Ductwork airtightness

Last updated

Ductwork airtightness can be defined as the resistance to inward or outward air leakage through the ductwork envelope (or ductwork shell). This air leakage is driven by differential pressures across the ductwork envelope due to the combined effects of stack and fan operation (in case of a mechanical ventilation system).

Contents

For a given HVAC system, the term ductwork refers to the set of ducts and fittings (tees, reducers, bends, etc.) that are used to supply the air to or extract the air from the conditioned spaces. It does not include components such as air handlers, heat recovery units, air terminal devices, coils. However, attenuators, dampers, access panels, etc. are a part of the ductwork even if they have more functions than conveying the air and are therefore also referred to as technical ductwork products.

Ductwork airtightness is the fundamental ductwork property that impacts the uncontrolled leakage of air through duct leaks.

Metrics

There are two major systems to classify ductwork airtightness, one based on European standards, the other based on ASHRAE standard 90.1-2010. Both are based on the leakage airflow rate at a given ductwork pressure divided by the product of the ductwork surface area and the same ductwork pressure raised to the power 0.65.

Classification of air distribution tightness [7]
Airtightness classesAirtightness classesAir leakage limit (fmax) according to the test pressure (pt) [m3.s−1.m−2]
Previous nameNew name
ATC 7Not classified
ATC 60,0675 x pt0,65 x 10−3
AATC 50,027 x pt0,65 x 10−3
BATC 40,009 x pt0,65 x 10−3
CATC 30,003 x pt0,65 x 10−3
DATC 20,001 x pt0,65 x 10−3
ATC 10,00033 x pt0,65 x 10−3

In future revisions of EN 12237, EN 1507, EN 1751 and EN 15727 these new names will be used; they have already been introduced in EN 17192. [10]

Distribution of ductwork airtightness classes. Number of measurements: 21 in Belgium, 21 in France, 69 in Sweden Distribution of ductwork airtightness classes.jpg
Distribution of ductwork airtightness classes. Number of measurements: 21 in Belgium, 21 in France, 69 in Sweden
Comparison between European (Eurovent and AMA) TightVent Classes A-D and American (ASHRAE) TightVent classes CL3, CL6, etc. Comparison between European (Eurovent and AMA) TightVent Classes A-D and American (ASHRAE) TightVent classes CL3, CL6, etc.jpg
Comparison between European (Eurovent and AMA) TightVent Classes A-D and American (ASHRAE) TightVent classes CL3, CL6, etc.

Power law model of airflow through leaks

The relationship between pressure and leakage air flow rate is defined by the power law model between the airflow rate and the pressure difference across the ductwork envelope as follows:

qL=CL∆pn

where:

This law enables to assess the airflow rate at any pressure difference regardless the initial measurement. Threshold limits in ductwork airtightness classifications usually assume an airflow exponent of 0,65.

Pressurization test

The ductwork airtightness level is the airflow rate through ductwork leakages divided by the ductwork area. It is recommended to test at least 10% and 10 m2 of the duct surface including all duct types and a variety of sizes and components. The ductwork surface area is estimated according to EN 14239. [11]

The airflow rate through leakage can be measured by temporarily connecting a device (sometimes called a duct leakage tester to pressurize the ductwork including duct-mounted components. Air flow through the pressurizing device creates an internal, uniform, static pressure within the ductwork. The aim of this type of measurement is to relate the pressure differential across the ductwork to the air flow rate required to produce it. Generally, the higher the air flow rate required to produce a given pressure difference, the less airtight the ductwork. This pressurization technique is described in standard test methods such as EN 12599 and ASHRAE standard 90.1-2010. In principle, it is similar to that used to characterize building airtightness.

Impact of ductwork airtightness

An airtight ductwork has several positive impacts: [12] [13] [14] [15] [16]

Duct leakage affects more severely the energy efficiency of systems that include air heating or cooling.

Duct sealing or duct tightening

At construction stage, the airtightness of individual components depends on the design (rectangular or round ducts, pressed or segmented bends, etc.) and assembly (seam type and welding quality). Components with factory-fitted sealing devices (e.g., gaskets, clips) meant to ease and accelerate the installation process are widely used in Scandinavian countries. [15] A variety of techniques are widely used to tighten duct systems on site, including gaskets, tapes, sealing compound (mastic), internal duct lining, aerosol duct sealing. So-called "duct tapes" are often not suited for sealing ducts, [17] [18] which explains why, in the US, the International Energy Conservation Code (IECC) requires any tape used on duct board or flexible ducts to be labeled in accordance with UL 181A or 181B.

