ARC 256 ELECTRICITY LIGHTNING AND LIGHTING.pdf

KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY DEPARTMENT OF ARCHITECTURE 1 ARC 256: BUILDING SERVICES [Credits: 2 ] COURSE EXAMINER: DE SM O N D O P O KU A.G. I. A DESO 2023/24 ...

KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY DEPARTMENT OF ARCHITECTURE 1 ARC 256: BUILDING SERVICES [Credits: 2 ] COURSE EXAMINER: DE SM O N D O P O KU A.G. I. A DESO 2023/24  ARC 256 BUILDING SERVICES CLASS: ARC. 2 SEMESTER: 2 CREDIT: 2 2 COURSE CONTENT Design and Installation of:  ELECTRICITY AND LIGHTING  WATER SUPPLY, SANITARY APPLIANCES AND DRAINAGE SYSTEMS  VENTILATION AND AIR CONDITIONING  FIRE CONTROL AND EQUIPMENT DESO 2023/24 COURSE CONTENT 3 Design and Installation of: Water Supply, Sanitary APPLIANCES and Drainage Systems Ventilation and Air Conditioning Electricity and Lighting DESO 2023/24 COURSE OUTLINE 4  Unit 1: ELECTRICITY AND LIGHTING  Electricity  Lighting  Electrical Drawings  Unit 2: WATER SUPPLY, SANITARY APPLIANCES AND DRAINAGE SYSTEMS  Water Supply  Soil and Waste Systems  Drainage Design  Sewage Design  Plumbing Drawings DESO 2023/24 COURSE OUTLINE (CONT’D) 5 Unit 2: VENTILATION AND AIR CONDITIONING  Ventilation Rates  Ducting  Design  Unit 4: FIRE CONTROL AND EQUIPMENT  Active control measures  Passive control measures DESO 2023/24 COURSE OBJECTIVES 6  Understand how cold - water pipe systems are designed;  Be capable of carrying out basic cold - water pipe- sizing calculations;  Allocate sanitary appliances appropriate to building usage;  Know how to design waste and drain pipes for ranges of sanitary appliances;  Calculate the capacities of cesspools and septic tanks; DESO 2023/24 COURSE OBJECTIVES (CONT’D) 7 Understand the basic design criteria for air movement control; Calculate ventilation air quantities; Explain how ventilation rates are measured; Choose suitable materials for air-conditioning ductwork; Understand the temperature effect of current; Calculate current and power in electrical circuits; DESO 2023/24 COURSE OBJECTIVES (CONT’D) 8 Calculate the number of lamps needed to achieve a design illumination level; Calculate lamp spacing for overall design; DESO 2023/24 COURSE OBJECTIVES (SUMMARY) 9 NOTE:  The first five objectives (slide 4) relate to - WATER SUPPLY, SANITARY APPLIANCES AND DRAINAGE SYSTEMS.  The next four objectives (slide 5) apply to – VENTILATION AND AIR CONDITIONING.  Objectives 10 to 13 (slides 5 and 6) concentrates on – ELECTRICITY AND LIGHTING. DESO 2023/24 FURTHER READING / REFERENCES 10  Worman C. Harris, Modern Air Conditioning Practice  Peter Burberry, Environmental and Services  F. K. Hall, Services Vol. I –III  David Etheridge and Mats Sandberg, Building Ventilation Theory and Measurement  R. Barry, Building Services  Fred Hall and Roger Greenor, Building Services Handbook, 4th Edition.  David V. Chadderton Building Services Engineering, 4th Edition. DESO 2023/24  STUDENTS’ ASSESSMENT CRITERIA 11  Continuous Assessment: Course works (2 No.) = 10% Mid Semester Examination = 15% Attendance = 5% Sub-Total (A) = 30%  End of Semester Examination Section A = MCQ = 40% Section B = Fill in Questions, Calculations & Essay = 30% Sub-Total (B) = 70%  Overall Total = A+B = 100% NOTE: 1. Marks Credit will be given to student(s) who contributes meaningfully in Class 2. Lateness to class would not be tolerated under no circumstances 3. Student(s) who absents themselves from class for medical reasons should officially communicate to the course lecturer through the HOD, Architecture. DESO 2023/24  ELECTRICITY AND LIGHTING UNIT 3 12 S e ss io n 1 : El e ct r ic it y  Electricity Generation  Power Sockets And Lighting Switches  Circuit Design  Cable Capacity and Voltage Drop  Testing  Lightning Conductors S e ss io n 2 : Lighting  Definitions  Lamp Types  Lumen Method Of Lighting Design DESO 2023/24  ELECTRICITY 13 ELECTRICITY GENERATION Sources of Electricity?  