DOMESTIC ELECTRICAL INSTALLATIONS

INTRODUCTION

The Institution of Electrical Engineers (lEE) guide (BS 7671) is used to assist in
design and installation of electrical services. Engineers follow the guide closely to
provide safe and efficient electrical systems in buildings.

Most domestic premises receive a single-phase supply of electricity from an area

electricity board at a rating of 240 volts and frequency of 50 hertz.

The area electricity board's cable, from which the domestic supply is taken, consists
of four lines, three lines each carrying a 240 volt supply and the fourth is the
common return line or neutral which is connected to earth at the transformer or
substation as a safety precaution should a fault occur on the electrical appliance.
Each line or phase is tapped in turn together with the neutral to provide the single-
phase 240 V supply.

ELECTRICITY BOARD INTAKE

The supply or intake cable may enter the building through an underground duct or
via an overhead supply.

An underground supply is preferred since all of the electrical service is hidden.

The supply cable is terminated in the area board’s fused sealing chamber which
should be sited in a dry accessible position. From the sealing chamber the supply
passes through the meter, which records the electricity consumed in units of
kilowatt/hours, to the consumer unit which has a switch controlling the supply to the
circuit breakers or circuit fuses.

These fuses are a protection against excess current or overload of the circuit since
when overloading occurs, the fuse or circuit breaker will isolate the circuit from the
source of the problem.

Sub-circuits

Distribution Combined in a
The consumer unit should be fitted close to the point of service entry and from here
the service is divided into a number of sub-circuits. It is normal in a domestic
installation to separate power circuits and lighting circuits so that if a fault occurs
then not all socket outlets or lights are isolated.

Sometimes an external cabinet is used for easy meter reading. This is located in an
outside wall as shown below.

Cabinet, Cable duct to

lockable inside building

Outside

Plastic pipe for

cable duct

Incoming cable
Foundation

EXTERNAL CABINET
POWER CIRCUITS

When deciding on the number of circuits for a house, a useful rule is; one power
circuit for every 100m2 of floor area. In larger houses this means that two circuits
can be used for power socket outlets, in a two-storey house this would be one
circuit for upstairs and one for downstairs. In some larger houses a separate power
circuit is also installed for the garage / utility area.

In all domestic installations a separate power circuit is required for the cooker since
the electrical demand is likely to be high. The immersion heater in the hot water
cylinder can also be supplied from a separate circuit since a 3kW load is quite high.

Ring circuits are used as a safe and economic method of distribution of electricity
to socket outlets.

Many consumer unit manufacturers produce 8 way and 12 way units.

13 amp, single sock

outlets, twin sock
outlets are common

Ring Circuit, earth not shown for

The drawing below shows the layout of conduit and conductors for a ring circuit in a
small building. Steel or plastic conduit is used in the walls to protect cables from
mechanical damage. The conduit is buried in the wall behind the plaster. This means
that the wall will be tracked to accommodate the circular or oval 20mm diameter
conduit.

The earth conductor may not be covered but the live and neutral are each
separately coated in a PVC covering. The three conductors (L,N & E) can be covered
in an outer covering of PVC to form PVC/PVC Twin and Earth. The typical size of
conductors for a ring circuit for domestic use is 2.5 mm2, this is the cross sectional
area of the conductor. The conductors are pulled through the conduit after it is
installed by a ‘fish’ wire.
Another method of installing a ring circuit may be to distribute the conductors
horizontally under the floor instead of above the ceiling. This reduces the length of
conduit buried in the wall. If a solid cement floor is constructed then the conductors
Steel or plastic
would need to be protected by galvanised steel conduit. conduit buried
If a suspended in wallfloor
timber to
is constructed then a PVC/PVC cable could be clipped to PVC/PVC
protect woodenconductors.
floor joists. This is
the method adopted for two-storey houses, for an upstairs ring circuit.
Twin Socket Conduit contains conductors either
Outlet encapsulated in a cable or individually.
PVC/PVC conduc
incorporating liv
CONSUMER’S MAINS EQUIPMENT and earth (twin
External wall
run at ceiling lev

