{"id":6837,"date":"2014-09-01T00:00:00","date_gmt":"2014-09-01T00:00:00","guid":{"rendered":"https:\/\/insulation.org\/io\/articles\/is-your-application-acoustically-acceptable-controlling-noise-levels-in-hvac-systems\/"},"modified":"2014-09-01T00:00:00","modified_gmt":"2014-09-01T00:00:00","slug":"is-your-application-acoustically-acceptable-controlling-noise-levels-in-hvac-systems","status":"publish","type":"articles","link":"https:\/\/insulation.org\/io\/articles\/is-your-application-acoustically-acceptable-controlling-noise-levels-in-hvac-systems\/","title":{"rendered":"Is Your Application Acoustically Acceptable? Controlling Noise Levels in HVAC Systems"},"content":{"rendered":"<p>When designing an HVAC system, noise should be one of the primary considerations. In many cases, HVAC systems have served the dual purpose of<br \/>\ntemperature control and white noise. A certain amount of &#8220;white noise&#8221; is considered beneficial because its masking benefits help keep conversations<br \/>\nprivate, have a relaxation effect, and can even help with concentration. If a system becomes too noisy, however, it can prove disturbing to occupants<br \/>\nand&mdash;depending on the circumstances&mdash;may require repair. It is important to ensure that the fine line between acceptable white noise and<br \/>\nintrusive noise is maintained. The acceptable noise level for a system is based on Noise Criteria (NC) curves, which were established in 1957 to<br \/>\nrepresent generally acceptable levels of HVAC system noise based on a specific room&#8217;s purpose. <\/p>\n<h2 style=\"color:#9C43E6;\">Terminology<\/h2>\n<p>To help ground a discussion of HVAC noise, here is a description of basic acoustic terms.<\/p>\n<ul>\n<li>Noise Criteria (NC) curve&mdash;Published data on the acceptable sound-pressure level for rooms, based on their intended use. This<br \/>\ndata has historically been used to determine acceptable levels of background HVAC noise.<\/li>\n<li>Airborne noise paths&mdash;These paths are the same as airflow paths and are easy to identify: if air comes out of it, so will<br \/>\nnoise. Common airborne noise paths include where noise exits the duct at diffusers or through the walls of the duct, and places where sound energy is<br \/>\ntransmitted through the common walls of adjacent spaces.<\/li>\n<li>Structure-borne noise paths&mdash;This type of noise is found by following the vibrational energy of equipment as it transmits<br \/>\ninto a space through the framework. This type of noise path can be more challenging to follow since all possible vibration paths need to be<br \/>\nconsidered&mdash;including vibration energy transmitted through the floor, ceiling, ducts, and common walls.<\/li>\n<li>Airborne\/structure-borne interaction&mdash;These paths can be the most complicated to determine because you must consider how<br \/>\nvibrational energy impacts the surrounding air, and the effect that airborne noise has on the structures nearby. For instance, vibrating equipment can<br \/>\ncause the surface area of a structure&mdash;such as a duct wall&mdash;to act as a loudspeaker. Alternately, loud, low-frequency sound waves can cause<br \/>\nvibration in lightweight structures such as ceilings.<\/li>\n<li>Sound absorbers&mdash;These reduce the amount of reverberant energy in an area by absorbing some of the energy in sound waves as<br \/>\nthose waves come into contact with the surface of the sound absorber.<\/li>\n<li>Noise barriers&mdash;These are designed to reduce the transmission of noise from one area to another. They are rated in Sound<br \/>\nTransmission Class (STC) value. The STC value indicates the change in noise levels, in a laboratory setting, when you move from one side of a barrier<br \/>\nto the other.<\/li>\n<\/ul>\n<h2 style=\"color:#9C43E6;\">Proper Equipment<\/h2>\n<p>In HVAC system design, proper equipment selection, placement, and installation are key. In addition, products such as duct silencers, duct liners,<br \/>\nvibration isolation mounts and pads, and acoustical lagging materials can be used to reduce the noise in a system. Duct silencers and liners are sound<br \/>\nabsorbers that are placed within a duct to absorb some of the sound energy as the noise transmits down the duct. Vibration isolation mounts and pads<br \/>\nreduce the transmission of vibration from an HVAC unit to its surrounding structure, reducing the sound energy transferred through vibration.<br \/>\nAcoustical lagging, which includes a heavy, mass-loaded vinyl, increases the STC value of the walls of the duct to significantly reduce break-in and<br \/>\nbreak-out noise.