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Volume : 44

Part : 2

Proceedings of the Institute of Acoustics

 

 

Objective and subjective analysis of the acoustic performance of a ZEB test-building

 

Chiara Scrosati1, ITC-CNR, San Giuliano Milanese, Italy

Michele Depalma, ITC-CNR, San Giuliano Milanese, Italy

Fabio Scamoni, ITC-CNR, San Giuliano Milanese, Italy

Ludovico Danza, ITC-CNR, San Giuliano Milanese, Italy

 

ABSTRACT

 

The paper describes an experimental campaign, including both objective and subjective analysis, carried out in a Zero-Energy full-scale test building and aiming at analyzing the acoustic performance of the construction and the acoustic comfort of the rooms. The objective analysis consists of sound insulation measurements of facades and partitions, noise level measurements of service equipment and environmental noise level monitoring. The subjective analysis is based on a survey carried out on 100 participants to collect the answers about their evaluation of the acoustic quality in two different test rooms. The outcomes of the questionnaire data show participants evaluation of Acoustic Quality as a not annoying environment.

 

1. INTRODUCTION

 

The reduction of carbon emissions and the consumption of energy resources due to the construction sector can only be achieved with the full implementation of the concept of Zero-Energy buildings (ZEB). The reported work is part of the research project “I-ZEB – Towards Intelligent Zero-Energy Buildings for a smart city growth” supported by Lombardy Region and the National Research Council of Italy (CNR). Within the research project, the technological solutions are implemented with a global and integrated assessment of the energy and environmental building performance in order to provide a support system for the construction sector aimed at the definition and optimization of innovative materials, components and systems. This system could also fulfil the increasingly stringent performance requirements imposed by Standards and Regulations in force [1]. The ZEB (Zero-Energy Building) Laboratory acts as a demonstrator for energy-environmental analyses aimed at evaluating the performance in real conditions of the envelope components and technological plant solutions, as well as the validation of models and monitoring tools and the control and management of the Internal Environmental Quality of the building (IEQ) [2] and its interactions with the external environment.

 

2. THE ZEB LABORATORY

 

The ZEB Laboratory (Fig. 1), designed and built at ITC, the Construction Technologies Institute of the CNR, in Milan, is the result of the refurbishment of an existing building that has achieved the requirements of Zero-Energy Building due to the envelope and plants components performance improvement and the integration with Renewable Energy Sources. Internally, the laboratory consists of 3 separate rooms: the two largest ones Room 1 and 2 (Fig. 1), naturally lit, are monitored and dedicated to the experimentations while the smallest one Room 3 (Fig. 1) is a service space suitable for the installation and control of technological plants.

 

 

Figure 1: Left: The ZEB Laboratory. Right: the objects of acoustic evaluations are indicated: 1) partition wall, 2) ETICS, 3) living wall, I) heat recovery systems.

 

3. ACOUSTIC ISSUES CASE STUDIES

 

The experimental campaign in the ZEB laboratory evaluated the acoustic performance of the building structures and systems as well as the acoustic comfort in the test rooms, in an IEQ view [2]. The acoustic quantities that can be evaluated in the ZEB laboratory include airborne sound insulation [3], façade sound insulation [4], impact noise, HVAC (Heating Ventilation and Air Conditioning) plant noise, reverberation time [5] and the internal and external noise levels.

 

2.1. Internal partition wall

 

The wall configuration under study was characterized on-site, in a situation that presented many issues related to flanking transmissions. In fact, due to the existing structures inside the building before the implementation of the I-ZEB laboratory, some elements between Room 2 and Room 3 (Fig.1) could be important acoustic bridges in the transmission of noise from one side to the other of the wall under evaluation. In order to minimize the flanking transmissions, modifications were made to the lateral elements, step by step. At each step, the measurement of the sound transmission loss was repeated until the highest possible value was reached.

 

The wall under study (Fig. 2) is a multilayered lightweight partition [3] consisting of three plasterboard layers with two cavities filled with double density stone wool rigid panels with nominal thickness of 60 mm and nominal average density of 70 kg/m3.