The flow of river (Hydro),  Steam produced from water heated by burning oil or coal (thermal),  Wind (Windmill),  Solar Energy (PV),  Nuclear fission  Coal  Natural Gas DESO 2023/24  TRANSFORMERS 14  A transformer is required for the conversion of electric power from high voltage to low (step-down) or vice versa (step-up).  A substation is required for the conversion, transformation and control of electric power. DESO 2023/24  TRANSFORMERS…CONT’D 15 A substation should be built on the consumers premises when a building requires more power than the local low or medium voltage distribution system. This is fed by high voltage cables from the Electricity Board’s (E.C.G or V.R.A) nearest switching station. Types of Transformers (Step Up and Step down)  600-1000KVA TRANSFORMER  300-500KVA TRANSFORMER  100-200 KVA TRANSFORMER DESO 2023/24  TYPES OF CURRENT 16 1. ALTERNATING CURRENT (A.C.)  Alternating currents are induced into coils of wires by moving magnetic fields.  A current which starts at zero, increases in one direction to reach a maximum, falls to zero, increases in the other direction to an equal but opposite maximum and then falls to zero again. DESO 2023/24  TYPES OF CURRENT 17 2. DIRECT CURRENT (D.C.) A current which flow Continuously in the same direction. Batteries produce direct currents. DESO 2023/24 TYPES OF CURRENT 18 DESO 2023/24 PUBLIC DISTRIBUTION OF ELECTRICITY 19  Power to large towns is taken by cables or overhead lines at 132kv or 33kv.  Heavy and light industries take power from the 33kv and 11kv respectively.  Finally, the high voltage power is converted to 415/240v for domestic consumers.  A more economical system is by large power stations with transmission system, known as the “grid”.  Interconnection of large power stations also ensures that each station can rely on the other during maintenance period thus keeping the amount of spare time to a minimum. DESO 2023/24 ELECTRICITY SUPPLY TO BUILDINGS SINGLE PHASE SUPPLY 20  The electricity supply to small buildings is usually provided by the connection of one phase wire and the neutral.  This is described as a single phase supply. It is unlikely that you will be connected to the same phase as your immediate neighbour.  The load must be balanced This is achieved by connecting buildings sequentially to the three different lines. DESO 2023/24 ELECTRICITY SUPPLY TO BUILDINGS. CONT’D 21 THREE PHASE SUPPLY….CONT’D Discuss observations Fig 4 DESO 2023/24  ELECTRICITY 22 Power Sockets and lighting Switches  Power sockets should be positioned between 150 mm and 250 mm above floor levels and work surfaces.  An exception is in buildings designed for the elderly or infirm, where socket heights should be between 750 and 900 mm above the floor.  Table 3.1 provides guidance on the minimum provision for power sockets in domestic accommodation.  The maximum appliance load (Watts) and plug cartridge fuse for single phase 240 V supply are found in table 2.3. DESO 2023/24  ELECTRICITY 23  The Building Regulations require reasonable provision for people, whether ambulant or confined to a wheelchair, to be able to use a building and its facilities.  Facilities include wall-mounted switches and sockets located within easy reach, to be easily operated, visible and free of obstruction.  For dwellings all switches and sockets should be between 450 and 1200 mm from finished floor level (ffl). DESO 2023/24  Table 3.1: Quantity of sockets in Domestic Accommodation Location Minimum Quantity of Sockets Living rooms 8 Kitchen 6 Master bedroom 6 Dining room 4 Study bedroom 4 Utility room 4 Single bedrooms 4 Hall and landing 4 Garage / workshop 2 Bathroom 1 double insulated shaver socket DESO 2023/24 24  Table 3.2: Appliance Load Fuses Maximum Plug Fuse Load Rating (amp) (W) 230 1 460 2 690 3 1150 5 1610 7 2300 10 2900 13 DESO 2023/24 25  Figure 34: Location of Sockets and Switches in a Dwelling DESO 2023/24 26  Figure 34: Location of Sockets and Switches in a Dwelling DESO 2023/24 27  CIRCUIT DESIGN 28  The resistance R ohms (Ω) of an electrical conductor depends on its:  specific resistance ρ (Ωm),  length, l (m) and  cross-sectional area A (m2).  