Determining the adventitious leakage of buildings at low pressure. Part 2: Pulse technique

Part 1 of this paper examined the uncertainties (errors) inherent in the determination of the low-pressure leakage of a building envelope. It was shown that a technique for direct measurement of Q₄ could reduce the uncertainty by a factor of three or more. In Part 2, a technique is described that enables such measurements to be made. There are three key features that lead to a successful technique. The first is to measure Δp a short time before and after the pulse, thereby allowing wind effects to be largely eliminated. The second is to choose the shape and duration of the pulse, such that a period of quasi-steady flow is obtained. The third is to minimise the variation of Δp during the quasi-steady period, such that envelope flexing is not a problem. Examples of measurements are presented that demonstrate these key features. Further evidence of the suitability of the technique is provided by demonstrating its ability to determine a known change of opening. Comparisons are also made between the new technique, the conventional steady technique, and a theoretical model. It is concluded that the new technique allows the low-pressure leakage of a building to be determined to an accuracy that has not previously been possible. Practical application: The technique described can be used to measure the low-pressure leakage of a building envelope and could eventually replace the conventional technique.