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

Transcription

1 Sound insulation of open Supply Air Windows, comparing laboratory and field measurements Lars Sommer SØNDERGAARD 1 ; Rune EGEDAL 2 ; Mads BOLBERG 3 ; Morten Bording HANSEN 4 1, 2, 4 DELTA a part of FORCE Technology, Aarhus, Denmark 3 DELTA a part of FORCE Technology, Hørsholm, Denmark ABSTRACT Sound insulation with open windows has had growing attention in recent years. In Denmark, this has 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 m 2 ) 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 the 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 the ISO series. For both projects, supplementary field measurements of sound insulation for the supply air window have been performed following either ISO or ISO , 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 (field minus laboratory) in single number quantities in the magnitude of -1 db (for R w ) and -1 to 0 db (for R w +C tr ) for the first project and -1 to +1 db (for R w ) and 2 to 4 db (for R w +C tr ) for the second project. This paper will present the results, and will consider explanations for the differences. Keywords: Open windows, Sound Insulation, Traffic noise I-INCE Classification of Subjects Number(s): 33, 51, INTRODUCTION This paper describes and compares corresponding field and laboratory measurements of open windows with the window type described as Supply Air Window. The measurements have been performed in two successive development projects. Both projects focused on acoustical optimization of open windows; the first focused solely on the Supply Air Windows, while the second investigated three window types, where one of them was the Supply Air Window. Both projects were conducted by DELTA in cooperation with HSHansen A/S. For both projects a large number of laboratory measurements were conducted, followed by a few comparable field / in-situ measurements. The purpose of the field measurements was partly to evaluate the sound insulation of the constructions in realistic settings and partly to ensure that no important systematic differences between laboratory measurements and field measurements occur. Both development projects are initiated from three guidelines from the Danish Environmental Protection Agency (8, 9 and 10). In these guides a requirement is set that in special situations, where the outdoor noise levels from e.g. road traffic or railroads is high, the indoor noise level in e.g. 1 lss@delta.dk 2 rue@delta.dk 3 mbl@delta.dk 4 mbh@delta.dk 4217

2 apartments and offices must be below a certain level with open windows, where the opening area is 0.35 m 2 for each openable window. The maximum allowable levels for apartments and offices from road traffic are L den 46 db and 51 db respectively. 2. THE SUPPLY AIR WINDOW 2.1 Principle The Supply Air Window is a double construction consisting of two separate parts. Both parts are fitted with a sash (vent) that can be opened. For the outer part the sash is fitted in the bottom of the window and for the inner part the sash is fitted in the top of the window. The outer sash is top hung and the inner is bottom hung see Figure 1. The construction is known for its good acoustic properties, this is due to the large vertical channel that the noise has to pass through before it reaches the outlet of the inner part. This alone yields an improved sound insulation. For further improvements of t he sound insulation it is possible to fit the cavity with various sound absorbing materials. The double construction of the Supply Air Window introduces a large cavity also when the window is closed. This leads to a very high sound insulation when both sashes are closed. The construction / principle is known under a variety of names beside Supply air window. To name a few: Russervindue ( Russian window a similar construction was used in the Winter Palace in Sct. Petersburg), Blumenfenster ( Flower window users often use the double window for flowers) and 3G / 3 rd generation windows. Figure 1 Left: Principle for the Supply Air Window. Right: Photo of an installed Supply Air Window 2.2 Project 1: Acoustical optimization of Supply Air Windows For easy reference the first of the two development projects will be described as Project 1. The title of the project was Acoustical optimization of Supply Air Windows and has been reported in (1-5). The project ran between The project investigated the primary parameters of significance for the sound insulation of the open window. Compared to a regular open window with the same opening area the Supply Air Window typically had 8-16 db (R w +C tr ) better sound insulation, 4218