The specific resistance ofannealed copper is 0.0172μΩm (μ, micro stands for 10−6) at 20◦C. R=ρlΩ A DESO 2023/24  CIRCUIT DESIGN…..CONT’D 29  The resistance of a cable increases with increase in temperature and the temperature coefficient of resistance α of copper is 0.00428Ω/Ω◦C at 0◦C.  If the resistance of the conductor is R0 at 0 ◦C, then its resistance at another temperature Rt can be found from Rt= R0(1 + α t)Ω where t is the conductor temperature (◦C).  The relation between applied voltage, electric current and resistance is given by Ohm’s law as: I (amp) = V (volt) R (ohms) DESO 2023/24  CIRCUIT DESIGN (CONT’D) 30 Example 3.1  Calculate the electrical resistance per metre length at 200 of a copper conductor of 2.5 mm2 cross-sectional area. Solution R = 0.0172 (Ωm) x 1 (m) x 106 (mm2) 106 2.5 (mm2) 1 (m2) = 0.0069 Ω Example 3.2  Find the resistance of a 2.5 mm2 copper conductor at 400C. The resistance per metre length of the copper conductor at 200C is 0.0069 Ω, and temperature coefficient of resistance α, is 0.00428Ω/ Ω0 C. Solution R40= (R20 + α x 20) Ω = 0.0069(1 + 0.00428 x 20) Ω = 0.0075 Ω DESO 2023/24  CIRCUIT DESIGN (CONT’D) 31 Example 3.3 Calculatethe power and resistance of a 240 V filament lamp if it has 1.5 A passing through it. Solution Power (Watts) = Volts x Amps = 240 x 1.5 = 360 W From Ohm’s law: I = V or R = 240 = 160 Ω R 1.5 Example 3.4 PVC insulation on a conductor carrying 415 V has an electrical resistance to earth of 500 mΩ. What leakage current could flow through the PVC when the cable is laid on an earthed metal support? Solution The difference between line and earth is 240 V. From Ohm’s law: I = V = ___240_ = 0.48 x 10-6 A R 500 x 106 = 0.48  A DESO 2023/24  CABLE CAPACITY AND VOLTAGE DROP 32 capacities and actual voltage  The maximum current-carrying drops according to the IEE Regulations for Electrical Installations for unenclosed copper cables which are twin- sheathed in PVC, clipped to the surface of the building, are given in Table 3.3.  Flexible connections to appliances may use 0.5mm2conductors for 3A and 0.75mm2 conductors for 6A loads.  The maximum voltage drop allowed is 4% of the 240V nominal supply. DESO 2023/24 CABLES, CONDUITS AND TRUNKING 33  A cable is conductor surrounded by insulative material. The conductors are commonly made from copper, which has a low electrical resistance. Aluminium and some other metals can also be used as conductors.  Insulated wire or wires is commonly termed cable to distinguish it from bare wire.  PVC is becoming the most commonly used insulating material for cables.  The size of the cable is described by the cross-sectional area of the wire. For example 1.0mm², 1.5mm² or 2.5mm².  Cables from 1.0mm² to 16mm² can be used for domestic installations and up to seven stranded wire.  The insulation can also be rubber, paper or plastic. All insulation materials have high electrical resistance; cables are also protected against mechanical damage. DESO 2023/24 DOMESTIC CABLE SIZING 34 DESO 2023/24 CABLE IDENTIFICATION 35  Green and yellow are reserved exclusively for earth conductors  Orange is used for special purpose cables  It is preferable to have the colour identification running the whole length of the cable DESO 2023/24 TYPES OF CABLE 36 1. One way of classifying electric cables is by the number of cores in sheath, viz.:  Single core- there is only one cable (one strand) which is enclosed in a sheath of insulating material.  Twin core with earth-Two cables and an earth wire, each separately insulated (the earth may be bare) and enclosed in an outer sheath.  Three core with earth-Three cables and an earth wire, each separately insulated and enclosed in an outer sheath of the same insulating material DESO 2023/24 TYPES OF CABLE…CONT’D 37 DESO 2023/24 TYPES OF CABLE…CONT’D 38 2. Mineral Insulated sheathe Cables (M.I.M.S.) These cables consist of single-strand conductors (rods) of either copper or aluminium enclosed in a thin tube of the same metal. The tube is the filled with insulation of finely powdered magnesium oxide which has been subjected to controlled drying. The magnesium oxide is an insulation material. DESO 2023/24  TYPES OF CABLE…CONT’D 39 2. Mineral Insulated sheathe Cables (M.I.M.S.)