Acoustic approach for building air permeability estimation

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Building and Environment 57 (2012) 18e27

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Building and Environment

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Acoustic approach for building air permeability estimation

Vlad Iordache, Tiberiu Catalina*

CAMBI Research Center, Technical University of Civil Engineering of Bucharest, Faculty of Building Services and Equipment, Bd. Pache Protopopescu 66,021414 Bucharest, Romania

a r t i c l e i n f o

Article history:Received 28 February 2012Received in revised form4 April 2012Accepted 6 April 2012

Keywords:Permeability lawAirborne noiseFacade transferExperimental measurements

* Corresponding author. Tel.: þ40 21 252 46 20, þ4252 68 80.

E-mail addresses: [email protected],(T. Catalina).

0360-1323/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.buildenv.2012.04.008

a b s t r a c t

Air infiltration represents an essential parameter for the building and for the HVAC design and thus itsaccurate estimation is very important. The classic approaches to estimate the leakage air flow for anexisting building present a series of disadvantages. The mathematical prediction models present errorsup to 100%, while the currently used experimental measuring approach is expensive and weatherdependent. In this paper we analyzed the leakage air flow using a different approach: an acoustic methodfor building air permeability measurement. We aim to determine if the air and noise transfer phenomenathrough window joints are correlated and what is the relation between the two transfer phenomena. Inorder to analyze this relation we measured both the infiltration air flow transfer and the airborne noisetransfer through window joints for the same building façade. Different joinery degradation cases weresimulated by different fixed positions of the joinery. For each case, two measurements were performed:the airtightness measurements in order to determine the air change rate and the airborne noise transferin order to determine the sound transmission loss. Finally, we found that the air change rate is inversecorrelated to the sound transmission loss; the higher the sound transmission loss, the smaller the airinfiltration rate. This acoustic estimation for the building air permeability presents multiple advantagescompared to the two classic approaches: good precision because it is an experimental approach, noexpensive measurement devices, free of climate changes and it also represents a fast tool for evaluatingbuilding air permeability.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The air permeability of the envelope represents an importantcharacteristic of the building which is significantly influencingdifferent parameters of the indoor environment [1]: the heatingload, the strategies of the ventilation system [2], the degree of theindoor air pollution [3,4], the indoor acoustic comfort [5] and theenergy performance of the building [6]. Therefore, predicting theairtightness is very important for both the design and the reha-bilitation stages of a building. Today, in the context of the thermalrehabilitation, in order to reduce energy consumptions, it appearsa major need to acknowledge the processes of permeability and theleakage air flow corresponding to a building with damaged joinery.

The leakage air flow rate might be evaluated using predictivemodels determined from experimental databases. In the specificliterature, there are several databases for many countries such as:

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the United States [7], Greece [8], Finland [9], Spain [10], France[11,12], Italy [13], Australia [14], Canada [15] which are extensivelyused to deduce mathematical models for the infiltrated air changerate for different types of buildings. The air infiltration models canbe classified into two major categories: singlezone models such asthe Lawrence Berkeley Laboratory (LBL) model [16,17] or the AIM-2model [18] and multi-zone models such as COMIS [19] and CON-TAM [20]. Previous studies [21] present a mean error for the singlezone LBL model of 26e46%, reaching up to 159% while the AIM-2single zone model [22] presents mean errors around 19% reach-ing up to 87%. Similarly, high errors are obtained for multi-zonemodels [23]. Such errors, up to 100% in some cases, are unaccept-able for the infiltration models given their importance in differentstudies. For example in the field of building energy performance,previous studies [24,25] proved that the air flow leakage mayrepresent well over 50% of the heat consumption. Thus, the error ofthe air infiltration rate is further amplified and leads to high errorsin the calculations of the heat consumption and wrong rehabilita-tion measures.

The experimental evaluation of the infiltration rate replaces thelack of accuracy of the current prediction models. The fan pres-surization method for measuring the transfer of air permeability

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V. Iordache, T. Catalina / Building and Environment 57 (2012) 18e27 19

of buildings [26] is more often used because it gives a character-ization of the building in various states of indoor high-pressure/low-pressure. The Blower Door system [3,18] built specifically forthis type of measurements is easily exploitable and can be used forareas such as rooms, apartments or villas. The measurementprotocol was further adapted to suit experimental measurementsfor higher volume buildings [27]. Thus, the experimental approachmay reach errors under 5% while measuring the entire building, orunder 15% while measuring one apartment of a building. Thisexperimental acknowledgment process of the building perme-ability presents a higher precision, but it also has some disadvan-tages, such as: the high cost of the blower door itself, the climatesensitivity, the technical/scientific background of the user and thefact that it’s a relatively time consuming technique.

