The Acoustics of the DG/ Backup Power Area

Usually, acoustic engineers are never consulted for this part of the design – we all think this has only to do with the Electrical contractors for the building, and all we need are specifications on how much power backup a building needs – which determines the number of DG sets for which to provision space.

Manufacturing Specification

Even more so, because all DG sets now come with an acoustical enclosure. The mandate below, out in 2002, clearly states that DG sets must come with their own enclosure. This actually mercilessly threw a lot of people out of business – these guys used to be design and build contractors for DG set enclosures. I know one of them personally. Very depressing times for them. Now they’ve all been forced to look for livelihood elsewhere. Click on the image below for a larger view of the text. 

Excess Noise in Residential Layouts

The funny part is, this mandate does not take into account the fact that DG sets confirming to 75 dB of noise at 1 m is only good for commercial or industrial areas. Residential areas need them to be quieter than 60 dB during daytime, and 45 dB during night time. Who on earth is now responsible to fill that gap? 

Case Study: This was exactly one of the cases we handled – a fertility clinic had opened up in the heart of a residential layout. The layout is one of the most beautiful, well planned layouts –  planned by the legendary Sir. M. Vishweshwaraiah, no less! – with lovely boulevards lining one of the most beautiful, tree-lined roads in Bangalore, and the layout on both sides of it. The residents refused to put up with the noise levels  – given that Bangalore faces a lot of power cuts in summer – the DG was required to be in use for good portions of the day. The Clinic people contacted us, and we asked them to move the DG set to the terrace, build a 4-inch thick enclosure around it, leaving enough open for ventilation, but blocking line of sight from nearby houses – what they don’t see daily won’t seem obvious to complain about. :).

Heating and Ventilation Issues

Now the other problem with DG sets in mid-size to large buildings may again seem unrelated to acoustics These large buildings could be office spaces, commercial outlets or residential buildings. I know of a case where a 17-storey residential complex wasn’t able to sell the houses in the ground floor of a building, because their DG area was located in the basement below that. The noise was so deafening that while taking measurements, my colleague and I had to use sign language to indicate dimensions to the other person to write down. We couldn’t hear ourselves shout over it!

What exactly is the problem? 

Now DG sets in buildings are almost always considered a necessary evil. Nobody wants to provision the space they really need, because it means giving up precious car parking space. As a result, these are often crammed into some corner of the basement, mostly as an afterthought.

But as it stands, correct provision must be made for the emitted hot air to be vented out either by giving space around it, or by providing artificial ventilation. Merely standing around such a DG set will tell you how hot these can get, and that you will feel most comfortable nearly 2.5 metres away from it. Not in the stipulated 1m space around it. Now usually, nobody affords that kind of space around a DG set these days – which means that in the absence of a ventilation system, these sets heat up and the DG operator walks over to the set and opens the door of the enclosure to let some air in for cooling. Now what’s the purpose of the acoustical enclosure again? Here is where a heating and ventilation issue becomes an acoustical issue. 

Now basements are usually bare bones by design, and provide ample empty space and bare walls for the sound to echo and reverberate in. I’ve heard huge basements echo with large amounts of noise, annoyingly audible 3 floors up. Three hotel floors up. Acoustical engineers are then required to design secondary enclosures based on the noise reduction needed.The good part is, unless you have staff sitting in the basement, you’re okay with having decent amount of noise there.

To summarise, noise is not the primary issue, but becomes one after a few months of the building’s commisioning.  The life of the engine is affected by these design decisions. The owner of the building spends time maintaining the set, replacing parts, etc, long after the building is up. In terms of acoustics, you only need to ensure that the sound reaching your compound wall and your building interiors is within the specified limits. This is easy to do, but is best done in foresight, not in hindsight.

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Steve, watch out for that pipe!

What does NIHD mean to you?

I’ve heard varied answers for this, with some people even guessing that it was a new kind of battery for cameras. I’m of course, talking about Noise Induced Hearing Deficiency. Given how commonplace it is now, it is surprising that nobody really knows about it. It is not surprising, it is actually alarming. The only explanation to this is that any form of deafness earlier was attributed to age, or accidents.  The truth is, NIHD is tragic. It is the most easily avoidable kind of occupational injury. Situations causing NIHD are much more rampant now.  This blog discusses NIHD in the Indian context, and how we owe it to ourselves to take the simple precautions that will help us keep our hearing mechanism healthy.

Here goes:

What is NIHD, and why should I give it any thought? 

Imagine not being able to hear half the consonants. “Steve, watch out for that pipe” sounds like ” ee, o ou o aa i “. You haven’t lost your hearing yet. But there’s no quality of life if there’s no quality of conversation. That’s what a person with NIHD will go through in their alarmingly near future.

Imagine sitting around with your best friends at your local cafe, sipping coffee, watching and hearing everyone talk and laugh, and not quite be able to make out the words. You hear sounds, but they don’t sound like the words you know.

 It is likely that you will spend this evening and all such evenings further on just sitting around, not really being a part of the conversations.  There are already enough teenagers in the US, who’ve battered their delicate hearing mechanism with abnormally loud music for hours on end, and who now cannot hear their friend whisper a remark into their ear while sitting in class.

Hearing loss affects the high frequency range of your hearing, and many consonants of our alphabet lie within that.  Here is a wonderful youtube video that explains more.

The solution?

• The previous post “Sound – the Fourth Dimension” lists steps you can take to make your hearing sharper.
• The simplest solution is to use ear plugs whenever you are unavoidably facing loud noise for long amounts of time. 

The hearing mechanism is so delicate, that the wonder of it deserves another post  – coming up soon! I hope you will be left with a feeling of awe at the end of it. :).  Meanwhile, Steve, watch out for that little pipe in your ear.  Use ear plugs.