LIGHTING AND VENTILATION



 LIGHTING AND VENTILATION

17 SPECIFICATIONS FOR LIGHTING AND VENTILATION

Introduction

Illumination levels for different tasks are recommended to be achieved either by day-lighting or artificial lighting or a combination of both.  This section adequately covers the illumination levels required and methods of achieving the same. 

Ventilation requirements to maintain air quality and control body occurs in terms of air changes per hour and to ensure thermal comfort and heat balance of body are laid for different occupancies and the methods of achieving the same by natural or mechanical means are covered in this section.

Climatic factors which normally help in deciding the orientation of the buildings to get desirable benefits of lighting and ventilation inside the buildings are also covered in this section.

The information contained in this section is largely based on the following Indian Standards.

IS: 2440-1975 Guide for day-lighting of buildings (second revision)

IS: 3103-1975 Code of practice for industrial ventilation (first revision)

IS: 3362-1977 Code of practice for natural ventilation of residential buildings (first revision)

IS: 3646 (Part II)-1966 Code of practice for interior illumination: Part II Schedule for values of illumination and glare index.

IS: 7662 (Part I)-1974 Recommendations for orientation of buildings Part I Non-industrial buildings.

17.1. Scope

This section covers requirements and methods for lighting and ventilation of buildings.

17.2. Terminology – See Glossary of Terms in Section 0.2.1.

17.3 Orientation of building

The chief aim of orientation of buildings is to provide physically and psychologically comfortable living inside the building by creating conditions which suitably and successfully ward off the undesirable effects of severe weather to a considerable extent by judicious use of the recommendations and knowledge of climatic factors.

17.3.2 Basic zones

For the purpose of orientation it would be convenient to divide the country into three broad climatic zones:

  1. Hot and arid.
  2. Hot/warm and humid, and
  3. Cold.

 It is to be remembered that there may not be uniform climatic factors in a particular zone. They might even vary during day and night in the same zonal region.  Each zone, all the same poses certain basic problems.

17.3.3 Climatic factors – From the point of view of lighting and ventilation, the following climatic factors influence the optimum orientation of the building:

  1. Solar radiation and temperature,
  2. Clouds,
  3. Relative humidity and d). Prevailing winds.

17.3.4 Solar radiation and temperature - The best orientation from solar point of view requires that the building as a whole should receive the maximum solar radiation in winter and the minimum in summer.  For practical evaluation, it is necessary to know the duration of sunshine, and hourly solar intensity on the various external surfaces on representative days of the seasons.  The total direct diurnal solar loads per unit area on vertical surface facing different directions are given in Table 2 for two days in the year, that is, 16 May and 22 December, representative of summer and winter, for latitudes corresponding to some important cities all over India. The total heat intake can be calculated for all possible orientations of the building for these extreme days of summer and winter.

Wherever possible, suitable sun breakers have to be provided to cut off the incursion of direct sunlight to prevent heat radiation and to avoid glare.

In order to ascertain good and bad aspects and to decide whether or not to take advantage of sun’s rays, day temperatures of the region, for which orientation is to be decided, should be studied in relation to the following broad classification of temperature ranges:

Below 15° C : Cold

Sun’s rays advantageous

15O to 200 C : Cool

200 to 300 C : Temperate

300 to 350 C : Hot

Protection from sun’s rays advantageous

Above 35O C : Very hot

17.3.5 Clouds - The clouds reduce not only the direct radiation from sun but also made sun protection devices of little advantage. It is, therefore, desirable to take note of cloudy periods of the year and if they are long enough and also coincide with hot periods, then, the ideas of sun protection should be given up, although high day temperatures may demand such protection. 

17.3.6 Relative humidity and prevailing winds - The discomfort due to high relative humidity in air when temperatures are also high can be counteracted, to a great extent, by circulation of air with electric fans or by ventilation.  In the past, simultaneously with heavy construction and surrounding verandahs to counter the effect of sun’s radiation, there was also an over emphasis on prevailing winds to minimize the adverse effects of high humidity with high temperatures.  With the introduction of electric fan to effectively circulate air and owing to taking into account the rise in cost of construction of buildings, it would perhaps be better to shift the emphasis on protection from solar radiation where temperatures are very high: When, however, there is less diurnal variation between morning and mean maximum temperatures along with high humidity, as in coastal areas, the emphasis should be on prevailing winds.

For the purpose of orientation, it is necessary to study the velocity and direction of the wind at each hour and in each month instead of relying on generalizations of a month or a period or for the year as a whole.  This helps to spot the right winds for a particular period of day or night. It is generally found that variation up to 30° with respect to the prevalent wind direction does not materially affect indoor ventilation (average indoor air velocity) inside the building.

A comparative study of relative humidity can be made under the following categories:

0 – 25      Percent:Very dry

25 – 50    Percent : Dry

50 – 75    Percent : Humid

75 – 100  Percent  : Very humid

When relative humidity is of the category of ‘dry’ and ‘very dry’, advantage can be taken of evaporative cooling in summers to cool the air before introducing it into the building.  This, however, raises the relative humidity to some extent.  But when the atmosphere is already ‘humid’ or ‘very humid’ it is desirable either to regulate the rate of air movement with the aid of electric fans or to take advantage of prevailing winds.

17.3.7. Aspects of daylighting – Since the clear design sky concept for daylighting takes care of the worst possible situation, orientation is not a major problem for daylighting in multistoried buildings, except that direct sunshine and glare should be avoided.  However, due allowance should be given to the mutual shading effects of opposite facades.

 Daily total direct solar radiation on vertical surfaces in g.cal / cm / day for two representative days

 

 

 

N

N-E

E

S-E

S

S-W

W

N-W

8° N

13° N

19° N

23° N

29° N

16 May

22 Dec

16 May

22 Dec

16 May

22 Dec

16 May

22 Dec

16 May

22 Dec

187

228

225

100

-

100

225

228

-

35

187

291

358

291

187

35

140

214

232

115

-

115

232

214

-

27

173

294

377

294

173

27

83

194

240

141

-

141

240

194

-

20

157

295

393

295

157

20

64

188

247

158

18

158

247

188

-

15

146

297

398

297

146

15

46

180

253

188

64

188

253

180

-

9

126

281

390

281

126

9

17.3.8 Planting of trees – Planting of trees in streets and in open spaces should be done carefully to take advantage of both shades and sunshine without handicapping the flow of natural winds.  Their advantage in abating glare and in providing cool and or warm pockets in developed areas should also be taken.  Some trees shed leaves in winter while retaining thick foliage in summer.  Such trees will be very advantageous, particularly where southern and western exposures are concerned, by allowing maximum sum during winter and effectively blocking it in summer.

17.3.9 For detailed information regarding orientation of buildings and recommendations for various climatic zones of country, reference may be made to code of practice. See Annexure-17-A.1.

17.4 SPECIFICATIONS FOR LIGHTING 

17.4.1 Principles of lighting

17.4.1.1. Aims of good lighting – Good lighting is necessary for all buildings and has three primary aims.  The first aim is to promote work and other activities carried out within the building; the second aim is to promote the safety of the people using the building; and the third aim is to create, in conjunction with the structure and decoration, a pleasing environment conducive to interest of the occupants and a sense of their well-being.

(1). Realization of these aims involves:

  1. careful planning of the brightness and colour pattern within both the working areas and the surroundings so that attention is drawn naturally to the important areas, detail is seen quickly and accurately and the room is free from any sense of gloom or monotony ( see 17.4.1.3);
  2. using directional lighting where appropriate to assist perception of task detail and to give good modeling;
  3. controlling direct and reflected glare from light sources to eliminate visual discomfort;
  4. in artificial lighting installations, minimizing flicker from certain types of lamps and paying attention to the colour rendering properties of the light;
  5. correlating lighting throughout the building to prevent excessive differences between adjacent areas so as to reduce the risk of accidents; and
  6. Installation of emergency lighting systems, where necessary.

17.4.1.2. Planning the brightness pattern – The brightness pattern seen within an interior may be considered as composed of three main parts – the task itself, immediate background of the task and the general surroundings of walls, ceiling, floor, equipment and furnishings.

In occupations where the visual demands are small, the levels of illumination derived from a criterion of visual performance alone may be too low to satisfy the other requirements.  For such situations, therefore, illumination recommendations are based on standards of welfare, safety and amenity judged appropriate to the occupations; they are also sufficient to given these tasks brightness which ensured that the visual performance exceeds the specified minimum.  Unless there are special circumstances associated with the occupation, it is recommended that the illumination of tall working areas within a building should generally be 150 lux, even though the visual demands of the occupation might be satisfied by lower values. 

