The air conditioning unit produces noise which propagates through the room, as shown by the purple arrows emanating away from the unit. This noise could cause disturbance to people working in the plant room. Airborne noise can also be transmitted through the ceiling, causing disturbance to the occupants of the offices above. The air conditioning unit may be supplying air to the offices and airborne noise will propagate through the ductwork and into the offices. If the duct is lined or an attenuator is installed then the noise will be reduced as it travels along the ductwork.
The air conditioning unit can also cause structure-borne noise, as shown by the red arrows. If the unit is installed with anti-vibration mounts structure-borne noise into the floor of the plant room will be reduced. Depending on the installation of the ductwork, structure-borne noise can also be transmitted through the ductwork.
Most sound tests fall into one of three categories – sound power, sound transmission and sound absorption.
For heat pumps, air conditioners and similar products the test standard is EN 12102, which refers back to EN 14511, and is specified for the UK MCS scheme and the European EHPA Quality Label. This standard specifies how to determine the sound power level of a product, with particular emphasis on carrying out acoustic testing at set conditions, as the noise produced by a product can change with the operation of a product.
Products such as louvres can be tested in accordance with EN 10140 to determine the sound transmission through the product. Finally building materials that are designed to absorb sound are tested in accordance with ISO 354 to determine the sound absorption coefficient of the material.
In some situations it is also appropriate to carry out vibration tests, in accordance with standards such as ISO 10816. This type of testing can be used for operational monitoring, acceptance tests and diagnosis of potential failures. Vibration levels are a strong indication of how a machine will perform over time and tests can be carried out to determine if specific components, such as bearings, are likely to fail.
Importance of test data
Accurate acoustic test data is very important as it will lead to an accurate noise impact assessment of the product for a particular site. This means that the product will be successfully installed and no unforeseen noise issues should occur.
On the other hand, inaccurate acoustic data where the product has not been tested at appropriate operating conditions or a suitable test standard can lead to an inaccurate noise assessment and ineffective mitigation. Once the product is installed it is more likely to receive noise complaints and then additional noise assessments and mitigation may be required. This can be a lengthy and costly process.
It is therefore essential to obtain robust, meaningful and reliable acoustic test data. This will allow installers to make a comprehensive judgment when selecting products for a particular site.
Typical acoustic data