Simulation of noise attenuation in straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stacks-chimneys using SILDIS® software

General information regarding the simulation of noise attenuation in straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stack-chimneys using SILDIS® software

The Module 4 of SILDIS®[0] software (in Excel format) enables the simulation of noise attenuation in straight ducts, such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stacks chimneys with circular or rectangular cross section, and also: 

  • of self-generated noise (due to flow)
  • of sound power level downstream of the duct/stack-chimney section in question (when the upstream sound power level is known)

Such calculation results can be used in various contexts:

  • for HVAC (Heating, Ventilation, and Air Conditioning) systems, as well as installations involving compressors or combustion turbines with their air intakes: to evaluate noise levels at either end of the network (e.g. regarding the prevention of noise nuisance for neighbors specifically for fresh air intakes and exhaust outlets, for ensuring acoustic comfort within premises) 
  • for stacks: to determine the sound power level at the gas discharge plane (if subject to specification) or to conduct environmental noise impact assessments (in terms of sound pressure levels at specified locations, e.g. against permissible limits, with or without applying "emergence" criteria refering to background noise levels)

The SILDIS® software can be used:

  • by ITS personnel responsible for programming, marketing, training, and support - in addition to performing calculations with the software in various contexts - ("internal use")
  • by external users who are not necessarily interested in having access to advanced features, such as those used in Research & Development (R&D) contexts ("external use")

Accordingly, a distinction is made below between the two modes of use: "internal use" and "external use"; however, this distinction is not rigid or definitive, as an external user may opt to utilize the extended features.

Input data can be selected by the user:

  • either by entering numerical values (as the software operates in Excel format, this is done in designated cells highlighted in yellow)
  • or by selecting a model from a drop-down menu for various stages of the calculations 

Regarding the names of the Excel worksheets in the workbook that make up the module(s) of the SILDIS® program (depending on the considered version), those with names beginning with:

  • "in": allow for user data input
  • "out": allow for the viewing of output data (e.g. calculation results)
  • "in-out": allow for both data input and the viewing of output data (e.g. calculation results)

Whether for "internal use" or "external use", simulating noise attenuation in straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stacks-chimneys using SILDIS® software involves three Excel spreadsheets (within the same workbook).

Summary of Excel spreadsheets related to the simulation of noise attenuation in straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stacks-chimneys using SILDIS® software (Table 1)

Excel spreadsheet Features
in COALA

Consideration of the fluid's thermodynamic data and of the sound power level upstream of the straight duct section
in COSIL Consideration of flow rate
in-out COSTDU (STraight DUct) Consideration of the straight duct section geometry and display of results

The calculations are performed in the 20 Hz – 20 kHz frequency range, using one-octave frequency bands (center frequencies from 31.5 Hz to 16 kHz). 

Procedure for simulating noise attenuation in straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or chimneys using SILDIS® software.

Simulating noise attenuation in straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or chimneys using SILDIS® software requires selecting specific models for various stages of the calculation.

Predicting the insertion loss for straight ducts (e.g. in HVAC systems or chimneys) using SILDIS® software involves models that:

  • account for cross-sectional dimensions entered by the user in the "in-out COSTDU" Excel sheet: VDI 2081-R, SMACNA-R, VDI 2081-C, 3733b-B-L, 3733b-B-M, 3733b-B-H, 3733b-S-L, 3733b-S-H
  • do not account for cross-sectional dimensions entered by the user in the "in-out COSTDU" Excel sheet, but are valid for specific duct cross-section dimensions:
    • rectangular (dimensions in mm shown at the end of the model name, representing the smallest and largest dimensions respectively): ASH 150*150, ASH 305*305, ASH 305*610, ASH 610*610, ASH 1220*1220, ASH 1830*1830
    • circular (dimensions in mm shown at the end of the model name, representing diameter D): ASH D≤180, ASH 180<D≤380, ASH 380<D≤760, ASH 760<D≤1520

Additionally, the ZER model corresponds to ZERo sound attenuation.