The thermal inspections of the building are still based uponvisual speculations (visible joints, light penetration through joints,damaged joinery) in order to approximate the infiltration rate. Butthese speculations lead to important errors due to both the lack ofexperience of the building thermal inspector performing theexpertise and the variation of the joints length characteristics. Eventechnical staff with experience in permeability measuring cannotevaluate the permeability of a building based only on the visibleaspects.

In this study we wish to bring forward an alternative way todetermine the permeability of a building façade using an analysison the relation between the air infiltration through joints and theoutdoor/indoor sound transmission. If such a relation exists, then itmeans we can determine the air infiltration rate by skipping overthe expensive permeability measurements. This associationbetween permeability and sound transmission was studied back inthe eighties bymeans of laboratory experiments [28e30]. However,no useful correlation law was determined! In this study we willfollow a different approach (experiments on real buildings) tofurther detail this phenomenon, in order to find a prediction modelfor the air leakage flow as a function of the sound attenuation loss.

The aim of this study is to determine, for real buildings, theexistence of a relationship between the air infiltration rate and theoutdoor/indoor airborne noise transmission. We will investigate ifthere is any correlation between the two transfer phenomena (airand noise transfer) for real buildings, and, if there is the one, whichis the mathematical relation that tides up the two phenomena?What is the form of this mathematical relation, is it a linear or not?

Beside the scientific importance of this study, we arealso attracted by its practical implications. If there is indeeda correlation between the two phenomena then the expensiveexperimental stand for permeability measurements, may be

Fig. 1. Location of the experimental site (a). Position of the

successfully replaced in certain cases by much cheaper measuringdevices. Furthermore, the acoustic measurement of the perme-ability would have the advantage of being less conditioned by theweather conditions compared to the present blower door stand. Asmentioned in EN 13829 [26] and [31] the needed conditions formeasurement validation are: wind speed should be less than 2 m/sand standard deviation of the outdooreindoor pressure differenceshould be less than 2 Pa.

This would be a simpler and less expensive experimental devicefor fast technical expertise that could be included in other studieslike: building certification, indoor air quality, HVAC design for olderexisting buildings. An experimental approach is employed in orderto determine the existence and the form of this relation betweenthe two phenomena. This paper presents the experimental study ofthe air and noise transfer through the same façade followed by thecorrelation between the two phenomena.

2. Dual measurements experiment

Themeasurement campaignwas organized in order to point outthe relation between the air and the noise transfer through thebuilding façade and especially through window joints. Therefore,two types of experiments were conducted: facade airtightnessmeasurements and sound level measurements, in accordance withthe European norms EN13829 [26] and EN 717-1 [32], respectively.

Both experiments were carried out in a test room situated in thebuilding of the Faculty of Building Services, University of CivilEngineering of Bucharest. The room position in the building it isa convenient one for the experimental study as it is situated at theground level (þ2.0 m) and it is surrounded on both sides by otheridentical rooms. It must be mentioned that the tested space facadeis facing an inner courtyard, so that the outdoor noise sources arelimited (Fig. 1). Moreover, the courtyard is surrounded by thebuilding, which limits the impact of the wind pressure on themeasurements. Consequently, the chosen test room is consideredto be almost ideal for this kind of research study.

The test room is a classroom of 3.95 m height and has a volumeof 195 m3. This chamber is well illuminated through three identicallarge windows (2.1 m � 0.7 m). The windows have a double-panewooden frame and they are not air sealed. Each of the two glasslayers thickness is of 3 mm. The floor surface material is made ofwood while the rest of the walls and ceiling are covered by a thinconcrete-cement layer. Also, inside the test room there are tenwooden chairs and tables.

The permeability measurements are carried out by means ofa classic blower door system consisting of the following equipment

experimental site, (b). Inner courtyard of the building.

Fig. 2. Geometrical characteristics of the test room.

Fig. 3. Acoustic measurement points C outdoor measurement point; indoormeasurement point.

V. Iordache, T. Catalina / Building and Environment 57 (2012) 18e2720

and measurement devices: extendable false door, radial fan withvariable speed, variable voltage device, double differential micro-manometer DG700, computer and software “Tectite”. We usedthis system in order to evaluate the air flow crossing the buildingfaçade and its variation as a function of the outdoor/indoor pres-sure difference. This system was mounted on the door of the testroom and the measurements were controlled by the “Tectite”software. These permeability measurements are characteristic ofthe entire room.

