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

Abstract

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 Q 4 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 Dp 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 Dp 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 lowpressure leakage of a building envelope and could eventually replace the conventional technique. List of symbolsA,b coefficients in equation (2) A effective area of opening (m 2 ) A p area of piston (m 2 ) l e effective length of opening (m) p w pressure due to wind (Pa) P absolute pressure (Pa) q flow rate through opening (m 3 /s) Q p piston flow rate (m 3 /s) Q leakage flow rate (m 3 /s) s piston displacement (m) t time (s) t p pulse duration (s) U reference wind speed (m/s) v piston displacement (m 3 ) V volume of space (m 3 ) g ratio of specific heats r density (kg/m 3 ) Dp pressure difference (Pa) dV volume displacement (m 3 ) Subscripts E external I internal L leakage test 4 a t4P a 50 at 50 Pa

A practical review of alternatives to the steady pressurisation method for determining building airtightness

“…Nevertheless, this method has shortcomings which were discussed previously. Early motivations for finding other methods [ 28 ] came from its disadvantages: The need of using large net fluid flow; The results might be degraded by noise significantly [ 75 ]; Inconsideration of fluid compressibility might lead to systematic error; Not easy to use, it takes long to set up [ 76 ]; 50 Pa is much higher than the infiltration pressure [ [ 13 , 19 , 77 ]]; Impact from varying wind pressure [ 78 ]; …”

“…The original drive behind the development of the Pulse pressurisation technique was the need of addressing the issues associated with measuring the leakage of large buildings by turning to the low pressure measurement so large amount of airflow could be avoided [ 94 ]. This technique is not a new idea [ 75 , [90] , [91] , [92] ], as similar concepts were proposed and investigated experimentally [ 75 , 92 ], but insufficient accuracy was achieved due to various reasons [ 77 ].…”

“…The Pulse technique reported herein releases a pulse of compressed air from an air tank to the building over seconds (typically 1.5 s) to create an instant pressure rise at low pressure level, which is then followed by a steady pressure drop to deliver a “quasi-steady” flow [ 77 ]. During this period, the pressure variations in the building and air tank are measured to establish the leakage-pressure correlation together with tank and building parameters.…”

A perspective on fifty years of natural ventilation research

“…None of these techniques was successful. More recently, the transient technique has been the subject of experimental and theoretical studies, [84], as has a pulse technique, [85], which is best described as a quasi-steady pulse technique. The latter technique has been shown to give promising results that are virtually independent of wind pressure fluctuations at the time of the test (see also E11.4.2.3).…”

Assessing uncertainty in housing stock infiltration rates and associated heat loss: English and UK case studies

“…Systematic uncertainty arises from the fact that the shape of the leakage characteristic is not known when 0 < < 10Pa and here Equation (1) may not hold [13]. A new measurement procedure may be required that satisfies this knowledge gap [14][15]. Nevertheless, these uncertainties mean that a value of , extrapolated from the high pressure measurements, is not used directly to predict an operational infiltration rate.…”