HVAC ductwork: constant-injection tracer-gas assessment of airtightness.

Constant injection of tracer gas was used to determine the airtightness of a straight length of300 X 300 mm square duct in a laboratory setting. Holes are performed in the ductwork which is connected to a fan with variable speed control to simulate leakages. The holes can be sealed with rubber bungs to simulate an airtight ductwork. 'Stationary' and 'mobile' methods have been developed. The stationary method is suitable for conditions where the locations of the leaks in the ductwork is known. The 'mobile' method is used to determine the airtightness of ductwork without any prior knowledge of the locations of leaks. Both methods were found capable of locating the leaks and of determining the leakage rate of the ductwork without disrupting the operation of the HVAC system. Algorithms were established for leakage rates in terms of airflow rates and for leakage rates in terms of pressure drops.