The effect of duct cleaning has been checked on 15 buildings. Indoor air quality measurements and questionnaires have been operated 3 months before cleaning and 1 month after. Questionnaires show that the perceived indoor air quality has been improved. Effects of cleaning on measurements can hardly be measured.

Maintenance is often limited to repair and failure response and not dedicated to indoor environment. The study defines levels of cleanliness depending on the method of measurement and compares surface values on the components to air pollution in order to decide if guidelines with limit values for surfaces are sufficient.

Visual inspection is a subjective method but yet necessary to control duct cleanliness. In order to improve its reliability, a visual scale has been realised and results from a panel of 10 inspectors have been compared to measurements.

Labelling of HVAC systems is a direct consequence of the publication of test procedures and recommended criteria in Finland. Cleanliness parameters are dust quantity, oil residues and odours emissions. Discussion isf continuing on filters classification including their efficiency (EN 779) but also odour emissions.

A new version of 'classification for indoor climate, construction and building material' has been published in 2001 in Finland, giving recommendation on ventilation systems and their cleanliness. Procedures to test values and check criteria are given.

Ways of removing from indoor air particulates smaller in diameter than 1 micrometer, through enhancement of particle deposition in a filter, were investigated using numerical simulation. Deposition enhancement is obtained using diamond-shaped three-dimensional roughness elements incorporated into filters. Numerical investigations performed were used to define the enhancement for laminar flow, in order to define the most efficient arrangement of enhancing elements.

Two models were applied to predict particle deposition in ducts, one theoretical, the other based on experiments. These models are described and a comparison of their predictions is compared to experimental results.

Measurements were carried out in a test chamber with displacement ventilation to know the vertical distribution of airborne particles generated by two human subjects having an activity representative of that of people working in an office. Particle concentration was observed as increasing with height. A threshold size of particles was found at 5 to 10 microns above which the displacement effect of particles by air flow started to decline. Negative concentration gradients were observed for large particles at the lowest ventilation rate, when the air flow does not displace them.

Resistance of louvers to the penetration of snow is a main parameter in Nordic countries. The study presents an experiment on 10 louvers tested in situ. The snow has been collected in bag filters and pressure drop variation was the chosen criteria for ranking the louvers.

On 75 air outlets of HVAC systems from 12 participating companies, fungal contamination was measured and compared to the incoming fresh air. For one of them with a significantly high level of fungi, dominated by one penicillium species, regular checks on a period of 14 months have been realised. The study concludes that this kind of measurement can be used as an indicator of the HVAC system hygienic condition.