3 depending on configuration and dimensions. The project consisted of literature study, laboratory measurements, field measurements and occupant s response. Beside the good results, it was concluded that it would be suitable to continue the work on the Supply Air Window, especially with regard to improving the sound reduction for the lower frequency range ( Hz). 2.3 Project 2: Open windows with good sound insulation Similarly, the second of the two projects will be described as Project 2. The title of the project was Open windows with good sound insulation and has been reported in (6-7). The project was conducted between For this project three overall window types have been investigated; 1: Further improving the Supply Air Window with special attention to low frequencies, e.g. different types, placement and dimensions of absorbers and resonators have been verified. 2: Double window with focus on the inner cavity between the windows, where different kinds and length of sound barriers have been explored. 3: Single window with different types and placement of (outer) attachments, in the form of sound traps. The project was initiated by a literature study followed by several laboratory measurement series and a field measurement study. Compared to a single window opened 0.35 m 2 the sound reduction improvements depending on window type are in the magnitude of 18/6/10 db (for R w +C tr ) for the three window types investigated in the project. 3. MEASUREMENT SETUP The following four sections describe the measurement setup for the four sets of measurements: two sets of laboratory measurements and two sets of field measurements. The order of the sections follows the order the measurements were conducted. 3.1 Project 1 - Laboratory measurements For Project 1 numerous laboratory measurements were performed, investigating the influence of different combinations of e.g. dimensions, opening area of the vents and the use of absorbing materials. The laboratory measurements for project 1 were conducted following the ISO series. For the measurements used in comparison with the field measurements, the outer dimensions of the used window were (width x height): 1230 mm x 1930 mm, and the internal distance between the glazings was 355 mm. The height of the outer and inner sash was 300 mm and 500 mm respectively. For the measurements a moving loudspeaker in the source room (outside) and a moving microphone with a circular path in both source (outside) and receiving room (inside) was used. The loudspeaker is moving in a cross sectional line in the room, similar setup as shown in Figure 5. Pink noise radiated from a dodecahedron loudspeaker was used as noise source. For the outside window 8 mm acoustic laminated single glazing was used. For the inside window a 4/0.38/ mm double glazing with Stadip Silence folio was used. Further relevant setup parameters are shown in Table 1. Photos of the window under test are shown in Figure 2. The opening of the vents was motorized in order to be able to open both windows, the motorized opening system could however be disabled in order to freely choose how much the vents should be opened. Two opening setups were used; 1. Opening as much as possible with the motorized setup, leading to an opening area of the outside vent of 0.14 m 2 and an opening area of the inside vent of 0.26 m 2, which in the following will be described as 0.14 m 2 / 0.26 m Disabling the motorized opening mechanism and both vents opened 0.35 m 2 Notice: for practical reasons the window was mounted upside-down for the measurements, in order to best achieve laboratory conditions similar to in-situ conditions. During the measurements the outer vent is thus placed at the top and the inner vent placed at the bottom. Table 1 Setup for Project 1 laboratory measurements, where V is the room volume, D is a distance to reflective surfaces (see Figure 2) and T 20 is the average reverberation time in the used frequency range V [m 3 ] D ceiling [m] [m] [m] [m] T 20 [s] Inside Outside

4 D ceiling D ceiling Figure 2 Photos for Project 1 laboratory setup (window installed upside-down). Left: Seen from outside (Source room side). Right: Seen from inside (Receiving room side). 3.2 Project 1 Field measurements For the field measurements one of the windows used for the laboratory measurements was reused. Adjacent to one of the roads with the highest traffic intensity in the Danish city of Aarhus (~ inhabitants per 2017) a row of empty houses was to be demolished, and access and use was granted to a suitable building. It was therefore possible to create optimal test conditions with a test opening to fit the non-standard sized window. In addition the inside room behind the opening could, by rising a lightweight wall, be changed into a regular room with only one window. The field measurements for project 1 are conducted following ISO (13) with a synchronized setup with one indoor rotating microphone and three outdoor stationary microphones. As with the laboratory measurement frame absorbers were not used, and the outer dimensions of the used window were (width x height): 1230 mm x 1930 mm, and the internal distance between the glazings was 355 mm. The area of the free test opening in which the test element was installed, S, was 2.44 m 2, and the same two sets of opening areas as for the laboratory setup was used; 0.14 m 2 / 0.26 m 2 and 0.35 m 2 / 0.35 m 2 The road is a four-lane road (Randersvej). The horizontal distance between the roadside and the window was approximately 4.8 m and the surface consisted of asphalt and pavement. The receiving room (inside) was unfurnished. The outdoor A-weighted noise level from traffic measured on the windows was db during the measurements. Further relevant setup parameters are shown in Table 2. Photos of the window under test are shown in Figure 3. The measurements were conducted in November Notice: The window was not mounted upside-down for the field measurements. Table 2 Setup for Project 1 field measurements, where V is the room volume, D is a distance to reflective surfaces (see Figure 3) and T 20 is the average reverberation time in the used frequency range V [m 3 ] D ceiling [m] [m] [m] [m] T 20 [s] Inside Outside

