Reliability of Standard Models for Operational Air Leakage Assessment in HVAC Air Systems

The research deals with the topic of assessing air leakage in aeraulic systems under operating conditions. To date, the issue is addressed on the basis of an empirically derived theory formulated in the 1980s for the classification of air distribution systems. According to this model, air leakage is proportional to the static pressure increased by an exponent n considered constant and equal to 0.65. Numerous tests and studies have shown that the value of this exponent is not constant and can vary considerably for systems with different construction technologies. Although the use of this model leads to significant errors, there are international standards that present simplified procedures based on this model. A numerical simulation shows how the adoption of the current model can introduce errors in estimation in the range of -19% to +47%. The objective of the presented research is to analyze the state of the art and motivate the need for change and the adoption of an improved model for the characterization of operational leakage. The proposed model is therefore a model that provides for the performance of more complete tests aimed at obtaining the value of the leakage exponent of the system under investigation, borrowing the techniques and tools already applied for years in the field of building envelope leakage.