Where work takes place over the whole utilizable area of room, the illumination over that area should be reasonably uniform and it is recommended that the diversity ratio of minimum to maximum illumination should be not less than 0.7.

Note – This diversity ratio does not take into account the effects of any local lighting provided.

When the task brightness appropriate to an occupation has been determined, the brightness of the other parts of the room should be planned to give a proper emphasis to visual comfort and interest.

A general guide for the brightness relationship within the normal field of vision should be as follows:

a)  For high task brightness (above 100 cd/m2)

Maximum

1) Between the visual task and the adjacent sources like table tops

3 to 1

2) Between the visual task and the remote areas of the room.

10 to 1

For low and medium task brightness (below 100 cd/m2):   The task should be brighter than both the background and the surroundings; the lower the task brightness, the less critical is the relationship.

17.4.1.3. Recommended values of illumination – Table 1 gives recommended values of illumination commensurate with the general standards of lighting described in this section and related to many occupations and buildings.  These are valid under most of the conditions whether the illumination is by daylighting, artificial lighting or a combination of the two.  The great variety of visual tasks makes it impossible to list them all and those given should be regarded as representing types of task. 

The different locations and tasks are grouped within the following four sections:

  1. Industrial buildings and process;
  2. Offices, schools and public buildings;
  3. Surgeries and hospitals; and
  4. Hotels, restaurants, shops and homes.

The illumination levels recommended in Table 1 are those to be maintained at all time on the task.  They represent good practice and should be regarded as giving the order of illumination commonly required rather than as having some absolute significance.  They may be exceeded where standards of visual performance or amenity higher than those set in this section are called for, provided other requirements of this section, such as freedom from visual discomfort, are satisfied. 

Where a visual task is required to be carried out throughout an interior, general illumination to the recommended value on the working plane is necessary; where the precise height and location of the task are not known or cannot be easily specified, the recommended value is that on horizontal plane 85 cm above level.

Note – For an industrial task, working plane for the purpose of general illumination levels is that on a work place which generally 75 cm above the floor level is.  For certain purposes, such as viewing the objects of arts, the illumination levels recommended are for the vertical plane at which the art pieces are placed.

Where the task is localized, the recommended value is that for the task only; it need not, and sometimes should not, be the general level of illumination used throughout the interior.  Some processes, such as industrial inspection process, call for lighting of specialized design, in which case the level of illumination is only one of the several factors to be taken into account. 

17.4.1.4 Glare – Excessive contrast or abrupt and large changes in brightness produce the effect of glare.  When glare is present, the efficiency of vision is reduced and small details or subtle changes in tone cannot be perceived.  It may be:

  1. Direct glare due to light sources within the field of vision.
  2. Reflected glare due to reflections from light sources or surfaces of excessive brightness, and
  3. Veiling glare where the peripheral field is comparatively very bright.

An example of glare sources in daylighting is the view of the bright sky through a window or skylight, especially when the surrounding wall or ceiling is comparatively dark or weakly illuminated.  Glare can be minimized in this case either by shielding the open sky from direct sight by louvers, external hoods or deep reveals, curtains or other shading devices or by cross-lighting the surroundings to a comparable level.  A gradual transition of brightness from one portion to the other within the field of vision always avoids or minimizes the glare discomfort.

17.4.1.5 Lighting for movement about a building – Most buildings are complexes of working areas and other areas, such as passages, corridors, stairways, lobbies and entrances.  The lighting of all these areas should be properly correlated to give safe movement within the building at all times. 

17.4.1.5.1 Corridors, passages and stairways – Accidents may result if people leave a well-lighted working area and pass immediately into corridors or on to stairways where the lighting is inadequate, as the time needed for adaptation to the lower level may be too long to permit obstacles or the treads of stairs to be seen sufficiently quickly.  For the same reason, it is desirable that the illumination of rooms, which open off a working area, should be fairly high even though the rooms may be used only occasionally. 

It is important, when lighting stairways, to prevent disability from glare caused by direct sight of bright sources to emphasize the edges of the treads and to avoid confusing shadows.  The same precautions should be taken in the lighting of cat-walks and stairways on outdoor industrial plants. 

17.4.1.5.2. Entrances – The problems of correctly grading the lighting within a building to allow adequate time for adaptation when passing from one area to another area are particularly acute at building entrances.  These are given below:

  1. By day, people entering a building will be adapted to the very high levels of brightness usually present outdoors and there is risk of accident if entrance areas, particularly any steps, are poorly lighted.  This problem may often be overcome by arranging windows to given adequate natural lighting at the immediate entrance, grading to lower levels further inside the entrance area.  Where this cannot be done, supplementary artificial lighting should be installed to raise the illumination to an appropriate value. 
  2. At night it is desirable to light entrance halls and lobbies so that the illumination level reduces towards the exit and so that no bright fittings are in the line of sight of people leaving the building.  Any entrance steps to the building should be well-lighted by correctly screened fittings.

Table 1.   Recommended values of illumination

Sl.No.

Visual Tasks

Illumination Lux

A  Industrial Buildings and Process

1.

 

General Factory Areas:

a.Canteens

b.Cloak – Rooms

Entrances, Corridors, Stairs

 

150

100

100

2.

Factory Outdoor Areas:                                                                                                                   Stock yards, main entrances and exit roads, car parks, internal factory roads

 

20

3.

Aircraft Factories and Maintenance Hangars:

a.Stock parts productions

b. Drilling, riveting, screw fastening, sheet aluminium layout and template work, wing sections, cowling, welding, sub-assembly, final assembly and inspection 

Maintenance and repair (hangers)

 

450

300

300

4.

Assembly Shops:

a.Rough work, for example, frame assembly and assembly of heavy machinery

b.Medium work, for example, machined parts, engine assembly, vehicle body assembly

c.Fine work, for example, radio and telephone equipment, typewriter and office machinery assembly

Very fine work, for example, assembly of very small precision mechanisms

* Optical aids should be used where necessary

 

150

300

700

1500*

 

5

Boiler Houses (industrial):

a.Coal and ash handling

b.Boiler rooms:

1.Boiler fronts and operating areas

2.Other areas

c.Outdoor  plants:

1.Cat-walks

2.Platforms

† Supplementary local lighting may be required for gauge glasses and instrument panels

 

100

100†

20 to 50

20

50

 

6

Electricity Generating Stations (Indoor Locations):

a.Turbine halls

b)   Auxiliary equipment, battery rooms, blowers, auxiliary generators, switchgear and transformer chambers.

c)Boiler houses (including operating floors) platforms, coal conveyors, pulverizers, feeders, precipitators, soot and slag blowers

d)Boiler house and turbine house

e) Basements

f) conveyor houses, conveyor gantries and junction towers

g) Control rooms:

  1. Vertical control panels
  2. Control desks
  3. Rear of control panels
  4. Switch houses

h) Nuclear reactors and steam raising plants:

  1. Reactor areas, boilers and galleries
  2. Gas circular bays

    3)    Reactor charge/discharge face

 

200

100

 

70 to 100

 

100

70

70 to 100

 

200 to 300

300

150

150

 

150

150

200

7

Electricity Generating Stations (Outdoor Locations):

a) Coal unloading areas

b) Coal storage areas

c) Platforms, boiler and turbine desks

d) Transformers and outdoor switchgear

20

20

50

100

8

Gauges and Tool Rooms: General

† Supplementary local lighting and optical aids should be used where necessary

700†

9

Inspection Shops ( Engineering):

a) Rough work, for example, counting and rough checking of stock parts, etc

b) Medium work, for example, ‘go’ and ‘no go’ gauges and sub-assemblies

c) Fine work, for example, radio and telecommunication equipment, calibrated scales, precision mechanisms and instruments

d) Very fine work for example, gauging and inspection of small intricate parts

e) Minute work for example, very small instruments

* Optical aids should be used where necessary

 

150

300

700

1 500

3 000*

10

Iron and Steel Works:

  1. Marshalling and outdoor stockyards
  2. Stairs, gangways, basements, quarries and loading docks
  3. Slab yards, melting shops, ingot stripping, soaking pits, blast-furnace working areas, picking and cleaning and cleaning lines, mechanical plant and pump houses
  4. Mould preparation rolling and wire mills, mill motor rooms, power and blower houses
  5. Slab inspection and conditioning, cold strip mills, sheet and plate finishing, tinning, galvanizing machine and roll shops
  6. Plate inspection

Tinplate inspection

 

10 to 20

100

100

150

200

300

Special lighting

11

Machine and Fitting Shops:

  1. Rough bench and machine work
  2. Medium bench and machine work, ordinary automatic machines, rough grinding, medium buffing and polishing
  3. Fine bench and machine work, fine automatic machines, medium grinding, fine buffing and polishing

150

300

700

 

12

Motor Vehicle Plants:

  1. General sub-assemblies, chasis assembly and car assembly
  2. Final inspection
  3. Trim shops, body sub-assemblies and body assembly
  4. Spray booths

300

450

300

450

13

Paint Works:

  1. General, automatic processes
  2. Special batch mixing

Colour matching

200

450

700*

14.

