Ventilation duct
Ventilation ducts or ventilation pipes are an essential part of ventilation systems and are mainly used to guide air. These air guidance systems mostly consist of rectangular or round components, that is to say of ducts or spiral-seam tubes . From a fluidic point of view, the use of pipes is the optimal variant, since only the hydraulic diameter is used in channels . Ventilation ducts can be installed in a space-saving manner, but the manufacturing, installation and material costs are significantly greater. As a compromise, smaller air distribution systems also use oval pipes.
The air flows in these duct or pipe systems as a laminar or turbulent flow , analogous to water. The same equations are used for the most important calculations as in water engineering . These include the Bernoulli's equation and the continuity equation . Detailed knowledge of the corresponding coefficients of friction (R value) of square pipes, the coefficients of friction (zeta value) of various fittings and the differential pressure of duct installation components expand the individual calculations and considerations. The planning of these air control systems is based on VDI 2087 or current standards according to DIN EN 13779 . (EN 13779 has been replaced by EN 16798)
Very large ventilation ducts, for air volumes of, for example, 300,000 m³ / h as at an airport , are bricked or poured from concrete, and can also be several kilometers long underground .
Another criterion for differentiating the quality of a ventilation duct or pipe is the differentiation between low-pressure, medium-pressure and special high-pressure systems. "According to DIN EN 12237 for pipes and fittings −750 to +2000 Pa, deviating from this, higher pressures can be achieved after testing and, if necessary, with additional measures." The following description refers to low and medium pressure systems within the meaning of DIN EN 12237.
Terminology
The air-guiding elements of a ventilation system are usually referred to in technology as air or ventilation ducts or, according to their design, as folded spiral ducts or flexible ducts .
By contrast, ventilation ducts often refer to the components of a drainage system that are used to ventilate the sewage system and the domestic sewage pipes .
Ventilation pipe is a neutral term for rather small-sized elements for air routing.
material
Most ventilation ducts and pipes in low and medium pressure systems are made of thin, galvanized sheet steel. For special requirements, ducts and pipes made of stainless steel , aluminum or various plastics are also used. In certain fire sections of a building , ducts and molded parts made of calcium silicate are also possible or even mandatory from a fire protection point of view.
Further quality features are the stability of the air duct, i.e. the material thickness and the mass-produced air duct profile frame made of rolled sheet metal strips, over which the individual duct segments are screwed together. In contrast, pipes are connected with collar collars, sleeves or nipples . Welded flanges are used for oil- and grease-tight welded ventilation ducts or pipes .
If there are requirements for the twisting of air ducts, these are set in the surfaces or ensured by stiffening in the duct. However, reinforcements made of profile steel are also welded onto the outside of a ventilation duct. In order to keep the air flow in molded parts laminar, inflow spheres or air baffles are installed in larger bends or molded parts , for example .
Switzerland: “Ventilation ducts must be made of non-flammable material. Within apartments and single-family houses, this does not apply to ventilation ducts, earth registers and ducts from systems with an air temperature of up to 40 ° C. With the exceptions mentioned, however, the fire code number 4.2 (VKF guidelines) must be observed. For kitchen exhaust (steam vent) does not apply to this exception. "
Fittings
A complete channel or pipe system also consists of matching fittings such as elbows, transitions, reducers , outlets, tees , Y-pieces , spigot, sliding flange, through the roof, deflector hood , etc.
Duct installation components
In addition to the air guide members channel or tube, are in a complete air handling system but duct components such as canvas connector , bag filters , ionizing , steam humidifier , electrostatic air cleaner , throttle valves , slide , swing check valves , baffles , sensors for temperature / humidity / CO, fire dampers , activated carbon filter , silencer , active Silencers, volume flow controllers , heating registers , cooling registers , air outlets , etc. are integrated directly into the intended duct or pipe section. These duct installation components also flow into the pressure loss calculation with their very own pressure loss and must be taken into account during hydraulic / pneumatic balancing.