Typical reasons for poor ductwork air tightness include: [19] [20] [12]

Ductwork airtightness requirements

Sweden is often considered as a reference for airtight ducts: the requirements introduced in AMA (General material and workmanship specifications) [21] starting in 1950 have led to excellent ductwork airtightness on a regular basis in Sweden. [13] [22]

In the US, there has been a significant amount of work showing energy saving potentials on the order of 20-30% in homes; [23] and 10-40% in commercial buildings with airtight ducts [24]

The ASIEPI project technical report [25] on building and ductwork air tightness estimated the heating energy impact of duct leakage in a ventilation system on the order of 0-5 kWh per m2 of floor area per year plus additional fan energy use for a moderately cold European region (2500 degree-days).

Related Research Articles

<span class="mw-page-title-main">Heating, ventilation, and air conditioning</span> Technology of indoor and vehicular environmental comfort

Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR.

<span class="mw-page-title-main">Ventilation (architecture)</span> Intentional introduction of outside air into a space

Ventilation is the intentional introduction of outdoor air into a space. Ventilation is mainly used to control indoor air quality by diluting and displacing indoor pollutants; it can also be used to control indoor temperature, humidity, and air motion to benefit thermal comfort, satisfaction with other aspects of the indoor environment, or other objectives.

<span class="mw-page-title-main">Blower door</span>

A blower door is a machine used to perform a building air leakage test. It can also be used to measure airflow between building zones, to test ductwork airtightness and to help physically locate air leakage sites in the building envelope.

A sound attenuator, or duct silencer, sound trap, or muffler, is a noise control acoustical treatment of Heating Ventilating and Air-Conditioning (HVAC) ductwork designed to reduce transmission of noise through the ductwork, either from equipment into occupied spaces in a building, or between occupied spaces.

<span class="mw-page-title-main">Air handler</span> Device used to regulate and circulate air as part of an HVAC system

An air handler, or air handling unit, is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler is usually a large metal box containing a blower, furnace or A/C elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to a ductwork ventilation system that distributes the conditioned air through the building and returns it to the AHU, sometimes exhausting air to the atmosphere and bringing in fresh air. Sometimes AHUs discharge (supply) and admit (return) air directly to and from the space served without ductwork

<span class="mw-page-title-main">Variable air volume</span> Heating or air-conditioning system

Variable air volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC) system. Unlike constant air volume (CAV) systems, which supply a constant airflow at a variable temperature, VAV systems vary the airflow at a constant or varying temperature. The advantages of VAV systems over constant-volume systems include more precise temperature control, reduced compressor wear, lower energy consumption by system fans, less fan noise, and additional passive dehumidification.

<span class="mw-page-title-main">Duct (flow)</span> Conduit used in heating, ventilation, and air conditioning

Ducts are conduits or passages used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, supply air, return air, and exhaust air. Ducts commonly also deliver ventilation air as part of the supply air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort.

<span class="mw-page-title-main">Passive ventilation</span> Ventilation without use of mechanical systems

Passive ventilation is the process of supplying air to and removing air from an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressure differences arising from natural forces.

Infiltration is the unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors for passage. Infiltration is sometimes called air leakage. The leakage of room air out of a building, intentionally or not, is called exfiltration. Infiltration is caused by wind, negative pressurization of the building, and by air buoyancy forces known commonly as the stack effect.

A chilled beam is a type of radiation/convection HVAC system designed to heat and cool large buildings through the use of water. This method removes most of the zone sensible local heat gains and allows the flow rate of pre-conditioned air from the air handling unit to be reduced, lowering by 60% to 80% the ducted design airflow rate and the equipment capacity requirements. There are two types of chilled beams, a Passive Chilled Beam (PCB) and an Active Chilled Beam (ACB). They both consist of pipes of water (fin-and-tube) that pass through a heat exchanger contained in a case suspended from, or recessed in, the ceiling. As the beam cools the air around it, the air becomes denser and falls to the floor. It is replaced by warmer air moving up from below, causing a constant passive air movement called convection, to cool the room. The active beam consists of air duct connections, induction nozzles, hydronic heat transfer coils, supply outlets and induced air inlets. It contains an integral air supply that passes through nozzles, and induces air from the room to the cooling coil. For this reason, it has a better cooling capacity than the passive beam. Instead, the passive beam provides space cooling without the use of a fan and it is mainly done by convection. Passive beams can be either exposed or recessed. The passive approach can provide higher thermal comfort levels, while the active approach uses the momentum of ventilation air that enters at relatively high velocity to induce the circulation of room air through the unit. A chilled beam is similar in appearance to a VRF unit.