5 D ceiling Figure 3 Photos for Project 1 field setup. Left: Seen from outside. Right: Seen from inside. 3.3 Project 2 Field measurements For the field measurements for Project 2 a suitable test location with both high traffic noise and easy access to creating/modifying a test opening to the laboratory test sizes was not found. Instead the opposite approach was used, and a site with already installed Supply Air Windows next to a road with high traffic noise was found. The chosen site is an (inhabited) apartment complex in the city of Odense (~ inhabitants per 2017). The inhabitants of two apartments agreed to participate in the measurements; one on the second floor and one on the third floor. The two apartments were positioned in the same building but placed in each end of the building. The apartment layout was mirrored but otherwise identical for the two apartments. For each apartment it had a small room with only a single Supply Air Window installed. The road in front of the building has a relatively high noise level from traffic. The actual windows had frame absorbers installed in the top and the sides of the window. The outer dimensions of the used window were (width x height): 910 mm x 2155 mm, and the internal distance between the glazings was 320 mm. The area of the free test opening in which the test element is installed, S, were 1.96 m 2. The height of both outer and inner sash was 490 mm. The road was a two-lane road (Østergade). The horizontal distance between the roadside and the window was approximately 6.7 m (3 rd floor) and 7.3 m (2 nd floor) and the surface was pavement and plant covered ground. The width of the road was approximately 10 m. The field measurements for project 2 are conducted following ISO :2016 (14), with a synchronized setup with one indoor rotating microphone and three outdoor stationary microphones. The outdoor A-weighted noise level from traffic measured on the windows was db during the measurements. Further relevant setup parameters are shown in Table 3. The measurements were conducted in August The actual windows (vents) could however not be opened to more than 0.21 m 2 for the outer vent and 0.24 m 2 for the inner vent (0.21 m 2 / 0.24 m 2 ), see Figure 1. Inspired by the 4 cm opening regulations from Hamburg Hafencity (15) it was chosen to perform a supplementary measurement with the vents opened approximately 4 cm, resulting in opening areas of 0.03 m 2 for the outer vent and 0.07 m 2 for the inner vent (0.03 m 2 / 0.07 m 2 ), see Figure

6 Table 3 Setup for Project 2 field measurements, where V is the room volume, D is a distance to reflective surfaces (see Figure 4) and T 20 is the average reverberation time in the used frequency range V [m3] D ceiling [m] [m] [m] [m] T 20 [s] Inside, 2 nd floor ~ Outside, 2 nd floor 3.3 Inside, 3 rd floor ~ Outside, 3 rd floor 6.3 D ceiling Figure 4 Photos for Project 2 field setup (2 nd floor). Left: Seen from outside. Right: Seen from inside. 3.4 Project 2 Laboratory measurements For the laboratory measurements a copy of the windows from the field measurements was produced and installed in the laboratory as identically to the field setups as possible. The laboratory measurements for project 2 were conducted following the ISO series (11). The outer dimensions of the used window were (width x height): 910 mm x 2155 mm, and the internal distance between the glazings was 320 mm. The area of the free test opening in which the test element was installed, S, were 1.96 m 2. The same opening areas as in the field measurements were used. For the measurements a moving loudspeaker in the source room (outside) and a moving microphone with a circular path in both source (outside) and receiving room (inside) were used. The loudspeaker is moving in a cross sectional line in the room, similar setup as shown in Figure 5. Pink noise radiated from a dodecahedron loudspeaker was used as noise source. Further relevant setup parameters are shown in Table 4. For the outside window a mm double glazing was used. For the inside window a mm double glazing was used. Photos of the window under test are shown in Figure 5. Notice: In contrast to the Project 1 laboratory measurements, the installed window for the Project 2 laboratory measurements was not upside-down. 4222

