Building Services: Electricity and Lighting Design

• Building Services 2: Electricity and Lighting Design (EEG 419) relates to architecture at the University of Lagos.

Course Description

• Provides knowledge of electricity and its distribution.
• Develops understanding of lighting and its importance for health and energy conservation.
• Includes lighting calculations and applications for various functions and architecture.
• Considers lighting as an aspect of interior design.
• Illustrates basic design approaches and the link to architectural practice.

Course Outcomes

• Able to explain fundamental issues of electricity, light, and lighting.
• Capable of incorporating electricity and lighting into architectural designs.
• Can apply lighting knowledge to different architectures and functions.

Part 1: Electricity

Introduction

• Centuries ago, it was discovered that rubbing certain materials together caused them to attract; rubbing silk and glass makes them stick together because of an attractive force.
• Identical rubbed materials repel each other.
• Electrons move from one material to another
• Objects are composed of atoms, which are composed of fundamental particles as protons, neutrons, and electrons.
• Nucleus is the tightly-bound clump of protons and neutrons in the center of the atom.
• The number of protons in the nucleus determines its elemental identity.
• Electrons have more freedom to move around in an atom than protons or neutrons.
• Electrons can be knocked out of their positions with less energy than nucleus particles.
• Electrons and protons attract one another over a distance; it explains attraction between rubbed objects due to electron movement.
• Static electricity is the imbalance of electrons between objects; displaced electrons tend to remain stationary after moving from one insulating material to another.

Conductors, Insulators, and Electron Flow

• Electrons in different types of atoms vary in their freedom to move around.
• In metals, outermost electrons are loosely bound and move chaotically due to room-temperature heat energy which are known as free electrons.
• Materials such as glass have electrons with little freedom to move around.
• Electrical conductivity is the relative mobility of electrons within a material; it depends on the atoms and how they are linked i.e. number of protons.
• Conductors have high electron mobility (many free electrons), while insulators have low electron mobility (few or no free electrons).
• Common conductors: silver, copper, gold, aluminum, iron, steel, brass, bronze, mercury, graphite, dirty water, concrete
• Common insulators: glass, rubber, oil, asphalt, fiberglass, porcelain, ceramic, quartz, dry cotton, dry paper, dry wood, plastic, and air
• Some materials change electrical properties under different conditions.
• Glass is a good insulator at room temperature but becomes a conductor when heated to high temperatures.
• Gases like air become conductive when heated to very high temperatures.
• Metals become poorer conductors when heated and better conductors when cooled.
• Many conductive materials become perfectly conductive (superconductivity) at extremely low temperatures.
• Normal motion of "free" electrons in a conductor is random.
• Electrons can be influenced to move in a coordinated fashion through a conductive material; this uniform motion is called electricity or electric current.
• Electrons moving uniformly through a conductor push each other, causing them to move as a group.
• Starting and stopping electron flow is virtually instantaneous from one end of a conductor to the other, even if the motion of each electron is slow.
• Analogy: a tube filled with marbles.
• With electricity, the overall effect happens at the speed of light.
• Wires facilitate electron flow made of conductive materials such as copper or aluminium.
• Continuous flow of electrons requires a source and a destination.
• Flow is interrupted if the conductive path is broken via a switch or breaker
• A bypass or parallel circuit can provide continuity from the source to the destination.

Electric Circuit

• Potential energy develops when electrons are poised in static condition (like water sitting high in a reservoir).
• Potential energy is stored in the form of electric charge imbalance.
• This stored energy capable of provoking electrons to flow through a conductor can be expressed as voltage or potential energy per unit charge of electrons.
• Voltage expresses potential energy, and is always referenced between two points.
• Connecting a wire from one end of the battery to the other forms a circuit, initiating continuous electron flow in a clockwise direction.
• The continuous, uniform electron flow through the circuit is a "current" given a continuous voltage.
• This single-direction flow of electrons is a Direct Current, or DC.
• Electric current is used for electric lighting; the simplest lamp is a tiny metal filament inside a clear bulb that glows white-hot when current passes through it.

Resistance

• Electrons encounter more opposition when passing through the thin metal filament.
• Opposition to electric current depends on the material type, cross-sectional area, and temperature - known as resistance.
• Conductors have low resistance and insulators have high resistance.
• Resistance limits the amount of current through the circuit.
• Friction is generated when electrons move against resistance.
• A lamp's filament generates a large amount of heat causing it to glow while connecting wires remain cooler due to their lower resistance.
• With a broken circuit continuity, electron flow stops, which means that the lamp will stop glowing.

