Proposal of a More Reliable Model and Procedures for Estimating Operational Leakage in Air Systems

The European Directive2024/1275 issued in April 2024 reiterates the goal of having zero-emission buildings in 2050.The consequences in terms of lost energy and performance of poorly tight air ducting are among the biggest waste factors related to HVAC systems and have to be considered. 
Nowadays, with the exception of a few specialist sectors, designers, installers and end users are not aware of the impact of leakage and are generally not in a position to measure or estimate it easily. 
The current regulatory framework also refers to models that were formalized in the 1980s for classification purposes only, at a time when the technology available for testing was very different from what it is today; namely, the model that it was decided to apply and subsequently inherited is based on a power law that expresses the dependence of the exfiltrated flow rates on the difference in static pressure between the inside and outside of the channel raised to a constant exponent and equal to 0,65.  
Both theory and experimental tests conducted and also reported by numerous authors in the scientific literature show that the exponent can vary in a range between 0.5 and 1, nevertheless the procedures reported by international standards and used to estimate operational leakage refer to that 0,65 model, introducing further ambiguities in the choice of pressure to be used in the evaluation under working conditions.  
Modern measuring devices today allow for more complete automated tests than those required by the DALT standard for classification and would allow for a more refined characterization of leakage behavior with a little effort. The paper proposes a critical review of the original framework inherited from modern standards and makes an attempt to point out the issues that could allow a more reliable estimation today, proposing more effective measurement methods for the characterization of a reliable model, in analogy to what is done today in related fields such as the tightness of buildings. 
The application of the advanced model shows, on the tests conducted for this study, a very high reliability, verifying, in one case tested, leakage exponents between 0.53 and 0.57 with values of the coefficient of determination R2 regularly exceeding 0,99.