Paint Shops and Spraying Booths:

a) dipping, firing and rough spraying

b) Rubbing, ordinary painting, spraying and finishing

c) Fine painting and finishing

d) Retouching and matching

*  Special attention should be paid to the colour quality of the light

150

300

450

700*

15

Sheet Metal Works:

  1. Bench work, scribing, pressing, punching, shearing, stamping, spinning and folding
  2. Sheet inspection

200

Special lighting

16

Structural Steel Fabrication Plants:

  1. General
  2. Marking off

150

300

17

Welding and Soldering:

  1. Gas and arc welding and rough spot welding
  2. Medium soldering, brazing and spot welding, for example, domestic hardware
  3. Fine soldering and spot welding, for example instruments, radio set assembly

d)    Very fine soldering and spot welding, for example, radio valves

150

300

700

150

18

Woodworking Shops:

  1. Rough sawing  and bench work
  2. Sizing, planing, rough sanding, medium machine and bench work, gluing, veneering and co-operage
  3. Fine bench and machine work, fine sanding and finishing

50

200

300

B.  Offices, Schools and Public Buildings

19

Airport Buildings:

  1. Reception areas (desks)
  2. Customs and immigration halls

c)    Circulation areas and lounges

300

300

150

20

Assembly and Concert:

  1. Foyers and auditorium
  2. Platforms
  3. Corridors
  4. Stairs

100 to 150

450

70

100

21

Banks:

  1. Counter, typing and accounting book areas
  2. Public areas

300

150

22

Cinemas:

  1. Foyers
  2. Auditoria
  3. Corridors
  4. Stairs

150

50

70

100

23

Libraries*

  1. Shelves (stacks)
  2. Reading rooms (newspapers and magazines)
  3. Reading tables
  4. Book repair and binding
  5. Cataloguing, sorting and stock rooms

      * For details reference may be made to good practice [VII-1(5)]

     † On vertical surfaces

70 to 150†

150 to 300

300 to 700

300 to 700

150 to 300

 

24

Museums art Galleries:

  1. Museums:
  1. General
  2. Displays

b)    Art Galleries

       1)    General

       2)    Paintings

‡For Galleries with separate picture lighting.  In small galleries without wall lighting the illumination should be increased to 200 lux

§ On vertical surface.  Special attention should be paid to the colour quality of the light

 

 

150

Special lighting

 

100‡

200§

25

Office:

  1. Entrance halls and reception areas
  2. Conference rooms and executive office
  3. General office
  4. Business machine operation
  5. Drawing office:
  1. General
  2. Boards and tracings
  1. Corridors and lift cars
  2. Stairs
  3. Lift landings
  4. Telephone exchanges:

1) Manual exchange rooms ( on desk )

2) Main distribution frame rooms

 

150

300

300

450

 

300

450

70

100

150

 

200*

150

26

School and Colleges:

  1. Assembly halls:
  1. General
  2. When used for examinations
  3. Platforms
  1. Class and lecture rooms:
  1. Desks
  2. Chalk boards
  1. Embroidery sewing rooms
  2. Art rooms
  3. Laboratories
  4. Libraries:
  1. Shelves, stacks
  2. Reading tables
  1. Manual training
  2. Offices

j)     Staff rooms and common rooms

  1. Corridors
  1. Stairs 

 * Special lighting will be required for switchboard

 † On vertical surfaces.     ‡ Special attention should be paid tot he direction and the colour quality of the light.

 

150

300

300

 

300

200 to 300†

700

450‡

300

 

70 to 150†

300

 

See appropriate trades

300

150

70

100

27

Theatres:

  1. Foyers
  2. Auditoria
  3. Corridors
  4. Stairs

 

150

70

70

100

28

Dental  Surgeries:

  1. Waiting rooms
  2. Surgeries:
  1. General
  2. Chairs

Laboratories

 

150

 

300

Special lighting

300

29

Doctors Surgeries:

  1. Waiting rooms and consulting rooms
  2. Corridors
  3. Stairs

d)    Sight testing (acuity) wall charts and near vision types

* The chart should be so illuminated that their brightness is substantially uniform over their whole area

 

150

70

100

450*

30.

Hospitals:

  1. Reception and waiting rooms
  2. Wards:
  1. General
  2. Beds
  1. Operating theatres:
  1. General
  2. Tables
  1. Laboratories
  2. Radiology departments
  3. Casualty and outpatient departments

g)     Stairs and corridors

h)     Corridors

 

150

 

100

150

 

300

Special lighting

300

100

150

100

300

31

Hotels:

  1. Entrance halls
  2. Reception and accounts
  3. Dining rooms (tables)
  4. Lounges
  5. Bedrooms:
  1. General
  2. Dressing tables, bed heads, etc
  1. Writing rooms (tables)
  2. Corridors
  3. Stairs
  4. Laundries
  5. Kitchens
  6. Goods and passenger lifts
  7. Clock-rooms and toilets
  8. Bathrooms

* Supplementary local lighting should be provided over kitchen equipment and at mirrors.

 

150

300

100

150

 

100

200

300

70

100

200

200*

70

100*

100*

 

32

Restaurants:

  1. Dining rooms:
  1. Tables
  2. Cash desks
  1. Self-carrying counters
  2. Kitchens

d)    Clock-rooms and toilets

* Supplementary local lighting should be provided over kitchen equipment and at mirrors.

 

 

100

300

300

200*

100*

 

33

Shops and Stores:

  1. General areas
  2. Stock rooms

† Supplementary local lighting should be used as required for counter and display areas.

 

150 to 300†

200

 

34

Homes:

  1. Kitchens
  2. Bathrooms
  3. Stairs
  4. Workshops
  5. Garages
  6. Sewing and darning
  7. Reading (casual)
  8. Homework and sustained reading

‡ Supplementary local lighting should be provided at mirrors

 

200

100‡

100

200

70

700

150

300

 17.3.1.6 For detailed information regarding principles of good lighting, reference may be made to the National Building Code 2005.

17.4.2   Day lighting – The primary source of lighting for daylighting is the sun.  The light received by the earth from the sun consists of two parts, namely, direct solar illumination and sky radiation.  For the purposes of delighting design, direct solar illumination shall not be considered and only sky radiation shall be taken as contributing to illumination of the building interiors during the day. 

17.4.2.1. The relative amount of sky radiation depends on the position of the sun defined by its altitude, which in turn, varies with the latitude of the locality, the day of the year and the time of the day.. 

17.4.2.2. The external available horizontal illumination which may be assumed for design purposes in this country, broadly covering India from north to south, may be taken 8 000 lux. 

Since the design is based on the solar position of 15° altitude, the corresponding illumination from the design sky has been found to be nearly constant all over the country.  However, the prevalent atmospheric haze which varies from place to place may necessitate a 25 percent increase in the value of 8 000 lux design illumination suggested in this section, where haze conditions prevail at design time. 

17.4.2.3. The daylight factor is dependent on the sky luminance distribution, which varies with atmospheric conditions.  A clear design sky with its non-uniform distribution of luminance is adopted for the purposes of design in this section.

17.4.2.4. Components of daylight factor – Daylight factor is the sum of all the daylight reaching on an indoor reference point from the following sources:

  1. The direct sky visible from the point,
  2. External surfaces reflecting light directly* to the point, and
  3. Internal surfaces reflecting and inter-reflecting light to the point.

Note – Each of the three components, when expressed as a ratio or percent of the simultaneous external illumination on the horizontal plane, defines respectively the Sky Component (SC), External Reflected Component (ERC) and the Internal Reflected Component (IRC) of the daylight factor.