7 Table 4 Setup for Project 2 laboratory measurements, where V is the room volume, D is a distance to reflective surfaces (see Figure 5) and T 20 is the average reverberation time in the used frequency range V [m 3 ] D ceiling [m] [m] [m] [m] T 20 [s] Inside Outside D ceiling D ceiling Figure 5 Photos for Project 2 laboratory setup. Left: Seen from outside (Source room side). Right: Seen from inside (Receiving room side). 4. RESULTS In the following the results are given as 1/3 octave band sound reduction indices in the frequency range 50/ Hz, and as single number quantities evaluated according to ISO (12). 4.1 Project 1 In Figure 6 the sound reduction indices for both field measurements (blue lines) and laboratory measurements (red lines) are shown, and the associated single number quantities are shown in Table 5. When the sound reduction index curves for field and laboratory measurements are compared for an opening area of 0.35 m 2 it is especially noticeably that at frequencies above 2000 Hz the laboratory sound reduction indices are higher than the field measurement sound reduction indexes. A plausible explanation for this could partly be the low height of the window above the road and partly due to the short distance between façade and road; hence a very direct sound radiation occurs into the open lower sash, primarily noise from tires. 4223

8 Laboratory Laboratory Field Field Figure 6 Sound reduction index. Left: Opening area of 0.35 m 2 / 0.35 m 2. Right: Opening area of 0.14 m 2 / 0.26 m 2. Table 5 Single number quantities for Project 1 Opening area [m 2 ] R w / R w R w +C / R w +C R w +C tr / R w +C tr Field 0.35 / Laboratory 0.35 / Field 0.14 / Laboratory 0.14 / The single number quantities for the traditional frequency area ( Hz) for the field measurement and laboratory measurement respectively are seen to have a good correlation with a difference of maximum 1 db. If the single number quantities are calculated for an extended frequency area (up to 5000 Hz) the difference between field measurement and laboratory measurement is 1-2 db for R w +C and R w +C tr, The observed difference for frequencies above 2000 Hz has therefore no noticeable influence on the windows sound insulation qualities regarding traffic noise. Similarly when the sound reduction index curves for field and laboratory measurements are compared for an opening area of 0.14 m 2 / 0.26 m 2 the same tendencies as with 0.35 m 2 / 0.35 m 2 are noticed, but now with even better correlation between field and laboratory. The laboratory sound reduction indices are now only noticeably higher than the field measurement sound reduction indexes from 3150 Hz and upwards. Since the only difference between the two sets of measurements is the opening area, the explanation is bound to be related to the opening area or the opening angle in combination with the low height of the window above the road and the short distance between façade and road. The single number quantities for the traditional frequency area ( Hz) for the field measurement and laboratory measurement respectively are again seen to correspond well with a difference of maximum 1 db. If the single number quantities are calculated for an extended frequency area (up to 5000 Hz) the difference between field measurement and laboratory measurement is 1 db for R w +C and R w +C tr, Again the observed difference for frequencies above 2000 Hz has no noticeable influence on the windows sound insulation qualities regarding traffic noise. The correlation between field and laboratory results was therefore satisfactory. 4224