The method used for measuring the permeability of a roominvolves that the analyzed space to be put in over or low-pressurecompared to outdoor, by means of the variable speed fan. Variouspressure points, between 70 Pa and 20 Pa, with a 5 Pa step, wereanalyzed. For each pressure point two parameters were recordedsimultaneously: the indooreoutdoor pressure difference Dp (Pa)and the air volumetric flow rate Q (m3/h). These values allow us todetermine the two coefficients C and n of the permeability law (ex.Q ¼ C*Dpn). We acknowledged a couple of permeability laws (high/low-pressure) for each experimental case. As the Fan Pressurizationtechnique cannot directly measure the volumetric flow rates at lowvalues of the pressure difference, it is necessary to extrapolate themeasurable behavior of the analyzed façade for these values of thepressure differences. There are two main error sources associatedto this technique: measurement errors and model specificationerrors. As proposed by Sherman and Palmiter [33] the uncertaintyrelated to the volumetric flow rate estimation through the fanpressurization method could be expressed by:

dQ ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffid2Qprecision þ d2Qbias

measurementþ d2Qmodelmodelization

s(1)

This relation has a confidence level of 95%. We used the methodproposed by Sherman and Palmiter [33] in order to estimate anuncertainty range of the volumetric flow rate values obtained fromthe permeability laws. Initially only five pressure measurementpoints were used to estimate the permeability law. This choiceconducted to an uncertainty range between 10% and 13%. Byincreasing the number of pressure points to 10, we managed toobtain a maximum uncertainty of 5.5%.

Sound level measurements were performed in order to deter-mine the degree of sound insulation of the room test facade.Measurements were carried out with and without weighting filterA using two types of sonometers. As it was mentioned in the arti-cle’s introduction, besides the scientific interest of this study, wewere also concerned about the practical use of this method toevaluate the façade air change rate. This concern leads us to the useof two types of sonometers: a professional one and a common

commercial one. If the first device allowed us to perform moreprecise measurements and discover more specific details on thenoise level spectrum or room reverberation time, the second onewas used to compare the results in order to validate its practicaluse. Because the experimentation is supposed to imply the use oftwo sonometers at the same time outdoor and indoor measure-ments, most of the engineers will prefer two commercial and lessexpensive versions of sonometers.

The sound pressure level was recorded by means of Sonometer“2250 Investigator” from Bruel & Kjaer, which is a class 1 precisiondevice. Several sonometer programs were used for this device (BZ7223 - Frequency Analysis Software andBZ 7227- ReverberationTime Software) in order to record the sound pressure level fordifferent frequencies or to estimate the reverberation time.Generally, for a building practical study it is commonly used thespectrum 125 Hze4000 Hz, but a more detailed analysis goeswithin the range of 63 Hze8000 Hz. For the A-weighted soundpressure level we also used two class 2 sonometers DT 8852 witha precision of �1.4 dB, which is an ideal instrument for noisemonitoring in appartments, schools, office building and trafficareas due to its simplicity and fast operation. The signals datawere collected from all sonometers by means of computerstorage cards and later analyzed by using specialized dataanalysis software.

The acoustic measurements were conducted on both sides ofeach window (see Figs. 2 and 3) with the purpose to analyze the


widow characteristics. The measurements points are placed in thewidow axis at 1 m height form the analyzed room floor. A distanceof 0.5 m between the window and the outdoor measurementpoints was considered a good option to record the noise on thebuilding façade, while inside the test room themeasurements werecarried out at 1 m.

An external noise source was installed 3.5 m in front of thefaçade, so that all windows would be influenced similarly by thenoise source (see Fig. 3). The type of external noise source is notrelevant and less important because we are not interested inobtaining a certain outdoor noise level, but we are concerned aboutthe difference between the indoor and outdoor sound pressurelevels. However there are certain constraints that must be applied:the noise source should not be linear; its sound pressure levelshould overpass the background noise with at least 15 dB. In ourcase the noise source produced a SPL of more than 100 dB (at least50 dB higher than the background noise).

During the experiments the background noise might disturb thesound pressure level measurements, thus one should assure a lowbackground noise during the experimental sequence [34,35]. Inorder to avoid undesired sources of noise, like occupant’s indooractivities or outdoor car circulation, the sound measurements weredone during weekend and night periods, when outdoor noise is notinfluencing the results.

Besides the actual analysis of the geometrical dimensions of thetest room and of the site plan, a detailed look was directed towardthe sound absorption materials found in the room. This estimationof the existing sound and vibration environment was necessary inorder to predict correctly the sound attenuation. As previouslystated, the background noise was not sufficiently strong to perturbthe measurements and the data collected were reliable andmeaningful for the research study.