* External surface reflection may be computed approximately only for points at the centre of the room and for detailed analysis procedures are complicated and these may be ignored for actual calculations.

 17.4.2.4.1. The daylight factors on the horizontal plane only are usually taken, as the working plane in a room is generally horizontal; however, the factors in vertical planes should also be considered when specifying daylighting values for special cases, such as daylighting on class-rooms, blackboards, pictures and paintings hung on walls. 

17.4.2.5. Sky component (SC) – Sky component for a window of any size is computed by the use of the appropriate table of the National Building Code 2005.

a) The recommended sky component level should be ensured generally on the working plane at the following positions:

  1. at a distance of 3 to 3.75 m from the window along the central line perpendicular to the window,
  2. at the centre of the room if more appropriate, and
  3. at fixed locations, such as school desks, black-boards and office tables.

b) The daylight area of the prescribed sky component should not normally be less than half the total area of the room.

The values obtainable from the tables are for rectangular, open unglazed windows, with no external obstructions.  The values shall be corrected for the presence of window bars, glazing and external obstructions, if any.  This assumes the maintenance of a regular cleaning schedule.

The corrections for window bars shall be made by multiplying the values read from tables given in the National Building Code 2005 by a factor equal to the ratio of the clear opening to the overall opening.

(1). Correction for glazing – Where windows are glazed, the sky components obtained from shall be reduced by 10 to 20 percent, provided the panes are of clear glass, tolerably clean.  Where glass is of the frosted (ground) type, the sky components read may be reduced by 15 to 30 percent.  Higher indicated correction corresponds to larger windows and/or near reference points.  In the case of openings and glazings which are not vertical, suitable correction shall be taken into account.

(2). Correction for external obstructions – There is no separate correction, except that the values shall be read only for the unobstructed portions of the window.

17.4.2.6 External reflected component (ERC) – The value of the sky component corresponding to    t he portion of the window obstructed by the external obstructions can be found by the use of methods described in accepted standards.

These values when multiplied by the correction factors, corresponding tot he mean elevation of obstruction from the point in question as given in Table given below can be taken as the external reflected components for that point.

Correction factor for ERC

Mean angle of elevation

Correction factor

5°

15°

25°

35°

45°

55°

65°

75°

85°

0.086

0.086

0.142

0.192

0.226

0.274

0.304

0.324

0.334

For method of calculating ERC, reference may be made to accepted standard / National Building Code 2005.

17.4.2.7 Internal reflected component (IRC) – The component of daylight factor contributed by reflection from the inside surfaces varies directly as the window area and inversely as the total area of internal surfaces, and depends on the reflection factor of the floor, wall and roof surfaces inside and of the ground outside.  For rooms white washed on walls and ceiling and windows of normal sizes, the IRC will have sizeable value even at points far away from the window.  External obstructions, when present, will proportionately reduce IRC.  Where accurate values of IRC are desired, reference to a precise method of evaluation given in the accepted standard may be made.

17.4.2.8 General principles of openings to afford good lighting

(1). Generally, while taller openings given greater penetrations, broader openings give better distribution of light.  It is preferable that some area of the sky at an altitude of 20 to 25 degrees should light up the working plane.

(2). Broader openings may also be equally or more efficient, provided their sills are raised by 30 to 60 cm above the working plane.

Note – It is to be noted that while placing window with a high sill level might help natural lighting, this is likely to reduce ventilation at work levels.  While designing the opening for ventilation also, a compromise may be made by providing the sill level about 15 cm below the head level of workers.

(3). For a given penetration, a number of small openings properly positioned along the same, adjacent or opposite walls will give better distribution of illumination than a single large opening.  The sky component at any point, due to a number of openings may be easily determined from the corresponding sky component contour charts appropriately superposed.  The sum of the individual sky component for each opening at the point given the overall component due to all the openings.  The same charts may also facilitate easy drawing of sky component contours due to multiple openings. 

(4). Unilateral lighting from side openings will, in general, be unsatisfactory if the effective width of the room is more than 2 to 2.5 times the distance from the floor to the top of the opening.

(5). Openings on two opposite sides will give greater uniformity of internal daylight illumination, especially when the room is 7 m or more across.  They also minimize glare by illuminating the wall surrounding each of the opposing openings.  Side openings on the side and clerestory openings on the opposite side may be provided where the situation so requires.

(6). Cross-lighting with openings on adjacent walls tends to increase the diffused lighting within a room.

(7). Openings in deep reveals tend to minimize glare effects.

(8). Openings shall be provided with chajjas, louvers, baffles or other shading devices to exclude, as far as possible, direct sunlight entering the room.  Chajjas, louvers, etc, reduce the effective height of the opening for which due allowance shall be made.  Broad and low openings are, in general, much easier to shade against sunlight entry.  Direct sunlight, when it enters, increases the inside illumination very considerably.  Glare will result if it falls on walls at low angles, more so than when it falls on floors, especially when the floors are dark coloured or less reflective. 

(9). Light control media, such as translucent glass panes (opal or matt) surfaced by grinding, etching or sandblasting, configured or corrugated glass, certain types of prismatic glass and glass blasts are often used.  They should be provided, either fixed or movable outside or inside, especially in the upper portions of the openings.  The lower portions are usually left clear to afford desirable view.  The chief purpose of such fixtures is to reflect part of the light on to the roof and thereby increase the diffuse lighting within, light up the farther areas in the room and thereby produce a more uniform illumination throughout.  They will also prevent the opening causing serious glare discomfort to the occupants but will provide some glare when illuminated by direct sunlight.

17.4.2.9 Availability of daylight in multistory block – Proper planning and layout of building can add appreciably to daylighting illumination inside.  Certain dispositions of building masses offer much less mutual obstruction to daylight than others and have a significant relevance, especially when intensive site planning is undertaken.  The relative availability of daylight in multistory blocks of different relative orientations is given in Table 2. For specified requirements for daylighting of special occupancies and areas, reference may be made to code of practice.

17.4.3. Artificial lighting

17.4.3.1 Artificial lighting may have to be provided.

  1. Where the recommended illumination levels have to be obtained by artificial lighting only.
  2. To supplement daylighting when the level of illumination falls below the recommended value, and
  3. Where visual task may demand a higher level of illumination.

17.4.3.2 Artificial lighting design for interiors – For general lighting purposes, the recommended practice is to design for a level of illumination on the working plane on the basis of the recommended levels for visual tasks given in Table 1 by a method called “Lumen Method”.  In order to make the necessary detailed calculations concerning the type and quantity of lighting equipment necessary, advance information on the surface reflectance of walls, ceilings and floors is required.  Similarly, calculations concerning the brightness ratio in the interior call for details of the interior décor and furnishing.  Stepwise guidance regarding designing the interior lighting systems for a building using the “Lumen method” is given in 17.4.3.2.1 to 17.4.3.2.4.

17.4.3.2.1. Determination of the illumination level – Recommended value of illumination shall be taken from Table 3.  Depending upon the type of work to be carried out in the location in question and the visual tasks involved.

17.4.3.2.2 Selection of the light sources and luminaires – The selection of light sources and luminaires depends on the choice of lighting system, namely, general lighting, directional lighting and localized or local lighting.

17.4.3.2.3 Determination of the luminous flux

  1. the luminous flux (f) reaching the working plane depends upon the following:
  1. lumen output of the lamps,
  2. type of luminaire,
  3. proportion of the room (room index) (kr)
  4. reflectance of internal surfaces of the room,
  5. depreciation in the lumen output of the lamps after burning their rated life, and
  6. Depreciation due to dirt collection on luminaire and room surface. 

Table 2 Relative availability of daylight on the window plane at ground level in four-storeyed building blocks (clear design-sky as basis, daylight availability taken as unity on an unobstructed facade, values are for the centre of the blocks)

 

Distance of separation between Blocks

 

Infinitely long parallel blocks

 

Parallel blocks facing each other

( length = 2 x height)

 

Parallel blocks facing gaps between opposite blocks

(length = 2 x height)

0.5 Ht

  1. Ht

1.5 Ht

  1. Ht

0.15

0.30

0.40

0.50

0.15

0.32

0.50

0.60

0.25

0.38

0.55

0.68

Coefficient of utilization or utilization factor

The compilation of tables for the utilization factor requires a considerable amount of calculations, especially if these tables have to cover a wide range of lighting practices.  For every luminaire, the exact light distribution has to be measured in the laboratory and their efficiencies have to be calculated and measured exactly.  These measurements comprise:

The luminous flux radiated by the luminaires directly to the measuring surface,

The luminous flux reflected and re-reflected by the ceiling and the walls to the measuring surface, and

The inter-reflections between the ceiling and wall which result in the measuring surface receiving additional luminous flux.