The air in a duct or pipe system flows in the desired amount and in the intended air direction, due to the targeted use of fans that increase the pressure in the system and determine the direction. Depending on the ventilation system, radial or axial fans with different performance curves are installed. Compact ventilation devices with various built-in components for changing the air temperature , humidity , etc. are also calculated, dimensioned and installed.
Attachment
A duct or pipe system is mostly installed on or in ceilings , but also in floors or in risers. It is attached to the duct using angle plates and to the pipe using pipe clamps , with threaded rods on ceilings or walls. Various profile steels in the form of consoles, traverses , stands, suspensions, etc. are possible at any time to absorb the weight . The decoupling of the ventilation duct from the building structure is absolutely necessary from a sound-technical point of view and is done using round rubber buffers or foam rubber strips in the clamps.
Tightness
The tightness of air control systems, which is defined in tightness classes, has a major influence on the construction and operating costs of a ventilation system. Leaks mostly occur at flange connections. The higher the tightness requirement, the higher the effort involved in manufacturing the duct and pipe parts themselves and in assembling them properly in the building.
“A certain tightness class can be specified directly in the contract. This is also possible indirectly, if reference is made in the contract to a standard that defines the tightness measurement. For example, the EN 12237 standard relates to the pipeline system and the EN 12599 standard to the handover. "
There are four airtightness classes (LDK A - LDK D). Permissible leakages are defined in the individual airtightness classes. The airtightness required there always relates to an "installed (air duct) system", ie not just to a single component of the duct. It must also be noted that this tightness has nothing to do with the airtightness of buildings, i.e. the blower door test , and must not be confused with it.
Sealing measures
According to VDI 6022, increased attention to cleanliness is necessary when manufacturing and installing air ducts . On the one hand, the production and processing of the air ducts as such must be of high quality and, on the other hand, suitable assembly systems must be used to achieve the required airtightness class. The air ducts must be checked for damage even before the actual processing or installation. A high airtightness class can be achieved by using suitable sealing tape or other suitable assembly systems.
Air duct profiles with inserted seals are increasingly being used and sealing compound is injected into the folds during the manufacturing process. Another possibility to meet increased tightness requirements is the use of molded profiles. There is no material separation between component and flange because the flange is formed out of the component.
There are special requirements for tightness, especially in the case of oil- and grease-tight ducts or pipes, for example in kitchen systems or in the case of oil mist extractors on CNC machines. During commissioning , the overall tightness can be assessed , measured and calculated.
Proof of airtightness - airtightness test
To ensure that the air duct system is tight and that the required airtightness class is maintained, an airtightness test must be carried out. This is, for example, in the standards DIN EN 13779 "Ventilation of non-residential buildings - General principles and requirements for ventilation and air conditioning systems", DIN EN 12599 "Test and measurement procedures for the handover of ventilation and air conditioning systems" and VDI 3803 Part 1 "Central ventilation systems - Structural and technical requirements "required.
Reasons for an airtightness test
Leaky ventilation systems use energy unnecessarily (see Energy Saving Ordinance ) and increase the risk of hygienic impairments, which must be avoided. In the VDI 6022 guideline , a “hygienically perfect indoor air quality” is required.
Procedure for an airtightness test
The airtightness test should be carried out as long as the system is accessible so that any rework can be carried out. Ideally, this should be done in sections and, due to the high effort involved, randomly. Various calibrated test devices such as B. the airtightness tester airLPT113. These determine the airtightness class according to DIN EN 13779, DIN EN 1507 and DIN EN 12237 in ventilation and air conditioning systems. In order to check the tightness, the air control system to be tested must be hermetically sealed by the rest of the system. The use of adhesive tape or foil for sealing should be avoided and instead use professional closures, e.g. B. be made through end covers. Before the test, the test surface must be determined in accordance with DIN EN 14239.
