former values as follows: "The demand for effectiveness – to do the right thing – and efficiency – to do things right – has existed in building services engineering for a long time. If we had already consistently complied with these requirements, now we would not need many of the technical and legal regulations. A legally prescribed airtightness class for ductwork would not be necessary. To be allowed to be involved in the process of manufacturing, planning, installing and operating ventilation and air conditioning systems, we must be competent, no doubt about that. Should not effectiveness and efficiency be part of the ethos of a professional? I believe it should." Christian Podeswa agrees and believes that it is time for a change: "Since ventilation ducts represent a considerable part of a system, this is where we should start, to make them more airtight in future and thus enable quiet and efficient operation of the fans and the entire system. This will lead to a trend that will develop in line with our demands of making duct networks more airtight and thereby more efficient in future." Valerie Leprince also sees a need for action: "A change of perception is needed to pave the way to an increased awareness of the importance of airtight ductwork. To this end, a mandatory airtightness test of the entire system should be systematically carried out during commissioning. This will enable proprietors, engineers and installers to see quickly and easily that airtightness is usually poor without additional measures. The additional costs this entails – also in terms of heating and cooling loads and the energy consumption of fans – can easily be calculated with equations and demonstrated using the results of numerous field measurements. A good approach here would also be to investigate the impact of leaks on previously neglected aspects, such as noise, dust accumulation and indoor air quality, in future research work and to incorporate these in the equations. And last but not least, lower measurement uncertainty should be guaranteed and an internationally standardized and improved measurement protocol along with a mandatory airtightness class C should be introduced."

Airtightness class C as mandatory standard

Podeswa and Leprince are not alone in their desire for airtight ductwork. More and more experts, associations and specialists are also expressing a desire to establish airtightness class C as a minimum standard. A perfect opportunity to prescribe this paradigm shift normatively would be to specify a minimum airtightness class (C) in the [German] Building Energy Act (BEG). For example, it would make sense to stipulate a minimum airtightness class to be specified in tenders as a mandatory requirement that must, also, be verified by independent inspectors for the entire duct system as part of the handover of a ventilation or HVAC system. For new or rehabilitated existing installations, a handover with adjustment protocols would be advisable.

However, all these requirements can only be realistically implemented if the existing ductwork construction process is completed with a further step in addition to the minimum airtightness class to be observed and verified for the entire system: the subsequent sealing of complete duct systems using reliable and innovative methods. This is the only way to ensure right from the outset that airtightness class C, as the new standard for complete air duct systems, can be achieved reliably and in the long term.

An ideal solution for sealing complete duct systems would be, for example, the Aeroseal procedure that was developed and patented in the USA and which MEZ-TECHNIK GmbH introduced to Germany in 2015, from where it has spread throughout Europe. Suitable for both new and existing ventilation and HVAC systems, Aeroseal reliably seals ductwork from the inside out in just a short time and without the need to first find the leaks. By applying a hygienically safe sealant that meets the requirements of VDI 6022, it permanently eliminates leaks with a diameter of up to 15 mm. In most cases, this does not even require any intervention in the actual building and the system's downtime is limited to the duration of the sealing process, which can usually be completed within just a few hours by only one or two people. Unlike with conventional methods, the payback periods are generally only one to five years. With integrative planning, the total costs for a contractor can be reduced. Both the cost and time required for the sealing work itself are low. This concept is favoured by a growing number of installers and enterprises and is meanwhile being successfully used by 28 contractual partners of MEZ TECHNOLOGY GmbH in 16 countries, and the trend is rising.

A pioneer in energy efficiency

The Aeroseal process was used, for example, by Aerotechnik GmbH, Münsingen, which was commissioned to build the ventilation system of BV Daimler Office V in Vaihingen. To ensure airtightness class C, which the tender text specified for the entire system, only ductwork components of airtightness class C were initially ordered, delivered and installed. To avoid leaks via screws, the ducts were suspended using profile rails. Only in the shafts did mounting holes have to be drilled into the ductwork. Once completed, a tightness test showed that the risers only reached airtightness class A instead of the required class C. As initially planned, the entire system was then sealed using the Aeroseal process. This required the fire dampers to be closed to isolate the runs on the individual floors. The sealing system was connected to the individual risers to be sealed via a single connection point – a riser in the roof area – through which all other risers were interconnected. Having connected the sealing system and the riser via clear flexible tubing, the sealant, which is atomised using pressure and temperature, is introduced and flows, together with the air, through the leaking ductwork. Since leakage points cause the pressure to drop locally, the sealant-laden air is deflected there and flows through the leaks to the outside. As it does so, it deposits small quantities of the sealant on the edges of the leaks, gradually closing up and permanently sealing any leaks with a diameter of up to 15 mm – without the need for a prior search, without additional effort, without dirt and without dust. The result: within only a few hours, the leakage flow was reduced to the extent that, starting from airtightness class A, the required airtightness class C was easily achieved. In addition to a duct system that meets the specified requirements overall, the client benefits from a guaranteed long-term airtightness and minimized operating costs.

