Robust Acoustics Improvements for Dwellings Next to Airports

Transcription

1 Robust Acoustics Improvements for Dwellings Next to Airports Marta Fuente González, Alberto Esteban González LABEIN Technological Centre, Acoustics Area, Parque Tecnológico de Bizkaia, C/ Geldo, Edif. 0, 481 Derio, Spain. Susana Escudero, Mª José de Rozas Representing to the Acoustic Area of the Laboratory for Quality Control in Dwellings of the Basque Government, Agirrelanda 10, Vitoria, Spain. The acoustical quality of dwellings in Spain is guaranteed up today with the compliance of the Building Regulation NBE-CA88, which establish laboratory requirements to each construction element. However, the new Spanish Building Regulation (CTE), searching a higher level of comfort in dwellings is increasing its requirements and is considering the building as a product itself. The environmental noise is transmitted inside the housings through different elements, although the main path is the façade, there are other ways like ventilation ducts, grilles, etc. This paper shows a research about different constructive alternatives for improving the acoustical quality in a particular dwelling next to an airport in Spain, including the façade improvements and the analysis of noise transmission through natural ventilation ducts (shunts). The aim is not only to fulfil the Standars, but also to protect the residents under a comfort point of view. 1 Introduction VISESA is a Building State-Owned Company of the Basque Government in Spain, which builds state subsidized housings. In 04 during the built of dwellings next to an airport, it was decided to carry out actions to minimize the acoustical impact over the future inhabitants, focusing on two critical aspects: - Façade insulation. - Noise transmission through natural ventilation ducts. In this frame it started a research project in cooperation with LABEIN, not only for fulfilling the Standars, but also for protecting the residents under a comfort point of view. 2 Objetives The principal objective of this research is to analyze different constructive alternatives, concerning both, façade design and transmission through ventilation ducts, in order to minimize the annoyance of the future residents in a dwelling affected by aircrafts noise. This objective is not only focused on that particular building, but also its aim is to define general guidelines for their implementation in other future dwellings. The façades usually have windows and balconies, therefore, there are two more objectives: - Evaluate the change in acoustic insulation of a façade when the window area increases. - Evaluate the change in acoustic insulation of a façade when the air gap between windowpanes increases. 3 Working Process 3.1 Acoustic Comfort Criteria The current Spanish Building Regulation: Noise in Buildings NBE-CA 1988 indicates that the minimum acoustic insulation of the façade building elements must be A (laboratory measurements). Regarding to the sound transmission through ventilation ducts, the NBE-CA 1988 doesn t demand any requirement, only recommends a good design. For the façades, the future Spanish Building Regulation (CTE) will establish different requirements depending on the type of environmental noise: traffic noise, railway noise and aircraft noise. Besides, the acoustic requisites will be in situ. In this research, the starting point has been the analysis of the sound levels of the different aircrafts that pass next to the dwellings. The analysis is based on the maximum noise levels of each aircraft (Lmax) because it is the representative parameter of the annoyance of this type of noise source. In this case, all the measured global maximum levels are between and 85 A. The spectrum of the most unfavourable aircraft, i.e. the one with the maximum global level (85 A), is considered as the reference exterior level for this research, The design criterion has been the noise level inside that is given by different NC-Curves depending on the use of the considered room. In the case of sitting rooms and bedrooms, it is recommended the NC-25 curve (35 A). For the research of sound transmission through ventilation ducts, which usually are in kitchens and L 177