Electrical Theory

• Electrical current (I) is measured in amperes (amps).
• Electrical pressure or potential difference (V) is measured in volts.
• Electrical resistance (R) is measured in ohms.
• Ohm's Law is V = I x R, i.e. Voltage = Current x Resistance
• Electrical power (P) is measured in watts.
• Formula: P = V x I
• Examples of calculating current and power:
  • A 1 kW electric heater at 240 volts requires a current of 4.167 amps.
  • A heater element with 38.4 ohms resistance at 240 volts has a current of 6.25 amps and a power of 1.5 kW.

Alternating Current

• Direct Current (DC) is the kind of electricity made by a battery or by rubbing materials.
• DC has electricity flowing in a constant direction or possessing a voltage with constant polarity.
• Alternating Current (AC) is produced when voltages alternate in polarity, reversing positive and negative over time.
• AC: Current direction switches back and forth.
• In some applications AC has no advantage, when electricity dissipates energy in heat form, polarity or current direction is irrelevant.
• AC facilitates building electric generators, motors, and power distribution systems which are more efficient than DC.
• AC generators are called alternators, with AC voltage produced as their shaft is rotated.
• DC generators have wire coils mounted in the shaft, magnet is on the AC alternator.
• AC is useful for mutual induction, as two or more coils of wire placed create changing magnetic field and a voltage
• Energizing one coil with AC will generate an AC voltage in the other coil, a device known as a transformer.
• Significance of a transformer is to step voltage up or down from one coil to another.
• AC voltage induced in the unpowered coil equals AC voltage across the powered coil multiplied by secondary coil turns to primary coil turns.
• Primary coil current multiplied by the ratio of primary to secondary turns determines the current through the secondary coil.
• Transformers step voltage and current up or down, useful in power distribution which is more efficient when stepped up voltages and current are used.

Electricity Generation

• There are seven fundamental methods of directly transforming other forms of energy into electrical energy:
  • Static electricity: via separation and transport of charge (tribo-electric effect and lightning).
  • Electromagnetic Induction: where an electrical generator transforms kinetic energy into electricity.
  • Electrochemistry: direct transformation of chemical energy into electricity (battery, fuel cell, nerve impulse).
  • Photoelectric Effect: transforms light into electrical energy (solar cells).
  • Thermoelectric Effect: direct conversion of temperature differences (thermocouples etc.).
  • Piezoelectric Effect: from mechanical strain of electrically anisotropic molecules or crystals.
  • Nuclear Transformation: creation and acceleration of charged particles (beta-voltaic or alpha particle emission).
• Static electricity was the first form discovered.
• Almost all commercial electrical generation uses electromagnetic induction.
• Mechanical energy rotates an electrical generator, by heat engines, hydro, wind and tidal power.
• Direct conversion of nuclear energy to electricity by beta decay is used on a small scale.
• Nuclear power plants use heat of a nuclear reaction to run a heat engine to drives a generator to convert mechanical energy into electricity by magnetic induction.
• Most electric generation is driven by heat engines utilizing:
  • Fossil fuels to supplies most of the heat, nuclear fission.
  • Modern steam turbine (invented by Sir Charles Parsons in 1884) produces about 80 percent of the world's electric power using a variety of heat sources.
• Efficient long distance electric energy transmission is enabled via Transformers.
• Transformer technology and electricity distribution via efficient, long-range electric power is cost prohibitive except close distances.
• Advantages of using High Voltage to transmit power:
  • Reduced line current for a given amount of power lessens the need for conductors.
  • Reduced current capacity result in the less volume of conductor for a given length.
  • Reduced I^2R loss with a reduction in line current.
  • Better efficiency due to lesser line losses from reduced I^2*R loss.
  • Improved voltage regulation with decreased line current reducing the voltage drop across line.
  • Better efficiency due to improved voltage regulation and the higher voltages increases the power transfer, as P=VsVrsin (8) /Xs.

Domestic Electrical Installation

• Most premises receive single-phase electricity at 230 volts, 50 hertz.
• 3-phase 400V and 50Hz is used if the building load exceeds 18kVA.
• Cables enter building underground duct of overhead supply.
• Cable terminates in board's fused sealing chamber in dry accessible position.
• Supply passes to meter, records electricity consumption and connected to consumer unit.
• Consumer Unit: switch controlling supply to circuit breakers or circuit fuses.
• Fuses protect against excess current or circuit overload will isolate from circuit source.
• Consumer units are normally 8-way and 12-way units.
• Installations separate power and lighting circuits, ensuring no general socket outlet / light fault if a fault occurs.

