Don’t turn it up
I think it’s safe to assume that when you ended up on this page, you are very well aware of the importance of compressed air. Around the world, compressors are used in an (extremely) wide variety of applications and industries. Unfortunately, while highly valued as a utility, they have a severe drawback: noise. The noise doesn’t have a single cause. But most of it can be contributed – or blamed – on friction. Like your favorite heavy metal band, the more moving parts it has, the louder it gets. Add a diesel-driven engine to the equation and dB’s go up and up and up.
But we can’t put all of the blame on compressors. The surroundings also contribute to its noisiness. Concrete floors, open areas, and so much more can amplify noises. How loud is loud? Well … Pretty loud. But how is “loud” determined? Sound intensity is measured in decibels – or dB and can be shown in power level or pressure level. Each one is used on different occasions. Sound power is used in calculation models to generate an impact on the environment. Sound pressure is used to show the impact on an object - most of the time impact on the operator. When we start calculating, it can also be a little confusing as sound is measured on a logarithmic scale. This means that for sound power a sound level of 103dB is twice as loud as a sound level of 100dB (2x more energy). But for sound pressure, you need to raise 6dB to measure 2x more pressure. And on top of that, a typical human being’s sensed doubling of noise level is a different thing all together.
Many studies have shown that loud noises negatively impact work morale and harm productivity due to a decrease in communication. And it’s annoying. On another note, there are increasingly stricter governmental regulations (local and regional) for urban construction sites in regard to noise (pollution). The solution? Electric-driven compressors. Luckily, Atlas Copco Rental has been “electrifying” for a while.
More electric, less noise
While ear protection does (some of) the trick, it’s not the golden ticket. But what is? Electric-driven compressors already eliminate one major contributor to noise: the engine. VSD / VSD+ technologies are a major contributor to noise reduction. But that’s not the only moving part, of course, that impacts noise. Rotary screw air compressors have a lower sound volume. Less moving parts, less noise. Now, you probably have two questions:
What is VSD technology?
A variable speed drive (VSD), speed-controller or frequency-controlled, compressor automatically adjusts its motor speed to the air demand. Its counterpart, fixed speed or “idling compressor”, or “load/unload compressor, is either on full throttle or off.
Compare it to a car: an “idling compressor” either drives 100 km per hour or not at all. That is fine if the application requires either full load or no load compressed air supply. However, most applications don’t. They have a fluctuating air demand and that is where a VSD compressor step into the spotlight.
A Variable Speed Drive compressor simply adjusts its motor and elements speed to match the demand. The advantage is obvious: a variable speed drive only runs at the required speed, which saves considerable amounts of energy. When compared to an idling compressor, a VSD allows for energy savings of 35% on average, a GA VSD+ even 50% on average. Those savings do matter. Even when you only temporarily rely on an Atlas Copco Rental Total Solution.
How does a rotary screw air compressor work?
A rotary screw air compressor is one of the two types of positive displacement gas compressor. It uses two rotors to create the pressure needed to compress air. They are one of the easiest types of air compressor to use and maintain
The other type of positive displacement compressor is the reciprocating or piston compressor.
Equivalent to positive displacement compressors, are dynamic compressors, like centrifugal compressors. The former compresses air by forcing gas into a chamber under high pressure, the latter by accelerating the air inside the mechanism.
The main screw compressor parts are the male and female rotors, which rotate in opposite directions. This draws in air that is compressed as the space between the rotors and their housing decreases.
Each screw element has a fixed, built-in pressure ratio that is dependent on its length, the pitch of the screw and the form of the discharge port. To attain
Let’s not get loud
We’ve established that our fleet has the right technologies and on paper, it “sounds” great. But what about numbers? As mentioned before there are variables we can’t take into account like the unit’s location. If your production facility has the acoustics of a concert arena, it will always get loud. However, here are a few highlights of “signature” Atlas Copco Rental units. No, wait … First we have to talk about certification.
What is ISO 2151: 2004 certification?
ISO 2151:2004 specifies methods for the measurement, determination and declaration of the noise emission from portable and stationary compressors and vacuum pumps. It prescribes the mounting, loading and working conditions under which measurements are to be made, and includes measurement or determination of the noise emission expressed as the sound power level under specified load conditions and the emission sound pressure level at the work station under specified load conditions.
It is applicable to compressors for various types of gases, oil-lubricated air compressors, oil-flooded air compressors, water injected air compressors, oil-free air compressors, compressors for handling hazardous gases (gas compressors), compressors for handling oxygen, compressors for handling acetylene, high pressure compressors (over 40 bar/4 MPa), compressors for application at low inlet temperatures (i.e. below 0 °C), large compressors (over 1 000 kW input power), portable and skid-mounted air compressors, and rotary positive displacement blowers and centrifugal blowers and exhausters in applications of 2 bar/0,2 MPa or less. It is not applicable to compressors for gases other than acetylene having a maximum allowable working pressure of less than 0,5 bar/0,05 MPa, refrigerant compressors used in refrigerating systems or heat pumps, nor to hand-held portable compressors.
Now that we have that behind us, here are two extremes. A portable E-Air small compressor and a large Full Feature compressor. Two very different machines in size, applications, and sound. Or … are they?
