Assessing the impact of pressure drop and leak distribution on ductwork airtightness measurements

Proposal of a New Method for the Characterization and Operational Air Leakages Assessment in Hvac Systems

“…For this reason, some Standards (ASTM E779 [24] and ASTM E1554/1554 M [25]) applicable for different situations such as tightness tests for building envelopes require a defined number of increasing pressure tests to be carried out to determine also the value of the n exponent valid for the specific case. A further reason why DALT tests do not provide information on leakage under working conditions is that during the test flow rate values are so low that the static pressure remains almost constant throughout the portion of the system tested with little variations depending on the tightness (Leprince et al [26]). This situation is not representative of normal operating conditions, as air leakage under working conditions depends on a pressure value that varies progressively due to pressure losses caused by friction along the ducts and in fittings and balancing devices.…”

“…Second, in DALT tightness tests, the friction losses can be neglected in small systems and/or higher tightness classes (Leprince et al [26]), so that the pressure can be assumed as constant along the whole system. This hypothesis is also relevant for Shut-Off test, however, as in this case test pressures are much lower than those of DALT, these will be more easily verified.…”