mixing

In this paper it is our intention to consider that ventilation is the circulation or passage of an air supply through an enclosure resulting in the displacement of some or all of the air contained in that enclosure by thesupply air. Depending on the character and condition of the supply air it can dilute or change the quality of the air in an enclosure as well as alter its temperature and humidity. A mathematical analysis of the ventilation process appears later in this paper.

Uses a multi-channel infra-red gas analyser to measure nitrous oxide tracer gas concentration at six points round a house. Combines concentrations to give overall house ventilation rates and to estimate the air exchange between individual rooms. The gas analyser is also used to measure air movement between the house and its roof (with 5 sampling points in the house and one in the roof). Results show that typically 20-30% of the air that enters a houseleaves via the roof space through gaps in the ceiling.

Compares the air change rates measured with SF6 and CO2 using the tracer gas decay technique and the fan extraction method over a wide variety of test chamber sizes and mixing systems. Shows that the conventional air handling orportable floor fans can provide adequate mixing for SF6 tracer gas decay measurements of infiltration. Warns that the mixing operation may become the dominant driving force of infiltration during calm climatic conditions. Finds that +-0.08 ach/h is a reasonable measure of experimental error at the 95%confidence level using SF6 as the tracer gas.

Reports experiments using sulphur hexafluoride as a tracer gas to obtain quantitative data on actual residence time distributions in rooms and hallways and contamination caused by reentry of laboratory fume hood exhausts into a building. Defines a factor k which gives a measure of the mixing of fresh withstale air in part of a room. Measured values of k varied from 0.3 to 0.7 insmall rooms without fans. Discusses two experiments to find the amount of exhaust fumes reentering the ventilation system of a building.

Estimates of air infiltration in houses based on tracer gas measurements have usually assumed house is a single perfect mixing chamber with incoming air instantaneously and uniformly diffused to all parts of the interior. Points out that in reality some parts of the house - basement or rooms with doors closed - exchange air only very slowly with other parts so that actual mixing is far from instantaneous. Presents theory and mathematics necessary to apply tracer gas method to buildings of many chambers.

Describes experiments emitting a gaseous tracer (methane) into a ventilated test room and measuring gas concentration with rapid-response hydrocarbon analyser. Parameters were contaminant source location, sample location and ventilation rate. Measures equilibrium concentrations and rates of decrease in concentration following cessation of tracer release. Subjects data to multifactorial analyses.