- E-Air H250 VSD: 75dB(A) @1m
- ZT 160 VSD FF: 76dB(A) @1m
Two very different units, made for two very different applications, but with one thing in common (besides our branding). Their noise-levels are somewhere between a casual conversation and a blender. How does it compare to diesel-driven counterparts? Well, these units, under the same distance parameters, close in on – or exceed - triple digit numbers.
Power and pressure
If only it was that simple … So far we took a more simplified look at sound. The basics let’s say. However, there’s much more that comes to sound. Loud isn’t just loud. There are a lot of terminologies and descriptions to take into account:
What is sound pressure level?
These are pressure variations in the air created by sound waves. The lowest sound pressure we humans can hear is called “the hearing threshold.” The highest is the “pain treshold.”
Measurement unit: Pa (Pascal)
What is sound power level?
Sound power is the total acoustical energy created by a source.
Measurement unit: W (Watts)
What is sound intensity level?
The flow of sound through a specific area in a direction.
Measurement unit: dB (Decibel)
Three different terms, yet they sound similar. No pun intended. Let’s use an analogy. Heat is a good one – if I say so myself. A heater generates heat which spreads throughout the room. At every position in a room, there is a specific temperature level. This is measured in degrees. Sound is the same thing.
We hear sound pressure, but a source’s power causes it. For example, that heater in the room generates a certain amount of heat per hour. This is measured in Watts. Sound power is kind of the same principle. The power of sound is a property of the object that produces the sound. And this is also measured in Watts …
Now the heat starts traveling throughout the room. The heat flow has a direction and temperature. Sound intensity also has a level and direction. If you’re far away from the heater, it will take longer for the heat to reach you – and by the time it does, it’s not as hot. Just like sound.
You might have noticed, but we used dB(A) earlier when we talked about the E-Air and ZT. Where does that A come from? When dB(A) is used, the measurement has been adjusted to consider our hearing to different sound frequencies. Regulatory guidelines have been put into place which prefer dB(A) measurement on the belief that it is better correlated with the risk of hearing loss. Worker protection against hearing loss and noise exposure is regulated by the EU.
What is Directive 2003/10/EC?
The objective of this Directive is to lay down minimum requirements for the protection of workers from risks to their health and safety arising or likely to arise from exposure to noise and in particular the risk to hearing.
The Directive defines the physical parameters that serve as risk predictors, such as peak sound pressure, daily noise exposure level and weekly noise exposure level.
It sets exposure limit values and exposure action values in respect to the daily and weekly noise exposure level as well as peak sound pressure. The exposure limit values fixed at 87 decibels shall take into account of the attenuation provided by personal protective equipment (hearing protectors) worn by the workers. The exposure action value is fixed at 80 decibels (lower value) and 85 decibels (upper value).
The employer shall assess and, if necessary, measure the levels of exposure to noise to which workers are exposed. This has to be done in accordance to the obligations laid down in the Framework Directive 89/391/EEC. Results of the risk assessment have to be recorded on a suitable medium and kept up to date on a regular basis. The risk assessment shall be furthermore updated on a regular basis, particularly if there have been significant changes which could render it out of date, or if the results of health surveillance show it to be necessary.
Carrying out the risk assessment, the employer must give particular attention to level, type and duration of exposure, exposure limit / action values, health effects spreading from particular sensitivity of the worker, interractions with other risks (ototoxic substances, vibrations), the exposure to noise beyond normal working hours under his responsibility, and noise caused by warning signals at work.
The risks arising from exposure to noise shall be eliminated or reduced to a minimum. The reduction of risks arising from exposure to noise shall be based on the general principles of prevention set out in Directive 89/391/EEC, e.g. by working methods or equipment that require less exposure to noise, instructions on the correct use of equipment, technical measures (shield, noise absorbing coverings) or organisational measures in order to reduce duration and intensity of exposure.
If risk can not banned by other means, the employer has to provide properly fitting personal protective equipment (hearing protectors), in accordance to Directive 89/656/EEC.
The exposure limit values must not be exceeded. If they are exceeded, the employer has to take adequate measures immediately in order to reduce the exposure.
The employer shall ensure that workers who are exposed to risks from noise at work and/or their representatives receive any necessary information and training relating to the outcome of the risk assessment provided for in Article 4 of the Directive.
Member States must adopt provisions to ensure the appropriate health surveillance of the workers (preservation of the hearing function).
Source: European Agency for Safety and Health at Work
Sounds like no trouble
In conclusion, there are many benefits to going electric, but reduced noise pollution is probably one that is most likely to be overlooked. But with ever-growing conserving to personal health and well-being, electric-driven units, besides being the greener solution, have another major benefit …
At Atlas Copco, we have been turning industrial ideas into business-critical benefits since 1873. By listening to our customers and knowing their needs, we deliver value and innovate with the future in mind. Great ideas reinforce sustainable development. At Atlas Copco Specialty Rental, we team up with our customers to set up state-of-the-art temporary air, flow, steam and nitrogen solutions. Our passionate experts have extensive application and equipment knowledge. We understand our customers' needs and can provide a total solution for any industry, no matter if it is for emergencies or planned projects. We are a division of the Power Technique business area, headquartered in Boom, Belgium and offer specialty rental solutions under several brands around the globe.