The airtightness tester is connected to already prepared measuring openings (collar, inspection openings with corresponding connections). The pressure should now be selected either as overpressure for supply air lines or as negative pressure for exhaust air lines in the order of magnitude of 200 Pa, 400 Pa or 1000 Pa, so that the regulations of DIN EN 12559 are met. The system is pressurized, the test pressure is automatically regulated and kept constant (according to DIN EN 1507 or DIN EN 12237 ± 5%) and the amount of leakage air is determined. According to DIN EN 1507 and DIN EN 12237, the measurement process takes 5 minutes. The measurement protocol can be sent to the integrated thermal printer or to a USB stick.
Measures if the amount of leakage air is too high
If, after testing, it turns out that the amount of leakage air is too high, i.e. the required airtightness class has not been achieved, repair work must be carried out. A visual inspection of the closed air line ends, the connection and flange points should be done first. If this does not provide clarification, a competent company should be consulted for the examination. If leaks or their effects are noticeable afterwards, this usually results in considerable costs.
Hydraulic channel or pipe network calculation
With a sewer network calculation, the components of a system are hydraulically dimensioned in such a way that the required volume flows are actually set during operation. For an air duct network calculation , these are the outside air flow ( ODA ), supply air flow ( SUP ), exhaust air flow ( ETA ), exhaust air flow ( EHA ), circulating air flow ( RCA ) and mixed air flow ( MIA ). These vary in size depending on the real situation and must be designed individually.
For the simplified pressure loss calculation one needs, among other things, the Bernoulli equation , the continuity equation as well as knowledge of the friction values (R value) of square pipes and the pressure loss coefficient ( zeta value ) of fittings and system components such as filters, etc.
There are basically three approaches for a simplified view:
- Sewer network calculation through assumption of speed,
- Sewer network calculation according to constant pressure gradient,
- Sewer network calculation based on the given pressure difference.
In extensive computer programs and algorithms, the current / desired parameters such as air velocities , flow indicators , pipe friction coefficients , resistance coefficients , etc., which dimension the system, are entered for a wide variety of applications .
Complete sewer and pipe network calculations can already be carried out before the actual implementation on the building site, on the basis of drawings of the sewer system. This simplified theoretical approach is used to estimate the necessary pressure increase ( Pascal ) and to determine the appropriate fan type (axial or radial fan) or power consumption (kW).
In addition to the simplified approach, in which the experimental pressure losses of the individual resistances are added, numerical fluid dynamics (CFD: Computational Fluid Dynamics ) takes into account the interaction of all components connected in series and enables a much more precise dimensioning of the fan or the optimal operating point.
Pneumatically unbalanced duct systems are subject to the following aspects:
- Duct systems with air velocities that are too low are oversized in the duct or pipe cross-section and are a pure waste of material and space.
- Duct systems with too high air velocities are undersized and cause loud flow noises.
- Duct systems with an excessive proportion of unfavorable molded parts and, as a result, increased flow resistance, may exceed the previously designed fan output and thus cannot realize the planned air volumes. More powerful fans simply consume more electricity.
- Duct systems with hydraulically nonsensical outlets or connections and inadequate regulation options (throttle valve) lead to over- or undersupply of various sub-areas (lack of air or drafts + flow noise).
- Duct systems with a differential pressure load that is much too high tend to have an audible and even visible bulge or soffit of the ventilation ducts, which occur when the fans are switched on and lead to considerable damage.
- Canal systems that permanently decay from an ideal laminar flow to a turbulent flow , consume considerably more energy for this turbulence , which can only be compensated by increasing the pressure (more drive energy).
Electrolytic voltage series
Complete duct and pipe systems usually consist of very different materials after they have been fully assembled under construction. These different voltage potentials lead to an electrolytic series of voltages, whereby the material with the lowest voltage potential is the first to dissolve (rusts / corrodes). But also because of the permanent air flow in the system and the resulting frictional losses, the electrolytic voltage series is additionally supplied with energy.
