Analysis of Errors Associated with Passive Ventilation Measurement Techniques

In small buildings where ventilation is the primary mechanism for removing indoor air pollutants, interest in converting the resulting energy load on the heating or cooling system of the building is significant. The desire of making field measurements of this time varying quantity has led to the development of many approaches. The simplest one is called the passive ventilation measurement technique which typically measures the average concentration of a constantly emitted tracer gas from which the average ventilation rate can be estimated. This study relied on mathematical models combined with typical weather data to calculate how an ideal passive ventilation measurement would perform; simulations were then conducted based on two house types in four seasons and six climates. It was found that the passive technique significantly underpredicted the average ventilation and that the use of multiple tracers accomplished marginal improvement. Inadequate mixing was found to be a major impediment to the interpretation of the results and could completely invalidate the measurement. Not covered in this report are the additional errors associated with measurement uncertainty, instrumentation limitations, and non-ideal experimental conditions.