Subsidies for greater efficiency

As these aspects are convincing arguments for building owners, ever more consultants and installers are planning and specifying the use of subsequent sealing with Aeroseal right from the start. This trend is further encouraged by state subsidies available where the use of Aeroseal in existing buildings leads to an EnEV-relevant energy upgrade of the ventilation or HVAC system. For example, a subsidy programme for individual measures in existing buildings can subsidise the initial installation or renewal of a ventilation system if the renewal or repair achieves at least a metrologically verified airtightness class B (according to DIN 1507:2006-07 or DIN 12237:2003-07). Specifically, a repayment bonus of up to 20 % is granted on a loan from the KfW Bank. In the field of process ventilation, subsidies of up to 40 % are available under the non-technology-specific "Energy Efficiency in Industry" (EEW) subsidy programme, which also requires airtightness class B to be achieved. The level of the subsidies is determined by expected CO2 reductions, which are equated to energy savings, compared to existing buildings.

Although the extent to which airtightness class B is a sufficient qualifier for subsidies is a matter of contention for many experts, this approach is welcomed, as Marcel Riethmüller explains: "One can often be glad when companies check their ductwork for leakage at all. And to receive a subsidy, verification through a measurement protocol is required." A verified airtightness class B with leakage rates of 2 % compared to the previous leakage rates of 15 % and more – and thus not even airtightness class A, even though self-imposed regulations, standards and norms demand better – is, after all, an important step in the right direction. It represents a step towards airtight ductwork with a mandatory airtightness class (C) and an important basis for any energy-saving and efficiency-enhancing measures in the field of ventilation, partial air conditioning and HVAC systems. It is also an important and positive step towards an (almost) climate-neutral building stock, which should be achieved throughout Germany by 2050 at the latest.

ANNEX

Airtightness classes

¹ Ductwork for special requirements
p_prüf [Pa] Test pressure - design pressure difference of the duct system or subsystem to be tested

Example illustrations of transport damage

Typical transport damage with negative effects on the airtightness of the ductwork components and thus on the entire system is caused, for example, by ...

... handling and unavoidable distortion – especially of large air duct components.

...by an (almost) improper, but often not otherwise feasible transport of the air duct components to the construction site.

Example illustrations of assembly problems

Typical assembly faults that can lead to leakage in the overall include...

...air duct components, in the corners of which sealing compound has been applied very generously.

...poorly applied sealing tape that does not comply with the state of the art.

...a trial-and-error approach, which results in holes that are often not sealed after installation and remain as leakage points in the duct system.

...distorted parts that no longer fit together exactly.

...incorrectly positioned or the wrong number of air duct clamps.

...carelessly and unprofessionally executed connections of various air duct components.

...complicated oversized parts that must be made on site according to production standards and are often connected to the rest of the ductwork in confined spaces.

Example illustrations of visual tightness testing

Visual tightness testing with spray mist or soapy water, which forms bubbles at leakage points, is used to find leaks that are not immediately evident. Typical points of leakage are ...

...edges and seams..

...joints.

Example illustrations of defects caused by other trades

Once air duct components reach the construction site, their condition and therefore their airtightness is no longer only in the hands of the installer. Other tradespeople also have a considerable influence on the airtightness of the final air duct system. The reasons are numerous and so it is not uncommon for air duct components....

...to be used as seating.

...to get in the way of other construction work after their installation, prompting workers to simply place wooden boards or similar on the sensitive ductwork and effectively misuse them as stepping aids.

Example illustrations from BV Office Daimler V

During the first tightness test, leakage of around 700 l/s was detected in the newly constructed duct system at BV Daimler Office V. To reduce this and achieve an overall airtightness class of C, the duct system was subsequently sealed using the Aeroseal process.

The finely atomised sealant is introduced through clear flexible tubing, which connects the sealing system to the entire network of ducts via a connection point in the roof area.

Photos of the commentators

Jens Amberg, inventor of the air energy meter and managing director of Luftmeister GmbH

Valerie Leprince, Managing Director of PLEIAQ

Detlef Malinowsky, expert, consultant for building services engineering, KfW- and BAFA-listed consultant as well as member of the board of the energy cooperative and trade association

Christian Podeswa, training consultant of Helios Ventilatoren GmbH & Co. KG

Sven Rentschler, CEO of Reven GmbH

Wolf Rienhardt, self-employed as an engineer, trainer and HVAC technology consultant, and member of the German professional association for air and water hygiene (DFLW)

Marcel Riethmüller, Managing Director of ecogreen Energie GmbH & Co. KG

Reinhard Siegismund, publicly appointed and sworn expert and consulting engineer of the association of consultant engineers VBI

Jörg Mez, Managing Director of MEZ-TECHNIK GmbH (co-author)

Tina Weinberger – copywriter, Dr.-Ing. in mechanical engineering (power engineering) and freelance journalist