The electrolytic voltage series is to be counteracted by the professional installation of protective conductors in the entire system and subsequent equipotential bonding by earthing on an equipotential bonding rail.
Air has an oxygen content of approx. 21% and therefore has a certain oxidation potential itself. The outside air in the outside space, i.e. in cities, rural areas or in mountain regions, has different ion concentrations. An ion concentration of approx. 1700 ions / cm³ is most comfortable for humans, because the oxygen uptake through the lungs is optimal.
When this outside air is transported in the canal system, the charged oxygen releases most of its oxidation energy to the canal system and later reaches its destination in the interior with a lower ion concentration.
insulation
Ventilation ducts are insulated outside or inside to avoid heat or cold losses or to avoid the formation of condensation. The insulation can be dispensed with if the air transported in the ventilation ducts has the same temperature as that of the surroundings or if heat transfer via the duct surface is not regarded as critical. Typical is the use of rock wool , mineral wool (aluminum-laminated) or hard / soft foam panels, for example made from Armaflex, Kaiflex or Styrodur. The material thickness / thickness of the insulation was based on the expected temperature difference and the thermal conductivity of the insulation used. The material to be used also depends on whether condensation should be prevented on or in the duct surface by falling below the dew point. In these areas, insulation made of diffusion-tight soft foam panels is often chosen. Air duct systems are also available in segmented construction, which themselves consist of stiff insulating material and do not use a classic air duct. In accessible areas / walkways, this insulation is protected by sheet metal cladding on a ventilation duct. Bumpers in the head area are also provided with buffers and signal bands. In the case of special duct sections , for example fire shafts, heat-resistant inner insulation made of kieselguhr or rock wool is also used.
hygiene
Air is a basic foodstuff for humans and animals. The "transport" of these in a ventilation duct must be checked regularly. "The DIN EN 15780 standard describes requirements and procedures for assessing cleanliness and the possible need for cleaning, especially for air duct systems in central air conditioning systems."
Ventilation ducts and pipes should be provided with as many large and small inspection openings as possible, i.e. re-closable covers, in order to be able to carry out regular visual inspections or controls in accordance with VDI 6022 . The minimum dimensions of cleaning openings in ventilation ducts and pipes are specified in DIN EN 12097.
Dirty ventilation ducts form an ideal breeding ground for microorganisms that multiply and permanently release toxins, viruses, spores and bacteria into the air flow. These reach people's living space via the "supply air" and also spread there.
It is the responsibility of the system operator to monitor the ventilation system. In the case law of the Federal Court of Justice it says: " The plant operator is responsible for instruction, selection and monitoring obligations insofar as he delegates tasks or activities to employees or contractors ". These are specified in: §4, number 7 ArbSchG and §15, SGB VII and the accident prevention regulations issued thereafter.
Norms
There are relevant standards in Germany and throughout Europe.