All these measurements have to be made for different reflection factors of the ceiling and the walls for all necessary room indices.  These tables have also to indicate the maintenance factor to be taken for the luminous flux depreciation throughout the life of an installation due to ageing of the lamp and owing to the deposition of dirt on the lamps and luminaires and room surfaces.

2. The values of the reflection factor of the ceiling and of the wall are as follows:

White and very light colours - 0.7

Light colours - 0.5

Middle tints - 0.3

Dark colours - 0.1

For the walls, taking into account the influence of the windows without curtains, shelves, almirahs and doors with different colours, etc, should be estimated. 

Calculation for determining the Luminous Flux

              mf

Eav = ----------

             A

Eav A

or.                        

f  = ----------      for new condition

m

                 Eav A

And  f  = -----------     for working condition

                      m

Where

f =  The total luminous flux of the light sources installed in the room in lumens;

Eav = The average illumination level required on the working plane in lux;

of the working plane in m2 ;

all =  the utilization factor in new conditions; and

d = maintenance factor.

In practice, it is easier to calculate straightaway the number of lamps or luminaires from:

                Eav A

Nlamp = ---------------

               m d flamp

or

                     Eav A

Nluminous = ---------------

                      m d fluminous  

Where

famps =  luminous flux of each lamp in lumens

fluminaire =  luminous flux of each luminaire in lumens

Nlamp = total number of lamps

Nluminaire = total number of luminaires.

17.4.3.2.4 Arrangement of the luminaires – This is done to achieve better uniformly distributed illumination.  The location of the luminaires has an important effect on the utilization factor.

  1. In general, luminaires are spaced ’a’ metre apart in either direction, while the distance of the end luminaire from the wall is ‘1/2 a’ metre.  The distance ‘a’ is more or less equal to the mounting height ‘Hm’ between the luminaire and the working plane.  The utilization factor tables are calculated for this arrangement of luminaires. 
  2. For small rooms where the room index (kr) is less then 1, the distance ‘a’ should always be less than Hm, since otherwise luminaires cannot be properly located.  In most cases of such rooms, four or two luminaires are placed for good general lighting.  If, however, in such rooms only one luminaire is installed in the middle, higher utilization factors are obtained, but the uniformity of distribution is poor.  For such cases, references should be made to the additional tables for kr = 0.6 to 1.25 for luminaires located centrally.

17.4.3.3. Integration of lighting and air conditioning system –  It is desirable to design air-conditioning and lighting system integrally.  The fundamental idea in this integration is that the return air after air conditioning the space is passed through luminaires or other lighting fittings so that it is brought into close contact with the means of illumination.  Hence, a large part of the heat generated by the lighting is removed at source and only a small portion of the warmth is dissipated within the premises.  Detailed design of integration of lighting and air-conditioning system shall be done in accordance with good practice. 

17.4.3.4 Artificial lighting to supplement daylighting

The need for general supplementary artificial lighting arises due to diminution of daylighting beyond design hours, that is, for solar altitude below 15° or when dark cloudy conditions occur. 

The need may also arise for providing artificial lighting during the day in the innermost parts of the building which cannot be adequately provided with daylighting, or when the outside windows are not of adequate size or when there are unavoidable external obstructions to the incoming daylighting.

The need for supplementary lighting during the day arises, particularly when the daylighting on the working plane falls below 100 lux and the surrounding luminance drops below 19 cd/m2 and the working plane illumination level to a range of 100 to 150 lux.

The requirement of supplementary artificial lighting increases with the increase in daylighting availability.  Therefore, conditions near sunset or sunrise or equivalent conditions due to clouds or obstructions, etc, represent the worst conditions when the supplementary lighting is most needed. 

The requirement of supplementary artificial lighting when daylighting availability becomes poor can be determined from Fig.2 for an assumed ceiling height of 3.0 m, depending upon floor area, fenestration percentage and room surface reflectance.  Cool daylight fluorescent tubes are recommended with semi-direct luminaires.  To ensure a good distribution of illumination, the mounting height should be between 1.5 and 2.0 m above the work plane for a separation of 2.0 to 3.0 m between the luminaires.  Also the number of lamps should preferably be more in the rear half of the room than in the vicinity of windows.  The following steps may be followed for using Fig.2 for determining the number of fluorescent tubes required for supplementary day lighting.

Determine fenestration percentage of the floor area, that is,

Window Area

-------------------------   x 100

Floor Area

In Fig.2, refer to the curve corresponding to the percent fenestration determined above and the set of reflectance of ceiling, walls and floor actually provided.

For the referred curve of Fig.2 read, along the ordinate, the number of 40 W fluorescent tubes required, corresponding to the given floor area on the abscissa.

For detailed information on the design aspects and principles of artificial lighting, reference may be made to good practice.

For specific requirements for lighting of special occupancies and areas, reference may be made to code of practice..

Electrical installation aspect for artificial lighting shall be in accordance with Section-16-Electrical Installations.

17.5 Ventilation 

17.5.1 General – Ventilation of buildings is required to supply fresh air for respiration of occupants, to dilute inside air to prevent vitiation by body odours and to remove any products of combustion or other contaminants in air and to provide such thermal environments as will assist in the maintenance of heat balance of the body in order to prevent discomfort and injury to health of the occupants.

17.5.2. Design considerations

17.5.2.1 Respiration – Supply of fresh air to provide oxygen for the human body for elimination of waste products and to maintain carbon dioxide concentration in the air within safe limits rarely calls for special attention as enough outside air for this purpose normally enters the areas of occupancy through crevices and other openings.

Even in the worst ventilated rooms, the content of carbon dioxide in air rarely exceeds 0.5 to 1 percent and is, therefore, incapable of producing any ill effect.  The amount of air required to keep the concentration down to 1 percent is very small.  The change in oxygen content is also too small under normal conditions to have any ill effects; the oxygen content may vary quite appreciably without noticeable effect, if the carbon dioxide concentration is unchanged.

17.5.2.2 Vitiation by body odours – Where no products of combustion or other contaminants are to be removed from air, the amount of fresh air required for dilution of inside air to prevent vitiation of air by body odours, depends on the air space available per person and the degree of physical activity; the amount of air decreases as the air space available per person, and it may vary from 20 to 30 m3 per person per hour.  In rooms occupied by only a small number of persons such an air change will automatically be attained in cool weather by normal leakage around windows and other openings and this may easily be secured in warm weather by keeping the openings open.   No standards have been laid down under the factories act 1948 asregards the amount of fresh air required per worker or the number of air changes per hour.  Section relating to the over-crowding requires that at least 14 to 16 m3 of space shall be provided for every worker and for the purpose of that section no account shall be taken of any space in a workroom, which is more than 4.25 m above the floor level.

Note – Vitiation of the atmosphere can also occur in factories by odours given off due to contaminants of the products itself, say for example, from tobacco processing in a ‘Bidi’ factory.  Here the ventilation will have to be augmented to keep odours within unobjectionable levels. 

17.5.2.2.1 Recommended values for air changes-The following standards of general ventilation are recommended based on maintenance of required oxygen, carbon dioxide and other air quality levels and for the control of body odours when no products of combustion or other contaminants are present in the air:

Air Changes schedule

Space to be ventilated

Air changes per hour

* Assembly Halls/Auditoria        

3 – 6

* Bed Rooms/Living Rooms

3 – 6

Bath Rooms/Toilets      

6 – 12

* Cafes/Restaurants

12 – 15

Cinemas/Theatres ( Non-smoking)

6 – 9

Class Rooms   

3 – 6

* Factories (Medium metal work)

3 – 6

* Garages

12 – 15

* Hospital Wards

3 – 6

* Kitchens ( Common)   

6 – 9

* Kitchens (Domestic)   

3 – 6

Laboratories

3 – 6

* Offices

3 – 6

  *Smoking  

17.5.2.3. Heat balance of body – Specially in hot weather, when thermal environment inside the room is worsened by heat given off by machinery, occupants and other sources, the prime need for ventilation is to provide such thermal environment as will assist in the maintenance of heat balance of the body in order to prevent discomfort and injury to health.  Excess of heat either from increased metabolism due to physical activity of persons or gains from a hot environment has to be offset to maintain normal body temperature (37°C)  heat exchange of the human body with respect to the surroundings is determined by the temperature and humidity gradient between the skin and the surroundings and other factors such as age of personnel, clothing etc, and the latter depends on air temperature (dry bulb temperature), relative humidity, radiation from the solid surroundings and rate of air movement.  The volume of outside air to be circulated through the room is, therefore, governed by the physical considerations of controlling the temperature, air distribution or air movement.  Air movement and air distribution may, however, be achieved by recalculation of the inside air rather than bringing in all outside air.  However, fresh air supply or the circulated air will reduce heat stress by dissipating heat from body by evaporation of the sweat, particularly when the relative humidity is high and the air temperature is near body temperature. 

