Ten years ago the automated constant concentration tracer gas (CCTG) method was conceived at the Technological Institute, Tastrup, Denmark. This technique is now used by researchers toexamine a wide variety of air infiltration and ventilation related problems. At this juncture it would seem appropriate to summarise the development of the CCTG system and examine its use in present day research.

After the oil crisis in the seventies the main aims of ventilation research changed. Many energy saving measures had been taken by the authorities, among them the reduction of infiltration heat losses. The Ministry of Building and Urban Development ordered the production and installation of better quality airtight windows, and the draughtproofing of existing window assemblies.

Some guidelines on indoor-air quality specify a maximum allowable exposure to CO2. In a room ventilated by a mechanical extract system a control program on the CO2 concentration may, by anappropriate sampling strategy, supply information about the exhausted flowrate. This paper briefly outlines a simple analytical model for estimating the exhausted flowrate by measuring the CO2 concentration and keeping a record of the occupancy of the room.

The task of this study is not the analysis of these influences when calculating the heat losses. Instead the influence of wind and temperature on the total heat losses at 1% probability exceedance of the heat losses is being investigated. Thecalculation is based on the correlation of the outdoor temperature, the wind speed and its direction, the transmission coefficient correlation and the air-leakage of the curtain wall.

The object of this article is to compare the performance of these two flow representations against a small set of measurement data using the concepts outlined in the Air Infiltration and Ventilation Centre's Calculation Techniques Guide.2 A particular aspect of the approach presented is that in each case an identical solution technique, flow network and pressure field has been applied, thus enabling a direct comparison of each of the flow representations to be made. The tests were by no means exhaustive and further evaluation is recommended.

A range of calculation techniques is available for the calculation of air infiltration and ventilation in buildings. The choice is largely dependent on intended application, while the level of complexity ranges from straightforward empirical techniques to detailed multi-zone numerical methods. The objective of this article is to outline some of the techniques currently available and to indicate the purposes for which they are most suited.

The air leakage distribution in a building is, in certain circumstances, difficult to determine. One example of this is the ceiling of the dwelling illustrated in figure 1 and 2. It is almost impossible to make the ceiling perfectly airtight; thismeans that a measurement by difference is impossible. The inclined roof is not airtight at all. A rather simple and easy technique is to perform measurements using tracer gas and pressurisation equipment at the same time.

There are several methods by which the airtightness of a building can be measured. One method involves the use of a fan to pressurize or depressurize the building. This creates a known pressure difference across the building envelope. Thecorresponding air flow through the fan is measured and this is an indication of the airtightness of the building. This air flow rate can be expressed as the number of building air changes per hour, a useful unit when comparing buildings of different volumes. So far only simple methods have been employed to analyse this condition.

This paper describes the extension of the previously described UMIST technique for the determination of airflows between two interconnected cells to the case of three connected cells, and gives the results obtained for a series of validation experiments carried out under controlled conditions.

Air movement within enclosures, which may result from a combination of infiltration, mechanical ventilation and convective heat transfer effects, is important for considerations of thermal comfort, ventilation efficiency and energy conservation.