9 4.2 Project 2 In Figure 7 the sound reduction indices for both field measurements (blue and green lines) and laboratory measurements (red lines) is shown, and the associated single number quantities are shown in Table 6. Notice: For the field measurements with the 0.21 / 0.24 m 2 opening the distance to the background noise was adequate, however for the field measurements with the 0.03 / 0.07 m 2 opening, the distance to background noise at the frequency range Hz and Hz was not adequate. Resultingly the sound reduction at these frequencies should be treated as minimum values. Field, 2 nd floor Field, 2 nd floor Laboratory Field, 3 nd floor Laboratory Figure 7 Sound reduction index. Left: Opening area of 0.21 m 2 / 0.24 m 2. Right: Opening area of 0.03 m 2 / 0.07 m 2. Table 6 Single number quantities for Project 2 Opening area [m 2 ] R w / R w R w +C / R w +C R w +C tr / R w +C tr Field, 3 rd floor 0.21 / Field, 2 nd floor 0.21 / Laboratory 0.21 / Field, 2 nd floor 0.03 / Laboratory 0.03 / Comparing the sound insulation for laboratory measurements and field measurements it is seen that the sound insulation is highest for the field measurements for frequencies below 250 Hz. In the remaining frequency range the sound insulation is approximately comparable for both field and laboratory measurements, with a tendency of higher sound insulation for the field measurements for frequencies above 800 Hz and differences for single 1/3-octave bands of up to 4 db. Regarding the single number quantities they are also relatively comparable for R w and R w +C, while the difference is larger for R w +C tr. For R w and R w +C the difference between field and laboratory measurements is up to 2 db, while the difference for R w +C tr is up to 4 db. If the single number quantities for an extended frequency range are investigated ( Hz and Hz), the difference between laboratory and field measurements is similar or less than the differences found for 4225

10 the single number quantities in the Hz frequency area. A difference of up to 4 db for R w +C tr is a significant difference, however to the benefit of the user since the highest sound reduction was measured for the field measurements. This difference should be investigated further. 4.3 Summary For Project 1, the difference in single number quantities is very small: For R w /R w it is 1 db and for R w +C tr /R w +C tr it is 0 db. For Project 2, the difference in single number quantities is larger: For R w /R w it is -1 to +2 db and for R w +C tr /R w +C tr it is 2-4 db. Overall the sound reduction index curves follow the same trends. For most of the measurements the sound reduction in the frequency range below 315 Hz are lower for laboratory measurements than field measurements. For the project 1 measurements the sound reduction in the frequency area above 500 Hz are higher for laboratory measurements than field measurements. However for the project 2 measurements the sound reduction in the frequency range above 500 Hz are either comparable to or higher for the field measurements than the laboratory measurements. For both projects there seems to be a little better correlation between laboratory and field measurements for the smaller opening angle than for the larger opening angle. The major physical differences between the two projects are summed in Table 7. Table 7 Major differences between the two projects Project 1 Project 2 Laboratory setup upside-down Laboratory setup not upside-down Field measurements at ~1 st floor Field measurements at 2 nd and 3 rd floor Medium sized inside room at field measurements Small sized inside room at field measurements Four-lane road Two-lane road Acoustical hard surface between road and façade Acoustical soft surface between road and façade Opening area of 0.35 / 0.35 m 2 and 0.14 / 0.26 m 2 Opening area of 0.21 / 0.24 m 2 and 0.03 / 0.07 m 2 The upside-down laboratory setup for Project 1 means that the distance between the outside vent and the first reflecting surface (in the diffuse field source room) is 1.6 m, where it for the Project 2 laboratory setup is 0.4 m. The corresponding distances for the field measurements were 2 m (Project 1) and 3.3 / 6.3 m (Project 2). For Project 1 the surface was acoustically hard and with tall reflective buildings on the opposite side of the road. For Project 2 the ground was mostly acoustically soft with only few reflective structures on the other side of the road. Overall the similarity between laboratory and field setup were closer for Project 1 than Project 2, which might explain why the differences between laboratory measurements and field measurements are smaller for Project 1 compared to Project CONCLUSIONS In general the variance between field measurements and laboratory measurements are relatively small, confirming that the laboratory setup for measurement of airborne sound reduction with open Supply Air Windows is usable, and yields results comparable to field measurements except for R w +C tr for Project 2 where differences in the magnitude of 3-4 db are observed. One should be cautious drawing firm conclusions for the limited number of measurements shown in this paper, where the physical setup also varied. However some tendencies are observed and should be noted; most notably the variance between field measurements and laboratory measurements are clearly smallest for the Project 1 setup compared to the Project 2 setup, and indicates that the distances between open sash/vents and reflective surfaces in the source room must be chosen wisely. Since the highest sound reduction is found for the field measurements, the users will be protected, however the measurement setup should be investigated further in order to limit the differences between laboratory and field measurements. 4226

