Sound insulation of open Supply Air Windows, comparing laboratory and field measurements

Sound insulation with open windows has had a growing attention in recent years. In Denmark, this have been due to the Danish Environmental Protection Agency's guideline from 2007 "Noise from roads", which introduces noise limits with open windows (opening area of 0.35 m2) for situations with a high traffic noise level. Traditional (Danish) windows have a low sound insulation when opened, and therefore windows with better sound insulation in open position are becoming a demand. Two projects have been investigating windows with better sound insulation in open position, with special attention to the Supply Air Window, which is a double window construction consisting of an outer part, with a top hung vent in the lower part of the window, and an inner part, with a bottom hung vent in the upper part of the window. For both projects a large number of laboratory measurements have been performed following either the ISO 140 series or the ISO 10140 series. For both projects, supplementary field measurements of sound insulation for the supply air window has been performed following either ISO 140-5 or ISO 16283-3, depending on which was the actual standard at the time. When comparing results for laboratory and field measurements of sound insulation a general good correlation is observed, but with differences in single number quantities in the magnitude of 1 dB (for Rw) and 0 dB (for Rw+Ctr) for the first project and -1 to +1 dB (for Rw) and 2 to 4 dB (for Rw+Ctr) for the second project. This paper will present the results, and will consider explanations for the differences.