Financial impact of leaky ductwork in buildings – a calculation tool to raise awareness

In the context of energy saving, new buildings are becoming more airtight and purpose-provided, often central mechanical ventilation is required to create and sustain a healthy indoor air quality (IAQ). This policy is summed up by the well-known energy efficiency mantra “Build tight, ventilate right”.
Central mechanical ventilation systems require ductwork systems to distribute air inside the building, but in practice, they are often not airtight. The numerous issues caused by leaky ductwork, including excessive fan energy use, acoustic discomfort and possibly even poor IAQ, if the ventilation system is not commissioned correctly, have been well outlined in literature, but there still appears to be a lack of awareness about the impact of such issues in the construction industry.
A simple tool was developed using a simplified model to estimate the financial impact of leaky ductwork in buildings over their whole life. It assumes that the design or hygienic flow rates in all habitable and wet rooms are achieved, and it is based on two previous publications from the 40th (Leprince et al., 2019) and 42nd (Hurel and Leprince, 2022a) AIVC Conferences. The purpose of this user-friendly tool is to help to raise awareness about this issue and encourage the design and installation of airtight ventilation ductwork systems, which are readily available on the market.
Case studies for 4 houses and one of the 10 AHU of a school building are presented as examples of energy and financial impact of ductwork leakage. It is found that if the fan fully compensates, a very leaky ductwork (class 3A) induces an increase of fan energy use ranging between 58% and 173% for the 4 single-family houses, and of 33% for the school AHU. The financial impact of this poor ductwork airtightness level for 80 years of operation ranges from 4.0 k€ to 33.2 k€ for the 4 single houses and reaches 74 k€ for the school AHU (out of the 10 AHU).