English

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.

The suitability of night ventilation for cooling for the UK is first assessed by presenting plots of summer weather data on the bioclimatic chart for three locations within the country. These indicate that most of the external weather conditions lie within the thermal mass and ventilation effectiveness areas of the charts. To confirm this, thermal simulations of a typical office module under a variety of internal conditions and summer weather data were performed.

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.

Natural ventilation is being applied to an increasing number of new buildings to minimise reliance on mechanical ventilation and so reduce emission of greenhouse gases. However, passive stack ventilation (PSV) systems are currently designed without incorporating heat recovery leading to significant wastage of energy. Heat recovery systems have not been used in naturally-ventilated buildings because the pressure loss caused by a conventional heat exchanger is large compared to the stack pressure and could cause the ventilation system to fail.

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.

Ventilation is necessary to provide a good indoor air quality to occupants in office buildings but is however a major energy consumer. In that manner, ventilation in itself can contribute to much more than 50% of the energy consumption for heating in well insulated office buildings. Likewise, the general trend in standards to augment ventilation requirements would still increase its energy costs. Thus, it seems obvious that an intelligent control of ventilation in office building allows to obtain substantial reductions of energy consumption.

Water use is distributed throughout building structures. Energy used to pump the water to higher levels in the building is not currently recovered, and is dissipated by performing work on air in the ventilation system which is vented to the atmosphere, when the water is discharged into the drainage stack. This energy can be utilised productively, however, by strategically placing the air inlet for the drainage stack inside the building, thereby utilising the potential energy stored in the water to draw air through the building.

This paper describes the ventilation analysis undertaken during the design of a new music centre for which it was desired to avoid the use of air conditioning and conventional ducted mechanical ventilation. The main objective was to predict the thermal comfort of occupants in the centre's main auditorium during summertime performances. The analysis was done using computational fluid dynamics (CFD) and a dynamic thermal model.

A study of the reliability of systems by considering the ability of different systems to maintain a required air flow rate over time is included in a subtask of IEA Annex 27 "Evaluation and Demonstration of Domestic Ventilation Systems". Measurements and calculations were performed to determine the variation in ventilation rates due to variation in climate and variation in performance of the ventilation system. Dwellings with passive stack, mechanical exhaust and mechanical exhaust-supply ventilation, representative of the Swedish housing stock, were studied.

To ensure indoor air quality an efficient ventilation system should provide fresh air in those parts of a room where it is required. To assess whether the ventilation system fblfils the main objective, different definitions of local ventilation efficiency (the local mean age of air, the local ventilation rate, the local purging flow rate and the local air exchange rate) are reported in literature.