Before and after each series of measurements a sound calibratorwith an accuracy of �0.3 dB (class 1 according to EN 60942 [36])was applied to the sonometer in order to check the calibration ofthe entire measuring system at one or more frequencies overthe frequency range of interest, which in our case it was of125 Hz O 4000 Hz. In the vicinity of the sonometer, no obstaclesdisturbed the sound field.

The experimental campaign was divided in two parts: perme-ability and sound measurements. The first analyzed case also calledReference Case (C0) represents the façadewith an almost perfect airsealing. This was done using foam and adhesive tape all along thewindows joints (Fig. 2). The second case considered (C1) wasa medium sealed façade where a part of the previous adhesive tapewas removed. The actual real case in the test room also named C2s isrepresented by the window frame in their original state withoutany air sealing measures. Cases C3 and C4 describe a façade withlarger air infiltrations, which were manually introduced by largerwindow joints. A test was also done on a single wooden framewindow and it will be mentioned of as C5. For each case both typesof measurements were carried out: by using the blower doorsystem the test roomwas depressurized and pressurized in order toobtain the room permeability laws and secondly, the sound levelmeasurements were taken at three measurement points inside andoutside the test room (see Fig. 3).

Themeasurement campaignwas organized in order to underlinethe relation between the air and the noise transfer through thebuilding façade and especially throughwindow joints. However, thesound wave transfer though window joints represents only onetransfer path for the sound wave, the other transfer paths beingthrough: the glazing, the façadewall, sidewalls and adjacent rooms.In order to unveil only the transfer through joints, we proposeda measurement protocol that would maintain the other transferpaths of the soundwave constant. Thus, we carried out experiments

on the same roomand the same façade, the only difference betweenthe analyzed cases being the airtightness of the window.

Next paragraphs will present the measurement data and theiranalysis so that the correlation study of the two phenomena can beachieved.

3. Permeability measurements results

In this paragraph wewill present the results of the permeabilitymeasurements for each of the studied cases and the further treat-ment in order to determine the façade permeability for each case.Room permeability measurements were carried out for both under-pressure and overpressure scenarios. The measured values present,for each case, very close permeability curves for the two scenarios(Fig. 4). This is the expected result, given the widow type: doublewindow where the indoor panel opens inside and the outdoor oneopens outside. A visual comparison among the five different typesof façade shows that the smallest values were recorder for theReference Case (1200m3/h at 100 Pa) while the highest values wererecorder for Case 4 (2800 m3/h at 100 Pa).

The permeability law of the room represents the average curvebetween the under-pressure and the overpressure curves, accord-ing to EN 13829 [26]. The average permeability curves of the roomfor each case were calculated (Fig. 4) and further used to determinethe façade permeability curves.

The façade permeability law of the non-sealed windowsrepresents the difference between the room permeability (averagevalue) with non-sealed windows and the room permeability withsealed windows, which is the Reference Case [27,37]. Thus, thefaçade permeability was calculated for cases 1e4 (Fig. 5). Thecomparison among the four different types of façade shows that thesmallest values were obtained for the Reference Case (200 m3/h at100 Pa)while the highest valueswas obtained for Case 4 (1650m3/hat 100 Pa).

While the façade permeability law show the variation of the airflow infiltration through window joints, the permeability is the airflow infiltration in accordancewith building characteristics [26,38].Further, we used the air change rate (ACH) as a permeabilityparameter, due to its calculation as the infiltration air flow dividedby the room volume [27].

Themost common ACH value is determined at 50 Pa [3] as this isa representative value for the pressure difference. However, duringthe operation, the building is exposed to an average value of 4 Papressure difference; this value corresponds to real buildingsexposure in Romania. Thus the air change rate for real buildingsexposure is calculated as the air flow at 4 Pa divided by the roomvolume. The transformation coefficient between the two air flowsat 50 Pa and 4 Pa is calculated as F ¼ ACH50Pa/ACH4Pa.

Fig. 6 presents the ACH calculation of the two pressure differ-ence values, and the transformation factor. One can notice that thefour cases are different according to the ACH4Pa. Case 4 is charac-terized by the highest value of air change rate while Case 1 ischaracterized by the smallest value.We can add to these four pointsof the hierarchy a fifth one, corresponding to an airtight façade, thatis Case 0. Such airtight façades are characterized by an air changerate around 0e0.2 (1/h) [39e41].

Further in the paper we will present the hierarchy of the Cases0e4 according to the noise transfer phenomenon, and finallycorrelate the two phenomena.

4. Acoustic measurements results

The purpose of this paragraph is to present the acousticmeasurements and their analysis in order to determine if there is anacoustic hierarchy of different cases of the façade airtightness.

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Mean values

Case 1Case 2Case 3Case 4Case 0

Fig. 4. Room permeability laws.