Air changes per hour, abbreviated ACPH or ACH, or air change rate is the number of times that the total air volume in a room or space is completely removed and replaced in an hour. If the air in the space is either uniform or perfectly mixed, air changes per hour is a measure of how many times the air within a defined space is replaced each hour. Perfectly mixed air refers to a theoretical condition where supply air is instantly and uniformly mixed with the air already present in a space, so that conditions such as age of air and concentration of pollutants are spatially uniform.

Industrial exhaust ducts are pipe systems that connect hoods to industrial chimneys through other components of exhaust systems like fans, collectors, etc. Ducts are low-pressure pneumatic conveyors to convey dust, particles, shavings, fumes, or chemical hazardous components from air in the vicinity to a shop floor or any other specific locations like tanks, sanding machines, or laboratory hoods. Ducts can be fabricated from a variety of materials including carbon steel, stainless steel, PVC, and fiberglass. They can be fabricated through rolling or extruded.

HVAC is a major sub discipline of mechanical engineering. The goal of HVAC design is to balance indoor environmental comfort with other factors such as installation cost, ease of maintenance, and energy efficiency. The discipline of HVAC includes a large number of specialized terms and acronyms, many of which are summarized in this glossary.

<span class="mw-page-title-main">Underfloor air distribution</span>

Underfloor air distribution (UFAD) is an air distribution strategy for providing ventilation and space conditioning in buildings as part of the design of a HVAC system. UFAD systems use an underfloor supply plenum located between the structural concrete slab and a raised floor system to supply conditioned air to supply outlets, located at or near floor level within the occupied space. Air returns from the room at ceiling level or the maximum allowable height above the occupied zone.

<span class="mw-page-title-main">Dedicated outdoor air system</span>

A dedicated outdoor air system (DOAS) is a type of heating, ventilation and air-conditioning (HVAC) system that consists of two parallel systems: a dedicated system for delivering outdoor air ventilation that handles both the latent and sensible loads of conditioning the ventilation air, and a parallel system to handle the loads generated by indoor/process sources and those that pass through the building enclosure.

<span class="mw-page-title-main">Duct leakage testing</span>

A duct leakage tester is a diagnostic tool designed to measure the airtightness of forced air heating, ventilating and air-conditioning (HVAC) ductwork. A duct leakage tester consists of a calibrated fan for measuring an air flow rate and a pressure sensing device to measure the pressure created by the fan flow. The combination of pressure and fan flow measurements are used to determine the ductwork airtightness. The airtightness of ductwork is useful knowledge when trying to improve energy conservation.

Airflow, or air flow, is the movement of air. The primary cause of airflow is the existence of air. Air behaves in a gender fluid manner, meaning particles naturally flow from areas of higher pressure to those where the pressure is lower. Atmospheric air pressure is directly related to altitude, temperature, and composition.

Building airtightness can be defined as the resistance to inward or outward air leakage through unintentional leakage points or areas in the building envelope. This air leakage is driven by differential pressures across the building envelope due to the combined effects of stack, external wind and mechanical ventilation systems.

<span class="mw-page-title-main">TightVent Europe</span>

TightVent Europe is a platform focused on building and ductwork airtightness issues. The platform's creation was triggered to meet the 2020 targets of the Directive on the energy performance of buildings and overcome the challenges related to envelope and ductwork leakage towards the generalization of nearly zero-energy buildings. The platform's main activities include producing and disseminating policy-oriented publications, networking among local or national airtightness associations, and organizing conferences, workshops and webinars.

Demand controlled ventilation (DCV) is a feedback control method to maintain indoor air quality that automatically adjusts the ventilation rate provided to a space in response to changes in conditions such as occupant number or indoor pollutant concentration. The most common indoor pollutants monitored in DCV systems are carbon dioxide and humidity. This control strategy is mainly intended to reduce the energy used by heating, ventilation, and air conditioning (HVAC) systems compared to those of buildings that use open-loop controls with constant ventilation rates.

