Impact Noise Reduction of Underfloor Heating Systems

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1 Impact Noise Reduction of Underfloor Heating Systems Antonino Di Bella, Leonardo Luison DFT - Department of Technical Physics, University of Padova, Padua, Italy. Summary Underfloor heating systems are becoming very popular in building technology, principally due to advantages related to energy saving and thermal comfort. Even if the materials used for the radiant heating panels are well optimized to achieve necessary thermal insulation, rarely these materials have been designed also for a good impact noise reduction of the floor they are applied to. An experimental analysis was carried out in laboratory according to ISO , in order to study the acoustic behaviour of floors with integrated radiant heating systems with a built-in resilient layer for impact noise insulation. These heating systems have been set up both on a beam and clay block floor and concrete slab for the evaluation of impact noise according to ISO and the influence of the top finishing has also been investigated. Comparison among noise level reduction data of different floors and radiant heating systems are presented and problems related to dynamic stiffness optimization and performance fitting are pointed out. PACS no Kd, Ti 1. Introduction Resilient heating systems technology is very useful to improve thermal comfort, energy saving and impact noise insulation in buildings. The combination of a heating system with a sound insulating material can be very useful, because of several reasons: they are applied nearly at the same time during the construction of the building and the laying techniques can have common details (for example the application of the edging strip). The sound reduction properties of such systems can be sometimes difficult to predict, in particular case of multilayer materials and because of the complex composition of the whole floor, which takes into account piping and manifold installation, different flooring selection and different kind of base floors (concrete slab, wooden joist, beams and clay blocks). To study the behavior of these kind of floating floors with complex layout, an experimental analysis of floor heating systems acoustic insulation in laboratory has been carried out: the tested products are polystyrene panels combined with a resilient layer made of different kind of recycled rubber mats. The materials have been installed on two base floors, a reference concrete slab and a beam and clay block floor, to compare the standard laboratory conditions according to ISO [1], with a common application (c) European Acoustics Association on a typical Italian floor, also diffused all over southern Europe. Two partner companies contributed to this study, providing resilient materials and heating systems. The reference floor is a standard 14 cm concrete slab, while the other is a 25 cm beam and clay block floor (20 cm blocks and 5 cm slab). 2. Experimental setup The measurements were carried out in laboratory on two permanent floors with flanking transmission suppression. Impact noise was measured for five combinations of polystyrene and rubber materials applied to the beam and clay block floor and three of them were applied to the reference concrete floor. The resilient heating panels under test are made of a layer of expanded polystyrene (two kinds with different compression behaviour) combined with recycled rubber mats of different kind: tires rubber granules, rubber from industrial waste and a mix of tires and cork granules. In Figure 1 a scheme of the samples is presented. On the reference concrete slab, the edging strips have been placed on the borders and then the panels have been placed. The junctions of each panel have been sealed with adhesive tape and then the piping has been installed on the panels: the piping was plugged to a manifold and filled with water pressure of 6 bar at room temperature. A common sand and cement screed (6 cm total width) was built and over it two different finishing floorings were placed: floating parquet and ceramic tiles. The parquet was applied without 1719