2 Forum Acusticum 05 Budapest bathrooms, the proposed curves are NC-/35 (between and 45 A). 3.2 Façade Design With the noise level outside and the requirement of noise level inside, it is possible to calculate the minimum insulation that the façade must fulfil. In Figure 1, these data are represented in frequencies. The necessary minimum traffic sound reduction index for the façade must be: Rw + Ctr= Double wall of hollowed brick (11,5 cm), air gap (16 cm) and cladding with two sheets of plasterboard and mineral wool (Figure 3). Double door (2,15 m x 2,1 m): outside sliding door (4+4), air gap (45 cm) and inside sliding door (4+4). All the windows and doors are monoblock type with roller blinds. Mortar 263 mm Plasterboard Noise Level Inside: NC-25 (35 A) Hollowed Brick Mineral wool ( mm y kg/m 3 ) Necessary Minimun Insulation (Rw + Ctr =45 ) Framework (48 mm) mm Maximun Outside Level (85 A) Figure 2: Wall of façade configurations 1, 2, 3 and Frequency (Hz) Figure 1: Façade Design (octaves). In the façades, the window is the weakest spot, and when the acoustic requirements are high, as in this case, it is necessary to consider double windows. Besides, other criteria have been taken into account like constructive, thermic, economic and security ones. Taking into account all the data, restrictions and the acoustic criteria, five different configurations for façades have been characterized acoustically in laboratory: 1. Wall of hollowed brick (11,5 cm), air gap (4 cm) and cladding with two sheets of plasterboard and mineral wool (Figure 2). Without window. 2. Wall 1 with double window (1,4 m x 1,18 m): outside sliding window (4+4), air gap (15 cm) and inside casement window (4/6/4). 3. Wall 1 with double window (1,4 m x 1,18 m): outside sliding window (4+4), air gap (15 cm) and inside sliding window (4+4). 4. Wall 1 with double door (2,15 m x 2,1 m): outside sliding door (4+4), air gap (15 cm) and inside sliding door (4+4). outside Morter Hollowed Brick Morter (1,5 cm) 145 mm 1 mm 263 mm 118 mm inside Pasterboard Mineral Wool ( mm y kg/m 3 ) Framework (48 mm) Polyethylene (3 mm) mm Figure 3: Wall of façade configuration 5. Table 1 shows the results of tests carried out in the acoustic laboratory for the different configurations of façades, with the two indices, traffic and pink noise. The insulation curves are shown in the Figure 4. L 178

3 Forum Acusticum 05 Budapest Table 1: Laboratory results* of the different façade options. Façade configurations Insulation Index Traffic noise Rw + Ctr Pink noise Rw + C 1. Cladding wall without window Casement window 4/6/4 + Sliding window 4+4 (1,6 m 2 ) (air gap 15 cm) 3. Double sliding window 4+4 (1,6 m 2 ) (air gap 15 cm) 4. Double sliding door 4+4 (4,4 m 2 ) (air gap 15 cm) 5. Double sliding door 4+4 (4,4 m 2 ) (air gap 45 cm) * Laboratory for Quality Control in Dwellings of the Basque Government, Vitoria (Spain). Variation of air gap between windows: Also, as it was expected, an increase of the air gap between windows implies an increase in the façade global insulation. For example: an increment from 15 to 45 cm of air gap, involves an increase of 6 in façade insulation. R () 3. Double sliding window 4+4 (1,6 m2) (air gap 15 cm). Rw+Ctr=51 4. Double sliding door 4+4 (4,4 m2) (air gap 15 cm). Rw+Ctr=47 5. Double sliding door 4+4 (4,4 m2) (air gap 45 cm). Rw+Ctr=53 1. Cladding wall without window. Rw+Ctr= Sound Reduction Index () Frequencies(Hz) 2. Casement window 4/6/4 + Sliding window 4+4 (1,6 m2) (air gap 15 cm). Rw+Ctr=51 3. Double sliding window 4+4 (1,6 m2) (air gap 15 cm). Rw+Ctr=51 4. Double sliding door 4+4 (4,4 m2) (air gap 15 cm). Rw+Ctr=47 5. Double sliding door 4+4 (4,4 m2) (air gap 45 cm). Rw+Ctr=53 Necessary Minimum Insulation (Rw + Ctr =45 ) Figure 4: Sound Insulation Curves (octaves). Figure 5: Sound Insulation Curves. By means of the estimation of the in situ insulation of all the façade configurations (with window or door), the expected sound levels inside the dwellings have been calculated and they are shown in (Figure 6). As the façade insulation was quite high, EN was used to estimate flanking transmission between façades and floor, and the results showed that those transmissions were negligible. 45 Noise Level Requirement Inside: NC-25 Variation of window area: As it was expected, an increase of the window area implies a reduction in the façade global insulation. In Figure 5 it is shown how the traffic insulation index of the door (bigger windowpane area) decreases 4 comparing to the smallest one: from 47 to 51. Although in medium-high frequencies, the differences are higher (up to 10 ). At those frequencies there is a fall in the curve of the configuration 4 (the one with the door). The configuration 5 (door with higher air gap) keeps the same tendency. This behaviour could be due to a particular vibration mode of the windowpanes or due to a longer space between the two sashes of each sliding window. However, this effect needs an additional study Global (A) configuration 2 configuration 3 configuration 4 configuration 5 Figure 6: Estimated maximum noise levels inside, from aircrafts, with different façades. L 179