 

A longitudinal steel beam passes across the ceiling from Room 2 to Room 3 and a transverse steel beam crosses the ceiling of Room 2 leaning on two steel beam shoes fixed on the side wall of Room 2 (Fig. 2 top Right). In order to minimize the effect of the acoustic bridges, subsequent interventions were made on the different elements; in particular, a suspended ceiling consisting of plasterboard panels and double density stone wool panels was installed to enclose the steel beams (Fig. 2 bottom Right).

 

 

Figure 2: Left side: the lightweight wall under study. Right side: the steel beams on the ceiling of Room 2 before (top) and after (bottom) the interventions [3].

 

Figure 3 shows the initial and final apparent sound reduction index as a function of frequency and the related single numbers. The uncertainty is estimated by using the reproducibility standard deviation obtained in a Round Robin Test of field measurements on a similar lightweight partition [6].

 

Starting from the laboratory measurements (Rw = 66.2 ± 2.4 dB) of exactly the same partition wall, the on-site acoustic insulation performance was also estimated by using the calculation model defined in standard ISO 12354-1:2017. The results are indicated in Table 1 [3].

 

 

Figure 3: On-site measurement results: initial (black line) and final (red line) apparent sound reduction index and related single numbers. [3].

 

Table 1: Simulation results under different configurations of the partition under test [3]

 

 

As it is widely known, the on-site performance of the lightweight partition is below the one obtained in laboratory without flanking transmission, as it can be seen by comparing the single numbers obtained in this different situation, which differ by 13 dB. The expected decrease in performance of the partition under study when installed on-site has been partly mitigated by the interventions on the main acoustic bridges (Fig. 2).

 

The comparison of the results obtained with the measurements highlighted that the simplified calculation method is not adequate to simulate real situations that differ from those most commonly considered by the model [7]. Even without taking into account the effect of acoustic bridges passing through the partition, the prediction model underestimates the performance of the partition wall measured on-site. On the other hand, the prediction model takes into account the improvement due to the suppression of the flanking transmission of the steel beams on the ceiling of Room 2; the increase of R’w of the model (3.2 dB) is comparable to the on–site measurements R’w increase (4.1 dB).

 

2.2. Façade with external thermal insulation system

 

The External Thermal Insulation Composite Systems (ETICS) represent the most widespread solution in Italy for the renovation of facades in order to increase the thermal insulation; it is therefore important to assess their acoustic performance. The façade with ETICS under study comprises two outside walls (see Fig. 1), one with a window (F2) and one without (F1).

 

To evaluate the improvement of acoustic insulation due to the ETICS, measurements [4] were made before and after the application of the ETICS. Both the outside walls of the Room 2 were tested.

 

 

Figure 4: section of the facade under study after the installation of the ETICS.

 

As done in the case of the internal lightweight partition wall, starting from the laboratory measurements [4] of exactly the same base wall (without) and the same base wall plus the same ETICS (with), the on-site acoustic insulation performance (of F1, the wall without the window) was also estimated by using the calculation model defined in standard ISO 12354-1:2017. The improvement calculated was equal to 4.97 dB [4]. It is important to underline that, in general, the typology of the façade, the layers and mass of the wall, the portion of window surface and their Rw together with all the other features provided a basis for complex division of the typology of façades in key categories [8] and, therefore, the results that can be obtained with ETICS depends on all these features. The results obtained from the measurements highlighted that the stone wool ETICS under study, designed to fulfil the I-ZEB thermal requirement, effectively improves the sound insulation of the treated façade. Moreover, the calculation model applied to the field situation (ΔRw = 4.97) shows a significant agreement with the measurements results (ΔD2m,nTw = 5 dB).

 

2.3. Living wall

 

The living wall under study, consisting of a modular structure in PVC panels covered with three layers of felt designed to be mounted to a base wall, is an innovative system in which plants are rooted in felt layers and grown in hydroponics instead of planted in pockets of growing medium.

 

 

Figure 5: The living wall under study (left), before (center) and after (right) its installation on the partition.

