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Together with the provision of thermal comfort and sound control, lighting and ventilation provide the initial environmental aspects of a building which ensure the physiological and psychological well-being of its occupants. However, the advancement of technology has led to some degree of complacency on the part of designers concerning the influence which the provision of acceptable lighting and ventilating standards has on the overall appearance and construction method of a building. Apart from purely functional requirements, they provide the principal means of creating aesthetic atmosphere and character. Nevertheless, whereas these functions once derived purely through an interrelationship between architectural form and construction method, it’s becoming increasingly possible to design a building where fashion can be made to function by the use of artificial devices. In all but the simplest form of building, often it may be considered normal to make 'corrections' in the lighting levels not achieved from the designed building by the use of electric light systems. Similarly, air-conditioning apparatus can be made to compensate for the lack of sufficient natural ventilating openings (windows, chimney openings, etc.). Indeed, artificial systems may even be oversized to make the thermal environment acceptable because of ill-considered decisions about siting, orientation or the amount of glazing in a building envelope. Standards Although the size, position and amount of window openings are necessarily controlled by current needs to conserve the use of energy and to ensure safety from the spread of fire or the intrusion of unwanted sound, a sensible balance must be achieved between these aims and acceptable lighting/ventilating standards. This can be accomplished by detailed analysis of each requirement, careful design decisions and adoption of suitable construction methods. Artificial lighting is required for certain activities to assist concentration without eye strain, and also after natural light periods. A building with a deep plan form required by virtue of optimum function, e.g. large office floor spaces, warrants continuous artificial light sources. In this case a suitably designed system can convert the otherwise wasted heat, generated by the lamp, into useful back-up or supplementary space heating for a building. The residue energy can be similarly used from artificial ventilating systems required by a large building, or a building with the external envelope entirely sealed against noise or extremes of climate. --- ----1 Typical recommended minimum daylight factors for rooms with side lighting only Building type Location Daylight factor* (%) Dwellings Living rooms (over 1/2 depth, but for minimum area 8 m^2) 1 Bedrooms (over 3/4 depth, but for minimum area 6 m2) 0.5 Kitchens (over 1/2 depth, but for minimum area 5 m2)2 Offices and banks General offices, counters, accounting guide areas, public areas 2 Typing tables, business machines, manually operated computers 4 Drawing offices General 2 Drawing boards 6 Assembly and concert halls Foyers, auditoriums, stairs (on treads) 1 Corridors (on floors) 0.5 Churches Body of church 1 Chancel, choir, pulpit 1.5 Altars, communion tables (depending on lighting emphasis required) 3-6 Vestries 2 Libraries Shelves (on vertical surfaces of guide spines), reading tables (additional lighting on guide stacks) 1 Art galleries and museums General 1 On pictures (but special provision for conservation where required) 6 (max.) Schools and colleges Assembly and teaching areas 2 Art rooms 4 Laboratories (benches) 3 Staff rooms, common rooms 1 Hospitals Wards 1 Reception rooms, waiting rooms 2 Pharmacies 3 Sports halls General 2 Swimming pools Pool surfaces 2 Surrounding floor areas 1 --- Natural lighting Among its many other vital functions, the sun provides the sources of natural light which create the first psycho logical connection between the inside and the outside of a building. The influence of the sun in creating shaded areas affecting the vegetation and human enjoyment of spaces is a critical factor when considering the dimensions and shape of a building and its distance from others. The use of 'natural' colored daylight to illuminate interior spaces can create interesting effects, caused by variations in intensity during the day influencing the shading of planes and the hue and depth of colored surfaces. Daylight is admitted into a building through 'holes' in external fabric (windows, roof lights, etc.), which in adverse climates generally incorporate glass or an alternative transparent material to control the effects of heat loss and/or inclement weather on the interior spaces. The amount of light received inside a building is usually only a small fraction of that received outside - because of modifications imposed by the size and position of openings - and will also constantly vary, owing to the influences