modelling

Computer modelling is becoming an everyday tool for the building services engineer to ensure that a ventilation design will work early on in the development process. This paper describes this process in relation to Novartis' new office building in the UK. In this case, airflow modelling was used to fine-tune a conceptual idea for the atrium air conditioning. This influenced the solar shading incorporated into the architectural design and allowed engineers to optimise the volume of air used and the location of supply air terminals.

Efficient control of ventilation systems needs information on indoor air pollutant concentration. But most of the time, the pollutant concentration is not measured. However, outdoor air pollution forecast models are becoming operational and a relation between outdoor and indoor pollutant concentration may be used to predict pollutant concentration peaks and to infer recommendations to reduce its value . A prediction model of the outdoor/indoor air pollutant transfer, based on experimental data, was obtained using multiple linear regression.

The provision of a healthy and satisfactorily clean indoor environment requires that consideration be given to a range of issues, such as the type of indoor environment, indoor and outdoor sources, indoor activity and others. The selection of relevant measures to achieve the required indoor air quality (IAQ) depends on knowledge and understanding of the mechanisms and parameters affecting the concentration levels indoors.

Measurement campaign was conducted in a controlled office environment during January 1999 to get indoor/outdoor ratio for particles less than 0.5 micrometers in diameter. Aerosol concentrations for diameters between 7-500 nanometers were measured simultaneously indoors and outdoors with two DMPS systems. Other continuously measured quantities included temperature, ventilation rate, relative humidity, air pressure and four inorganic gases (S02, NO, NOx and 03). The measured room was practically airtight and had a mechanical ventilation system.

When it is required to predict the local mean age of air, the calculations are often carried out assuming that there is no recirculation that is that all of the supply air is fresh. However, local mean age values will be greater than in the fresh air case when some of the exhaust air is recirculated. This paper examines and discusses the effect of recirculation and shows that, for many systems the increase in local mean age due to recirculation can be calculated by means of an elementary analysis that leads to a simple algebraic expression.