17.5.2.3.1 Limits of comfort and heat tolerance – Thermal comfort are that condition of thermal environment under which a person can maintain a bodily heat balance at normal body temperature and without perceptible sweating.  Limits of comfort vary considerably according to studies carried out in India and abroad.  In terms of effective temperature, the upper limit of comfort may be 27.5°C for every day work in industry.  This is also the temperature for most efficient production.  Air movement is necessary in hot and humid weather for body cooling.  A certain minimum desirable wind speed is needed for achieving thermal comfort at different temperatures and relative humidities.  Such wind speeds are given in Table 3.  These are applicable to sedentary work in offices and other places having no noticeable sources of heat gain.  Where somewhat warmer conditions are prevalent., such as in godowns and machine shops and work is of lighter intensity, and higher temperatures can be tolerated without much discomfort, minimum wind speeds for just acceptable warm conditions are given in Table 4.  For obtaining values of indoor wind speed above 2.0 m/s, mechanical means of ventilation may have to be adopted.

17.5.2.3.2.  There will be a limit of heat tolerance when air temperatures are excessive and the degree of physical activity is high. This limit is determined when the bodily heat balance is upset, that is, when the bodily heat gain due to conduction, convection and the radiation from the surroundings exceeds the bodily heat loss, which is mostly by evaporation of sweat from the surface of the body.  The limits of heat tolerance for Indian workers are based on the study conducted by the Chief Advisor Factories, Government of India, Ministry of Labour and are given in his report on Thermal Stress in Textile Industry (Report No.17) issued in 1956.  According to this Report, where workers in industrial buildings wearing light clothing are expected to do work of moderate severity with the energy expenditure in the range 235 to 330 kcal/h, the maximum wet bulb temperature shall not exceed 29°C and adequate air movement subject to a minimum air velocity of 30 m/min shall be provided, and in relation to the dry bulb temperature, the wet bulb temperature of air in the work room, as far as practicable, shall not exceed that given in Table 5.

17.5.3 Methods of ventilation – General ventilation involve providing a building with relatively large quantities of outside air in order to improve general environment of the building.  This may be achieved in one of the following ways:

  1. natural supply and natural exhaust of air;
  2. natural supply and mechanical exhaust of air;
  3. mechanical supply and natural exhaust of air; and
  4. Mechanical supply and mechanical exhaust of air.

17.5.3.1 Control of heat – Although it is recognized that general ventilation is one of the most effective methods of improving thermal environmental conditions in factories, in many situations, the application of ventilation should be preceded  by and considered along with some of the following other methods of control.  This would facilitate better design of buildings for general ventilation, either natural or mechanical or both, and also reduce their cost. 

17.5.3.1.1 Isolation – Sometimes, it is possible to locate heat producing equipment, such as furnaces in such a position as would expose only a small number of workers to hot environment.  As far as practicable, such sources of heat in factories should be isolated. 

In situations where relatively few people are exposed to severe heat stress and their activities are confined to limited areas as in the case of rolling mill operators and crane operators, it may be possible to enclose the work areas and supply conditioned air to such enclosures.

17.5.3.1.2 Insulation – A considerable portion of heat in many factories is due to the solar radiation falling on the roof surfaces, which, in turn, radiate heat inside the building.  In such situations, insulation of the roof or providing a false ceiling or double roofing would be very effective in controlling heat.  Some reduction can also be achieved by painting the roof in heat reflective shades.

Hot surfaces of equipment, such as pipes, vessels, etc, in the building should also be insulated to reduce their surface temperature.

17.5.3.1.3 Substitution – Sometimes, it is possible to substitute a hot process by a method that involves application of localized or more efficiently controlled method of heating.  Examples include induction hardening instead of conventional heat treatment, cold riveting or spot welding instead of hot riveting, etc.

17.5.3.1.4. Radiant shielding – Hot surfaces, such as layers of molten metal emanate radiant heat, which can best be controlled by placing a shield having a highly reflecting surface between the source of heat and the worker, so that a major portion of the heat falling on the shield is reflected back to the source.  Surfaces such as of tin and aluminium have been used as materials for shields.  The efficiency of the shield does not depend on its thickness, but on the reflectivity and emissivity of its surface.  Care should be taken to see that the shield is not heated up by conduction and for this purpose adequate provision should be made for the free flow upwards of the heated air between the hot surface and the shield by leaving the necessary air space and providing opening at the top and the bottom of the sides.

Table 3 Desirable wind speeds (m/s) for thermal comfort conditions

(clause 17.5.2.3.1)

Dry bulb    tempera-ture,      0° c

Relative humidity ( percentage)

30

40

50

60

70

80

90

28

29

30

31

32

33

34

35

*

*

*

*

0.20

0.77

1.85

3.20

*

*

*

0.06

0.46

1.36

2.72

*

*

*

0.24

0.94

2.12

*

*

0.06

0.53

1.59

3.00

*

*

0.24

1.04

2.26

*

0.06

0.53

1.47

3.04

*

0.19

0.85

2.10

*   None.

†  Higher than those acceptable in practice.

 

Table  4  Minimum wind speeds  (m/s)  for just acceptable warm conditions

( Clause 17.5.2.3.1 )

Dry bulb tempera-ture, 0° C

Relative humidity ( percentage)

30

40

50

60

70

80

90

28

29

30

31

32

33

34

35

36

*

*

*

*

*

*

0.15

0.68

1.72

*

*

*

*

*

0.04

0.46

1.36

2.70

*

*

*

*

*

0.24

0.94

2.10

*

*

*

*

0.09

0.60

1.60

3.05

*

*

*

*

0.29

1.04

2.26

*

*

*

0.06

0.60

1.85

3.05

*

*

*

0.23

0.94

2.10

* None,

†  Higher than those acceptable in practice.


Table  5  Maximum permissible wet bulb temperatures for given dry bulb temperatures

( Clause 17.5.2.3.2 )

Dry bulb temperature ºc

Maximum wet – bulb temperature ºc

30

35

40

45

50

29.0

28.5

28.0

27.5

27.0

Note 1 – These are limits beyond which the industry should not allow the thermal conditions to go for more than 1h continuously.  The limits are based on a series of studies conducted on Indian subjects in psychometric chamber and on other data on heat casualties in earlier studies conducted in Kolar Gold Fields and elsewhere.

Note 2 – Figures given in this table are not intended to convey that human efficiency at 50ºC will remain the same as at 30ºC, provided appropriate wet bulb temperatures are maintained.  Efficiency decreases with rise in the dry bulb temperature for a given wet bulb temperature attained and efforts should be made to bring down the dry bulb temperature as well, as much as possible.  Long exposures to temperature of 50ºC dry bulb / 27 º C wet bulbs may prove dangerous.

Note 3 – Refrigeration or some other method of cooling is recommended in all cases where conditions would be worse than those shown in this table.

17.5.3.2. Volume of air required The volume of air required shall be calculated by using both the sensible heat and latent heat gain as the basis.  The larger of the two figures obtained should be used in actual practice.

17.4.3.2.1 Volume of air required for removing sensible heat – When the amount of sensible heat given off by different sources, namely, the sun, the manufacturing processes, machinery, occupants and other sources, is known and a suitable value for the allowable temperature rise is assumed, the volume of outside air to be provided for removing the sensible heat may be calculated from:

           2.9768 Ks

Q1 = -------------------

              t

 Where,

Q1 = Quantity of air in m3/h,

Ks = sensible heat gained in W and

t = allowable temperature rise in ºC

17.5.3.2.2. Temperature rise refers mainly to the difference between the air temperatures at the outlet (roof exit) and at the inlet openings for outside air.  As very little data exist on allowable temperature, rise values for supply of outside air in summer months, the values given in Table 6 related to industrial buildings may be used for general guidance.