Internal wall
The consumer's mains equipment is normally fixed close to the point at which the
supply cable enters the building. To meet the requirements of the IEE Regulations it
must provide:

1. Protection against electric shock -Section 471

2. Protection against overcurrent-Section 473
3. Isolation and switching -Section 476.

Protection against electric shock is provided by insulating and placing live parts out
of reach in suitable enclosures, earthing and bonding metal work and providing Conduit to cei
fuses or circuit breakers so that the supply is automatically disconnected under fault level.
conditions. To provide overcorrect protection it is necessary to provide a Consumer
device
which will disconnect the supply automatically before the overload current can
cause a rise in temperature which would damage the installation. A fuse or
miniature circuit breaker (MCB) would meet this requirement.

An isolator is a mechanical device, which is opened manually and is provided so that

the whole of the installation, one circuit or one piece of equipment may be cut off
from the live supply. In addition, a means of switching off for maintenance or
emergency switching must also be provided.

A switch may provide the means of isolation but an isolator differs from a switch in
RING CIRCUIT
that it is intended to be opened when the circuit LAYOUTisINnot
concerned SMALL BUILDING
carrying current.
Its purpose is to ensure the safety of those working on the circuit by making dead
those parts, which are live in normal service. One device may provide both isolation
and switching provided that the characteristics of the device meet the Regulations
for both functions. The switching of electrically operated equipment in normal
service is referred to as functional switching.
Circuits are controlled by switchgear, which is assembled so that the circuit may be
operated safely under normal conditions, isolated automatically under fault
conditions, or isolated manually for safe maintenance.

These requirements are met by good workmanship and the installation of proper
materials such as switches isolators, fuses or circuit breakers.

The equipment belonging to the supply authority is sealed to prevent unauthorised

entry, because if connection were made to the supply before the meter, the energy
used by the consumer would not be recorded on the meter.

In practice it is the aim to bring the Electrical supply to the appliance with as small a
loss of voltage through the conductor as possible. This means that the wiring must
have the smallest resistance that is economical.

EARTHING SYSTEMS

These have been designated in the IEE Regulations using the letters: T, N,
C and S. These letters stand for:

T - terre (French for earth) and meaning a direct connection to earth.

N - neutral
C - combined
S - separate.

When these letters are grouped, they form the classification of a type of
system.
The first letter denotes how the supply source is earthed.
The second denotes how the metalwork of an installation is earthed. The
third and fourth indicate the functions of neutral and protective
conductors.

TT SYSTEM

A TT system has a direct connection to the supply source to earth and a

direct connection of the installation metalwork to earth. An example is an
overhead line supply with earth electrodes, and the mass of earth as a
return path as shown below.
Note that only single-phase systems have been shown for simplicity.

TN-S SYSTEM

A TN-S system has the supply source directly connected to earth, the
installation metalwork connected to the neutral of the supply source via
the lead sheath of the supply cable, and the neutral and protective
conductors throughout the whole system performing separate functions.

The resistance around the loop P-B-N-E should be no more than 0.8 ohms.
TN-C-S SYSTEM
A TN-C-S system is as the TN-S but the supply cable sheath is also the
neutral, i.e. it forms a combined earth/neutral conductor known as a PEN
(protective earthed neutral) conductor.
The installation earth and neutral are separate conductors.
This system is also known as PME (protective multiple earthing).

The resistance around the P-B-N-N loop should be less than 0.35 ohms.

SUMMARY OF EARTHING SYSTEMS

The TT method is used mostly in country areas with overhead transmission lines. In
contrast to the TN-S system there is no metallic path from the consumer's terminals
back to the sub-station transformer secondary windings. Because the earth path
may be of high resistance, a residual current circuit-breaker (R.C.C.B.) is often fitted
so that if a fault current flows in the earth path then a trip disconnects the phase
supply.
For protection against indirect contact in domestic premises, every socket outlet
requires an RCCB with a maximum rated current of 30mA.