imposed on the 'whole sky' illumination level by clouds, buildings and/or other reflecting planes. Therefore, it’s impracticable to express interior daylighting in terms of the illumination actually obtainable inside a building at any one time, for within a few minutes that figure is liable to change with corresponding changes in the luminance of the sky. For practical purposes, use is made of the daylight factor. This is a percentage ratio of the instantaneous illumination level at a reference point inside a room to that occurring simultaneously outside in an unobstructed position. Typical daylight factors are indicated. A simple rule of thumb can also be used to approximate the daylight factor: D = 0.1 × P where: D = Daylight factor P = Percentage glazing to floor area e.g. given a room of 100 m^2 floor area with 20 m^2 of glazing: D = 0.1 × (20 ÷ 100) × (100 ÷ 1) = 2% This can be more usefully represented in calculation of the natural luminance at the reference point inside a building by applying the following formula: D = (Ei ÷ Eo) × 100 where: D = Daylight factor Ei = Illuminance at reference point in building Eo = Illuminance at the reference point if the room was unobstructed Both factors of E are measured in lux (lumens per square meter), with Eo taken as a standard 5000 lux for unobstructed sky in the US. So, transposing the formula to make Ei the subject: Ei = (D × Eo) ÷ 100 Ei = (2 × 5000) ÷ 100 = 100 lux A comparison of illumination levels is shown below. Daylight reading of a reference point in a room can be made up of three components: sky component, or the light received directly from the sky; externally reflected component, which is the light received after reflection from the ground, building or other external surface; and internally reflected component, which is the light received after being reflected from the surfaces inside a building. The design of a building must take into account these three factors if the 'correct' amount of daylight is an essential factor in its function and if the design and construction method are closely related. ----1 indicates various arrangements to achieve acceptable daylight factors within a building for specific visual functions. The arrangement of the windows and other openings in the walls provides the main architectural character of a building, generally called fenestration. No account is taken of the influence of direct sunlight, but various methods of calculating daylight factors have been devised for overcast sky conditions. Modifications to values can be made for glazing materials other than clear glass, dirt on the glass and reductions caused by the window framing. If windows or skylights are within the normal field of vision inside a building, they are likely to be distractingly bright compared with other things occupants may wish to study. To reduce this apparent brightness, or glare, the openings should generally be placed away from interior focal points. Glare can also be reduced by reducing the brightness of the light source (tinted glass, louvers or curtaining) while increasing the brightness of the interior spaces by better light distribution techniques, such as the use of lighter colors for surfaces, or in extreme conditions by supplementary artificial lighting. Although exerting a very pleasing influence, brightening interior colors and providing both psychological and physical warmth, direct sunlight in a building can cause intensive glare, overheating and fading of surface colors. For this reason, sunlight used to illuminate a building is also often diffused or reflected to reduce its intensity. Shading and reflecting devices include trees, vines, overhangs, awnings, louvers, blinds, shades and curtains. Overhead shading devices (brise soleil) block or filter direct sunlight, allowing only reflected light from the sky and ground to enter a building. Louvers and blinds are capable of converting direct sunlight into a softer, reflected light. Artificial lighting The chief drawback of daylighting is its inconsistency, especially its total unavailability after dusk and before sunrise. Artificial lighting can be instantly and constantly available, is easy to manipulate and can be controlled by the occupants of a building. However, daylighting and artificial lighting should be regarded as complementary. Artificial lighting is used mainly for night-time illumination and as a daytime supplement when daylighting alone is insufficient. An acceptable balance of brightness within a building can be accomplished by an integration between the design of natural daylight sources and artificial supplementary lighting to provide the combined level of light appropriate to a specific visual task. During daylight hours natural light should appear dominant wherever possible. However, quite apart from artificial light sources supplementing lighting levels, the use of artificial lighting in a building could lead to more flexible internal planning