Table 6 Allowable temperature rise values

Height of outlet opening m

Temperature rise ºC

6

9

12

3 to  4.5

    1. to  6.5

6.5  to  11

Note 1 - The conditions are limited to light or medium heavy manufacturing processes, freedom from radiant heat and inlet openings not more than 3 to 4.5 m above floor level.

Note 2 - At the working zone between floor level and 1.5 m above floor level, the recommended maximum allowable temperature rise for air is 2 to 3ºC above the air temperature at the inlet openings.

17.5.3.2.3 Volume of air required for removing latent heat – If the latent heat gained from the manufacturing processes and occupants is also known and a suitable value for the allowable rise in the vapour pressure is assumed:

          4127.26 x K1

Q2= ------------------

               h

Where,

Q2 = quantity of air in m3/h

K1 = latent heat gained in W, and

h = allowable vapour pressure difference in mm of mercury.

Note - In majority of the cases, the sensible heat gain will far exceed the latent heat gain, so that the amount of outside air to be drawn by ventilating equipment can be calculated in most cases on the basis of the equation given in 17.5.3.2.1.

17.5.3.2.4 Ventilation is also expressed as m3/h per m2 of floor area.  This relationship fails to evaluate the actual heat relief provided by a ventilation system, but it does give a relationship that is independent of building height.  This is amore rational approach, because, with the same internal load, the same amount of ventilation air, properly applied to the work zone with adequate velocity, will provide the desired heat relief quite independently of the ceiling height of the space, with few exceptions.  Ventilation rates of 30 to 60 m3/h per m2 have been found to give good results in many plants.

17.5.4 Natural ventilation – The rate of ventilation by natural means through windows or other openings depends on: 

a) direction and velocity of wind outside and sizes and disposition of openings (wind action), and

b) convection effects arising from temperature of vapour pressure difference (or both) between inside and outside the room and the difference of height between the outlet and inlet openings (stack effect).

17.5.4.1 Ventilation of non-industrial buildings – Ventilation in non-industrial buildings due to stack effect, unless there is a significant internal load, could be neglected, except in cold regions, and wind action may be assumed to be predominant.

In hot arid regions, the main problem in summer is to provide during day protection from sun’s heat so as to keep the indoor temperature lower than those outside under the sun and for this purpose windows and other openings are generally kept closed and only minimum ventilation is provided for the control of odours or for removal of prod9ucts of combustion.

In hot humid and warm humid regions, the problem in the design of non-industrial buildings is to provide free passage of air to keep the indoor temperature’s as near to those outside in the shade as possible, and for this purpose the buildings are oriented to face the direction of prevailing winds and windows and other openings are kept open on both windward and leeward sides.

Adequate number of circulating fans should be installed to serve all interior working areas during summer months in the hot arid and hot/warm humid regions to provide necessary air movement at times when ventilation due to wind action alone does not afford sufficient relief.

In winter months in cold regions, the windows and other openings are generally kept shut, particularly during night; and ventilation necessary for the control of odours and for the removal of products of combustion can be achieved either by stack action or by some infiltration of outside air due to wind action. 

17.5.4.2 Ventilation of industrial buildings – In providing natural ventilation of all industrial buildings having significant internal heat loads due to manufacturing process, proper consideration should be given to the size and distribution of windows and other inlet openings in relation to outlet openings so as to give, with due regard to orientation, prevailing winds, size and configuration of the building and manufacturing processes carried on, maximum possible control of thermal environment.

In the case of industrial buildings wider than 30 m, the ventilation through windows may be augmented by roof ventilation.

17.5.4.3 General rules for natural ventilation

17.5.4.3.1 By wind action

a. Inlet openings in the building should be well distributed and should be located on the windward side at a low level and outlet openings should be located on the leeward side near the top, so that incoming air streams is passed over the occupants.  Inlet and outlet openings at high levels may only clear the top air without producing air movement at the level of occupancy.  When outlets serve also as inlets, they shall be located at the same level. 

Maximum air movement at a particular plane is achieved by keeping the sill height of the opening at 85 percent of the height of the plane.  The following levels of occupancy are recommended:

1. For sitting on chair  =  0.75 m

2. For sitting on bed  =  0.60 m

3. For sitting on floor = 0.40 m.

b) Inlet opening should not, as far as possible, be obstructed by adjoining buildings, trees, signboards or other obstructions or by partitions inside the path of air flow.

c) Greatest flow per unit area of openings is obtained by using inlet and outlet openings of nearly equal areas. For a total area of openings (inlet and outlet) of 20 to 30 percent of floor area, the average indoor wind velocity is around 30 percent of outdoor velocity. Further increase in window size increases the available velocity but not in the same proportion.  In fact, even under most favorable conditions the maximum average indoor wind velocity does not exceed 40 percent of the outdoor velocity.

d) Where the stream of wind is quite constant and dependable, the openings may be readily arranged to take full advantage of the wind.  Where the wind direction is quite variable, the openings shall be so arranged that as far as possible there are approximately equal areas on all sides and the openings shall be located at the same levels.  Thus, no matter what the wind direction is, there are always some openings directly exposed to wind pressure and others to air suction and effective movement through building is assured. 

Note – For data on outdoor wind speeds at a place, reference may be made to Climatological and Solar Data for Design of Buildings for Comfort in India, published by the Central Building Research Institute, Roorkee.

17.5.4.3.2. By stack effect – Natural ventilation by stack effect occurs when air inside a building is at a different temperature than air outside.  Thus in heated buildings or in buildings wherein hot processes are carried on and in ordinary buildings during summer nights and during pre-monsoon periods, the inside temperature is higher than that of outside, cool outside air will tend to enter through openings at low level and warm air will tend to leave through openings at high level.  It would, therefore, be advantageous to provide ventilators as close to ceilings as possible.  Ventilators can also be provided in roofs as, for example, cowl, ventpipe, covered roof and ridge vent.

17.5.5 Mechanical ventilation

17.5.5.1 General – Where adequate air changes specified in 17.5.2.2.1 or for providing thermal environment within the limits specified in Table 7 whichever is higher, cannot be obtained by natural ventilation, mechanical ventilation either by exhaust of air or by positive ventilation or a combination of the two shall be provided; and in case of positive ventilation where necessary, air before being brought into the area of occupancy may be cooled by evaporative cooling or by air-conditioning (Section 18 Air-conditioning and heating).

Fans and other equipment for mechanical ventilation may be located in convenient positions having regard to the intake of fresh air, accessibility for maintenance and noise control

17.5.5.2 Exhaust of air – Exhaust fans are provided in walls on one side of the building or in the attic and roof to draw large volumes of air through the building.  These fans are usually of propeller type, since they operate against little or no resistance.  It is important that windows and other openings near the fans are kept closed, as otherwise the fans would draw outside air from these openings and cause what is termed as ‘short-circuiting’.  Adequate inlet openings shall be provided on opposite side of the building so as to limit inlet velocities.

When fans are centrally located on an attic or other unused space and arranged to draw proportionately from several areas of occupation or from exhaust appliances with ductwork, these are predominantly centrifugal type so as to overcome the resistance from duct work.

17.5.5.3 Positive ventilation – Positive ventilation is provided by centrally located supply fans which are usually of the centrifugal type or sometimes axial flow types, since this application requires ductwork with a wide range of satisfactory and quiet operation against high pressures.  Considerable advantage may be achieved by incorporating the ducts and risers with air discharge outlets into the building structure and by having the interior surfaces carefully finished to render them smooth and airtight and treated to prevent the possibility of dust being scoured from the walls by the passing air. 

Unit ventilators may be provided for individual rooms and may be placed against outside wall near the central line of the room.

Both central system and unit ventilators could be equipped to provide, besides the function of ventilating, cooling by evaporative cooling or by cooling coils.  Typical installations are equipped with a system of controls that permits ventilating and cooling effect to be varied, while the fans are operating continuously, in accordance with the room requirements. 

17.5.5.4 Combined systems – The combined systems with positive ventilation and with exhaust of air have the advantage of providing better control conditions and better distribution of air over the entire area of occupancy, particularly in wider buildings.  By supplying sufficient volumes of air in proportion to heat load generated in the respective areas at suitable velocities at the required areas through duct work and by extracting the air in the return ducts in proportion to the supply air quantities and re-circulating the air or a part of it after properly mixing it with cool fresh air, completely satisfactory ventilation is obtained.  In a combined system, it is preferable to provide slight excess of exhaust if there are adjoining occupied spaces and a slight excess of supply if there are no such spaces, unit exhausters can also be used to match unit ventilators’ exteriors and located along the outside wall. 

