Technical Guideline on Boundary Noise Limits For Air Conditioning And Mechanical Ventilation Systems In Non-Industrial Buildings

This guideline sets out the maximum boundary noise emission limits for air conditioning and mechanical ventilation systems in non-industrial buildings.

The adoption of the guideline would help minimise noise nuisance from such sources. It was developed by NEA in consultation with the industry associations [i.e. Singapore Institute of Architects (SIA), Institute of Engineers Singapore (IES), the Association of Consulting Engineers Singapore (ACES), the Singapore Contractor Association Ltd (SCAL)], the academia [i.e. National University of Singapore (NUS)] and the government agencies [Building and Construction Authority (BCA), Urban Redevelopment Authority (URA)].

Qualified Persons may use the Guideline in their specification, design and installation of air conditioning and mechanical ventilation systems in nonindustrial buildings.

Air-conditioning – The process of treating air so as to control simultaneously its temperature, humidity, cleanliness and distribution to meet the requirements of the conditioned space.

Mechanical Ventilation – The process of supplying or removing air to or from a building or part thereof by mechanical means or devices.

Non-industrial building – Any permanent or temporary building or structure used for the purposes of trade, business or commerce and includes any shopping complex, financial institution, office tower, hotel, educational institution, hospital, transport infrastructures, community infrastructure, sport and recreational infrastructure but does not include any factory and residential premises.

Noise Sensitive Premises – Any premises used for purposes that require peace and quiet and includes any nature reserves, health care facilities, educational institution, place of worship, library and court of law.

Residential Premises – Any premises used for residential purposes.

Commercial Premises /Others – Any premises used for the purposes of trade, business or commerce and include any shopping complex, offices and hotel but does not include any factory premises.

Factory Premises – Any premises used for any industrial or manufacturing purposes, and includes any repair or processing workshop, and warehouse, but does not include any construction sites¹

Note:¹ Please refer to the Environmental Protection and Management (Control of Noise at Construction Sites) for the definition of a construction site.

The noise level from the air conditioning or mechanical ventilation system should not exceed the following boundary noise limits subject to applicable correction factors as per paragraphs 5 and 6.

Note:

1. If the affected premise is a mixed-use development comprising both commercial and residential, the more stringent residential noise limits should apply.

2. Qualified Persons should make reference to the latest URA master plan at URA website (https://www.ura.gov.sg) to verify the intended uses of adjacent premises. The more stringent noise limits should be used when the current and intended land uses differ.

For equipment installed at ground level, the noise measurements should be made at the site boundary. For equipment that is installed above ground level e.g. at roof-top, the noise measurements should be taken at least 1m from the noise source and at the same height as the equipment. The noise level shall be computed for a point that is at the site boundary and at the same height as the equipment. The locations for noise measurements are at Annex 1. The methodology/example of the computation to be used is at Annex 2.

The adjusted value for the maximum permissible noise limit shall be obtained by adding the correction factor corresponding to the difference between the maximum permitted level and the background noise level, set out in the Table below, to the higher of the 2 noise levels.

Where a noise source contains certain characteristics, such as tonality, impulsiveness, intermittency, irregularity or dominant low frequency content, there is evidence to suggest that it can cause greater annoyance than other noise at the same level and a penalty of 5 dBA shall be added for each of the following characteristics, up to a maximum of 10 dBA, in accordance with Annex 3.

On the other hand, some sources may cause less annoyance where only a single event occurs for a limited duration. The adjustments for duration are also given in Annex 3.

Measurement of noise levels for the purpose of this Guideline shall be carried out with a calibrated integrating sound level meter which complies with the standards specified in the International Electrotechnical Commission Publication 61672 (Type 1) and Publication 804 (Type 1), or any other comparable standards.

The following points provide general guidance in the design of mechanical ventilation system(s) for the proposed development:

1. All mechanical ventilation exhaust outlets, in particular bin centre, kitchen and carpark exhaust outlets, should avoid facing directly immediate and nearby residential units, and common circulation areas within the development, where technically feasible.

2. All mechanical ventilation exhaust outlets, in particular bin centre, kitchen and carpark exhaust outlets, should avoid facing directly walkways outside the development, residential units and any common areas of the adjacent developments, where technically feasible.

Environmental Protection and Management (Boundary Noise Limits for Factory Premises) Regulations, 2008, National Environment Agency, Singapore

New South Wales Industrial Noise Policy, Jan 2000, New South Wales Environment Protection Authority, Australia

Note:

1. If noise barrier is installed, noise measurements are to be carried out at least 1m behind the noise barrier and at its mid-height.

2. If it is not practical to measure at 1m away from mechanical ventilation outlet, the noise measurements should be taken farther away from the outlet within the site boundary [and apply a correction factor for the additional distance accordingly (refer to Annex 2)].

Definitions to support the modifying factor corrections

Tonal noise - Containing a prominent frequency and characterised by a definite pitch.

Low-frequency noise - Containing major components within the low frequency range (20Hz-250Hz) of the frequency spectrum.

Impulsive noise - Having a high peak of short duration or a sequence of such peaks.

Intermittent noise - The level suddenly drops to that of the background noise several times during the assessment period, with a noticeable change in noise level of at least 5 dB.

Adjustment for duration - Applied where a single event noise is continuous for a period of less than two and a half hours in any 24-hour period. The acceptable noise level may be increased by the adjustment shown in Table 1.2. This adjustment is designed to account for unusual and one-off events, and does not apply to regular high-noise levels that occur more frequently than once per day.

Maximum adjustment - The maximum correction to be applied to the criteria or the measured level where two or more modifying factors are present. The maximum adjustment is 10 dBA where the noise contains two or more modifying factors (excluding the duration correction).

Note:

1. Corrections to be added to the measured or predicted levels.

2. Where a source emits tonal and low-frequency noise, only one 5-dB correction should be applied if the tone is in the low-frequency range. If FFT is used for analysis, the correction (penalty) is to be quantified according to the audibility calculation (Please refer to ISO 1996-2, DIN 45681, Joint Nordic Method, or equivalent reference for audibility calculation).

3. Please note that air-conditioning compressors, bifurcated kitchen exhaust and axial fans could cause tonal noise.