Acoustic Measurements for SCALA Bench-mounted fume … · 2012-01-31 · All rights by LTG Aktiengesellschaft. ‐ 4 ‐ Oktober 2009 ev_09_13: Acoustic Measurements for SCALA Bench‐

CMS Project Service Division Report

EV - 09 – 13

Acoustic Measurements for SCALA Bench-mounted fume cupboards made by WALDNER Laboreinrichtungen

Sound power level measurements using reverberation room technology

1st Edition This report includes a total of 24 pages Customer Waldner Laboreinrichtungen

GmbH &Co.KG Haidösch 1 D‐88239 Wangen im Allgäu Date October 2009 Issued by Dr. Hermann Leis Measurements by Dr. Hermann Leis Order No. 5568798/09 Key words Sound power measurement

Reverberation room Lab fume cupboard Search codes 11, 41 Circulation k

All rights by LTG Aktiengesellschaft. Subject to technical alterations. No duplication and reproduction of this report, in its entirety or in parts, without express written approval of LTG.

LTG Aktiengesellschaft

D‐70435 Stuttgart Grenzstraße 7 D‐70405 Stuttgart P. O. Box 40 05 25 (0711) 82 01‐180 Fax (0711) 82 01‐720

All rights by LTG Aktiengesellschaft. ‐ 2 ‐ Oktober 2009

ev_09_13: Acoustic Measurements for SCALA Bench‐mounted fume cupboards made by WALDNER Laboreinrichtungen

Table of Contents

ABSTRACT ................................................................................................................................ 3

1 BASICS ........................................................................................................................... 4

1.1 Acoustics Theory ........................................................................................................... 4 1.1.1 Frequency...................................................................................................................... 4 1.1.2 Sound Pressure Level Lp ................................................................................................ 4 1.1.3 Sound Power Level LW ................................................................................................... 5 1.1.4 The Difference between Sound Pressure Level Lp and Sound Power Level LW ............ 6 1.1.5 Noise Rating: A‐weighting ............................................................................................. 7 1.1.6 Room Absorption in Typical Labs .................................................................................. 8 1.1.7 Sound Level Calculations .............................................................................................. 9

1.2 Measuring Technology ................................................................................................ 11

1.3 Sound Power Measurements in LTG Aktiengesellschaft’s Reverberation Room ........... 11 1.3.2 Pressure Measurement ............................................................................................... 14 1.3.3 Flow Rate Measurement ............................................................................................. 15

2 TEST SET‐UP................................................................................................................. 16

3 MEASURING RESULTS .................................................................................................. 19

4 NOTE TO THE REVERBERATION ROOM REPORTS ANNEXED ......................................... 22

5 MEASURING EQUIPMENT USED ................................................................................... 24



Abstract

LTG Aktiengesellschaft has been asked by WALDNER Laboreinrichtungen GmbH & Co. KG to perform sound power level measurements for different SCALA Bench‐mounted fume cupboards using reverberation room technology. Among the varying factors were: air flow rate, sliding door position (open or closed), baffle and the Secuflow system (on/off). The measuring program was defined by WALDNER Laboreinrichtungen GmbH & Co. KG.

The following fume cupboards have been investigated:

1. WALDNER Bench‐mounted fume cupboard RWI‐TA 1500 x 900 ‐ 900

2. WALDNER Bench‐mounted fume cupboard RWI‐SF‐TA 1500 x 900 ‐ 900

3. WALDNER Bench‐mounted fume cupboard SI‐TA 1800 x 900 – 900

4. WALDNER Bench‐mounted fume cupboard SI‐SF‐TA 1800 x 900 – 900

Measurements with these 4 fume cupboards were performed realizing the following connections to the duct system:

FAZ* Main duct 250

FAZ* Main duct 315

AC** Main duct 250 with damper setting 70°

AC** Main duct 315 with damper setting 70°

*FAZ= Extract air function display

**AC= Airflow Controller

Reverberation reports have been created for each sound level measurement. The measuring results are listed in the chart in Chapter 3 of this report.