arrangements and to the incorporation of fewer or smaller windows. Thus daytime supplementary artificial lighting schemes directly affect the appearance of a building and its economy of construction. Against this must be levied the probability of greater energy usage, although reference has already been made to the effects which artificial lighting installations have upon the heating load for a building, and the possible economic advantages obtained by the recycling of heat generated by lamps, etc. The objective of lighting design is to achieve an appropriate brightness or luminance for a visual task to be performed. When establishing desired luminance levels, account must be taken of the appearance (position, colour, shape and texture) of all wall, ceiling and floor surfaces, as well as the selection of suitable light fittings not only to light the task to be performed, but also to provide appropriate amounts of reflected light. Luminance should not be confused with illuminance. Illuminance is the measure of light failing on a surface (lumens per square meter or lux), whereas luminance refers to light reflected from it or emitted by it (candela per square meter or alternatively a post ilb-illuminance × reflection factor). Table 2 lists illumination levels suitable for a range of situations: the quality of these levels could be influenced by glare and an acceptable limiting index is also shown. The glare index is calculated by considering the light source location, the luminances of the source, the effect of surroundings and the size of the source. Glare indices for artificial light range from about 10 for a shaded light fitting having low output to about 30 for an unshaded lamp. As seen, various basic decisions have to be made concerning lighting objectives and whether the system involves daylight, electric light or a combined system. With electric or combined systems, further decisions must be taken concerning the way light is distributed by particular fittings, and upon their positions relative to each other as well as in relation to the surface to be illuminated. As with daylighting, light-colored and highly reflective room surfaces help to provide more illumination from the same amount of energy source. For artificial lighting there is also a problem concerning the way the internal colors of a building may be changed depending upon the way they are affected by the light source. Designers must always ensure not only that particular light fittings provide the correct level of illumination in the required direction, but also that the light (energy) source allows the desired colour rendition of the objects to be illuminated. In this respect, the reflectance value of the surrounding surfaces and the contrast created between them also play an important role by reducing the effects of glare. Particular attention should be paid when two or more sources are visible together, such as daylight and supplementary artificial light, or tungsten (incandescent) and fluorescent fittings. The ease with which the maintenance and cleaning of artificial lights can be carried out will depend upon design of fittings and how they are incorporated into a building. Generally, fittings, lamps and auxiliary gear should be readily accessible, and it’s an advantage if fittings can be easily removed for replacement and servicing. Access for servicing, whether by reaching, ladders, demountable towers, winches, catwalks or external access from the roof, will depend upon the fixing height, space allocation and the general structural/constructional design details adopted for a building. However, maintenance of light systems must not be considered in isolation since it generally forms part of similar needs for other services, equipment and perhaps even of window-cleaning procedures. A building of special importance is often floodlit for prestige or security. and there is often a need for emergency or safety lighting in public buildings, e.g. theatres, cinemas and department stores. This is generally supplied from an independent energy source and could involve the use of gas, batteries or an automatic-start diesel generator. This type of lighting must again form an essential part of the design of a building and its construction method. ---1 Effects of window shape and position on penetration and distribution of daylight. ---2 Artificial supplementary lighting. ---- Illumination levels and limiting glare indices for various functions: Location | Illuminance (lux or lm/m^2) | Limiting glare index Entrance hall 150 22 Stairs 150 22 Corridors 100 22 Outdoor entrances 30 22 Casual assembly work 200 25 Rough/heavy work 300 28 Medium assembly work 500 25 Fine assembly work 1 000 22 Precision work 1 500 16 General office work 500 19 Computer room 750 16 Drawing office 750 16 Filing room 300 22 Shop counter 500 22 Supermarket 500 22 Classroom 300 16 Laboratory 500 16 Public house bar 150 22 Restaurant 100 22 Kitchen 500 22 Dwellings Living