How ductwork can help you achieve the Target Emission Rate (TER)
Ductwork can have a significant impact on whether a building achieves its TER due to the energy required to run the ductwork system and the various aspects that can affect this. This post explores why….
Measuring the air-leakage of a ductwork system is an important element of the 2013 Building Regulations as the air-leakage of a ductwork system will have a significant impact on electrical consumption due to the heating and cooling loads and relative fan energy use. In this blog, you’ll learn about the regulation prescribed to achieve the standard detailed in both Approved Document AL2A and AL2B for the air-leakage of ductwork installed into new and existing non-domestic buildings.
Each fixed building service in a building, including air-conditioning and mechanical ventilation systems, should be at least as efficient as the minimum acceptable value for the particular type of service as set out in the 2013 edition of supporting document the ‘Non-domestic Building Services Compliance Guide’ (NDBSCG), published by DCLG. The NDBSCG is the supporting document to both ADL2A and ADL2B.
The NDBSCG states that in order to limit air-leakage, ventilation ductwork should be made and assembled so as to be reasonably airtight. Satisfactory ways of meeting this requirement would be to comply with the specifications given in the following:
- BS EN 13403 (Ventilation for buildings. Non-metallic ducts. Ductwork made from insulation ductboards);
- BS EN 1507 (Ventilation for buildings. Sheet metal air ducts with rectangular section. Requirements for strength and leakage);
- BS EN 12237 (Ventilation for buildings. Ductwork. Strength and leakage of circular sheet metal ducts); or
- B&ES DW/144 (Building & Engineering Services Association – Specification for Sheet Metal Ductwork).
The above documents provide guidance on several aspects of ductwork fabrication. It is accepted that the air-leakage occurs largely at the seams and joints of the ductwork system so guidance is provided on the correct products to use, which have been tested to DW / TM1 (acceptance scheme for new products – rectangular cross joint classification), which has now been superseded by BS EN 1507: 2006 (Ventilation for buildings. Sheet metal air ducts with rectangular section. Requirements for strength and leakage).
In addition, it is agreed that the level of air-leakage of ductwork is relative to the pressure at which the ductwork is operating. Therefore, within all the above mentioned specifications, ductwork is classified according to its pressure classification: A, B, C or D. Air-leakage limits are defined for each pressure class. Class D represents ductwork operating at the highest pressures and requires the lowest air-leakage limit, whilst Class A operates at the lowest pressures and requires the least stringent air-leakage limit. The more stringent the air-leakage limit, the greater the contribution towards reducing the overall CO2 emissions per square metre of useable floor area of the building when setting the TER.
With Class C and D air-leakage limits now being included into SBEM calculations, it is clear that using airtight ductwork can contribute significantly to reducing the BER.
The maximum allowable air-leakage rates, expressed as litres of air per second per surface area of duct (l/s/m²), for each pressure class over a range of design pressures are shown below.
|Design Static Pressure|
|Duct Pressure Class||Maximum Positive (Pa)||Maximum Negative (Pa)||Maximum Air Velocity||Air-leakage Limit (l/s/m²)|
|Low Pressure – Class A||500||500||10||0.027 x Δp0.065|
|Medium Pressure – Class B||1000||750||20||0.009 x Δp0.065|
|High Pressure – Class C||2000||750||40||0.003 x Δp0.065|
|High Pressure – Class D||2000||750||40||0.001 x Δp0.065|
|Where p is the differential pressure in Pascals (Pa)|
ADL2A and L2B require ductwork air-leakage testing, as part of the commissioning process, where required and in accordance with the procedures set out in B&ES DW/143 (A Practical Guide to Ductwork Leakage Testing) and B&ES DW/144, on systems served by fans with a design flow rate greater than 1 m3/s .
DW/143 does not recommend testing for low pressure ductwork, however ADL2A says that where at least 10% of low-pressure ductwork is tested and achieves the low-pressure standard, the NCM (National Calculation Methodology) recognises an improvement in the BER.
ADL2A and ADL2B also states that if a system fails to meet the air-leakage limit, remedial work should be carried out as necessary to achieve satisfactory performance in retests and further ductwork sections should be tested as set out in B&ES DW/143.
There are a variety of standards that provide guidance on how to ensure a ductwork system is airtight, so many that sometimes it can become confusing. However, ultimately, the air-leakage of a ductwork system relies heavily upon the quality of materials and procedures used during fabrication. Therefore, the best way is to ensure that you are achieving the TER (Target Emission Rate), prescribed in ADL2A and ADL2B, is to use ductwork systems that are inherently airtight such as the KoolDuct System. To find out more about heat transfer in ductwork read our earlier blog post.
The image above shows the UK’s largest residential scheme so far designed to meet the demanding Passivhaus Standard, in which The Kingspan KoolDuct System contributed to the energy savings required to meet this Standard. Follow the link below for more information.
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