Windows are the critical weak component of the sound insu-lation of the building façade with lower sound transmission loss(STL) than the walls and other major façade components. Airbornesound transmission through windows is governed by the samephysical principles that affect walls, but the noise control measuresare influenced by the glass properties and the air leaks around thewindow frame. The aim of the acoustic measurements campaign isto analyze the STL for the different façade cases previouslydescribed. In this part there are presented the results of an exten-sive series of in-situ measurements on the sound insulation of thetest room facade. These results include measurements of soundpressure levels on 1/3 octave and on reverberation time. Theadditional lower frequency measurements were particularly

y = 28.728x

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important because typical outdoor sound sources may containsignificant low-frequency sound energy.

The first acoustic experiment consisted in measuring the soundpressure level (SPL) outdoor and indoor, while the difference DLp(dB) between the two SPL is further calculated. Fig. 7 illustrates thedata of the three measurement points (O1, O2, O3 and I1, I2, I3)corresponding to outdoor and indoor sound pressure levels for Case2. It can be noticed that on the 1000 Hz frequency the SPL reachedits maximum value. The outdoor SPL has basically the same fluc-tuation for all the three measurements with a maximum value of97.3 dB and a minimum one between 45.5 dB at 125 Hz. As for themaximum value of the difference outdooreindoor SPL, it is noticedthat this value is reached on 1000 Hz frequency with a value of

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eability laws.

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Transformation factor F

Case 1: F = 3.56 Case 2: F = 3.54 Case 3: F = 3.68 Case 4: F = 4.13

50

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Fig. 6. Air changes per hour.


33.9 dB. Despite the various differences at mid and higherfrequencies (1000 Hze4000 Hz), the results in Fig. 7 show that wehave essentially the same outdooreindoor SPL differences. A recentstudy [42] has shown, that at frequencies above 1 kHz, more soundenergy is transmitted through the window frame than throughglass; thus the frame joints represent acoustic bridges for thefaçade structure. This may be another contributing factor to therelatively lower sound transmission loss at higher frequencies(above 1 kHz).

Knowing that the test room has three windows and on each oftheir sides were taken sound measurements, we have found that itis important to define the difference between outdooreindoor SPLas a single average value: DLp ¼ (DLp1 þ DLp2 þ DLp3)/3,where DLp1 ¼ Lp(O1) � Lp(I1), DLp2 ¼ Lp(O2) � Lp(I2) andDLp3 ¼ Lp(O3) � Lp(I3) are the differences corresponding to eachwindow. Using this average value we can compare more easily thedifferent façade cases that were studied in this article.

The SPL differences represent the result of two superposedphenomena: the sound transmission through the building façadeand the multiple reflections of sound inside the test room. We usedthe reverberation time measurement of the test room in order toseparate these two phenomena. The reverberation time wasmeasured for the test room by means of the “2250 investigator”sonometer, in the form of the two common parameters T20 which

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Fig. 7. Indoor/outdoor sound pressure levels and

is the 60 dB decay time calculated by a line fit to the portion of thedecay curve between �5 dB and �25 dB and T30 calculatedbetween �5 and �35 dB.

Further, we calculated the reverberation time of the test room asan average value of these two measured parameters (Fig. 8a). Thereverberation time was found to be between 1.1 s for lowerfrequencies and 1.4 s for medium range frequencies. Next, wecalculated the STL based on the outdooreindoor difference of thesound pressure level and the reverberation time (Eq. (1)). It is foundthat the STL has slightly higher values than the SPL difference.

STL ¼ DLP � 10log10

0B@0:161$V

TrS

1CA (2)

The resulting values of the sound transmission loss and theoutdooreindoor sound pressure level difference are compared inFig. 8b. The maximum values of these differences are low andmostly less than 1 dB which leads us to the conclusion that themean absorption value of the room is high.

A comparison between the experimental STL and the theoreticalvalue was also conducted from the need to understand theimportance of other ways of outdooreindoor sound transmissionthat are superposed over the transmission through window joints.

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attenuation level for different frequencies.

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(d

B)

Frequency (Hz)

STL, dBΔLp, dB

/LTSnosirapmoC ΔLp

a b

Fig. 8. Calculation of the sound transmission loss (STL) (a) Reverberation time (b) Comparison STL/DLp.

Table 1A-weighting global sound pressure level.