… Advantages  The cable provides an excellent earth conductor and is the safest form of installation.  It is also resistant to corrosion and is unaffected by extremes of heat.  It can be fixed neatly and quickly to all types of surfaces and does not normally require protection from mechanical damage.  Suitable for surface wiring. However, in some situations, the sheath does not provide sufficient protection and it is usual to run cables inside metal or plastic conduit to provide protection and to facilitate withdrawing and rewiring of cables if necessary DESO 2023/24  TYPES OF CABLE…CONT’D 40 3. PVC Insulated / PVC Sheath Cables Majority of cables used for electrical wiring in buildings today are insulated and sheathed in PVC. PVC is tough, in combustible, chemical inert plastic that does not deteriorate with age. The cables, however, do not provide much protection from mechanical damage and heat. PVC softens at temperature above 80ºc and should not be used where ambient temperatures are above 70ºc. DESO 2023/24  TYPES OF CABLE…CONT’D 41 4. Tough Rubber Sheath (TRS) Cables  This is form of cable is essentially similar to PVC but has superseded it to a great extent.  The cable is generally manufactured with one, two or three copper conductors insulated with rubber and covered with rubber sheath  The cables do not resist direct sunlight, oil or chemical attack to the same extent as PVC sheath colours.  They can also not be obtained in a wide range of colours as PVC sheathed cables.  They are therefore, not as popular as PVC sheath cables, but are often used for extension leads. DESO 2023/24  TYPES OF CABLE…CONT’D 42 5. Armoured Cables Armoured cables are strong and offer protection against mechanical damage, and moisture resistant cables. The conductors are multi-stranded with overheat tolerant materials used for mains and sub-mains and laid usually below ground level. DESO 2023/24 Table 3.3: Electrical Cable Capacities (mm2) Maximum Voltage current drop in rating (A) cable (mV/Am) 1 15 44 1.5 19.5 29 2.5 27 18 4 36 11 6 46 7.3 10 63 4.4 16 85 2.8 DESO 2023/24 43  Example 3.5 44 Find the maximum lengths of 1, 1.5 and 2.5 mm2 copper cable which can be used on a 240 V circuit to a 3 kW immersion heater. Solution Current = 3000 (W) 240 (V) = 12.5 A The maximum voltage drop allowed is 4% of the 240V nominal supply. i.e. Allowed voltage drop = 4 x 240 100 = 9.6 V DESO 2023/24 Example 3.5 45 Maximum length or run = maximum voltage drop allowed (mV) load current (A) x voltage drop (mV/Am) For 1 mm2 cable: l = 9.6 x 103 12.5 x 44 = 17.5 m For 1.5 mm2 cable: l = 9.6 x 103 12.5 x 29 = 26.5 m For 2.5 mm2 cable: l = 9.6 x 103 12.5 x 18 = 42.7 m DESO 2023/24 TESTING 46  Inspection and testing of an electrical installation is carried out before it is put into service and at regular intervals during use.  The main reasons for this are to ensure that its operation will be entirely safe, in accordance with the demands put upon it, and energy efficient.  The work entails the following tests: 1. Verification of correct polarity A visual inspection is carried out of all fuses and switches to check that theyare fitted into a line conductor. The centre contact of each screwlamp holder isconnected to the line conductor. Plugs and sockets must be correctly connectedand wire rigidly held. DESO 2023/24 2 Tests of effective earthing There are four separate tests: Test of the protective conductor A 40V 50 Hz supply of up to 25A is injected into the earth conductor. Its resistance is not to exceed 1Ω. An impedance test meter is used. Earth loop impedance test: A line-earth loop impedance test meter is attached to a 13A three-pin plug. This is plugged into each power socket and the meter injects a current into the earth protective conductor. The current