11 6. DISCUSSION The correlation between the laboratory measurements and the field measurements for the Supply Air Windows in general is good. The window type however has its opening towards the noise source for the field measurements. In a diffuse field laboratory the orientation of the opening (of an open window) seems to be irrelevant (6). For windows mounted in situ, it is probably not irrelevant whether the window opening is towards the sound source or not. It would therefore be logical to assume that the correlation between laboratory measurements (diffuse field conditions) and field measurements (free field conditions) might be worse for window types that have their openings not facing towards the noise source. ACKNOWLEDGEMENTS The projects were partly financed by the Danish Ministry of the Environment under the development programs Miljøeffektiv Teknologi 2008 (Environment Efficient Techonolgy 2008) and Grøn Teknologi 2013 (Green Technology 2013). REFERENCES Notice that reference 1, 2, 3, 6, 8, 9 and 10 are available only in Danish, and reference 15 is only available in German. 1. Søndergaard LS, Olesen HS. Lydmæssig optimering af "Russervinduer" - Miljøprojekt nr. 1417, 2012 (Acoustical optimization of Supply Air Windows - Environment project no. 1417, 2012). DELTA/Danish Ministry of the Environment, Søndergaard LS, Olesen HS. Designguide for bestemmelse af "Russervinduer" lydisolation. (Design guide to determine sound insulation of Supply Air Windows). DELTA, Legarth SV, Søndergaard LS. Spørgeskemaundersøgelse og lydmålinger af Russervinduer monteret i Kollektivhuset, Hans Knudsens Plads 1, 1. sal, København Ø. (Questionairy and sound measurements of the Supply Air Window mounted in Kollektivhuset, Hans Knudsens Plads 1, 2. floor, Copenhagen East). DELTA, Søndergaard LS, Olesen HS. Investigation of sound insulation for a Supply Air Window. Proc. 43rd Forum Acusticum; 27 June - 1 July 2011; Aalborg, Denmark 5. Søndergaard LS, Legarth SV. Investigation of sound insulation for a Supply Air Window field measurements and occupant response. Proc. 43rd International Congress on Noise Control Engineering, Inter-noise; November 2014; Melbourne, Australia 6. Søndergaard LS, Egedal R, Hansen MB. Åbne vinduer med god lydisolation - Miljøprojekt nr. 1940, 2017 (Open windows with good sound insulation - Environment project no. 1940, 2017). DELTA/Danish Ministry of the Environment, Søndergaard LS, Egedal R. Open windows with better sound insulation. Proc. 45nd International Congress on Noise Control Engineering, Inter-noise; August 2016; Hamburg, Germany 8. Danish Ministry of the Environment, 2007, Vejledning 4/2007, Støj fra veje (Guidance 4/2007 Noise from roads) 9. Danish Ministry of the Environment, 2007, Tillæg til vejledning nr. 5/1984: Ekstern støj fra virksomheder (Addition to guidance 5/1984: Environmental noise from plants) 10. Danish Ministry of the Environment, 2007, Tillæg til vejledning nr. 1/1997: Støj og vibrationer fra jernbaner (Addition to guidance 1/1997: Noise and vibration from railroads) 11. ISO 10140:2010, Acoustics - Laboratory measurement of sound insulation of building elements - Part 1, 2 4 and ISO 717-1:2013, Acoustics Rating of sound insulation in buildings and of building elements Part 1: Airborne sound insulation. 13. ISO 140-5:1998, Acoustics -- Measurement of sound insulation in buildings and of building elements -- Part 5: Field measurements of airborne sound insulation of façade elements and façades 14. ISO :2016, Acoustics - Field measurement of sound insulation in buildings and of building elements -- Part 3: Façade sound insulation 15.Untersuchung der Schalldämmung von gekippten Einzel- Und Doppelfenstern. Sog. HafenCity - Fenster sowie Fenster mit schallabsorbierenden Laibungs- und Sturzverkleidungen Hamburg Hafencity 4227