Measurement point Outdoor SPL, dB(A) Indoor SPL, dB(A) DLp, dB(A)

Case 0e1 92.30 56.475 35.83Case 0e2 90.36 58.57 31.79Case 0e3 89.20 56.96 32.24Case 0eAverage 33.29Case 1e1 100.20 65.965 34.24


This theoretical estimation of the STL is based on the theoreticalcalculation of the STL through walls, windows and air [1]. Finally,the façade STL is calculated as a-weighted mean of the three STL(wall, windows and air) as follows:

STLm ¼ 10log10

0BBB@

Pni¼1 SiPn

i¼1 Si10�STLi

10

1CCCA (3)

The measured and calculated values of the sound transmissionloss are plotted as a function of the frequency, on the entire range31.5 Hz O 16,000 Hz, in Fig. 9. It can be noticed that the experi-mental values of this sound transmission loss are smaller than thetheoretical values, which proves the existence of other ways ofsound transmission between the two environments.

The highest differences are noticed in the case of lowerfrequencies (>10 dB) meaning that in real situations the sound isalso transmitted through the adjacent chambers or other noisebridges (e.g. electric sockets or wiring). This lack of precision on thetheoretical modeling due to the existence of other transmissionway for the sound wave, leads to the conclusion that we cannot usethe comparison between the experimental and the theoreticalvalues to estimate the leakage area. Thus, for now, a mathematicalrelation between the two transfer phenomena is the only way toestimate the leakage area and the leakage air flow.

Even if the STL is the adequate scientific variable that describesthe noise transfer though the building facade, it still presents manyimportant inconveniences from a practical point of view:

� its evaluation implies the use of a professional sonometer,which is also a more expensive one,

0

10

20

30

40

50

60

So

un

d a

tte

nn

ua

tio

n lo

ss

(d

B)

Frequency (Hz)

ExperimentalTheoretical

Fig. 9. Sound transmission loss comparison between the theoretical and the experi-mental data.

� the calculation through the entire frequency spectrum isneeded,

� a time reverberation measurement is needed for the STLevaluation.

In conclusion it cannot be stated that the STL is a false estimatorfor permeability measurement, but the amount of work implied byits use is hardly achievable in a fast and non-expensive way.Consequently, we look forward toward a simpler estimator that canbe easily used for the building thermal inspections.

Next step during the acoustic experimental campaign wasrecording the A-weighting values of global sound pressure level.The A-weighting values follow the frequency sensitivity of thehuman ear at low levels as it predicts quite well the damage risk ofthe ear. The low-frequency noise is filtered with higher valuessimilar to the response of the human ear. Another reason for usingof this scale is that most of the less expensive sonometers recordonly this value and not the SPL by frequency. Table 1 summarizesthe whole measurements campaign, where the maximum soundattenuation DLp of 33.3 dB(A) is found for the Reference Case 0 (airsealed façade), while a minimum value is recorded for Case 5 (non-sealed façade) with DLp ¼ 22,4 dB(A).

Case 1e2 94.00 62.6 31.40Case 1e3 92.00 60.695 31.31Case 1eAverage 32.31Case 2e1 93.1 62.225 30.88Case 2e2 98.05 66.15 31.90Case 2e3 98.125 66.455 31.67Case 2eAverage 31.48Case 3e1 96.17 67.29 28.88Case 3e2 89.7 63.655 26.05Case 3e3 91.77 57.76 34.01Case 3eAverage 29.65Case 4e1 94.34 71.37 22.97Case 4e2 99.12 68.56 30.56Case 4e3 95.7 67.635 28.07Case 4eAverage 27.20Case 5e1 92.08 71.8 20.28Case 5e2 95.96 72.255 23.71Case 5e3 94.50 71.285 23.22Case 5eAverage 22.40


One can notice that the sound attenuation varies from Case 0 toCase 5, meaning that the air sealing is an important component inthe outdooreindoor sound transfer phenomena. Thus, the exis-tence and the quality of the air sealing can improve or degrade theoverall sound performance of the windows. However, even thewindows with better air sealing are poor barriers to airborne noisetransfer because the sound wave transmission through the glasshas a higher weight in the overall sound transfer.

5. Correlation between noise transfer and infiltration rate

In the previous two paragraphs it was found that there is a clearvariation of air leakage flow and noise transfer for the studied cases.In this chapter we will put together the two variations in order tostudy the simultaneity of the two transfer phenomena. To show thissimultaneity, the SPL differences DLp and the air change rate areplotted on Fig.10a. For higherDLp (about 30O 35 dB)we found lowerair change rates (0e0.2 h�1) while for the lower values of DLp (about22 O 27 dB) a maximum air change rate of about 2 h�1 was found.

The results display a drop in the acoustical performance of thebuilding façade, simultaneously with the raise of the air infiltrationand the room air change rate. Thus, the joinery degradation has twosimultaneous consequences: the raise of the air flow leakage andthe indoor noise transfer.