flows along the supply authority’s cable sheath to the local transformer and back to the power socket along the line conductor. Test of residual current devices: A test transformer providing 45V is connected to a socket outlet. A short- circuit current is passed from the neutral to the protective conductor, causingthe residual current device to trip instantaneously. Measurement of consumer earth electrode resistance: Where this is used, a test electrode is put into the ground and a steady 50 Hz current is passed between the electrode and the consumer’s earth electrode to determine its circuit resistance. DESO 2023/24 47 3. Insulation resistance tests An insulation test meter is connected between the line and protective conductors. A 500V direct current is applied to this circuit by the meter and an electrical resistance of 0.5MΩor more must be shown. 4. Test of ring circuit continuity Each ring circuit is tested for resistance at the distribution board with an ohmmeter. Probes are connected to each side of the line conductor ring and a zero resistance proves a continuous circuit. The test is repeated on the neutral and protective conductor circuits and spur branches. Tests on installations must be carried out in accordance with the IEE Wiring Regulations by a competent person, who should preferably be a professionally qualified electrical engineer having installation experience. IEE Completion and Inspection Certificates are issued by the engineer. DESO 2023/24 48 LIGHTNING CONDUCTORS 49 Rules are provided (BS Code of Practice 326: 1965) to determine whether a protection system is required. This depends on: o building construction, o degree of isolation, o Height of the structure, o topography, o consequential effects and o lightning prevalence. Recommendations on system types, including those for temporary structures, are given. DESO 2023/24 o Copper and aluminium 10mm rod, 25mm×3mm strip, PVC-covered strip, copperstrand and copper braid are used for conductors. o The air terminal is sited above the highest point of the structure and a down conductor is bolted to the outside of the building so that side flashing between the lightning conductor and other metalwork will not occur. o Ground termination is with a series of earth rods driven to depths of up to 5m, castiron or copper plates 1m square horizontally or vertically oriented 600mm below ground, or a copper lattice of flat strips 3m×3m at a depth of 600 mm. o Where large floor areas containing earth rods are to be concreted, a precast concrete inspection pit is built over the rod location. o The electrical resistance to earth of the whole system is not to exceed 10Ω. Calculation of the ground earthing resistance R requires a knowledge of the earth type (BS Code of Practice 1013: 1965) and resistivity. Typical values of earthresistivity are:  10 Ωm for clay,  50Ωm for chalk,  100Ωm for clay shale and  1000 Ωmforslateyshales. DESO 2023/24 50 The resistance of a rod electrode in earth is where l = earth rod length (m) d = earth rod diameter (mm) ρ= resistivity of the soil (Ωm) A number of rods are connected in parallel and spaced3.5m apart to provide the required resistance. Example 3.5 Design a lightning conductor system for a building 30m high in an area where thunderstorms are expected. The ground has a high chalk content and rod electrodes 4m long are to be used. The conductors are to be 25mm×3mm copper strip. The specific resistance ρ of copper is 0.0172μΩm. Solution Length of conductor = air terminal + down conductor + ground lead Take the length of the conductor as 40 m. resistance of conductor R = ρlΩ DESO 2023/24 51 where A is the conductor cross-sectional area (m2); hence R = 0.0172 × 10−6 (Ωm) x 40 (m). (0.025 x 0.003) (m2) = 0.092Ω Resistance R of earth = 0.37ρlog(4000l)Ω l ( d ) where the earth resistivity ρ is 50Ωm, the electrode length l is 4m and the electrode diameter d is 10 mm; hence R = 0.37 × 50(Ωm) x log (4000 x 4) Ω 4 (m) ( d ) = 4.625 x logm1600 = 14.819 Ω. DESO 2023/24 52 The resistance