C73 - Proposal for a procedure for the characterization of air systems based on an extended model

Duct Air Leakage Tests (DALT) are carried out on air distribution systems according to the procedures prescribed by specific International Standards. All these Standards, without exception, refer to an equation that estimates leakage as the product of a leakage coefficient (f) multiplied by a leakage area value (A), multiplied by the static pressure differential raised to an exponent (n), The exponent is assumed to be constant and equal to 0,6 or 0,65 which are average values based upon databases of actual measurements. Within certain limits, this simplified assumed-exponent model fulfils the classification requirements but does not prove reliable for the analysis of leaks under operating conditions and, thus, for verifying the increase in energy consumption associated with air distribution system leakage. For such purposes, as already discussed in previous works by some co-authors, the application of variable -exponent model appears to be necessary; this requires a test procedure capable of obtaining the n-value. This paper proposes a procedure for obtaining the f and n parameters. It stems from the procedure currently used for leakage characterization of building envelopes, including some operational strategies for improving the quality of measurements and reducing test times. The methodology was applied on a real system and the values were identified. Finally, this paper proposes a method to translate this leakage characterization into the classifications used in existing standards.