LTG Aktiengesellschaft

On behalf of

Ralf Wagner Dr. Hermann Leis



1 BASICS

1.1 Acoustics Theory

1.1.1 Frequency

Frequency f is the number of sonic vibrations per second measured in Hertz (Hz). With a vibration time of T applies:

fT

1

f 20 50 100 200 500 1000 2000 5000 10000 Hz

‐‐‐‐‐‐‐‐‐‐‐Air conditioning‐‐‐‐‐‐‐‐‐‐‐‐‐

1.1.2 Sound Pressure Level Lp

Sound pressure is the root mean squared value of sound change pressure in the propagation of a sound wave

dtpT

pT

eff21

Acoustics calculations use the term „level“ which means the logarithm of the quotient of two physical parameters, such as intensities or sound pressures:

0

10II

lgL in dB (decibel)

Sound pressure level Lp The sound pressure level Lp refers to the hearing threshold po: p0 = 2 10

‐5 Pa (referring to 1000 Hz)

02

0

2

2010p

plg

p

plgL



Sound Root mean square value of sound pressure in Pascal

Sound pressure levelin dB

Whispering leaves 0.0002 20

Conversation in low tone 0.002 40

Loud calling at a distance of 1m 0.2 80

Air hammer at a distance of 1m 2 100

Pain threshold 20 120

The sound pressure level is depending on the location and may be measured directly using a microphone! 1.1.3 Sound Power Level LW

Determination of the sound power P:

The surface integral over the sound intensity I is the sound power passing through the surface S:

P SI d

s

The total output of a sound source is obtained from the surface integral over any closed far‐field surface S surrounding the source entirely:

S

ges dSIP

Expressed in level it may be derived as follows:

From: 0

10P

PlgLW and the reference sound power P0 = 10

‐12 Watts and S0 = 1m² applies:

with P and P0 plugged in:

010

010

020

010

2

010

S

Slg

pL

WL

S

Slg

p

plg

S

Slg

p

plg

WL

P0 p0

2 S0

Z



1.1.4 The Difference between Sound Pressure Level Lp and Sound Power Level LW

A sound source (here: fume cupboard) is clearly defined by the sound power level. Stating the sound power levels is part of a lab fume cupboard’s technical specifications for a defined operating state.

If levels are given in "dB" please check whether they mean the sound pressure or the sound power!

The sound power level is larger than the sound pressure level if the reference surface is larger than 1 m2.

If sound pressure levels are given with reference to the sound source (here: lab fume cupboard) the measuring distance is important! The level decreases with the distance to the source and it is also affected by the sound absorption ability and the reflections of the surrounding room.

The term 10 lg S / S0 only applies to free field. Inside of a room it is replaced by

room absorption L. Inside rooms the following applies: LW = LP + L in [dB]



1.1.5 Noise Rating: A‐weighting

In 1968, DIN phon rating based on ISO was replaced by DIN 45633 based on

A‐weighting LA in dB (A)

B‐weighting LB in dB (B)

C‐weighting LC in dB (C)

In air conditioning, the A‐weighting is common use. C‐weighting is used e.g. to assess aviation noise.

Frequency‐dependent correction of A‐weighting:

Octave band/

Third octave band

fm A‐correction

50 63 80

‐30.2 ‐26.2 ‐22.5

100 125 160

‐19.1 ‐16.1 ‐13.4

200 250 315

‐10.9 ‐8.6 ‐6.6

400 500 630

‐4.8 ‐3.2 ‐1.9

800 1.000 1,250

‐0.8 0.0 +0.6

1,600 2,000 2,500

+1.0 +1.2 +1.3

3,150 4,000 5,000

+1.2 +1.0 +0.5

6,300 8,000 10,000

‐0.1 ‐1.1 ‐2.5

A‐weighting Curve



A‐frequency‐weighting considers the sensitivity of our hearing with view to certain frequencies. The sum level LA is a measure describing the “loudness“ of a noise. The LA‐value often conceals low‐frequency duct noises caused by resonance or insufficient vibration isolation or insufficiently large sound absorbers behind the fans. It says nothing about the annoyance. Noises with small‐band level maxima, so‐called tonal shares, must be assessed based on their annoyance.

For flow noises of diffusers, dampers, ducts due to turbulence and flow separation, A‐weighting is a good standard of comparison and a useful computable value as “individual parameter”. The dependency on the flow speed or air flow rate can be clearly depicted.

1.1.6 Room Absorption in Typical Labs

Room absorption depends on the sound absorption and the reflections of the room (here the lab) in which the sound source (here the fume cupboard) is located. The higher the sound absorption (described by the reverberation time) the greater the room absorption.