room 50 N/A Reading room 150 N/A Study 300 N/A Kitchen 300 N/A Bedroom 50 N/A Hall/landing 150 N/A Library Reading area 200 19 Tables 600 16 Counter 600 16 --- Recommended minimum rates of fresh-air supply to buildings for human habitation Type of space | Recommended m /h per person* Factory Open-plan office Shops 18-30 Department store Supermarket Theater Cafeteria Dance hall Hotel bedroom 30-43 Laboratories Private offices Residential Cocktail bar Function room 43-65 Luxury residential Restaurant /commercial dining room Boardroom Executive office 65-90 Conference room Type of space | Recommended m^3/h per m^2 of floor area Corridors 5 Domestic kitchen 36 Commercial kitchen 72 Sanitary accommodation 36 * To convert to air changes per hour, divide by room volume and multiply by the number of occupants, e.g. a function room of 200 m3 volume designed to accommodate 20 people requires: 65/200 × 20 = 6.5 air changes per hour ---- Approximate air change rates: Accommodation Air changes per hour Offices, above ground 2-6 Offices, below ground 10-20 Factories, large and open 1-4 Factories/industrial units 6-8 Workshops with unhealthy fumes 20-30 Fabric manufacturing/processing 10-30 Kitchens, above ground 20-40 Kitchens, below ground 40-60 Public lavatories 6-12 Boiler accommodation/plant rooms 10-15 Foundries 8-15 Laboratories 10-12 Hospital operating theatres <20 Hospital treatment rooms <10 Restaurants 10-15 Smoking rooms 10-15 Storage/warehousing 1-2 Assembly halls 3-6 Classrooms 2-4 Domestic habitable rooms ~1 Lobbies/corridors 3-4 Libraries 2-4 --- ----3 Natural ventilation. ----4 Stack effect in a naturally ventilated tall building. ----5 Ventilation of dwellings. ----6 Trickle ventilator. ----7 Passive stack ventilation. ----8 Artificial ventilation provides clean air uniformly throughout a building. --- ----5 Requirements for domestic ventilation Accommodation Ventilation provision; Extract rate (l/s) Rapid or purge Background* (mm^2) Habitable room Openable window area 5 000 N/A > 1/20 floor area Bathroom with WC Openable window or 5 000 15 or PSV+ intermittent mechanical Openable window or 5 000 8 or PSV continuous mechanical Bathroom without WC Intermittent mechanical 5 000 15 or PSV Continuous mechanical 5 000 8 or PSV Kitchen Intermittent mechanical 5 000 30 in cooker hood 60 elsewhere or PSV Continuous mechanical 5 000 13 or PSV Sanitary accommodation Openable window 5 000 N/A (if separate from Intermittent mechanical 5 000 6 or PSV bathroom) Continuous mechanical 5 000 6 or PSV Utility room Intermittent mechanical 5 000 30 or PSV Continuous mechanical 5 000 8 or PSV ---- Natural ventilation The simplest ventilation system in a building uses external air as its source, the wind as its motive force, and openings in the external enclosure for fresh air intake on the wind ward side and stale air extraction on the leeward side. In a tightly constructed building, air infiltration is slow, but in a building with loose-fitting components, doors and windows, air movements will be excessive and cause draughts and high heat losses. The idea, therefore, is to create a naturally ventilated building using correctly fitting components of sizes and configurations which provide the optimum amount of air changes for the occupants, according to their activities, and also permit a minimum amount of heat loss. Tables 3 and 4 indicate the desirable minimum fresh-air requirements for persons taking part in various activities. These figures are also known as ventilation rates or air change rates. In practice these rates may be very difficult to achieve by natural methods of ventilation because airflow will be governed by areas of openings, the degree to which their use can be controlled by obstruction within a building restricting air movements, and by the pressure differences causing the flow. Also, the recommended quantities of air will need some adjustment relative to the possible presence of offensive fumes or smells (including tobacco smoke), as well as for the moisture content of the ventilating air (relative humidity). It’s usually considered that relative humidities of 30-70 per cent are acceptable as healthy, and increased ventilation rates will be required to reduce higher levels. For natural ventilation, windows are used to control the volume, velocity and direction of airflow, and they are designed so as to provide openings capable of adjustment. Without wind forces, airflow through a building is simply produced by the migration of air from a high-pressure zone to a low-pressure zone by convection currents created through the difference in density between warmer air and cooler air. Unless employing sealed-duct devices, fuel-burning plant such as --- replaces, boilers or furnaces draw oxygen from the external air via interior spaces, and produce a stack effect which will also assist ventilation. This technique often avoided the build-up of air in an interior space containing a large amount of water