Table of Contents
With the down trend in the construction of departmental bulidings and going for private accomodation that too in load centres the need for saving in space requirement and noise and poluution control has increased. Also there is increased awareness of noise and pollution and these are to be kept under permissible statutory limit.
As per the notification of Delhi Pollution Control Board (DPCB) given in 1999 the following norms has been issued to minimise air pollution from EA sets:
EA sets (5 kVA and above) should be provided with proper exhaust muffler and acoustic enclosure or kept in a acoustically treated room to achieve a minimum 25 dB insertion loss and the following ambient noise standards:
- The insertion loss may be measured by any of the approved laboratory of DPCB.
The table of the permissible ambient noise is as below:
Sl. No. Type of Area Permissible Ambient Noise Standards dB (A) Day Time Night Time 1. Industrial Area 75 70 2. Commercial Area 65 55 3. Residential Area 55 45 4. Silence Zone 50 40
Day time is reckoned from 6.00 AM to 9.00 PM.
Night time is reckoned from 9.00 PM to 6.00 AM.
The minimum stack height should be provided with the EA sets as per the calculation of the following formulae:
H = h + 0.2 √Q meters, where h is the building height and Q is the capacity (kVA) of the EA set.
Generally the chimeney stack should be two/three meters above the roof top.
- EA sets of above 1 kVA should not be used in the residential areas.
By the above notification it was also brought to the notice of the public that four stroke engines or silent engines causes less damage to the environment.
The other guidelines on the noise level are given below:
AMBIENT AIR QUALITY STANDARD IN RESPECT OF NOISE. (Schedule III inseted vide GSR 1063(E) dated 26/12/1989 published in the Gazette no. 643 dated 26/12/1989)
|Area Code||Category of Area||Limits in dB (A)|
|Day Time||Night Time|
- Day time is reckoned from 6.00 AM to 9.00 PM.
- Night time is reckoned from 9.00 PM to 6.00 AM.
- Silence zone is defined as area upto 100 meters around such premises as hospitals, educational institutes and courts. The silence zones are to be declared by competent authority. Use of vehicular horns, loudspeakers and bursting of crackers shall be banned in these zones.
- Mixed categories of areas should be declared as one of the four mentioned above by the competent authority and the corresponding standard shall apply.
Extracts From IS 1950 : 1962 (CODE PRACTICE FOR SOUND INSULATION FOR NON INDUSTRIAL BUILDINGS.
4. Maximum Acceptable Noise Levels.
4.1 The maximum acceptable noise levels inside buildings from point of view of comfort, economy and practical considerations under the conditions prevailing in the country may be taken as given in the table below:
TABLE: MAXIMUM ACCEPTABLE NOISE LEVELS
Sl. No. Type of Building Noise Level in dB 1. Offices 50 to 60 2. Dwellings (Houses and Flats) 45 to 55 3. Schools (Class/Lecture Rooms) 45 to 50 4. Hospitals 40 to 50
5. Recommended Sound Insulation Standards.
5.1 The desirable sound insulation required to be provided for various types of buildings is given below:
TABLE: SOUND INSULATION FOR VARIOUS BUILDINGS
Sl. No. Type of Bulding Insulation for Air-borne Noise Insulation for Impact Noise (Floor/Ceiling Construction dB) Noisy 90 dB level Quiet 70 dB level 1. Hospitals 50 30 50 to 60* 2. Schools 45 25 45 to 50* 3. Dwellings 45 25 45 to 55* 4. Offices 40 20 40 to 50*
Note: * The higher values correspond to concrete, stone or similar solid floor / ceiling construction.
Also as per the study for development of standards/guidelines for control of noise from EA sets carried out by M/s Lotus Energy Systems, Bangalore under the guidance of Prof. M.L. Munjal, IISc Bangalore and discussed by National Committee on Noise Pollution, the noise standards / guidelines as agreed are given below:
NOISE STANDARDS FOR EA SETS (15 – 500 kVA, WATER COOLED).
The total sound power level, Lw, of a EA set should be less than,
i) 94 + 10 log10 (kVA) dB (A), at the manufacturing stage,
ii) 96 + 10 log10 (kVA) dB (A), at the user’s end, where, kVA is the normal power rating of EA set.
These levels should fall by 5 dB (A) every five years, till 2007 i.e. in 2002 and then in 2007, to encourage continuing efforts in noise reduction at the source.
MANDATORY ACOUSTIC ENCLOSURE / ACOUSTIC TREATMENT FOR STATIONARY EA SETS (BOTH AIR?WATER COOLED, 5 kVA & ABOVE).
The user should control noise from the EA set by providing an acoustic enclosure or by treating the room acoustically.
The acoustic enclosure/ acoustic treatment for the room should be designed for 25 dB (A) insertion loss or for meeting the ambient noise standards whichever is on the higher side. (If the actual ambient noise is on the higher side, it may not be possible to check the performance of the caoustic enclosure / acoustic treatment. Under such circumstances, the installation free from vibration and exhaust gas leak should be designed.)
The typical noise levels around the EA set are depicted in Fig below:
ACOUSTIC CANOPY FOR EA SETS
The advent of new technology in the switching equipments and multi vendor system has considerably reduced the supply and installation period to 2 to 3 months. Also increased demand for telephones, privatization are compelling factors to provide services expediously. Also as the department is going for rental accommodation, so the canopy is becoming a must. The objectives of a canopy should be:-
- Should occupy less space.