Factors of influence for sound absorption and consequently the room absorption, in that case of the lab, are:

Nature of the ceiling (e.g. acoustic, suspended, solid – in this sequence with decreasing sound absorption capacity)

Nature of the floor (e.g. carpet, PVC, tiling => in this sequence with decreasing sound absorption capacity)

Vertically enclosing surfaces such as walls, doors, windows (e.g. drywall, wood, concrete, glass => in this sequence with decreasing sound absorption capacity)

Based on the room volume V and the reverberation time T the equivalent absorption area A may be calculated in Sabine characterizing the sound absorption capacity of the room. The reverberation time is the time that passes until an event has achieved a 60 dB sound reduction. Just like the absorption capacity of the room it is frequency‐dependent.

For a lab (reverberation time T = 2 secs) with a floor area of 7.5 m x 7.5 m and clearance of 3 m the equivalent absorption area A is as follows:

SabinemT

VA ²75.13

2

35.75.7163.0163.0

Based on VDI 2081 Book 1, Chapter 3.1 Table 2 a chemistry lab working room can be expected to have a reverberation time T of 2.0 seconds.

The room absorption for the diffuse sound field may be rough calculated in sufficient distance to the sound source (and thus only depending on the equivalent absorption area). It applies:



dBSabinemA

L 5²75.13

4lg10

4lg10

1.1.7 Sound Level Calculations

Sum‐up of Sound Levels

Sound levels L require logarithmical sum‐ups:

...1010lg1010lg10 101010

21 LL

n

L

SumL

Example of a level sum‐up of L1 = 60 dB and L2 = 56 dB via logarithmical level sum‐up:

dBLSum 5.611010lg10 10

56

10

60

Sum‐up of sound sources of the same intensity

LnnnLLL

n

L

Sum

lg1010lg10lg1010lg1010lg10 101010

Example of calculation for sound level changes if 3 sound sources of the same intensity with L = 60 dB are turned off:

5 sources: 60 dB + 10 lg 5 = 67.0 dB => 3 sources turned off = 2 sources operating: 60 dB + 10 lg 2 = 63.0 dB => ‐ 4 dB sound reduction

50 sources: 60 dB + 10 lg 50 = 77. 0 dB => 3 sources turned off = 47 sources operating: 60 dB + 10 lg 47 = 76.7 dB => ‐ 0.3 dB sound reduction



To lower the level of 50 sound sources by 3 dB 25 sound sources would have to be turned off!

Subtraction of Sound Sources

Subtraction of sound sources is performed in analogy to their sum‐up. Via subtraction, possibly existing background noises during measurements may be subtracted.

1010 101010HHM LL

M lgL

LM = Sound level of the machine or the investigated sound source

LM+H = Measured total sound level of the machine including background noises

LH = Background noise only

0,0

5,0

10,0

15,0

20,0

25,0

0 20 40 60 80 100

Lev

el

incr

ease

Number of sound sources

Level increase with sound sources of the same intensity



1.2 Measuring Technology

1.3 Sound Power Measurements in LTG Aktiengesellschaft’s Reverberation Room

Measurements in LTG’s reverberation room are performed based on EN ISO 3741:1999 “Determination of sound power levels of noise sources using sound pressure ‐‐ Precision methods for reverberation rooms (class 1)“. The following excerpt from the “LTG Test Center“ documentation provides an overview of technical key data.

Reverberation Room

A reverberation room serves to determine the sound power level of air technology devices. Contrary to a sound absorbing room where measurements are realized in a closed area encasing the sound source, the reverberation room provides a uniform, i.e. diffuse sound field with a sound pressure level that is converted into sound power levels depending on the frequency using room correction factors.

Great attention has been paid to a low quietness level, i.e. to a good sound insulation of the reverberation room walls and as little a low‐frequency vibration pickup as possible via the foundation. The internal pressure loadable concrete body (differential pressures at 5000 Pa, dynamic) is supported by 2.5 Hz harmonized spring packages placed on a concrete frame firmly cast with four supports. Two supports each are connected through a foundation strip isolated from the building floor.

