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.

Advertisements

Types of Noise (Part 3): Noise in Office Spaces

This is part 3 of a multi-part article dealing with common sources of noise in the urban environment.  Part 1 talks about Community Noise, and Part 2 talks about Road Traffic Noise. 

Now this may raise eyebrows, because a lot of us go to quiet, plush offices that don’t sound sharp or reverberant. The carpets provide absorption for both, footfalls and some amount of reverberation. Offices are supposed to be quiet anyways – if you’re talking, your boss won’t like it too much.  But there are enough scenarios in Bangalore alone, listed below. Again, each of these are what I have personally experienced.

  • Fancy glass exteriors, with inaccurate glazing specification, let in road noise and vibrations.
  • Whirring printers and coffee machines.
  • Irritating hum of the air conditioning system.  I know of an office space where the ventilation duct above the false ceiling turned into a resonator of sorts, and sitting below that was like sitting below a jet engine.
  • Porous meeting rooms.  Privacy issues are huge. I know of a time when improper glazing made someone’s appraisal discussion public.
  • Some job profiles revolve around phone calls. The others nearby could do with some quietness for 8 long hours.
  • Creaky revolving doors.
  • Typing noise
  • Machine hum. I once sat next to the only server test bed in our office, and experienced crazy amounts of heat and noise.
  • Lift noise. This is a problem in hospitals too. My little one was constantly jolted out of her sleep each time the lift was called up.
  • Highly reverberant meeting rooms. Speech intelligibility issues, especially during conference calls where you can’t lip read.
  • Last but not the least, aircraft noise that makes boardroom windows rattle. This is a case at hand. In business hotels, this can be a big factor affecting business – corporates don’t want to rent boardrooms that have deafening noise coming  through the window, muffling speech during conferences.

All said and done, offices are among the quieter spaces we experience, and only specific issues like the ones listed above are what we acousticians constantly address.  Speech privacy and speech intelligibility are the main aspects here. All these issues are easily solvable, even in retrofit cases.