Summary of models to be entered into the "in-out COSTDU" Excel spreadheet for the predictive calculation of insertion loss in straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or chimneys using SILDIS® software for "external use."

Parameter Models
Model for rectangular HVAC (Heating Ventilation Air Conditionning) air duct

VDI 2081-R
SMA-R
ASH 150*150
ASH 305*305
ASH 305*610
ASH 610*610
ASH 1220*1220
ASH 1830*1830
Model for circular-section HVAC (Heating Ventilation Air Conditionning) air duct  VDI 2081-C
ASH D≤180
ASH 180<D≤380
ASH 380<D≤760
ASH 760<D≤1520
Model for Brick stack-chimney 3733b-B-L (faiblement encrassée)
3733b-B-M (moyennement encrassée)
3733b-B-H (fortement encrassée)
Model for Steel stack-chimney 3733b-S-L (faiblement encrassée)
3733b-S-H
Model for ZERo sound attenuation ZER (fortement encrassée)

The predictive calculation of the self noise (flow-induced) of straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stacks-chimneys using SILDIS® software involves various models:

  • a general model for flow-generated sound power (to calculate a single, overall value for clean, dry air at ambient conditions)
  • a model for thermodynamic correction (to adjust this value based on fluid characteristics at operating conditions) 
  • a model for spectral correction (to obtain levels for the various frequency bands) 

Summary of models to be entered into the "in-out COSTDU" Excel spreadsheet for the predictive calculation of self-generated noise (caused by the flow of the transported fluid) in straight ducts -such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stacks-chimneys using SILDIS® software for "external use"

Parameter  Models
General models for flow sound (acoustic) power 

2081a
2081b
2081c
2081d
2081d*
2081e
2081e*
3733a
3733b
3733c
3733c*
KRE+ 
 Models for thermodynamic correction 3733a
3733b
3733c for conditions other than ambient
ZER i.e. ZERo: for ambiant conditions
Models for spectral correction  2081a
2081b
2081c
2081d
2081e
3733a
3733b
3733c

For an "external use," the recommended model(s) are those that are both underlined and displayed in bold in the table above.

Input data for simulating noise attenuation in straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stacks-chimneys using SILDIS® software

Input data for simulating noise attenuation in straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stacks-chimneys using SILDIS® software must be entered into three separate Excel sheets (cf. table 1):

  • in the "in COALA" Excel sheet (for "external use," i.e. with clean, dry air):
    • fluid temperature and pressure
    • frequency spectrum of the noise to be attenuated (i.e. sound power level Lw0)
  • in the "in-out COSIL" Excel sheet:
    • fluid mass flow rate
  • in the "in-out COSTDU" Excel sheet:
    • insertion loss model
    • length of the straight duct/stack-chimney
    • general flow-generated sound power model, thermodynamic correction model, spectral correction model
    • for a circular duct: diameter
    • for a rectangular duct: largest and smallest dimensions    

Results of noise attenuation simulation for straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stacks-chimneys using SILDIS® software

The output data i.e. the results from the SILDIS® software simulation of noise attenuation in straight ducts such as those found in HVAC (Heating Ventilation Air Conditionning) systems or stacks-chimneys are as follows, listed in the "in-out COSTDU" Excel spreadsheet:

  • insertion loss with airflow, excluding self-generated noise (Di')
    • table: per octave and 1/1 octave frequency band (as well as an A-weighted overall value, calculated relative to the reference noise spectrum Lw0)
  • self-generated noise (sound power level of flow-induced noise)
    • table: per 1/1 octave frequency band (as well as an A-weighted overall value)
  • sound power level with silencer (Lw1)
    • table: per 1/1 octave frequency band (as well as an A-weighted overall value)
  • insertion loss with airflow, including self-generated noise (Di)
    • table: per 1/1 octave frequency band (as well as an A-weighted overall value, calculated relative to the reference noise spectrum Lw0)

[0] Sound Impact Limitation - Design for Industrialized Solutions