The most common experimental measurements in acousticalanalysis is the dB(A) level, therefore the final correlation graph(Fig. 10b) presents the variation of the air change rate as a functionof the A-weighted values of sound attenuation and has thepotential to be an useful tool for façade expertise. Themathematicalrelation between the two transfer phenomena was obtained in theform of a single variable second degree regression model using theleast square estimator: ACH4Pa ¼ �0.0462DLp2 þ 2.5413DLp � 33.29.

The regression analysis made possible a good correlationbetween sound attenuation and the airtightness as illustrated inFig. 10. The proposed model can give a prediction of the air changerate as a function of sound attenuation level, where its values arewithin the range 27 dB(A) O 34 dB(A) which corresponds to mostof the façade types in Romania for closed windows situation.

Fig. 10. Correlation between sound attenuation and air change rate (a). Simultaneousvariation (b). Physical correlation between air infiltration and sound attenuation (validrange: 27e33.5 dB(A)).

The short interval of the sound attenuation level reflects the lowinfluence of the joints upon the sound transfer through the buildingfaçade for this closed window situation. Despite the reducedinterval for the variation of the sound attenuation level, themathematical model:

� presents an accurate prediction characterized by high confi-dence, and

� leads to a complete cover of the air change rate interval ofvalues corresponding to the closed windows situations.

Both these arguments testify the applicability of this model,while its simple form makes from it an ideal tool for helping thebuilding thermal investigators.

6. Comparison between experiment and prediction models

Apart from developing the prediction model, another aim of thispaper is to compare different methods to predict the air infiltration.In the last few years different statistical models have been created,among which we mention McWilliams et al. (2006) [43], Montoyaet al. (2009) [10] or Chan et al. [7].

In order to compare the results of different existing predictionmodels with our new model based on acoustic experimentation,we need some form of normalized description. The pressure chosenis conventionally 50 Pa and most of the published data quotes airflow at 50 Pa. The first analyzed statistical model [43] proposes thecalculation of the normalized leakageNL (�) based on the age of thebuilding, the number of stories, its age, its energy efficiency and thefloor area:

NL ¼NLCZ$bsize�1area $bNstorey�1

height $bPeff3 $bageage$bPfloorfloor

$�bageLI;age$b

size�1LI;area$bLI

�PLI (4)

where NLCZ is based on the type of climate (eg. NLCZ ¼ 0.53 for coldclimates), b are known as regression coefficients, Peff depends onthe type of energy efficiency program (Peff ¼ 1 if building has anenergy efficiency program and Peff ¼ 0 if there is no program), Pfloor(Pfloor ¼ 1 for low income households and Pfloor ¼ 0 otherwise), Ageas the years since its construction and size calculated as the ratiobetween the floor area and a reference area (Aref ¼ 100 m2).

Montoya et al. (2010) made a statistical model to predict theairtightness of Catalan dwellings. Their study resulted in an equa-tion for C0, which is a simplification of the leakage coefficient C inthe air flow power law:

C’ ¼ exp�aþ barea$Areaþ bST$ST þ bage$Ageþ bNS$NS

�(5)

q50 ¼ C’ðDpÞ2=3Aenvelope

where ST is a factor that takes into account the type of building(ST ¼ 1 if the structure is light and ST ¼ 0 if it is a heavystructure) and NS for the number of stories (NS ¼ 1 if one storeyand 2 otherwise), q50 the air permeability (l/s m2), Dp thepressure difference (Pa) and Aenvelope is the façade surface (m2).The last model used for comparison is the model proposed byChan et al. [7] developed based on a high amount of air leakagemeasurements:

NL ¼ expðb0 þ b1$Ageþ b1$Areaþ b3$IE þ b4$ILÞ (6)

where IL takes value of 1 if the house is occupied by a low incomehousehold and 0 otherwise and IE takes value of 1 if the house isenergy efficient and 0 otherwise. Further, the total air flow through

R² = 0.9917; R=0.9958

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0

200

400

600

800

1000

1200

1400

25 26 27 28 29 30 31 32 33 34 35

Air

c

ha

ng

e rate

(1/h

)

Q (

m/h

)

Sound attenuation ΔLp, dB(A)

C1

Experimental value: 517m /hMontoya et al. 811 m /h

Co

C2

C3

C4

McWilliams et al. 830 m /hChan et al. 871 m3/h

Fig. 11. Comparison between statistical models and experimental data.


the envelope and the air change rate at 50 Pa will be calculated asfollows:

NL ¼ ELAAfloor

$

�H2:5

�0:3

ELA ¼ V50ffiffiffiffiffiffiffiffiffi2Dpr

s

ACH50 ¼ V50

V

(7)

where n50 is the air change rate at 50 Pa (1/h), V50 is the air flowthrough the envelope at 50 Pa pressure difference (m3/s), V thebuilding volume (m3) and r the air density (kg/m3).