vapor and thus reduced the possibility of condensation. However, the need to conserve energy and reduce room heat losses has given rise to a technology which endeavors to reduce air movements in an interior space to a minimum compatible with the functions to be carried out. The spaces created by joints between components are now reduced, finer tolerances are possible and, where gaps are inevitable, rubber or synthetic seals are used to ensure small amounts of air circulation from the exterior to the interior of a building. This often means that fresh air ducts or grilles now have to be provided to allow sufficient air for both combustion of fuel and the well-being of the occupants in a building. To satisfy the Building Regulations, open spaces should be provided outside ventilating openings in domestic buildings to ensure an adequate volume of air for ventilation. Nevertheless, when a building is subjected to high-velocity winds which are likely to cause excessive ventilation or draughts, as well as high heat losses, care should be taken to locate openings in the building exclusively on the leeward side, or to protect them by shielding devices such as fences or trees. With contemporary construction practice, it’s essential to provide controlled ventilation in occupied rooms. Table 5 indicates rapid and background means to achieve 0.5-1.0 volume air change per hour, sufficient to complement current high standards of insulation and prevent condensation. This may be by trickle ventilators, fanned extracts or passive stack ventilation. Where kitchens, utility rooms, bathrooms or lavatories are located without an external wall an extract fan is effected with the lighting switch. The fan has a time delay mechanism to provide for intermittent use with an automatic 15-minute overrun facility. An air inlet of, or equivalent to, a 10 mm gap under the door must also be provided. Passive stack ventilation (PSV) combines with trickle ventilators to create air movement by the stack effect principle, i.e. warm air rises and gains velocity in the small vertical (or almost vertical) ducts from kitchens and bathrooms, to be replaced by cool fresh air drawn in through ventilation grilles in the window frames of the habitable rooms. Plastic drainpipes or flexible wire reinforced tubes, 100 mm in diameter, are adequate for the application. A mechanically assisted PSV system may be installed where several internal rooms (no external walls) would otherwise each require an extract fan, e.g. kitchens and bathrooms in a block of flats. The ducted PSV system is linked to each room to provide permanent ventilation and only one extract fan is positioned at the duct outlet. Activation of the fan is from each compartment light switch and inlet air is through a ventilation gap under the door as previously described. Artificial ventilation Where a reliable and positive flow of air for ventilation is required, fans can be installed in a building to extract stale air, which is immediately replaced by fresh air from the outside flowing through gaps around window and door frames, or through purposely designed grilles. Fans in more elaborate ventilation schemes are connected to systems of ductwork for better air distribution throughout a building. Separate duct systems can be installed to pull away stale air from those used to distribute clean air. Often such systems are coupled with heating and cooling plant in such a way that the clean air is distributed at the selected temperature for thermal comfort air-conditioning. Artificial ventilation systems are usually employed for internally located rooms; crowded rooms where natural ventilation is insufficient; special rooms needing closely controlled humidity and/or freedom from any dust (e.g. computer rooms and operating theatres); and where polluted air is required to be either removed or prevented from entering internal spaces. Certain high buildings will need artificial air movement control to ensure a balanced thermal environment because of the otherwise exaggerated 'stack effect' causing the highest parts to be hot as a result of rapidly rising warm air. The selection, design and integration of artificial ventilation and especially air-conditioning systems into a building require specialist knowledge, techniques and skills. It’s essential that the implications of a chosen scheme are realised at a very early stage in the design of a building. The effects of plant, exposed or concealed ductwork, additional fire protection to prevent the spread of fire through ductwork, etc., suspended ceilings, and additional sound control must all be carefully considered as they may have a profound effect on the appearance of the building and other technical aspects, including construction method. The integration of plant and ductwork within the dimensional discipline of the structure of a building requires particular attention. Previous: Fire
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