In the context of the definition of new national ventilation cleanliness classes in Finland, it is important to develop a clean method for the installation of ducts. An important factor that makes the inner duct surfaces dirty is the metal dust that is accumulated while side grinder is used to cut the ducts.

The aim of this study was to evaluate the amount of dust in supply air ducts in 18 recently installed ventilation systems constructed according to two different class of cleanliness. Dust accumulation into the duct can be partly avoided by duct protection during the whole of the construction phase.

The demand for duct cleaning has been increasing exponentially over the last few years and to determine objectively if the duct is dirty and has to be cleaned is necessary.All air-handling units from a school district (18 buildings) and representative portions of their associated ductwork were assessed. Results of dirt and contamination are compared to dirt criterias and commented.

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.