<\/p>\n<h2 style=\"color:#9C43E6;\">Design Tips<\/h2>\n<p>Designing HVAC systems with proper acoustics can seem like a daunting task, but with appropriate equipment selection, placement, and installation,<br \/>\nit can be achieved. In addition to selecting equipment with lower noise ratings, consider proper isolation mounts, ducts (including duct stiffness),<br \/>\nfan size of diffusers and grills, and the use of variable speed drives over variable vane controls in variable air volume (VAV) systems. It is also<br \/>\nuseful to remember that not all spaces will have the same NC curve, which can be used to your advantage. A mechanical room, for example, should not be<br \/>\nplaced near a noise-sensitive space with a low NC curve, but it may be appropriate in spaces where the NC curve is higher. When required, make sure to<br \/>\nplace vibration isolation equipment and silencers as close to the noise source as possible, and avoid 90-degree elbows or sharp turns when designing<br \/>\nthe duct layout, as this can increase noise. In addition, avoid placing any duct turns near fan inlets or outlets, and remember that duct branches<br \/>\nshould be at least 3 dimensions away from any noise source. When installing the duct work, be sure to use silencers, liners, and lagging materials in<br \/>\nappropriate locations to reduce the noise traveling down and breaking through the walls of the duct. Make sure that roof top units (RTU) will be<br \/>\nmounted on stiff roof sections and run RTU ductwork along the roof top before it enters the building. In rooms located directly below RTU, consider<br \/>\nusing a noise barrier on the back side of traditional ceiling tiles to reduce noise in that space.<\/p>\n<p>Here are 5 steps to follow when determining if a space will be acoustically correct.<\/p>\n<ol>\n<li>\n<h3 style=\"color:#43A4E6;\">Determine the NC curve for the space.<\/h3>\n<p>When working on a project, architects and engineers should<br \/>\nrefer to published NC curves. For example, in a private hospital room, the NC curve would be 25; while in a restaurant, NC curve of 45 would be<br \/>\nacceptable. The appropriate noise levels will change depending on the purpose of the room.<\/li>\n<li>\n<h3 style=\"color:#43A4E6;\">Identify each sound path that affects the area being analyzed.<\/h3>\n<p>It is imperative to take all<br \/>\npotential noise paths into consideration. For example, noise from a HVAC system can follow 3 types of paths to enter an occupied space: airborne noise<br \/>\npaths, structure-borne noise paths, and airborne\/structure-borne interaction paths. <\/li>\n<li>\n<h3 style=\"color:#43A4E6;\">Evaluate each path for individual noise contributors.<\/h3>\n<p>What are the noise sources that will enter a<br \/>\nspace through the noise paths identified? For example, if there is a diffuser in the space being evaluated, what are the noise sources that will<br \/>\ntravel through the ductwork and exit at that diffuser? Some of the noise sources will be obvious, such as the noise generated from a RTU that enters<br \/>\nthe ductwork. However, some noise may be contributed along the noise path from sharp transitions and elbows, as well as any noise generated by the<br \/>\nduct itself, such as the popping and banging sound caused by expansion and contraction of the duct.<\/li>\n<li>\n<h3 style=\"color:#43A4E6;\">Total the sound levels from all noise paths and sources to determine the overall sound level in the<br \/>\narea being analyzed.<\/h3>\n<p>At a specific location, the ambient sound level will be a combination of all noise levels from all sources along all paths to<br \/>\nthat location. There are algorithms available that can help you accurately calculate the effect of each contributing noise source.<\/li>\n<li>\n<h3 style=\"color:#43A4E6;\">Compare!<\/h3>\n<p>Does the ambient sound level calculated in step 4 exceed the design level determined in<br \/>\nstep 1? If so, steps need to be taken to minimize the noise levels. Once the acoustical design criteria is achieved, everyone involved in the project<br \/>\nmust work together to make sure the HVAC system works as designed.<\/li>\n<\/ol>\n<p>HVAC systems make our home and work environments comfortable, but the noise they generate contributes to the satisfaction&mdash;or<br \/>\ndissatisfaction&mdash;of the occupants. As with any design element, it is most cost effective to design an acoustically correct HVAC system in the<br \/>\ninitial planning stage, rather than trying to correct the problem later in the project. While it may be a challenge, with thought and planning, it is<br \/>\npossible to design a HVAC system with minimal noise so the affected spaces are acoustically beneficial. <\/p>\n","protected":false},"excerpt":{"rendered":"<p>When designing an HVAC system, noise should be one of the primary considerations. In many cases, HVAC systems have served the dual purpose of temperature control and white noise. A certain amount of &#8220;white noise&#8221; is considered beneficial because its masking benefits help keep conversations private, have a relaxation effect, and can even help with<\/p>\n","protected":false},"author":[258],"featured_media":0,"template":"","categories":[],"class_list":["post-6837","articles","type-articles","status-publish","hentry","author-mary-riemenschneider"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v24.0 (Yoast SEO v24.6) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Is Your Application Acoustically Acceptable? 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