COOLING TOWERS
Being a good neighbour
Scott Maurer, SPX Cooling Technologies global product manager, discusses the importance of accurate sound testing.
N
oise pollution is a growing concern for communities around the world. With expanding urban and industrial
development, commercial buildings and process facilities are faced with increasing and strictly enforced noise ordinances. These noise directives are especially stringent in many European and Middle Eastern locations, as there is generally less land area away from densely populated areas for cooling towers to operate. In the United States, the National Park Service (NPS) has mapped out noise-polluted areas to demonstrate impacts by human influence, generally higher in urban areas and the densely populated East Coast. Cooling towers – a part of large-scale HVAC or process cooling systems – are often located near medical centres, universities, hotels, high-rise residential complexes, industrial facilities and power plants. Noise generated by
20 April 2019
towers can be a public nuisance, so directives exist to keep the sound levels of these towers and other equipment in check. When developing cooling systems, manufacturers must be knowledgeable about regulations and permissible sound levels. However, defining the actual noise or sound level of a cooling tower can be challenging. It is difficult to verify whether a measured level is accurate once the cooling tower is installed in the field, because there is no single, governing sound test criterion practiced across the cooling tower industry. Given these issues, SPX Cooling Technologies, a global cooling tower manufacturer, depends on the Cooling Technology Institute (CTI) for third party sound guidance. Recognising the international CTI Test Method ATC-128 and following its methodology for sound testing is one way to address the challenging landscape of noise
regulations worldwide. There are a number of important considerations for sound level verification. Sound is defined as a disturbance through a physical substance, perceived by the listener as a pressure wave superimposed on the ambient air pressure. Sound in the cooling tower industry is determined, or specified, in two ways. One is by sound pressure level. The sound pressure level is the sound level as it is perceived by our ears from a given distance. This level is expressed in decibels (dB), and varies with distance from the sound source. The amount by which the sound pressure varies by distance is influenced by a number of factors. In the near field (close to the source), the variation with distance does not track closely to theoretical calculations and typically requires analysis based on testing. Far field distance reductions are more likely
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