 

 

Figure 6: The living wall: apparent sound reduction index (left) and reverberation time of the Room1 (right) before and after the installation of the living wall on the partition wall [5].

 

The living was applied to the indoor partition between Room 3 and Room 1 (see Fig. 1 and 5). Its contribution in terms of both the improvement of the sound insulation between Room 1 and Room 3 and the reduction of the reverberation time in Room1 has been verified with on-site measurements. The obtained results, summarized in Figure 6 [5], highlighted that the installation of the living wall has improved the acoustic insulation of the base wall by 6 dB; moreover, the presence of the internal living wall improved the sound absorption in the room in which it was installed, as evidenced by the decrease of the measured reverberation time.

 

3. SUBJECTIVE ANALYSIS

 

The test rooms were equipped with several sensors aimed at analyzing different aspects of the IEQ, energy consumption, envelope thermal behavior and outdoor environmental conditions through a weather station installed near the laboratory. For the measurement of the outdoor noise level, one microphone was installed in front of each facade Room 1 and Room 2 of the north-east wall at a distance of 2 m and at a height of 1.5 m above the floor of the receiving room. Internally, the cooling service was provided by direct expansion heat pumps, the air change per hour was ensured by two recovery systems [9] operating in ventilation systems in Room 1 each set at 30 m3/h and one in Room 2 set at 30 m3/h.

 

The test rooms are equipped with several sensors to detect all variables influencing the different aspects of the IEQ [11]. In each room, different sensors are placed closest to the users. Figure 4 shows the experimental setup of each desk: 1 thermo-hygrometric sensor,1 globe-thermometer, 1 hot wire anemometer, 1 CO2 concentration sensor, 1 luxmeter and 1 microphone positioned at listening height.

 

 

Figure 4: Experimental setup [2].

 

The experimental campaign was conducted in Room 1 and Room 2 involving 100 participants, where they judged the acoustic environments by the noise annoyance, as specified in ISO/TS 15666 [10] with a 4-point one-pole scale. For this purpose, two single noise events were simulated during the survey: an aircraft overflight outside the façades of both the rooms and a flushing of water generated in Room 3.

 

The results of the questionnaire indicated “Not annoying” acoustic environments. The noise produced during the survey by the overflight confirm good performance of the façade. On the other hand, the noise produced by the equipment should have resulted in a greater perception of the disturbance by users with respect to the design value of the acoustic performance of the rooms. But the different background noise in the two rooms leads to different results.

 

The equipment noise LAeq,nT is equal to 44.6 dB(A) for Room 1 and 40.5 dB(A) for Room 2 (Cat.III/Uncomfortable). The results of the questionnaires show how Room 2 is mainly affected by the acoustic and air quality conditions. In Room 1 the equipment noise level is about 4 dB(A) higher than in Room 2, where a different system is operating. Nevertheless, the lower background noise in Room2 than in Room1 and the lower sound insulation of the separating wall between Room2 and Room3 allow to clearly hear the flushing noise, and this results in a greater acoustic discomfort in Room2. In fact, none of the participants in Room 1 has heard the flushing noise coming from Room3.

 

While, for AQ the differences are due to a negative classification of the equipment noise level by the design data only, which corresponds to “Uncomfortable” with respect to the participants’ prevailing assessment of “Slightly uncomfortable". Generally, in the AQ evaluation, the difference between the monitoring-based and the questionnaire-based results is that the design parameter defined in EN 16798-1 standard is not completely representative of the indoor acoustic quality.

 

 

Figure 5: Acoustic Quality response (left: Room 1 and right: Room 2) of participant (0 - Not annoying; 1 - Slightly annoying; 2 – Annoying; 3 - Very annoying) [2].

 

Then, the relation between IEQ and the indoor environmental factors (i.e. thermal and visual comfort and acoustic and indoor air quality) was studied by a multiple linear regression [2]. The analysis showed how the indoor air quality weight much more than the other variables, about 60%. Wherever, Acoustic quality weights about 13-17% of the IEQ in a Zero-Energy Build-ing (Table 2).