The TN-S system of wiring uses the incoming cable sheath as the earth return
path and the phase and neutral have separate conductors. The neutral is then
connected to earth back at the transformer sub-station.
Remember in TN-S, the T stands for earth (terre), N for neutral and S denotes that
the protective (earth) and neutral conductors are separate.

The TN-C-S system has only two conductors in the incoming cable, one phase and
the other neutral. The earth is linked to the neutral at the consumer unit. The
neutral therefore is really a combined earth/neutral conductor hence the name PME.

In order to avoid the risk of serious electric shock, it is important to provide a path
for earth leakage currents to operate the circuit protection, and to endeavour to
maintain all metalwork at the same potential. This is achieved by bonding together
all metalwork of electrical and non-electrical systems to earth.
The path for leakage currents would then be via the earth itself in TT systems or by
a metallic return path in TN-S or TN-C-S systems.
NOTES

Older houses in towns use TNS (solid) i.e. separate earth say cable
sheath.
Around Towns new houses use (PME) TNCS i.e. neutral and earth shared.
Single House in country with own transformer uses TT i.e. own buried
earth electrode.
Petrol stations, Swimming pools, Changing rooms etc. are not allowed to
be PME.

LAMPS

The oldest source of artificial light is the flame from fires, from candles and from oil
lamps where light is produced as one of the products of chemical combustion.
Modern sources of artificial light convert electrical energy light energy and are of
two general types: incandescent sources and discharge sources.

Incandescent Lamps

Incandescent sources produce light by heating

substances to a temperature at which they glow
and are luminous. lncandescence can be achieved
by heating with a flame but in an electric lamp,
such as the light bulb, a metal wire is heated by
an electric current.

Discharge Lamps

Discharge lamps produce light by passing an

electric current through a gas or vapour that has
become ionised and hence able to conduct
electricity. At low gas pressures, a luminous arc or
discharge is formed between the electrodes and
useful quantities of light are given off. Discharge
lamps need special control gear in their circuits
and the colour quality of their light is often poor.
The fluorescent tube is one type of discharge
lamp.
The characteristics of the electric lamps used in modern lighting are summarised
in the table at the end of this section.

Further details of these lamps and their properties are given in the following
sections.

Incandescent Lamps

1. Tungsten Filament Lamps

Electric incandescent lamps work by passing an electric current through a filament

of metal and raising the temperature to white heat. When the metal is
incandescent, at around 2800 K, useful quantities of light are given off. Tungsten is
usually used because it has a high melting point and low rate of evaporation.

To prevent oxidation (burning) of the metal the tungsten coil is sealed inside a glass
envelope and surrounded by an inert atmosphere of uncreative gases such as argon
and nitrogen. During the operation of the lamp tungsten is evaporated from the
filament and deposited on the glass causing it to blacken. The filament therefore
thins and weakens and must eventually break.

The simple tungsten lamp, such as a light bulb, is the oldest, shortest-lived and
least efficient type of electrical light source and is being replaced by more efficient
lamps. But the properties of filament lamps have been greatly improved by using
halogen gases and lower voltages, as described below, and these lamps are useful
in modern lighting design.

2. General Lighting Service Lamp

The general lighting service (GLS) lamp, or common light bulb, has a coiled filament
contained within an envelope (bulb) of glass which may be clear or frosted. inside
the lamp is a fuse and typical construction is shown in

figure 1.2.

FIG. 1.2

TUNGSTEN FILAMENT LAMP

The filament lamp produces a spectral distribution of light which is continuous but
deficient in blue. This quality of light is seen as 'warm' and is considered generally
suitable for social and domestic applications.

The cost of a tungsten filament lamp is low and its installation is simple, but the
relatively short life (1000 hours) of the lamp can cause the labour costs of
replacement to be high. The low luminous efficacy of the lamp produces high
electrical running costs. Only about 5 per cent of the electrical energy is converted
to visible light and most of the energy consumed is given of as heat, especially
radiant (infra-red) heat.
Incandescent lamps come in a variety of shapes and sizes and have a number of
different fittings: Bayonet cap (BC), Small Bayonet cap (SBC), Edison screw (ES or
E27) and Small Edison Screw (SES or E14). The Edison screw types are becoming
more popular in the UK. Several different coatings are also available with the
following properties: Pearl is an all over frosting which diffuses the light and is best
used in a light fitting with shades. Clear bulbs are more attractive when used in
fittings where the bulb is visible or a sparkle is required such as crystal chandeliers.