The weighted sound reduction index Rw of 59 dB is the result of the following measures:

30 cm reinforced concrete walls

Openings equipped with two‐leaf, tight‐closing, antidrumming armor‐plated doors

Twin‐shell sound absorbers connected to the reverberation room

Very high attenuation of the air outlet sound absorber

With these measures quietness levels of 18 and 22 dB(A) may be achieved at daytime.

The relatively smooth curve shape of reverberation time over frequency (third‐octave) shown in Figure 1 indicates that the sound field is relatively well diffused. This is achieved by sound‐reflecting walls and diffusers on the ceiling and in front of the walls with an oblique‐angled arrangement to one another. In addition, two low‐frequency absorbers were installed for room correction.

Registration data of the levels from six microphones distributed in the room are sufficient to meet DIN EN ISO 3741, Precision methods for reverberation rooms. Standard deviations above the room’s limit frequency of 110 Hz are significantly below the DIN limits (refer to Chart 1). In the range of 40‐80 Hz the results are sufficiently good. For specific measurements, the number of measuring points and consequently the low‐frequency precision may be increased.



As can be taken from the basic scheme, the reverberation room has been provided with a total of five measurement sections including sound absorbers and centrifugal fans. Flow rate and fan pressure increase may be adjusted either via dampers or via speed (frequency converter).

The flow rate in the range of 0‐22000 m3/h is determined via

one nozzle measuring chamber (large section of measurement)

three orifice measuring sections with quick‐change devices and tube diameters of 100, 225, 315 mm.

Using the large measurement section, decision whether to extract air from the reverberation room, blow into it or run the system with recirculating air is made by opening or closing the dampers. By changing the flexible connecting lines of the two smaller fans each orifice measurement section may be used for either supply or return air.

Due to duct sound absorbers the background noise level emitted by the fans into the reverberation room is negligibly small versus the level to be measured. It varies in the range of 200‐36000 m3/h between 18 and 50 dB(A).

The measurement is performed based on comparison method with the use of a standard sound source. As standard sound source a free‐wheeling blade of a drum rotor is used with a sound power frequency spectrum measured and officially certified by the Federal Physical‐Technical Institute. After each test set‐up or alteration the reverberation room correction, i.e. the



conversion from sound pressure to sound power level is measured anew and saved electronically.

During the measuring procedure the microphones are read in sequence one by one and the time average values of each position are determined logarithmically and converted into sound power levels. The resulting octave and third‐octave spectra (charts), the octave spectrum (bar chart), and the linear and A‐weighted sum levels are saved and printed.

Chart 1: Reverberation room standard deviation (Sh): Comparison of actual standard deviation (Sh) with the required standard deviation (SS) according to DIN 45635 Part 2. The calculated lower limit frequency of the reverberation room is 110 Hz.

Figure 1: Reverberation times



Chart 2: Measurement Section Data

Measurement section Flow rate max.

Large measurement section with 3 nozzles

Nozzle D=150 2 000 m³/h

Nozzle D=315 10 000 m³/h

Nozzle D=500 22 000 m³/h

Orifice measurement section D=315

Orifice D=250 5 000 m³/h


Orifice D=100 600 m³/h







Orifice D=45 120m³/h

Chart 3 Reverberation Room Data

Volume 254 m³

Total weight 2010 kN

Springs on structure‐borne sound insulating boards

14

Resonance frequency 2.5 Hz

Weighted sound reduction index of the reverberation room wall

59 dB

1.3.2 Pressure Measurement

The initial operating pressure or differential pressure of the fume cupboard in a defined operating state of the investigated fume cupboard equals the difference between static duct pressure in [Pa] in direction of air flow behind the extract air main duct and the ambient pressure. Measurement of this differential pressure is performed using a calibrated SI‐special Instruments GmbH micromanometer.



1.3.3 Flow Rate Measurement

Investigation of the acoustic characteristics of air technology devices requires to determine the exact air flow rate. For this purpose, LTG uses a variety of orifice and nozzle measuring sections. Via fan, an air stream is either supplied into or sucked out of the reverberation room. Sections of measurement of varying diameters permit a wide range of controllable and measurable air flow rates. Using a standard orifice based on DIN1952 and VDI/VDE 2040 allows to determine the air flow rate from the measured differential pressure via orifice if density and temperature of the air are known factors. The flow rate may be controlled via dampers or fan speed using a frequency converter.