of one electrode in the ground plus the down conductor is greater than the 10Ωallowed, and so we find the combined resistance of two electrodes connected in parallel: 1 = 1 + 1 R R 1 R2 1 = 1 + 1 R 14.8 14.8 = 7.4 Ω Two electrodes and the down conductor connected in series have a total resistance of: R = (7.4 + 0.0092)Ω= 7.4Ω This is less than the 10Ωallowed and is satisfactory. The resistance of the lightning conductor is negligible in relation to that of the earth electrodes. The calculations have been made on the assumption that the lightning discharges in a direct current. Lightning energy can produce a current to earth of 20 000A for a few milliseconds DESO 2023/24 53  Lighting Session 2 54 Definitions Luminous intensity (candela (cd)): a measurement of the magnitudeof luminance or light reflected from a surface, i.e. cd/m2. Luminous flux (lumen (lm)): a measurement of the visible light energy emitted. Illuminance - Lumens per square metre (lm/m2) or lux (lx) ameasure of the light falling on a surface. Efficacy: efficiency of lamps in lumens per watt (lm/W). Luminous efficacy = Luminous flux output  Electrical power input. Glare index: a numerical comparison ranging from about 10 for shaded light to about 30 for an exposed lamp. Calculated by considering the light source size, location, luminances and effect of its surroundings. DESO 2023/24 Table 3.4: Illumination Levels Activity / location Illumination Limiting glare (lux) index Assembly work : 250 25 (general) (fine) 1000 22 Computer room 300 16 House 50 to 300* n/a Laboratory 500 16 Lecture / classroom 300 16 Offices : (genera) 500 19 (drawing) 600 16 Public house bar 150 22 Shop / supermarkets 500 22 Restaurants 100 22 * Varies from 50 in bedrooms to 300 in kitchen and study. DESO 2023/24 55 Illumination produced from a light source perpendicular to the surface: E = I d2 E = illumination on surface (Iux) I = Illumination intensity from source (cd) d = distance from light source to surface (m). Illumination produced from a light source not perpendicular to the surface: E = I cosѲ d2 DESO 2023/24 56 Lamp Types o General lighting service (GLS) tungsten filament lamps are inexpensive, give good colour matching with daylight and last up to 2000 h in service. They can be controlled by variable-resistance dimmers and are used in a supplementary role to higher-efficacy illumination equipment. Tungsten halogen spot or linear lamps have a wide variety of display and floodlighting applications. DESO 2023/24 57 Lamp Types o Miniature fluorescent lamps (SL) can be used as energy-saving replacements for GLS lamps. Folded-tube and single-ended types are available. A typical folded lamp, SL18 18 W, produces 900 lumens at 100 h, has a correlated colour temperature of 2700 K, an Ra8 of 80 and a service period of 5000 h. Its lumen output is equivalent to a 75W GLS filament lamp. DESO 2023/24 58 Lamp Types o Low-pressure mercury-vapour-filled fluorescent tubular lamps (MCF) are the most common. The tube diameter is 38 mm. Electrical excitation of the mercury vapour produces radiation, which causes the tube’s internal coating to fluoresce. The colour produced depends on the chemical composition of the internal coating. High-efficacy 26mm diameter lamps (TLD) are filled with argon or krypton vapour and have a phosphor internal coating. DESO 2023/24 59 Lamp Types o Halogen Lamp A halogen lamp is an incandescent lamp consisting of a tungsten filament sealed in a compact transparent envelope that is filled with a mixture of an inert gas and a small amount of a halogen, such as iodine or bromine DESO 2023/24 60 Lamp Types o Light Emitting Diodes (LED): A semiconductor device that emits light when an electric current flows through it. When current passes through an LED, the electrons recombine with holes emitting light in the process. LEDs allow the current to flow in the forward direction and blocks the current in the reverse direction. DESO 2023/24 61 Table 3.5: Lamp Data DESO 2023/24 62  Lumen Method of Lighting Design