Germany
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DIN 1946 [2009-05] Raumlufttechnik
- Part 6: Ventilation of apartments - General requirements, requirements for dimensioning, execution and marking, handover / acceptance (acceptance) and maintenance
-
DIN 18379 [2012-09] VOB procurement and contract regulations for construction work
- Part C: General technical contract conditions for construction works (ATV) - ventilation systems
Europe
- DIN EN 1505 [1998-02] Ventilation of buildings - Air ducts and fittings made of sheet metal with rectangular cross-section - Dimensions
- DIN EN 1506 [2007-09] Ventilation of buildings - Air ducts and fittings made of sheet metal with round cross-section - Dimensions
- DIN EN 1507 [2006-07] Ventilation for buildings - Rectangular sheet metal ducts - Requirements for strength and tightness
- DIN EN 1751 [1999-01] Ventilation of buildings - Devices of the air distribution system - Aerodynamic tests of throttle and shut-off elements
- DIN EN 12097 [2006-11] Ventilation for buildings - Air ducts - Requirements for air duct components for the maintenance of duct systems
- DIN EN 12236 [2002-04] Ventilation of buildings - Suspensions and supports for air ducts - Requirements for strength
- DIN EN 12237 [2003-07] Ventilation of buildings - Air ducts - Strength and tightness of ducts with round cross-sections made of sheet metal
- DIN EN 12599 [2008-08] Test and measurement procedures for the handover of ventilation and air conditioning systems
- DIN EN 12792 [2004-01] Ventilation for buildings - Symbols, terminology and graphic symbols
- DIN EN 13180 [2002-03] Ventilation for buildings - Air ducts - Dimensions and mechanical requirements for flexible air ducts
- DIN EN 13779 [2007-09] Ventilation of non-residential buildings - General principles and requirements for ventilation and air conditioning systems
- DIN EN 14239 [2004-04] Ventilation for buildings - Air ducts - Measurement of duct surfaces
Web links
- Air ducting in angular air ducts - product description, legal information, detailed information ( Memento from March 15, 2013 in the Internet Archive ) (PDF; 517 kB) BerlinerLuft GmbH, accessed June 18, 2013
- Operation of ventilation and air conditioning systems in public buildings. (PDF; 500 kB). 2008. www.amev-online.de, accessed on August 19, 2013
Individual evidence
- ↑ Air ducts in stainless steel. (PDF; 484 kB). Lindab GmbH , accessed on May 23, 2013.
- ↑ Patent for ventilation duct reinforcement European Patent Office EP030982A2 www.epo.org , accessed on May 21, 2013.
- ↑ Dimensioning aid for comfort ventilation ( Memento from November 25, 2010 in the Internet Archive ) (PDF; 304 kB) Swiss Energy , accessed on July 4, 2013.
- ↑ Lindab leak tester (PDF; 204 kB) Lindab GmbH , accessed on May 23, 2013.
- ↑ Installation recommendation for square folded ducts / molded parts. ( Memento of May 18, 2015 in the Internet Archive ) Retrieved July 15, 2014.
- ↑ J. Lötfering: Test and measurement methods for ventilation and air conditioning systems - DIN EN 12599: 2013 Contents and significant changes , June 30, 2014.
- ↑ DIN EN 13779, Ventilation of non-residential buildings - General principles and requirements for ventilation and air conditioning systems; German version EN 13779, September 2007.
- ↑ M. Stahl: VDi 3803 sheet 1 - Requirements for central ventilation and air conditioning systems (VDI ventilation rules) 2010 , accessed on July 10, 2014.
- ↑ H. Mörchen: Hygiene in air conditioning systems: Requirements for air conditioning systems for office and administration rooms. 2001, ISBN 3-8169-2047-0 .
- ↑ VDI 6022 sheet 1.1, air conditioning, air quality - hygiene requirements for air conditioning systems - devices - testing of air conditioning systems, August 2012.
- ↑ A. Keune: News on indoor air quality according to the current standards VDI 6022, DIN EN 13779, 12792, 13779, 15251 etc. VDI 6022 Part 1, Hygiene requirements for air conditioning systems and devices , accessed on July 2, 2014.
- ↑ M. Trenner: Hygienic aspects with controlled living space ventilation in relation to the VDI guideline 6022. Norderstedt 2007, p. 88.
- ↑ H. Ackerschott, U. Fröhlich, C. Mühlenkamp: Technical building equipment: Commentary on VOB Part C ATV DIN 18379; ATV DIN 18380 ATV DIN 18381. Berlin 2013, p. 160 ff.
- ↑ J. Lötfering: Test and measurement methods for ventilation and air conditioning systems - DIN EN 12599: 2013 Contents and significant changes , June 30, 2014.
- ↑ Cleanliness of air duct components in the press according to VDI 6022 and DIN EN 15780 (PDF; 80 kB) PR Lindab GmbH , accessed on May 23, 2013.
- ↑ Lüftungskanal - Luftungsleitung , www.baunormenlexikon.de , accessed on September 4, 2013.