Air Leakage Measurements by the Tracer Dilution Method—A Review

Abstract

Air leakage (infiltration) represents an important part of the heating and cooling load of residential, commercial and industrial buildings. It is also an important parameter in indoor-outdoor air pollution relationships. Air leakage is difficult to quantify because it is not only a function of building tightness and configuration, but also of inside-outside temperature differences, wind speed, and of workmanship in construction. Standard formulas for calculating air leakage do exist, but they are at best rough approximations. The tracer dilution method has been used for a number of years to infer air leakage rates. This technique entails introducing small amounts of tracer gas into a structure and measuring the rate of change in tracer concentration. The air change rate can then be determined from the exponential decay rate in tracer concentration with respect to time. There exists no perfect or ideal tracer. Thus, the choice of tracer gas is dependent upon the characteristics inherent in the measurement, the structure being measured, and in the relative familiarity of the experimenter with a variety of experimental techniques. The various gases that have been used for performing tracer dilution measurements in the past are presented along with their methods of measurement. In addition, the basic experimental methodology for performing a tracer dilution measurement utilizing any tracer is discussed. The limitations and advantages of the method are described and recommendations for its use are made. The need for standard test methodology is explored with an emphasis on the ability to produce and provide data that can be intercompared at some later time. An uncertainty analysis of the method is provided.