Definitions 63 BZ classification: Maintenance British Zonal Classification of 1–10 for A planned maintenance schedule will the downward light emitted from a include regular cleaning of light fittings luminaire. The BZ classnumber relates and the lamp to ensure the most to the flux that is directly incidentupon efficient use of electricity. Ventilated the working plane in relation to the total luminaires in air conditioned buildings fluxemitted. BZ1 classification is for a remain clean for quite long periods as downward directionalluminaire. A BZ10 the air flow through the building is describes a luminaire thatdirects all its mechanically controlled and filtered. illumination upwards so that the roomis The lamp also operates at a lower illuminated by reflection from the temperature, which prolongs its service ceiling. and maximizes light output. Because of gradual deterioration of the Maintenance factor, MF: light output from all types of discharge an allowance for reduced light emission lamps after their design service period, due to thebuild-up of dust on a lamp or lamp efficacy could fall to half its within a luminaire.Normally 0.8 but 0.9 original figure. Phased replacement of if the lamps are cleaned regularlyor if a lamps after 2 or 3 years maintains ventilated luminaire is used. Light design performance and avoids lossfactor is preferred. breakdowns. Figure 40 shows a typical Utilization factor, UF: illuminance profile for a tubular fluorescent light fitting with 6-monthly the ratio of the luminous flux received cleaning and a 2-year lamp- at the working plane to the installed replacement cycle. flux. DESO 2023/24 Figure 35: Overall Fluorescent Light fitting Performance with Maintenance DESO 2023/24 64 Utilization Factor o The utilization factor is provided by the manufacturer and takes into account the pattern of light-distribution from the whole fitting, its light-distributing efficiency, the shape and size of the room for which it is being designed and the reflectivity of the ceiling and walls. o Values vary from 0.03, where purely indirect distribution is employed, the room has poorly reflecting surfaces and all the light is upwards onto the ceiling or walls, to 0.75 for the most energy-efficient designs. Spot lighting can have a utilization factor of nearly unity. o The ability of a surface to reflect incident light is given by its luminance factor fromBS 4800:1972. Table 3.6 gives sample values of the luminance factors for painted surfaces. The configuration of the room is found from the room index: Room index = lW___ H(l + W) where: l is the room length (m), W is the room width (m) and H is the height of the light fitting above the working plane (m). Utilization factors for a light fitting comprising a white metal support batten and two 58Wwhite fluorescent lamps 1500mm long (New Streamlite by Philips Electrical Limited) are given in table 3.7. DESO 2023/24 65  Table 3.6: Luminance Factors for Painted Surfaces Surfac Typical colour Luminance Factor range e (%) Ceiling White, cream 70 – 80 Ceiling Sky blue 50 – 60 Ceiling Light brown 20 – 30 Walls Light stone 50 – 60 Walls Dark grey 20 – 30 Walls Black 10 Floor --- 10 DESO 2023/24 66 Table 3.7: Utilization Factors for a Bare Fluorescent Tube Fitting with Two 58 W 1500mm Lamps (%) Luminance Room Index Factors Ceilin Walls 0.7 1 1.2 1.5 2 2.5 3 4 5 g 5 5 70 50 48 53 59 64 71 75 79 83 86 70 30 40 46 51 57 64 69 73 78 82 70 10 35 40 46 51 59 64 68 74 78 50 50 43 48 52 57 63 67 70 74 76 50 30 37 41 46 51 57 62 65 70 73 50 10 33 37 42 46 53 58 61 67 70 30 50 39 42 46 50 55 59 61 65 67 30 30 34 37 42 46 51 55 58 62 65 30 10 30 33 38 42 48 52 55 59 62 DESO 2023/24 67 The Lumen Design Method The number of light fittings is found from the total lumens needed at the working plane and the illumination provided by each fitting using the formula: Number of fittings = lux × working plane area m2 LDL × UF × MF Where: LDL = the lighting design lumens produced by each lamp, UF = the utilizationfactor and MF = the