Testing filters on the roof

Anne Berit Bjørken

On a roof at NTH, scientists have set up a rig for testing different types of ventilation air-filter. They want to find out what sort of filters are most suitable for removing airborne particles.

Professor Sten Olaf Hanssen demonstrates the test rig.

"We are carrying out long-term testing of five types of filter in current use in office building ventilation systems. Three of the filters are fibre-glass and the other two are plastic. We have installed them in the test rig on the roof, where they will stay for up to a year," says Professor Sten Olaf Hanssen of NTH's Dept. of Heating and Ventilation.

The filters are regularly removed from the rig and brought into the laboratory to check their particle removal efficiency.

The purpose of the new rig is to offer a standard national method for testing and checking air filters. Anticipated results include quality assurance and certification of the air filters that are on sale in Norway, product development in collaboration with Norwegian filter manufacturers, R & D in this area at NTH and SINTEF, and last but not least, better education in such topics as filtration, air purification and the indoor environment.

"There is an urgent need for quality assurance of air filters on sale in Norway, and for this reason suppliers and users of filters, as well as the health authorities, are very keen to have a standardized test rig operated by a recognised neutral body in this country," says Hanssen.

Great care must be taken in the selection of ventilation systems and filters. The quality of filters available on the market varies widely. Some of them are only suitable for stopping large coarse particles, and the selection is large and confusing. It is difficult for users to know which filter is best, because the filter industry itself disagrees about the best solution. One issue is that there are various standardized tests and methods for comparing different types of filter.

Good advice

"There is no doubt that a good ventilation system fitted with good filters improves the indoor climate, but on the other hand there is equally little doubt that a poor-quality ventilation system with low-quality, old filters can make a bad situation even worse. For this reason, it is important to select the right equipment, and to follow the instructions for use," says Hanssen.

The biggest mistake that people make is to leave filters in place for too long. They must be replaced regularly; otherwise they become choked with dirt. This in turn means that the quantity of supplied ventilation air is reduced, while the air blown through the filter may take dirt along with it and spreads it throughout the premises. The other mistake that users often make is to choose the wrong type of filter for their building and area of application, remarks Hanssen.