3. Reflecting Lamps

The relatively large size of the standard tungsten filament lamp makes it difficult to
control the direction of the light.

Spot lamps (PAR) are filament lamps with the glass bulb silvered inside and
shaped to form a parabola with the filament at the focus. This arrangement gives a
directional beam of light which is available in different widths of beam. Sealed beam
lamps use similar techniques.

Crown-silvered lamps (CSL) are standard filament lamps where the glass bulb is
silvered in front. When this lamp is used with a special external reflector it also
gives narrow beams of light.

4. Tungsten-Halogen Lamps

Halogen bulbs produce a very attractive light which closely resembles sunlight.
They are more efficient than incandescent bulbs using only half the energy to
produce the same light output and last twice as long. Generally they are small
lamps which generate a lot of heat so they can only be used in light fittings
designed to cope with the higher temperatures. There are two main types of
halogen lamp available in the domestic market:

Low voltage (12 volts) with transformer and Mains voltage.

Tungsten-halogen lamps have filaments which run at higher temperatures with the
presence of a small quantity of a halogen gas, such as iodine or bromine. When
tungsten evaporates from the filament it is deposited on the hot wall of the lamp
where it combines with the iodine. This new compound is a vapour which carries the
tungsten back onto the lamp and re-deposits it on the hot filament, while the iodine
is also re-cycled.
In order to run at higher temperatures the envelope of the tungsten-halogen lamp is
made of quartz instead of plain glass. The heat-resistance of the quartz allows the
construction of a very small bulb for applications such as spot lamps, projectors and
car headlamps where directional control of light is important. Tungsten-halogen
lamps also have the general advantages over simple tungsten lamps of increased
efficiency and longer life.

5. Low Voltage Systems

Tungsten halogen techniques have allowed the development of low-voltage bulbs

where, because a lower resistance is needed, the filaments can be shorter, thicker
and stronger. A common system uses 12 volt lamps fed from the mains by a
transformer.

The small size of these lamps gives them good directional qualities which make
them popular in shops for the display of goods. The relatively low heat output of
low-voltage systems is also an important property in stores where high levels of
illumination can cause overheating.

Discharge Lamps

Apart from the well-known tubular fluorescent lamp, gas discharge lamps have in
the past been restricted to outdoor lighting, such as for roadways where their
generally poor colour qualities have not been important. Modern types of discharge
lamp have a colour rendering that is good enough for large-scale lighting inside
buildings such as factories and warehouses. Continuing technical advances are
producing more discharge lamps suitable for interior lighting and the high efficacy
of such lamps can give significant savings in the energy use of buildings.

1. Fluorescent Lamps
Fluorescent gas discharge lamps work by passing an electric current through a gas
or vapour so that a luminous arc is established within a glass container.

The energised gas atoms emit ultra-violet (UV) radiation and some blue green
light. A coating of fluorescent powders on the inside of the glass absorbs the UV
radiation and re-radiates this energy in the visible part of the spectrum. The
fluorescent coating therefore increases the efficiency of the system and allows the
colour quality of the light to be controlled.

1.1 Tubular Fluorescent Lamps

The common tubular fluorescent (MCF) lamp is a form of gas

discharge lamp using mercury vapour at low pressure. Figure 2.1
illustrates the construction of a typical lamp and an example of
the electrical control gear that it requires. This gear is needed to
provide a starting pulse of high voltage, to control the discharge
current, and to improve the electrical power factor.

Modern types of control gear use electronic circuits instead of

wire-wound components.
SWITCH-START CIRCUIT QUICK-START CIRCUIT

When the main switch is closed, the mains In this system the cathodes are
heated

is developed across the electrodes, and by a small transformer and the

arc will

because they are close together, a glow not strike until the preheating
period is

discharge takes place between them. completed.