maintenance factor. The high output NewStreamlite luminaire with two Colour 84 fluorescent lamps, 1500mm long, emits 5100 lumens measured at 2000 h of use. This is known as its lighting design lumens (LDL) DESO 2023/24 68  Figure 36: Methods of Spacing Fluorescent Tubes DESO 2023/24 69 Example 3.6 An office 8 m long by 7 m wide requires an illumination level of 400 lux on the working plane. It is proposed to use 80 W fluorescent fittings having a rated output of 7375 lumens each. Assuming a utilisation factor of 0.5 and a maintenance factor of 0.8 design the lighting scheme. Solution Number of fittings = lux × working plane area m2 LDL × UF × MF = 400 x 8 x 7__ 7375 x 0.5 x 0.8 = 7.59 use 8 fittings The arrangement of the fittings is illustrated on figure 37. Example 3.7 A drawing office 16m×11m and 3mhigh has a white ceiling and light- colouredwalls. The working plane is 0.85mabove the floor. New Streamlite double-lamp luminaires are to be used and their normal spacing-to-height ratio SHR is 1.75. Calculate the number of luminaires needed and drawtheir layout arrangement. DESO 2023/24 70  Figure 37: Arrangement of the Luminaires in a Drawing Office in Example 3.6 DESO 2023/24 71 Solution From Table 3.7 the luminance factors are 70 for the ceiling and 50 for the walls.A high standard of maintenance will be assumed, giving a maintenance factor of 0.9. The lighting design lumens is taken as 5100 lm for the whole light fitting. From Table 3.4 the illuminance required is 600 lm/m2. The height H of fittings above the working plane is: H = (3 - 0.85) = 2.15 m Room Index = lW__ H (l + W) = 16 x 11____ 2.5 x (16 + 11) = 3.03 From table 3.7, for a room index of 3, Utilization factor = 79% = 0.79 Number of fittings = 600 lm x 16m x 11m x luminaire m2 0.79 x 0.9 500lm = 29.12 DESO 2023/24 72 The ratio of the spacing S between rows to the height H above the working plane is: SHR = S = 1.75 H Therefore S = 1.75 x 2.15 m = 3.76 m If it is assumed that windows are along one long side of the office and that rows of luminaires will be parallel to the windows, this will produce areas between rows where drawing boards, desks and VDU terminals can be sited to gain maximum benefit from side day lighting without glare and reflection. The perimeter rows of luminaires are spaced at about half of S, 1.74 m, from the side walls. Three rows of 10 luminaires are required, as shown in Figure 38, giving 30 luminaires and a slightly increased illuminance. The electrical power consumption of each luminaire is 140 W. For the room the power consumption will be 30 × 140W, that is, 4200 W, which is: 4200W = 23.86 W/m2 floor area 16m × 11m DESO 2023/24 73 Figure 38: Arrangement of the Luminaires in a Drawing Office in Example 3.7 DESO 2023/24 74 1)28m of copper conductor 4mm2 in cross-sectional area is covered with thermalinsulation, which causes the cable temperature to rise to 45 ◦C. Calculate the percentage increase in electrical resistance compared with its value at a cable temperature of 20 ◦C. 2)Find the maximum length of 6mm2 cable that can be used if the maximum currentcarryingcapacity is to be utilized on a 240V circuit. 3)Calculate the room index for an office 20m × 12m in plan, 3m high, where theworking plane is 0.85m above floor level. 4)Find the utilization factor for a bare fluorescent tube light fitting having two 58W,1500mm lamps in a room 5m×3.5m in plan and 2.5m high. The working planeis 0.85mabove floor level. Walls and ceiling are light stone and white respectively. 5)A supermarket of dimensions 20m × 15m and 4m high has a white ceiling andmainly dark walls. The working plane is 1m above floor level. Bare fluorescenttube light fittings with two 58W, 1500mm lamps are to be used, of 5100 lightingdesign lumens, to provide 400 lx. Their normal spacing-to-height ratio is 1.75 andtotal power consumption is 140 W. Calculate the number of luminaires needed,the electrical loading per square metre of floor area and the circuit current. Drawthe layout of the luminaires. DESO 2023/24 75