What is the impact of duct leakage on comfort, ventilation, indoor air quality and fire security?

Duct leakage is not only detrimental to energy efficiency, but also to indoor air quality (in terms of lower air change rates and ventilation efficiency in rooms), comfort, fire protection, noise, dust accumulation, moisture damage or even contamination issues. 

When the fan compensates for ductwork leakage by generating higher pressure and flow rates, energy losses are induced. When the fan does not (or only partially) compensate for leakage, the hygienic flow rate is not reached at every air terminal device, inducing indoor air quality (IAQ) issues especially in rooms located far away from the fan.

In a pandemic context, one can note that air leakage in extract ducts can also spread contaminants such as viruses to other parts of the building. Leaks located downstream the filter and upstream the fan can lead to polluted air bypassing the filter, leading to poor IAQ issues.

In Scandinavia good ductwork airtightness has largely been promoted together with indoor air quality benefits. Note that the Swedish VVS AMA guideline not only deals with energy issues related to ductwork airtightness but also with safety and indoor environment. [1].

In  [2], other effects than energy losses and IAQ issues are reported, such as changes in noise that tends to increase with increasing duct flows [3]. Leakages can have 3 noise related effects:

  1. Increasing fan flowrate and pressure needed will increase the noise produced by the fan
  2. Leaks can also increase the transmission of fan sound pressure
  3. Leaks can create their own “whistling” noise

It is also believed that leakages can increase dust accumulation in filters [4], heat exchangers and ducts, as there is more flow rate going through.

Moreover, ductwork leakages lead to uncontrolled airflows that may induce depressurization causing backdrafting of combustion equipment or pressurisation causing moisture damage in walls [5]. This unbalance may also weaken contamination protection of sensitive areas (operating theatres, clean rooms, etc.)

Finally, fire-rated ventilation ducts can avoid fire and heat spread between two building compartments, but this can be compromised by ductwork leakage.

References

[1] Guyot, G., and Carrié, F.R., 2010. Stimulation of good building and ductwork airtightness through EPBD. ASIEPI, 2010.

[2] Leprince V., Hurel N., and Kapsalaki M.,2020. VIP 40 Ductwork airtightness – A review.  AIVC, April 2020

[3] Richieri, F., et al., 2018. Ductwork design flaws and poor airtightness: a case study about a ventilation system reconditioning in a sealed building. Proceedings of the 39th AIVC-7 th TightVent-5 th venticool Conference, 18-19 September, Juan-Les-Pins, France. pp. 442-451.

[4] Dyer, David F., 2011. Case study: Effect of excessive duct leakage in a large pharmaceutical plant. Proceedings of the 32nd AIVC & 1st TightVent Conference, 12- 13 October. Brussels, Belgium. pp. 55-56.

[5] Modera, M., 2005. Fixing duct leaks in commercial buildings. ASHRAE journal, pp. 22- 28.

See also

Posted in: Ductwork airtightness, Energy Aspects, IAQ, Thermal Comfort