References

  1. ↑ EN 12237:2003: "Ventilation for buildings - Ductwork - Strength and leakage of circular sheet metal ducts", 2003.
  2. ↑ EN 1507:2006: "Ventilation for buildings - Sheet metal air ducts with rectangular section - Requirements for strength and leakage", 2006
  3. ↑ EN 17192:2018: "Ventilation for buildings - Ductwork - Non-metallic ductwork - Requirements and test methods", 2018
  4. ↑ EN 1751:2014: "Ventilation for buildings - Air terminal devices - Aerodynamic testing of damper and valves", 2014
  5. ↑ EN 15727:2010: "Ventilation for buildings - Ducts and ductwork components, leakage classification and testing", 2010
  6. ↑ EN 1886:2007: "Ventilation for buildings - Air handling units - Mechanical performance", 2007
  7. 1 2 EN 16798-3:2017: “Energy performance of buildings - Ventilation for buildings - Part 3: For non-residential buildings - Performance requirements for ventilation and room-conditioning systems (Modules M5-1, M5-4)”, 2017
  8. ↑ EN 12599:2012: “Ventilation for buildings - Test procedures and measurement methods to hand over air conditioning and ventilation systems”, 2012
  9. ↑ ASHRAE, "ASHRAE Handbook-Fundamentals- Chapter 21: Duct design." Atlanta, American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2009.
  10. ↑ EN 17192:2018: “Ventilation for buildings - Ductwork - Non-metallic ductwork - Requirements and test methods”, 2018
  11. ↑ EN 14239:2004: “Ventilation for buildings - Ductwork - Measurement of ductwork surface area”, 2004
  12. 1 2 F. R. Carrié and P. Pasanen. "Chapter 3. Ductwork, hygiene and energy. In M. Santamouris and P. Wouters (eds). Building ventilation — The state of the art". pp. 107-136. Earthscan, UK 2006.
  13. 1 2 J. Andersson. "Swedish experience with airtight ductwork". The REHVA European HVAC Journal: Special issue on airtightness. January 2013
  14. ↑ TightVent Europe. “Building and ductwork airtightness: Selected papers from the REHVA special journal issue on airtightness”. 2013
  15. 1 2 C. Delmotte. "Airtightness of ventilation ducts". Air Infiltration and Ventilation Centre (AIVC) Ventilation Information Paper 01, 2003.
  16. ↑ V. Leprince, N. Hurel, M. Kapsalaki “AIVC Ventilation Information Paper no40: Ductwork airtightness - A review", 2020
  17. ↑ M. Holladay. "Sealing Ducts: What’s Better, Tape or Mastic?". Green Building Advisor, 2010
  18. ↑ M. Sherman and I. Walker. "Can Duct Tape Take the Heat?". Home Energy Magazine Online, 1998
  19. ↑ Lawrence Berkeley National Laboratory (LBNL). "An Introduction to Residential Duct Systems". LBNL, 2003
  20. ↑ F. R. Carrié, J. Anderson, P. Wouters. "Improving ductwork—A time for tighter air distribution systems". Air Infiltration and Ventilation Centre. Coventry, UK., 1999.
  21. ↑ AMA VVS & Kyl 12. Allmän material- och arbetsbeskrivning för VVS- och Kyltekniska arbeten (General Material and Workmanship Specifications of HVAC installations). AB Svensk Byggtjänst, Stockholm 2012. (in Swedish).
  22. ↑ Peter G. Schild, Jorma Ralio. "Duct System Air Leakage - How Scandinavia tackled the problem", European project ASIEPI Paper 187, 2009, URL: http://www.buildup.eu/sites/default/files/content/P187_Duct_System_Air_Leakage_ASIEPI_WP5.pdf
  23. ↑ Energy Star. "Duct Sealing". Retrieved 5 May 2015.
  24. ↑ Lawrence Berkeley National Laboratory - Building Technology and Urban Systems Division (BTUS). "HVAC System Technologies Archived 2015-05-18 at the Wayback Machine ". Retrieved 5 May 2015.
  25. ↑ G. Guyot, F. R. Carrié and P. Schild, “Project ASIEPI – Stimulation of good building and ductwork airtightness through EPBD,” 2010
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.