The design of natural ventilation systems - the configuration and sizing of system components - assumes one of two generic forms: the nasty form based on thermal comfort criteria or the nice form based on specified airflow rates. The nasty form demands consideration of the complex coupled interaction of a building's airflow and thermal systems - a difficult and often intractable challenge. The nice form, on the other hand, is quite tractable, yet it is commonly approached using interactive and approximate techniques.

The necessity to provide and maintain high cleanness of air in the rooms of the highestcleanliness classes requires a proper adaptation of selection and designing methods for airfilters. The level of air cleanliness for such rooms is defined numerically by the determinationof the permissible number of dust particles whose diameters are equal or higher than the givenlimit values.

A large number of the studies have indicated that chemical indoor air pollution has become an important environmental factor which influences the population's health. Nitrogenmonoxide and nitrogen dioxide are mainly produced by combustion at high temperatures and are formed by reactions between nitrogen and oxygen. Both nitrogen in the fuel and nitrogen in the air participate in reaction, NO is further oxidized and transferred into N02 in the atmosphere. Nitrogen dioxide is the most toxic of the nitrogen oxides and is the most important from view-point of health.

Previous work by Linden, Lane-Serff and Smeed (1990) has developed a simple mathematical model for natural displacement ventilation of an enclosure. The work also introduced the experimental salt-bath technique, which uses salt solutions and fresh water to generate buoyancy forces that are analogous to those found in naturally ventilated buildings. The work claims that a good correlation exists between the predictions of the simple mathematical model and the results obtained using the salt-bath technique.

A mathematical model is developed to predict Volatile Organic Compound (VOC) emission rates from homogeneous materials. The model considers both mass diffusion and mass convection processes in the boundary layer between the material surface and the air flow. Establishing the relationship between the surface air flow and emission rate: the model therefore can predict the material emission rate under different environmental conditions.

The purpose of the work described in this paper is to develop a mathematical model of downdraft exhaust hoods in order that ways of improving these hoods efficiency can be examined. In this initial study the model developed is twodimensional. The flow has been assumed to be ideal and the complex potential considered. By use of conformal mappings the airflow in the vicinity of a bench, which is extracting air and also has air being blown down from above, is modelled. Various ratios of extraction to downdraft are considered in order to investigate the most efficient method of operation.

This paper describes the management of radon concentrations at the Hong Kong University of Science and Technology (HKUST). Applying our derived specific modification factor in the radon concentration predictive mathematical models, we were able to accurately estimate radon concentrations under different conditions of Heating, Ventilating and Air conditioning (HV AC) operations. Various combinations of HV AC operating schemes were tested mathematically. Many possible combinations demonstrate optimal effects.