 

Table 2: Weighting factors about the ZEB rooms [2]

 

 

4. CONCLUSIONS

 

The ZEB laboratory of ITC CNR has shown that it has considerable potential as a full-scale demonstrator of the acoustic behavior under real conditions of use of structures, building elements and materials; in particular, it made possible to evaluate its performance in the various phases of design, worksite, installation and renovation.

 

Although the occupants of the ZEB laboratory are much more sensitive to air quality issues, the acoustic quality represents an important aspect of ZEB design, closely linked to HVAC plants operation and indoor air quality as well.

 

5. ACKNOWLEDGEMENTS

 

This study was part of I-ZEB Project (2016–2019) which was funded by Lombardy Region and CNR (grant number no. 19366/RCC) with the collaboration of 16 companies of building industry.

 

6. REFERENCES

 

  1. Scrosati C., Belussi L., Danza L., Fabio Scamoni F., Smith S. & Currie J. Resolving clashes between net-zero energy and acoustics engineering specifications, to enhance low-carbon building performance, regulatory compliance and future skills. Laws and standards comparison between Italy and UK. Proceedings of INTER-NOISE 2022. Glasgow, U.K., 21-24 August 2022.

  2. Danza, L., Barozzi, B., Bellazzi, A., Belussi, L., Devitofrancesco, A., Ghellere, M., Salamone, F., Scamoni, F., Scrosati, C. A weighting procedure to analyse the Indoor Environmental Quality of a Zero-Energy Building, Building and Environment, Volume 183, 107155 (2020).

  3. Scrosati, C., Scamoni, F, Depalma M. and Gandolfi R. On-site acoustic insulation performance of a lightweight partition. Proceedings of the 26th international congress on sound and vibration (ICSV 2019), Montreal, Canada, 7–11 July 2019.

  4. Scamoni, F., Scrosati, C., Depalma, M., Danza L., Bellazzi A. and Gandolfi R. Sound insulation improvement of a façade with external thermal insulation system. Proceedings of the 27th inter national congress on sound and vibration (ICSV 2021), Virtual, Online 11-16 July 2021.

  5. Scamoni, F., Scrosati, C., Depalma, M., Barozzi, B. Experimental evaluations of acoustic properties and long-term analysis of a novel indoor living wall. Journal of Building Engineering, Vol ume 47, 103890, (2022).

  6. Scrosati C., Scamoni F., Bassanino M., Mussin M., Zambon G., Uncertainty analysis by a Round Robin Test of field measurements of sound insulation in buildings: Single numbers and low frequency bands evaluation - Airborne sound insulation. Noise Control Engineering Journal, 61 (3), May-June (2013).

  7. Di Bella, A., Mastino, C.C., Barbaresi, L., Granzotto, N., Baccoli, R. and Morandi, F. Comparative study of prediction methods and field measurements of the acoustic performances of buildings made with CLT elements. Proceedings INTER-NOISE 2017, Hong Kong, China, 27-30 Au gust, 2017.

  8. Masovic, D., Miskinis, K., Oguc, M., Scamoni, F., Scrosati, C. Analysis of façade sound insulation field measurements - Influence of acoustic and non- Acoustic parameters. Proceedings of 42nd International Congress and Exposition on Noise Control Engineering 2013 INTER-NOISE 2013: Noise Control for Quality of Life, 2, 1392-1401. Innsbruck, Austria, 15-18 September 2013.

  9. Danza, L., Barozzi, B., Belussi, L., Meroni, I., Salamone, F., Assessment of the performance of a ventilated window coupled with a heat recovery unit through the co-heating test. Buildings, 6 (1), (2016).

  10. ISO/TS 15666. Acoustics - Assessment of noise annoyance by means of social and socio-acoustic surveys. Geneve: International Organization for Standardization; 2003.

  11. Danza L., Belussi L., Ghellere M., Salamone F., Scrosati C., Scamoni F., et al. Design and testing of I-ZEB, a zero energy laboratory for the integrated evaluation of the performance of building components and HVAC systems. In: IOP Conference Series: Materials Science and Engineering, 2019.

 

1 scrosati@itc.cnr.it