This validation procedure will be carried out for the non-sealedfaçade of the building; this situation corresponds to Case 2. Themeasured permeability is compared with the predicted valueaccording to the acoustic measurements and the three mathe-matical models proposed in literature (Fig. 11). It is noticed that theprediction based on acoustic measurements is almost equal to themeasured value, while all three statistical models show a weakcorrelation compared with themeasured air change rate withmorethan 30% errors.

This result sustains the practical use of this method. The airchanges rate can indeed be determined based on a very simpleacoustic measurement of the outdoor/indoor sound pressuredifference and on the regression model from Fig. 10b. Finally, wecan conclude that this acoustic approach for building air perme-ability measurement is distinguished by precision, simplicity, andnon-expensive measurement devices.

7. Conclusions

The measurement campaign was organized in order to under-line the relation between air and noise transfer through thebuilding façade and especially through window joints. Thepermeability was measured by means of standardized pressuriza-tion technique using a blower door system. The sound transmissionloss between the outdoor and the indoor environment was recor-ded by means of two sonometers and a noise source; the indoorand outdoor measurements were carried out simultaneously.

We can answer at our initial concerns about the existence ofa relation between the two phenomena and its form. We foundindeed that the two transfer phenomena are inverse correlated; theair tighter of the building façade the smaller infiltration air flowrate and the higher the sound transmission loss. We recordedsound transmission losses between 27 and 33 dB. This relationbetween the two phenomena has the form of a second degreepolynomial function with a correlation coefficient R ¼ �0.9958.Thus, for buildings without any requirements on the use of a blowerdoor test, the developed regression model could replace field

experience and give a better estimation on the airtightness of thebuilding.

Moreover, a few aspects should be detailed. Firstly, the airchange rate of 0 (1/h) corresponds to an STL of 32 dB; this valuedepends on the room geometry, wall structure and window type(double glazing in our study). One might expect that, for a differenttype of window, the STL for an airtight façademight present slightlydifferent values, say: 38 dB for a triple glazing or 25 dB for simpleglazing. Secondly, we recorded a STL of 5 dB for an opened window,this being the case where the air change rate varies between 6 and10 (1/h). Thirdly, the in-between situations, ACH between 2 and 6(1/h), correspond to the partially opened windows and the STL mayvary considerably according to the type of windowand its openingsdirections (inside or outside). A comparison with other predictionmodels was carried out for the non-sealed façade. It was found thatthe new acoustic protocol leads to a far more accurate predictionthan the current prediction models.

Beside its scientific novelty, this relation between the twophenomena represents a powerful tool to be used in order toestimate the air change rate of a building façade. This model cansuccessfully replace the expensive, and weather dependentpermeability measurement with a much more simple acousticalsystem (one loudspeaker/sound source and two commercial son-ometers). This second system is by far less expensive and themeasurement can be done in just a few minutes. The error of thistype of measurement is around 5%, thus in the range of a usualstandardized permeability measurement.

The positive results obtained in this study for double-panewoodwindows show that this approach might be successfully applied toother window types, like metal or plastic frame windows withsimple or triple glazing.

We conclude by recommending this procedure for fast evalua-tion of the air change rate for any study (indoor environmentquality, building certification, rehabilitation measures) thatrequires an air infiltration estimation.

Acknowledgment

This work was supported by a grant of the Romanian NationalAuthority for Scientific Research, CNCS e UEFISCDI, project numberPN-II-RU-TE-2011-3-0209. We also would like to thank engineersAdrien Fauquin and Florent Lenoir for their contribution to thisstudy.

Nomenclature

Dp indooreoutdoor pressure difference (Pa)Q volumetric air flow rate (m3/h)ACH4Pa air change rate at 4 Pa difference (1/h)ACH50Pa air change rate at 50 Pa difference (1/h)STL sound transmission loss (dB)SPL sound pressure level (dB)DLp difference outdooreindoor sound pressure level (dB)Tr reverberation time (s)V volume (m3)S sum of absorbent indoor surfaces (m2)NL normalized leakage (�)b regression coefficients (�)Peff energy efficiency program (�)Age years since building construction (years)Size ratio between floor area and reference area (�)ST building structure factor (�)NS number of stories (�)V50 air flow through the envelope at 50 Pa pressure difference

(m3/s)


r air density (kg/m3)IL factor for household income (�)IE factor for energy efficiency (�)Afloor floor surface (m2)q50 air permeability (l/s m2)ELA Effective Leakage Area (m2)

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Documents

Acoustic approach for building air permeability estimation