This project is part of a long-term research programme to study the possibilities of using efficient air-cleaning technologies to improve the indoor air quality in buildings. The purpose of this part of the project was to study the energy-saving potential of combining the cooling and cleaning of air in offices. For this purpose, a mechanical filter with low pressure drop was selected for testing in a laboratory environment. The measurements included tests of the filter in a ductwork to study the efficiency of the filter. Moreover, the combined system of the filter and a chilled beam was tested in a room. The efficiency of the mechanical filter to remove ultrafine particles was examined using pure wax candles and salt as sources of emission of particles. The measurements in the duct showed that the efficiency of the filter ranged between 54% and 78% and that the pressure loss was less than 5 Pa (0.104 Ibf /ft2). Furthermore, the measurement results of the combined system showed that adding the filter accelerated the removal rate of the particles by 2 h-1. However, the efficiency of the chilled beam in exchanging heat was reduced by 38%.