- Reduce sound level.
- Easy to install, dismantle, transport and reinstall in least time.
- Environment friendly.
- Cost effective.
In a design of canopy, the two main factors are ventilation and sound reduction. The engine needs ventilation for:
- Combustion of fuel i.e. aspiration of engine.
- Air required for cooling of engine and alternator.
- Air required to remove excess heat from the engine room / canopy.
The sound reduction is achieved by using high density of layers of sound absorbtion material i.e. with glass wool.
Earlier in the department canopies made of metallic construction (MS) were being used, either supplied by firms like Kirloskar Electrodyne or were locally made. This types of enclosures served only as an alternative for EA set room occupying less space; but from the acoustic attenuation point of view, they proved only partly effective. Subsequently department has made effort to provide canopies made of prefabricated heavy gauge FRP (fibre reinforced plastic) and SMC (sheet moulding compound). These are strengthened with fabricated superstructure.
FRP is having excellent mechanical properties like light in weight, strength, non-corrosive, fire retarding and ic available in environment friendly shapes and shades. The interior of these canopies is lined with high density glass wool, which is retained by perforated aluminum sheets. The sound absorbing material is fire retarding and vermin prood and rubber gaskets are provided to all the doors and external joints for complete sound and weather proofing. The main advantages of FRP canopies are:
- Sound Reduction: Sound reduction to the tune of 25 to 30 dB, as laid down under statutory pollution control is achieved.
- Mobility: The FRP panels and associated items are factory made and are brought to site in dismantled condition and can be assembled in 3 / 4 days. The canopy can be dismantled, shifted wherever needed and reassembled easily, thus allowing optimum use of space.
- Minimum Civil Works: Except for plinth no other work is required and canopy can be kept in open space.
- Ease of Maintenance: For major overhauls, the FRP panels can be easily dismantled from inside.
- Long Life: As FRP pre-fabricated structure is galvanized, so the canopy is having long life.
- See-through Facility: See through window is provided to allow inspection of instruments on electrical panel.
- Aesthetic and Environment Friendly: Has good shades.
WATER COOLED EA SETS
The canopy for water cooled EA sets broadly consisting of 3 compartments, the middle one accommodating engine and alternator with a door at the center. It draws its required cold air for cooling i.e. aspiration, cooling of engine and alternator and chamber cooling through the third compartment, located behind the alternator, which houses electrical panel and fuel tank. The hot air from the radiator is released into 1st chamber, which expels into the atmosphere through sound boxes, which has Z louvers for dampening the noise. The resindential silencer is also located in the first chamber. Small 300 / 450 mm exhaust fan is kept in the middle chamber to remove the excess heat developed in the Engine chamber. Care should be taken to avoid exhaust fan perpendicular to the direction of radiator, as it may cause short circuiting of the air path. Service doors are provided in all the compartments. The rise in the temperature inside the canopy should not exceed 10° C and noise at a distance of 3 m should be around 70 dB (minimum 25 dB reduction). The drawings for a 250 kVA EA set canopy are shown in figure 2 and 4.
AIR COOLED EA SETS
The design of acostic enclosure for air cooled EA set becomes much difficult due to the phenomenon of temperature build-up inside the enclosure beyond permissible limits.
Model I: Basically it consists of 2 compartments, one to accommodate EA set and draws complete fresh air i.e. for aspiration of engine, cooling of Engine and alternator and for removing excess heat, directly from atmosphere through sound boxes (which have Z louvers to dampen the sound), and throws coo air over the cylinders. During this process cool air gets heated upto about 55 °C or above. The hot air is collected with the help of duct and thrown out with the help of exhaust fans. The second chamber accommodates fuel tank and control panel. Service doors are provided for both the compartments. The drawings for these are shown on figures 3, 5, and 6.
Model II: Here the enclosure is divided into two compartments, the first compartment provides the entry to main housing for the EA set and has i) a scientifically designed fresh air compartment ii) diesel tank, iii) fresh air fan and iv) electrical panel. The two compartments are sepated by a louvered sliding type of door. The primary objective of the first compartment is to effectively check the machine noise from reaching the ambient space outside.
The second compartment is housing the EA set on a concrete plinth. The surrounding walls are made of FRP panels, which are acoustically treated so as to attenuate the machine noise. The roof of the compartment is of the sloped construction again made of FRP panels. Some part of the roof is utilized to run the exhaust pipe and silencer. The heat dissipated is tackled in three different ways, namely:-
- A specially designed FRP cloth / canvas duct with the help of a small roof extractor fan takes away the intensive heat produced by the exhaust manifold of the engine.
- A small ducting with the exhaust fan is designed to remove the heat dissipated on the account of copper loss in the alternator.
- The remaining heat contributed from other sources in the EA set chamber is exhausted by a separate roof extractor. The void space above false ceiling and enclosed by sloped roof is serving as a hot air chamber.
The concept of tackling the three different hot air streams has proved very effective in minimizing the heat build-up inside the EA set space and temperature could be kept within permissible limits. Also a specially designed pent house resembling acoustic box has proven very effective in attenuating the noise contributed by the exhaust pipe/silencer. The drawing for a 40 kVA EA set canopy are shown in figures 7 to 10.