Power Circuits

• A useful rule for circuits is one power circuit per 100m² of floor area.
• A separate power circuit can be used for the garage or utility area.
• Separate power circuit is required for the cooker.
• Immersion heater can be supplied too i.e. 3kW load.
• Ring circuits serve as safe and economic electricity distribution to socket outlets.
• Steel or plastic conduit cables are used in walls to protect from mechanical damage.
• Three conductors (L, N & E) can be covered to form PVC/PVC Twin and Earth.
• Conductor is 2.5 mm² domestic.

Consumer's Mains Equipment

• Consumers' mains equipment is fixed close to the point where the supply cable enters.
• Meets IEE Regulations providing protection against electric shock (Section 471), overcurrent (Section 473), and isolation and switching (Section 476).
• Shock protection is by insulating and placing live parts out of reach, earthing/bonding, and fuses/breakers that disconnect supply under fault conditions.
• Overcorrect protection: a device will disconnect automatically before overload raises temperature, damaging the installation.
• An isolator is a manual device for cutting off supply to the installation, circuit, or equipment which allows switching off for maintenance.
• The switching of electrically operated equipment in normal service is referred to as functional switching.
• Switch is a means of isolation but is intended not to carry current.
• Circuits are controlled by switchgear, for operating safely under normal, isolated automatically under fault conditions, or manually for safe maintenance.
• These requirements are met good workmanship and materials i.e. switches, isolators, fuses or circuit breakers.
• The equipment belonging to the supply authority (PHCN) is sealed to prevent unauthorised entry, and unrecorded energy use.
• The goal is to provide an electrical supply to the appliance with minimum voltage loss through the conductor achieved by minimising wiring resistance.

Distribution in Commercial and High Rise Buildings

• Electrical room is a dedicated space for electrical equipment, proportional to the building size.
• Large buildings have a main distribution room and other smaller electrical rooms.
• Electric switchboards
• Distribution boards
• Circuit breakers and disconnects
• Electricity meter
• Transformers
• Busbars
• Backup batteries
• Fire alarm control panels
• Distribution frames
• Distribution systems in high-rise use busbars: solid copper bars that carries current.
• Busbars run vertically inside trunking.
• Supply to each floor is through tap-off units, spread between phases.
• Fire barriers are incorporated with the busbar chamber at each compartment floor level.

Electrical Safety

• Electric current (resistance) results in heat dissipation.
• It causes tissue damage via heat.
• Open flame damages are equal, except electricity also internally burns tissue.
• Electricity requires a circuit to continuously flow; static electricity is only momentary leading to few hazards.
• Two contact points on the body are needed for shock, motivating electrons to flow (voltage).

Theory of Electrical Shocks

• It is electric current that burns tissue.
• Electrical current requires voltage to motivate it
• Body presents resistance to current.
• Amount of current through a body is equal to the amount of voltage divided by resistance:
• Ohm's Law becomes Current = Voltage / Resistance.
• High voltage results in high current which is dangerous.
• Just how much voltage is dangerous depends on the power of the circuit to oppose the flow of electrons.
• Body resistance varies:
  • Resistance depends on being hand-to-hand
  • Depends on moisture: Sweat (rich with salts and minerals) is excellent conductor.
• Harmful current depends on individual body chemistry.
• Some are highly sensitive, which are indicated in milliamps.
• Emergency responses:
  • Shocked person needs disconnected.
  • Turn off the breaker or switch.
  • Pry/pull with a dry insulated object is breaker is off
  • Apply CPR is necessary to maintain oxygenation

Lightning Protection

• Lightning is a capricious, random and unpredictable event
• Characteristics are:
  • Current levels sometimes exceeding 400 kA
  • Temperatures to 50,000 degrees F
  • Speeds approaching one third the speed of light
  • Globally, some 2000 on-going thunderstorms cause about 100 lightning strikes to earth each second.
• A lightning strike can exceed 100 million Volt Amps.
• Any grounded object provides a path to earth with upwards.
• High voltage currents take the least path of resistance to ground.
• A lightning protection system (LPS) protects by ensuring a low-resistance path to ground.
• Phenomenology of lightning:
  • Downward leaders from the thundercloud pulse.
  • Ground-based objects emit electric activity.
  • Launched upward Streamers
  • Collection zone occurs a few of meters.
  • Leader s and Streamer s connect to a switch.
  • Lightning effects are both direct and indirect.
• An LPS does not attract lightning.
• Buildings at risk are at high altitudes, on hilltops or hillsides, or in isolated positions such as tall towers.