2 Table I. Resonance frequency of the whole floor (base floor and floating floor with resilient heating system), calculated with the two methods of (1) EN and (2) EN s [MN/m 3 ] f (1) 0 [Hz] f (2) 0 [Hz] Diff. [Hz] Figure 1. Floors tested: (A) concrete slab with heating system A1) flooring, A2) 6 cm sand and cement screed, A3) resilient heating system, A4) 14 cm concrete slab; (B) beam and clay block floor with heating system B1) flooring, B2) 6 cm sand and cement screed, B3) resilient heating system, B4) 10 cm light concrete, B5) beam and clay block floor, B6) plaster. glue on a separating layer made of corrugated cardboard. Ceramic tiles were glued directly to the screed by using a cement-based glue. Only for the beam and clay block floor, an additional light concrete layer under the resilient material has been added, to simulate a real application. Some pictures of the samples are reported in Figure 2. An aging time of three weeks was adopted for the screeds and two days for the tiles glue. For every sample, impact noise level L n was measured and for the application on concrete slab, also ΔL values were calculated. 3. Results on concrete slab In Figure 3 impact noise reduction for three products on concrete slab are presented. The curves show a good linear behavior starting from 125 Hz, but in the frequency range 1250 Hz Hz a small decrease occur. This lack of reduction has been noticed for all the three samples, but fortunately it has no effect on the calculation of the rating index. The reason of this behavior could be the multilayer characteristics of the elastic materials, in which resonance vibration transmission at medium and high frequencies can occur [2]. Because another common characteristic of the samples is the presence of piping (and manifold, kept disconnected from the structures), these factors could also be the reason of the deviation from linear behavior of the impact noise reduction curve in frequency, because make the global composition of the floor more complicated. Dynamic stiffness was also measured for the samples: values of s were found to be included between 37 and 45 MN/m 3. The tests were carried out according to EN [3], but waiting three weeks before measuring (approximately the same aging time of the screed). The prediction of the resonance fre- quency f 0 of the concrete slab - floating floor system was made using the formula from EN [4] ( 1 f 0 = 160 s m + 1 ) 1 m 2 which can gives a different estimation (in general a higher resonance frequency), compared to the formula from EN [5] (m 1 and m 2 are the mass values of the floating floor and the base floor in kg/m 2 ). This choice was made because the difference between the superficial mass of the base concrete floor is not so large, compared to the superficial mass of the floating screed (see [6]). A value of 320 kg/m 2 has been taken for the 14 cm concrete base floor, calculated from a density of 2300 kg/m 3, while the mass of the screed was measured about 120 kg/m 2, after the demolition of the samples. The difference between predicted values of f 0 tends to increase, as the material dynamic stiffness increase; in this case, in the considered dynamic stiffness range, the difference between the two formulas can be Hz. The predicted values are reported in Table I, while in Figure 3 a comparison between laboratory data and predicted reduction values using the worst dynamic stiffness values is presented (s =45MN/m 3 and f 0 = 115 Hz). In the considered frequency range 100 Hz Hz the laboratory data are included between the two predictive formulas. Also damping has probably an effect on the shape of the impact noise reduction curve, because the slope is between 30 and 40 db/decade and because the reduction seems to be zero, and not a negative value, for frequencies below the resonance. 4. Results on beam and clay block bare floor In Figure 4 normalized impact noise level data for five combinations of EPS panels and recycled rubber mats are presented. The behavior is quite similar for different combinations and at low frequencies impact noise level spectra are almost overlapped. Starting from 160 Hz, the difference among materials is more evident and in particular in the range 1250 Hz Hz there is a larger distribution. It is interesting to notice that in this range a particular resilient material, which is made of recycled tyre rubber granules, seems to work better than the other materials, with both kinds of 1720

3 FORUM ACUSTICUM 2011 Di Bella, Luison: Impact Noise Reduction of Underfloor Heating Systems Figure 2. Samples setup: (A) heating panels, (B) a screed built over the panels and piping (C) detail of the screed, (D) detail of floating parquet installation at manifold, (E) ceramic tiles setup, (F) a completed ceramic tiles flooring. Figure 3. Impact noise reduction measured for three heating system panels on the reference concrete slab. Every curve refers to a combination of a polystyrene panel (EPS1, EPS2) and a recycled rubber mat (RR1, RR2, RR3). EPS panels. In general, the application of a resilient system to this kind of floor seems to give a quite particular result: in the range 100 Hz Hz there is a good noise reduction, but starting from 630 Hz, im- pact noise level increases and reaches a maximum at 2000 Hz, then reduction is good again. This lack of insulation could be correlated to the non-linearity measured on the concrete slab and shown in Figure 3, but probably also the radiation characteristic of the beam and clay block floor can have an influence, amplifying the sound transmission. In Figure 5 impact noise reduction evaluated on this floor is presented. The reduction is quite different from that evaluated on the reference slab: for example in the lower part of the spectrum it starts from positive values and increases more rapidly; then in the range 1000 Hz Hz it is stationary and after 2500 Hz it increases reaching higher values than for concrete. Although the lack of reduction around 1600 Hz is more relevant, the better performance at lower frequencies is in general a good characteristic, specially for regulation requirements. In Figure 6 it is shown an example of this comparison, for the better combination of materials (EPS1 with RR2). 