This warms them up and they bend towards

each other until they make contact, allowing

current to flow through the lamp electrodes.

FIG 2.1

FLUORESCENT LAMPS

The colour quality of the light from a fluorescent lamp can be

varied by using suitable mixtures of the metallic phosphors which
make up the fluorescent coating. Lamps are available with colour
temperatures ranging from 3000 K ('warm') to 6500 K ('daylight').
The large surface area of this type of lamp produces lighting of a
relatively non-directional 'flat' quality and with low glare
characteristics.
 Like all discharge lamps, fluorescent lamps continuously decrease
in light output and efficacy as they are run and the lamp should
be replaced after stated number of hours. The lamp will usually
run for longer than its stated life but the light output will then fall
below the levels specified in the lighting design. The exact life of
a discharge lamp also depends on how often the lamp is switched
on or off.

It is possible for the cyclic nature of the gas discharge to be

annoying and to cause a stroboscopic effect - an apparent change
of motion, when viewing moving objects such as machinery.
These effects are avoided by the use of modern electronic control
gear operating at high frequency and the use of new lamps with
shielded electrodes and high-efficiency phosphors.

The luminous efficacy of a tubular fluorescent lamp is at least

five times better than that of a tungsten filament lamp, and
modern types of narrow diameter tube have even higher
efficacies. The initial cost of a fluorescent lamp is higher than that
of the tungsten filament lamp but this is soon offset by the lower
running costs arising from their longer life and cheaper electricity
costs.

6.2 Compact Fluorescent Lamps

Fluorescent lamps are available in compact form comparable in

size to traditional tungsten filament lamp. Some makes have the
control gear incorporated inside the lamp so that they can be
installed in a conventional light fitting, and other types have the
control gear in the fitting. Compact fluorescent lamps give a light
quality suitable for domestic purposes and the use of such lamps
are an important technique for low-energy lighting in homes. The
2-D lamp is small enough to fit into a bulkhead fitting.

2. Mercury Discharge Lamps

An uncorrected mercury lamp emits sharp spectral peaks of light at certain blue and
green wavelengths. A better spectral distribution is obtained by coating the glass
envelope with fluorescent powders (MBF lamps). An MBF lamp is shown below.

FIG 3.1

MERCURY DISCHARGE (MBF) LAMP

In the mercury halide (MBI) lamp, metallic halides are added to the basic gas
discharge in order to produce better colour rendering and to raise the efficacy.

3. Sodium Discharge Lamps

Low-pressure sodium (SOX) lamps produce a distinctive yellow light that is

virtually monochromatic and gives poor colour rendering. However, the efficacy of
the lamps is very high and they have been traditionally used for street lighting. Two
typical lamps are shown below.

TYPE SOX (Na) TYPE SLI (Nat)

Low pressure sodium lamp with Low pressure sodium lamp with
U-shaped arc tube enclosed in specially formed arc tube sealed into

clear outer glass tube, and with a clear glass outer tube.

cap at one end only. Usual ratings - 60W, 140W and 200W.

Usual ratings 35W to 180W.

High-pressure sodium (SON) lamps produce a continuous spectrum without much

blue light but with a colour rendering that is more acceptable than the low-pressure
sodium lamp. SON lamps are used in modern street lighting and for the economic
lighting of large areas such as forecourts and warehouses.

Two typical lamps are shown below.

TYPE SON TYPE SON - T

High pressure sodium lamp with sintered High pressure sodium lamp generally
as

aluminium oxide arc tube and elliptical SON but with a tubular clear glass outer

outer bulb with diffusing coating. bulb - single ended.

Usual ratings 250W to 1000W.

Properties Of Lamps

Luminous Efficacy
The ability of a lamp to convert electrical energy to light energy is measured by its
efficacy which is given by the following formula.

Efficacy = Light output (lumens) / electrical energy input

(Watts)

UNIT: lumens/watt (lm/W).

The electrical running costs of a lamp can be calculated from its efficacy.

