Train tunnels and subways are an interesting field of ventilation. Trains move air through tunnels at rates of 600 m³/s (over 2 x 10^6 m³ per hour) which is much more than flow rates in buildings. Air pressures can vary up to some 3000 Pa leading to air velocities in the range of 10 to 50 m/s. This can lead to unsafe situations and thermal discomfort. The development of high speed trains causes more concern for better tunnel design. Modern stations often house small shops and restaurants, that require lower air velocities for thermal comfort.

Although the power law has been broadly accepted in measurement and air infiltration standards, and in many air infiltration calculation methods, the assumption that the power law is true over the range of pressures that a building envelope experiences has not been well documented. In this paper, we examine the validity of the power law through theoretical analysis, laboratory measurements of crack flow and detailed field tests of building envelopes.

System safety of the performance of mechanical ventilation systems can of course be analysed by means of general methods for system safety analysis. Such methods are used a lot in industrial practice, especially in manufacturing industry. However applications on ventilation systems are more or less non-existing today. This paper summarises today's methods for system safety analysis and shows possible future ways of applying the methods on performance analyses of mechanical ventilation systems.

A Probabilistic model of air change rate in a single family house based on full-scale measurements has been developed. The probability of air change rate exceeding certain prescribed limits (risk of improper ventilation or excessive heat flow) is evaluated by utilising the distribution function based on calculated air flow rate. In this way the results are expressed in terms of the R-S model generally used in the safety analysis of structures.

Ad Hoc Group 4 of Working Group 2 of CEN TC156 (Ventilation) was set up to put forward standardised techniques for estimating ventilation rates in dwellings. The purpose of the standard is to ensure that different people carrying out calculations with the same input data will obtain the same result. This will allow the use of these results in energy, heating load, IAQ or other calculations. The methods proposed use two different techniques, an explicit and an implicit one. The explicit one involves more approximations, but can be carried out with a hand calculator.

While the use of heat energy has decreased since the middle of the 1970's the use of electricity in the Swedish stock of commercial buildings has increased dramatically. In the average Swedish office building, roughly 30 % of all electricity is used for heating, ventilation and air-conditioning WAC). Another 30 % is used for lighting, 20 % for office machines, and about 20 % for other loads. In order to study the use of electricity in Swedish office buildings in detail, the Swedish Council for Building Research initiated four monitoring and bddiing simulation projects in 1989.

Tracer gases are commonly used to evaluate the performance of ventilation systems. One way to reduce the time, complexity, and cost of such experiments is to use the carbon dioxide generated by occupants as a tracer gas. In this paper, a method for using the carbon dioxide generated by occupants as a tracer gas for determining the effective supply air flow rate to a zone or the relative air-change effectiveness of a zone is described. The approach is to make use of a model of the accumulation dynamics and a model of the way that occupants generate carbon dioxide.

Existing experimental techniques for calculating air flow through building cracks are usually based upon relationships derived from experimental studies employing relatively simple procedures. Typically, a fixed pressure difference, dP, is established across the crack of interest and then the air flow Q through the crack is determined. Most crack flow equations take the pressure differential dP to be steady-state. In reality, the wind forces which generate much of the driving pressures represent highly fluctuating signals.

This paper reports on the use of BRE's domestic ventilation model, BREVENT, to predict subfloor and whole house ventilation rates in a BRE/DoE test house. Before the model could be used though some minor adjustments were necessary because one of its underlying assumptions was that the subfloor temperature was equal to the external temperature. Temperatures measurements over a number of months showed this assumption to be false and so an extra stack term was introduced into the model. However, the overall difference this makes is still quite small, only a few percent at most.

The common way to determine air infiltration, exfiltration and interzonal flows from tracer gas measurements in multizoned buildings is to rely upon the standard single or multizone model, Vc(t) = Qc(t)+p(t) . Here c, p are zonal tracer concentrations and injections, t is time and V, Q are the sought volumes and flows. This model may work well provided that all zones are sufficiently well mixed and all flows really are constant during the measurements. The latter can be doubtful in naturally ventilated buildings, especially as the measurements may require several hours.