2 Test Set‐up

The test set‐up was realized based on EN ISO 5135:1999 requirements for reverberation room measurement test set‐ups. The connecting distance as a sound source is so small compared to the sound power level of the test device that it can be neglected.

Figure 2: Test devices RWI‐(SF‐)TA 1500x900 (left) and STI‐(SF‐)TA 1800x900 connected to the flow rate measuring section of the reverberation room

Chart 4 and Chart 5 give an overview of the investigated WALDNER SCALA Bench‐mounted fume cupboards. Varying factors were: air flow rate, connection to the duct system, sliding door position, and baffle.



Chart 4: Variants investigated with 1500‐wide Bench‐mounted fume cupboard type RWI

Connection to duct system Sliding door position Baffle Air velocity[m/s]

Flow rate [m³/h]

Fume cupboard RWI‐TA 1500 x 900 ‐ 900

V min BG 600

FAZ open (500 mm) V 0.3 m/s 785

Main duct large V 0.5 m/s not required

250 V min BG 600

closed V 0.3 m/s 785

large V 0.5 m/s not required

V min BG not required

FAZ open (500 mm) V 0.3 m/s 785

Main duct large V 0.5 m/s 1305

315 V min BG not required


large V 0.5 m/s 1305

V min BG 600

AC open (500 mm) V 0.3 m/s 785


250 V min BG 200

Damper 70° closed V 0.3 m/s not required



AC open (500 mm) V 0.3 m/s 785


315 V min BG 200



Secuflow fume cupboard RWI‐SF‐TA 1500 x 900 – 900

V min BG 410

FAZ duct open (500 mm) V 0.3 m/s 785

250 V min BG 410






V min BG 410

AC duct open (500 mm) V 0.3 m/s 785

250 V min BG 200


AC duct V min BG not required

315 open (500 mm) V 0.3 m/s 785

Damper 70° V min BG not required

closed V 0.3 m/s not required



T

Chart 5: Variants investigated with 1800‐wide Bench‐mounted fume cupboard type SI

Connection to duct system Sliding door position Baffle Air velocity[m/s]

Flow rate [m³/h]

Fume cupboard SI‐TA 1800 x 900 – 900

V min BG 630

FAZ open (500 mm) V 0.3 m/s 840


250 V min BG 630




FAZ open (500 mm) V 0.3 m/s 840




large V 0.5 m/s 1505

V min BG 630

AC open (500 mm) V 0.3 m/s 840


250 V min BG 200


large V 0.5 m/s 200


AC open (500 mm) V 0.3 m/s 840





Secuflow fume cupboard SI‐SF‐TA 1800 x 900 ‐ 900

V min BG 480


250 V min BG 480






V min BG 480


250 V min BG 200




315 V min BG 200




3 Measuring Results

Chart 6 and Chart 7 show the sound power level and pressure loss measuring results for the selected flow rates and also give the number of the corresponding measurement report. The composition of the charts equals that in Chapter 2. For each setting, a maximum of 2 data points was determined. Presentation in terms of diagrams seem not to make much sense since with only 2 points it cannot be verified whether we are dealing with linear, square, logarithmic or other relations. Measuring results are annexed to this report in PDF format on a separate data carrier (CD‐ROM).



Chart 6: Measuring results with 1500‐wide Bench‐mounted fume cupboard type RWI

Connection to duct system

Sliding door position

Baffle Air velocity [m/s]

Flow rate [m³/h]

Pressure loss [Pa]

Sum sound power level LWA [dB(A)]