5. Influence of the flooring For the samples built on the beam and clay block base floor, also finishing flooring has been investigated. Two types of coverings were tested for each combination of resilient heating system: ceramic tiles and wooden parquet. The parquet was posed without glue in floating application, with a separating layer made of corrugated cardboard (no loads were placed 1721

4 Figure 4. Impact noise level measured for five heating system panels on a beam and clay block bare floor in laboratory (without flooring). Every curve refers to a combination of a polystyrene panel (EPS1, EPS2) and a recycled rubber mat (RR1, RR2, RR3). Figure 6. Impact noise reduction for the combination of EPS1 and RR2 evaluated on both floors. floating parquet, with traditional cement-based glue. It was necessary to wait three days before starting measurements, to let the glue dry completely. In Figure 7 an example of flooring effect is presented, for the best combination of resilient layer and EPS panel. Applying the ceramic tiles to the screed has a very small influence on impact noise level. The two spectra (ceramic covering, bare screed) are almost overlapped and a small level increasing was noticed in the range 500 Hz Hz. On the contrary, the application of the floating wooden covering gave a great improvement in all the spectrum, in particular in the range 400 Hz Hz, in which impact noise is more critical in this case. 6. Impact noise rating Figure 5. Impact noise reduction measured for five heating system panels on a beam and clay block bare floor in laboratory (without flooring). Two kinds of polystyrene panels (EPS1, EPS2) and three of recycled rubber mats (RR1, RR2, RR3). over the covering surface). The choice of this kind of separating layer was made to test a poor material, without taking into account issues connected to global heat flow of the system through the covering, which could be probably affected by the presence of air in this case. The ceramic tiles, on the contrary, were glued directly on the screed after removing the In Table II rating index values of impact noise reduction and impact noise level are presented for the samples on concrete and beam and clay block floors. Reduction data are calculated applying ISO rating procedure; for the beam and clay block floor, the same procedure has been adopted, applying measured reduction values in frequency to the concrete reference spectrum. L n,w differences between bare and covered floor have also be taken into account. The systems under test have a similar noise reduction rating index, because frequency behaviors are also similar. Materials with ΔL w = db can provide a good impact noise reduction when used on a non-homogeneous floor like the one considered in this study, with L n,w values of db. It seems that on the beam and clay block floor, the evaluation of impact noise reduction provides better results, because of a better global performance at low frequencies (100 Hz

5 Table III. L n,w for the samples tested with different floorings (ceramic tiles and floating parquet) on the beam and clay block floor [db]. Sample Screed Ceramic Parquet BF/EPS1-RR BF/EPS1-RR BF/EPS2-RR BF/EPS2-RR BF/EPS2-RR Figure 7. Normalized impact noise level L n for the combination of EPS1 and RR2: influence of the flooring. For the other combinations of panels and rubber mats the behaviors are similar Table II. Rating index values for different samples tested on both floors according to ISO [7] (CS concrete slab, BF beam and clay block floor). ( ) beam and clay block impact noise reduction rating index calculated applying ISO procedure [8]. Sample L n,w [db] ΔL w [db] Diff. [db] Bare CS CS/EPS1-RR CS/EPS1-RR CS/EPS2-RR Bare BF BF/EPS1-RR ( ) 33 BF/EPS1-RR ( ) 37 BF/EPS2-RR ( ) 34 BF/EPS2-RR ( ) 37 BF/EPS2-RR ( ) 34 Hz). In Table III normalized impact noise rating index is given for every sample tested with the two floorings. The excellent performance given by the floating parquet application has be found for every sample. The influence of the ceramic finishing on the rating index is less important: in certain cases the performance is unchanged, for certain samples is 1-2 db higher or lower. 