4 Forum Acusticum 05 Budapest Outside The comparison between the estimated noise levels inside and the NC-25 curve (acoustic comfort criterion) shows that the configurations 2, 3 and 5 fulfil the requisite. The inside sound level with the configuration 4 (Double sliding door 4+4, air gap 15 cm) is over the NC-25 at medium-high frequencies (0 to 00 Hz), and the Global Level (37 A) rise above 35 A. Receivers Aeroplane 85 A Shunt 44 A 5º 3.3 Noise Transmission through natural ventilation ducts (Shunts) In order to know the attenuation in the sound transmission from the outside (the roof) to each of the rooms (kitchens and bathrooms) connected to the ventilation duct, in situ tests have been made in another dwelling, with similar characteristics (Figure 7). A pink noise source has been placed on the roof and sound levels measurements have been carried out in the interior bathrooms of every storey. This way, any sound transmission across the window is avoided. 4º 43 A 3º 39 A 2º 38 A 1º 31 A Figure 8: Estimated Global Maximum Sound Levels in bathrooms of the dwelling. In Spain the usual ventilation ducts are common natural duct systems made of concrete or ceramic blocks. In some dwellings there may be sitting rooms with the kitchen in the same space, and in those types of rooms there is an outlet of the ventilation duct. In order to analyze this kind of room (with an acoustic requisite higher than kitchens and bathrooms), an estimation in an hypothetical sitting room-kitchen, of about 24 m2, furnished and placed on the top floor of the building (more unfavourable situation) has been made. In Figure 9 it is shown how the sound levels transmitted to the sitting room-kitchen fulfil the criterion of NC-25 and the bathroom fulfil the NC-35. Sight of the roof Chimney pot Grille in bathroom Lp in bathroom Lp in sitting room with kitchen NC cm cm cm NC- 25 cm Concrete Block for Ventilation Duct NC Figure 7: Characteristics of the duct system tested With the measured sound attenuations and the sound spectrum of the maximum level of the aircrafts, it was estimated the noise levels transmitted to the bathrooms of the considered dwelling object of study (Figure 8) Global (A) Figure 9: Estimated maximum noise levels inside from the aircrafts transmitted through the shunt, in two different type of rooms. L 1

5 Forum Acusticum 05 Budapest Besides, it has been estimated the global result of the simultaneous contribution of the sound entering through the different types of façades, and the sound entering through the grille of the shunt, in that sitting room-kitchen. The contribution of the shunt to the global level is about Conclusions After analyzing all the results, the following conclusions have been obtained: - It is possible to design robust façades from the acoustic point of view for critical situations of environmental noise, even with big windowpanes. - There is an improvement of around 16 with a double window (Rw+Ctr = 51 ) compared with a single window (Rw+Ctr = 35 ). - In this research, it hasn t been detected the usual insulation drops due to the use of sliding windows. Each individual sliding window has had similar insulation to the casement window. The hermetic nature of window sashes and blinds systems is a very important factor that has a lot of influence. - In the analyzed sitting room with kitchen, with all the façades, the contribution of the sound transmitted through the natural ventilation duct is about 1-2. References [1] Data Base MAT: acoustical features of products. Published by the Acoustic Area of the Laboratory for Quality Control in Buildings of the Basque Government. [2] Spanish Building Regulation: Noise in Buildings. NBE-CA [3] Drafts of the new Spanish Building Regulations, found in [4] Acoubat Sound v3, Technical Documentation. [5] EN 12354: Building acoustics - Estimation of acoustic performance of buildings from the performance of elements. L 181