17.5.5.5 Evaporative cooling – In regions where high day-time temperatures prevail with reasonably low humidities, evaporative cooling may be employed effectively to lower the temperature of the air to near the wet bulb temperature and produce an air supply cool enough to take care of the indoor sensible heat loads without exceeding the upper safe limits or the temperature rise values at area of occupancy.  By positive ventilation, this air may be supplied to produce cooler environments with lower air volume than would be required under 17.5.3.2 as greater temperature rise than given under Table 10 may be tolerated.  Although the relative humidity of supply air will be increased, due to the large sensible heat loads, the resultant relative humidity of the air will be sufficiently lowered after mixing with the inside air to produce body cooling. 

Evaporative cooling with positive ventilation using a central system consisting of a water spray chamber and a fan to supply outside air into the area of occupancy through a distribution duct is preferable to spray head system, which will only humidify the air within space.  Where a spray head system only humidifies the air, the cooling capacity of the air will be improved very little; and none of the air which absorbs the heat given off by men and machinery and other sources is removed from the building under these conditions.

17.5.5.6 Air-conditioning – Where the desired temperatures and humidities cannot be obtained by mere ventilation, air-conditioning may be resorted to (Section 18 Air-conditioning and Heating).

17.5.5.7 Ventilation for contaminants control – When contaminants are given off during the manufacturing process, efficient local exhaust ventilation and/or dilution ventilation to reduce their concentration below the threshold value (TLV) shall be provided.

Recommended capture velocities for some of the manufacturing processes which are likely to give rise to the contaminants depending upon their condition of dispersion, are given in Table 7 as a guide.

17.5.5.7.1. Make-up air – Sufficient make-up air shall be brought into the work room by natural filtration or by positive ventilation at suitable points in relation to the exhaust points to replace the air exhausted by local exhaust ventilation or by dilution ventilation, and the air may be efficiently filtered or treated, when necessary.

Table 7 Range of recommended capture velocities

 (Clause 17.5.5.7)

Sl.No

Condition of dispersion of contaminant

Examples

Capture velocity m/s

1

2

3

4

i

Released at with practically no velocity into quiet air

 

Evaporation from tanks decreasing, etc.

0.25 – 0.5

ii

Released at low velocity into moderately still air

Spray booths; intermittent container filling, low speed conveyor transfers; welding; plating; pickling

0.5 – 1.0

iii

Active generation into zone of rapid air motion

Spray painting in shallow booths; barrel filling; conveyor loading; crushers

1.0 - 2.5

iv)

Released at high initial velocity into zone of very rapid air motion

Grinding; abrasive blasting, tumbling

2.5 - 10

Detailed design of local exhaust ventilation and dilution ventilation shall be done in accordance with code of practice.

17.5.6. Determining rate of ventilation

17.5.6.1. Natural ventilation – This is difficult to measure as it varies from time to time.  The amount of outside air through windows and other openings depends on the direction and velocity of wind outside (wind action) and/or convection effects arising from temperature or vapour pressure differences (or both) between inside and outside of the building (stack effect).

17.5.6.1.1 Wind action –  For determining the rate of ventilation based on wind action the wind may be assumed to come from any direction within 45º of the direction of prevailing wind.  Ventilation due to external wind is given by the following formula:

Q = K A V 

Where

Q = the rate of air flow in m3/h;

K  =  coefficient of effectiveness, which may be taken as 0.6 for wind perpendicular to openings and 0.3 for wind at an angle less than 45º to the openings;

A = free area of inlet openings in m2; and

V = wind speed in m/h.

Note 1 - The value of the coefficient of effectiveness K depends on the direction of the wind relative to the opening and on the ratio between the areas of two openings.  Figure 3 gives the increase in values of K by the percentage of unequal areas expressed as ratios of the two openings.

Note 2 - For wind data at a place, the local Meteorological Department may be consulted.

17.5.6.1.2 Stack Effect – Ventilation due to convection effects arising from temperature difference between inside and outside is given by: 

Where              

Q = the rate of air flow in m3/h;

A = free area of inlet openings in m2;

h = vertical distance between inlets and outlets in m;

tr = average temperature of indoor air at height h, in  °C; and

to =  temperature of outdoor air in  °C.

Note - The equation is based on 0.65 effectiveness of openings.  This should be reduced to 0.50 if conditions are not favorable. 

17.5.6.1.3.   When areas of inlet and outlet openings are unequal, ‘A’ given in equations under 17.5.6.1.1 and 17.5.6.1.2 will be the smaller area and the volume of air will be increased according to the percentage given in Fig.3.

Fig 3 Increase in flow caused by excess of one opening over another

17.5.6.1.4.  When both forces (wind and thermal) are together in the same direction, even without interference, the resulting air flow is not equal to the two flows estimated separately.  Flow through any opening is proportional to the square root of the sum of the two heads acting on that opening. 

Wind velocity and direction, outdoor temperature, and indoor distribution can not be predicted with certainty, and refinement in calculation is not justified.  A simple method is to calculate the sum of the flows produced by each force separately.  Then using the ratio of the flow produced by thermal forces to the aforementioned sum, the actual flow due to the combined forces can be approximated from Fig.4.  When the two flows are equal, the actual flow is about 30 percent greater than the flow caused by either force acting independently (see Fig.4). 

Fig 4 Determination of flow caused by combined forces of wind and temperature difference

Judgment is necessary for proper location of openings in a building especially in the roof, where heat, smoke and fumes are to be removed.  Usually windward monitor openings should be closed, but if wind is so slight that temperature head can overcome it, all openings may be opened. 

17.5.6.1.5 For method for determining the rate of ventilation based on probable indoor wind speed with typical illustrative example for residential building, reference may be made to accepted standards.

17.5.6.2 Mechanical ventilation

17.5.6.2.1 The volume of outside air by positive ventilation shall be measured using proper instruments, such as properly calibrated anemometer, velocity meter and pilot tube. 

To measure the average velocity of air flow, it is necessary to make a traverse of the instrument over the cross-sectional area of the inlet openings or ducts and obtain the average velocity from these results.  The volume of air is given by:                                                Q = A V  

Where,

Q = volume of air in m3/h,

A = free area of inlet openings or ducts in m2, and

V = average velocity of air in m/h.

17.5.6.2.2. When ventilation is achieved only by exhaust of air, the volume of exhaust air shall be measured in the same manner as in the case of positive ventilation by measurement of air velocity and area of exhaust ducts or openings and multiplying one with the other. 

17.5.6.3. Combined effect of different methods of ventilation – When combination of two or more methods of general ventilation is used, the total rate of ventilation shall be reckoned as the highest of the following three and this rule shall be followed until an exact formula is established by research:

  1. 1.25 times the rate of natural ventilation (see 17.5.6.1)
  2. Rate  of positive ventilation (see 17.5.6.2.1), and
  3. Rate of exhaust of air (see 17.5.6.2.2).

17.5.6.4. Air movement – The rate of air movement of turbulent type at the working zone shall be measured either with a Kata thermometer (dry silvered type) or heated thermometer or properly calibrated thermocouple anemometer.  Whereas anemometer gives the air velocity directly, the Kata thermometer and heated thermometer give cooling power of air and the rate of air movement is found by reference to a suitable Nomogram using the ambient temperature.   

Annexure 17-A.1

LIST OF STANDARDS

Sl No

Code

Details

1

IS: 7662  (Part I)-1974

Recommendations for orientation of buildings. Part I Non-industrial buildings

2

IS: 3646 (Part I)-1966

Code of practice for interior illumination. Part I principles of good lighting and aspects of design.

3

IS: 2440-1975

Guide for daylighting of buildings (second revision)

4

IS: 6060-1971

Code of practice for daylighting of factory buildings

5

IS: 7942-1976

Code of practice for daylighting of educational buildings

6

IS: 1944 (Parts I & II)-1970

Code of practice for lighting of public thoroughfares (first revision)

7

IS: 2672-1966

Code of practice for library lighting

8

IS: 4347-1967

Code of practice for hospital lighting

9

IS : 6665-1972

Code of practice for industrial lighting

10

IS: 3103-1975

Code of practice for industrial ventilation (first revision)

11

IS: 3362-1977

Code of practice for natural ventilation of residential buildings (first revision)

 

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