7. Discussion Heating systems with the addition of a resilient layer made of a recycled rubber mat seem to provide a good insulation from impact noise sources, even if the dynamic stiffness is a little higher than common optimized values. The prediction of the impact noise reduction on the reference concrete slab, starting from the dynamic stiffness, provides quite a good correlation, with experimental data that are included between the two linear predictions with slope 30 and 40 db/decade. For the application of the materials to the beam and clay block floor, a better reduction has been measured at low and high frequencies, but in the range 1000 Hz Hz the reduction is lower and it is not easy identifying the cause of this behavior. It could derive from the multilayer characteristics of the materials used or from the piping, and a worsening of the performance could also be due to the presence of the 10 cm light concrete screed (used in dwellings to cover the equipment). More studies should be carried out to verify these conditions. The higher levels revealed in the frequency interval 630 Hz Hz are quite negative for the impact noise rating index calculation. However, noise at medium frequencies is also easier to reduct and this is made quite well with the application of a floating flooring: for example, the application of the floating wooden parquet provided a very good insulation, reaching L n,w =48 51 db. In this work, when comparing results obtained on concrete slab and on beam and clay block floor, it has to be remembered that the global composition of the floors are not exactly the same, because in the beam and clay brick floor a light concrete layer has been added under the resilient material, to simulate a real application. In these conditions, the comparison between impact noise reduction evaluated on both floors is to be intended as a comparison between a laboratory setup and a typical site setup, not exactly the application of the same system. As regarding the evaluation of the performance with the rating index, it was noticed that even a material or system with a certain reduction (measured according to ISO and ISO 717-2) can show a different noise reduction when applied to another base structure, because of the different impact noise level of the bare floors. For a better description of the reduction applied to a base floor different from the concrete slab, a specific reference impact noise level spectrum should be used, which is not possible at the moment. 1723

6 8. Conclusions Resilient floor heating systems are a good choice to achieve a good impact noise insulation. In this work, multilayer materials made of EPS and recycled rubber were analyzed and through laboratory measurements, carried out according to ISO , it was possible to identify some critical behaviors of these systems. By the comparison of reduction data with impact noise performance on another kind of floor (in laboratory conditions), which is more common in Italian building technology, it was possible to give an estimation of performance in a real application. It would be important to verify laboratory data through site tests on the same materials applied in dwellings, to check also the influence of the flooring in site conditions. An interesting issue, that will be carried on after this work, is the comparison between impact noise reduction data for materials measured on the reference concrete slab and on the beam and clay block floor, to verify if the performance can be different and if it is necessary to adopt a specific reference curve. References [1] International Standard ISO : Acoustics - Laboratory measurement of sound insulation of building elements - Part 1: Application rules for specific products, [2] A. Schiavi, A. Pavoni Belli, F. Russo, M. Corallo: Misura della rigidità dinamica di materiali multistrato e possibilità di previsione dell isolamento al rumore di calpestio. Proc. 36 th Congr. of Acoustical Society of Italy AIA 2009 (in Italian). [3] European Standard EN : Acoustics. Determination of dynamic stiffness. Materials used under floating floors in dwellings, [4] European Standard EN : Building acoustics - Estimation of acoustic performance of buildings from the performance of elements - Airborne sound insulation between rooms, [5] European Standard EN : Building acoustics - Estimation of acoustic performance of buildings from the performance of elements - Impact sound insulation between rooms, [6] L. Luison, A. Di Bella, F. Loriggiola: Influence of the Sample Preparation for Dynamic Stiffness tests on the Calculation of Impact Noise Level Attenuation, Proc. 1 st EAA EuroRegio Congr., [7] International Standard ISO : Acoustics - Laboratory measurement of sound insulation of buildings elements - Measurement of impact sound insulation, [8] Intarnational Standard ISO 717-2: Acoustics - Rating of sound insulation in buildings and of building elements - Impact sound insulation,