Measurement report

Fume cupboard RWI‐TA 1500 x 900 ‐ 900

V min BG 599 ‐47 37.1 15886

FAZ open (500 mm) V 0.3 m/s 785 ‐70 42.5 15887


250 V min BG 601 ‐41 33.0 15889

closed V 0.3 m/s 786 ‐70 40.5 15888



FAZ open (500 mm) V 0.3 m/s 786 ‐41 37.3 15923

Main duct large V 0.5 m/s 1305 ‐94 48.0 15921


closed V 0.3 m/s 786 ‐41 33.6 15924

large V 0.5 m/s 1303 ‐96 45.6 15922

V min BG 600 ‐78 43.3 15880

AC open (500 mm) V 0.3 m/s 786 ‐131 51.0 15881


250 V min BG 200 ‐8 27.4 15879




AC open (500 mm) V 0.3 m/s 786 ‐59 41.3 15917


315 V min BG 200 ‐4 27.8 15918



Secuflow fume cupboard RWI‐SF‐TA 1500 x 900 ‐ 900

V min BG 410 ‐19 46,3 15891

FAZ duct open (500 mm) V 0.3 m/s 785 ‐69 47.8 15892

250 V min BG 409 ‐19 27.9 15890

closed V 0.3 m/s 785 ‐70 40.5 15888




closed V 0.3 m/s 786 ‐41 33.6 15924

V min BG 410 33 46.1 15872

AC duct open (500 mm) V 0.3 m/s 785 123 52.4 15874

250 V min BG 199 10.6 27.3 15876


AC duct not required

315 open (500 mm) V 0.3 m/s 788 ‐59 47.2 15916

Damper 70° V min BG not required

closed V 0.3 m/s not required



Chart 7: Measuring results with 1800‐wide Bench‐mounted fume cupboard type SI

Connection to duct system

Sliding door position

Baffle Air velocity [m/s]

Flow rate [m³/h]

Pressure loss [Pa]

Sum sound power level LWA [dB(A)]

Measuring report

Fume cupboard SI‐TA 1800 x 900 ‐ 900

V min BG 631 ‐39 35.9 15907

FAZ open (500 mm) V 0.3 m/s 840 ‐70 45.2 15911


250 V min BG 630 ‐40 33.9 15908

closed V 0.3 m/s 842 ‐72 43.3 15910



FAZ open (500 mm) V 0.3 m/s 840 ‐43 38.1 15896



closed V 0.3 m/s 840 ‐45 34.0 15895

large V 0.5 m/s 1503 ‐122 49.5 15898

V min BG 630 ‐71 44.9 15899

AC open (500 mm) V 0.3 m/s 841 ‐142 54.4 15905


250 V min BG 199 ‐8 27.4 15904


large V 0.5 m/s 200


AC open (500 mm) V 0.3 m/s 840 ‐62 42.1 15883





Secuflow fume cupboard SI‐SF‐TA 1800 x 900 ‐ 900

V min BG 480 ‐22 47.9 15915


250 V min BG 482 ‐23 47.5 15914

closed V 0.3 m/s 952 ‐93 50.1 15913




closed V 0.3 m/s 953 ‐57 38.6 15894

V min BG 481 ‐44 48.3 15901

AC duct open (500 mm) V 0.3 m/s 951 ‐181 58.3 15903

250 V min BG 199 ‐8 27.4 15904



AC duct open (500 mm) V 0.3 m/s 952 ‐80 50.0 15884

315 V min BG 205 ‐4 27.2 15885




4 Note to the Reverberation Room Reports Annexed

The measurement reports and this report have been established in compliance with EN ISO 5135 “Determination of sound power levels of noise from air‐terminal devices, air‐terminal units, dampers and valves by measurement in a reverberation room“ and EN ISO 3741 “Determination of sound power levels of noise sources using sound pressure ‐‐ Precision methods for reverberation rooms (Class 1)“.

The following page shows a reverberation room measurement report explaining key parameters.



Test device

Set‐up and operating state data

Third‐octave sound power level spectrum with A‐weighting (no sound pressure levels)

Third‐octave and octave values of the linear sound power level (without A‐weighting!)

Sum level of linear and A‐weighted sound power level. For a comparison with limit values, the room absorption will have to be considered

Flow rate and duct/ambiance differential pressure during measurement

Number of measuring report



5 Measuring Equipment Used

Parameter Description of measuring device

Device Class

Serial Number

Sound power

Realtime Third‐octave/Octave Analyzer 2144

C 06002

8‐Channel Multiplexer Type 2811 C 06003

Type 4204, Standardized sound source PTB calibrated, 100 Hz to 20 kHz

A 06013

Flow rate

Orifice section of measurements DN 315 with orifice plates 103 mm and 163 mm

Betz Manometer B 04005

Pressure

SI Digima LPU Micromanometer (Initial pressure‐connected duct versus ambient pressure)

B 04003

Acoustic Measurements for SCALA Bench-mounted fume … · 2012-01-31 · All rights by LTG Aktiengesellschaft. ‐ 4 ‐ Oktober 2009 ev_09_13: Acoustic Measurements for SCALA Bench‐

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