The luminous efficacy of a lamp varies with its type and its wattage so exact data
should be obtained from the manufacturer.

A GLS bulb has an efficacy range of 8 to 18 lm/W, a high pressure mercury

fluorescent MBF lamp has a range of 35 to 58 lm/W and a low pressure sodium
(SOX) lamp has a range of 100 to 200 lm/W.

Life

The luminous efficacy of a lamp decreases with time and for a discharge lamp it
may fall by as much as 50 per cent before the lamp fails. The nominal life of a
lamp is usually determined by the manufacturer by considering the failure rate of a
particular model of lamp combined with its fall in light output. In a large installation
it is economically desirable that all the lamps are replaced at the same time on a
specified maintenance schedule.

Colour Temperature

The qualities of light emitted by heated objects depend upon the temperature of the
radiating object and this fact can be used to describe the colour of light. A
theoretically perfect radiator, called a 'black body', is used as the standard for
comparison.
The correlated colour temperature (CCT) of a light source is the absolute
temperature of a perfect radiator when the colour appearance of the radiator best
matches that of the light source.

UNIT: Kelvin (K).

This method of specifying colour quality is most suitable for light sources that emit
a continuous spectrum, such as those giving various types of 'white' light. The lower
values of colour temperature indicate light with a higher red content. Some
examples of colour temperatures are given below.

Clear sky 12 000-24 000 K

Overcast sky 5000-8000 K

Tubular fluorescent lamps 3000-6500 K

Tungsten filament lamps 2700-3100 K

Colour Rendering

The colour appearance of a surface is affected by the quality of light from the
source. Colour rendering is the ability of a light source to reveal the colour
appearance of surfaces. This ability is measured by comparing the appearance of
objects under the light source with their appearance under a reference source such
as daylight.

The same colours, viewed with different light sources, can appear very different.
When choosing clothing from a department store we can find that when we get
home and take it into different lighting conditions it looks different. This because
the different light sources that the article was viewed under gave different colour
appearances.

GLS bulbs and some fluorescent tubes give average to poor colour rendering but
the advanced fluorescent tubes and metal halide lighting can provide excellent
colour rendition.
The colour appearance of a lamp is affected by its operating temperature and a
white source of light can be related to a ‘black body radiator’, this is known as
correlated colour temperature (CCT).

The table below shows the Correlated colour temperature classes.

Correlated Colour
Temperature (CCT) CCT class
(oK)

CCT < 3300 Warm

3300 to 5300 Intermediate

CCT > 5300 Cold

The table below gives typical colour rendering properties for lamps.

Lamp type CCT (oK) Class

GLS bulb 2800 Warm

Fluorescent tubes:
Warm white 2800 Warm
White 3500 Intermediate
Triphosphor 2700 Warm
Low pressure
lamps:
SOX - Sodium Yellow
High pressure
lamps:
MBF- Mercury Cold
fluorescent
SON - Sodium Warm / yellow
SON - Deluxe Warm
MBI - Metal halide Intermediate /
cold
The table below compares various lamps.

COMPARING LAMPS

COLOUR
LUMEN
LAMP REFERENCE WATTAGE
OUTPUT
APPEARANCE
Incandescent bulb GLS 60 Warm 710

Incandescent bulb GLS 150 Warm 2,180

Tungsten halogen TH 750 Warm 16,900

Tungsten halogen TH 1500 Warm 36,300

Fluorescent tube MCF 58 Warm or 4,600

Intermediate or Cold
Compact fluorescent PL 15 Warm 900

Compact fluorescent PL 23 Warm 1,500

Low Pressure sodium SOX 180 Yellow 3,300

High Pressure sodium SON deluxe 150 Warm 12,250

High Pressure sodium SON deluxe 400 Warm 38,000

High Pressure sodium SON plus 400 Warm 54,000

High Pressure mercury MBF 50 Cold 2,000

High Pressure mercury MBF 125 Cold 6,500

High Pressure mercury MBF 400 Cold 22,000

Metal halide MBIF 250 Intermediate cold 19,000

Metal halide MBIF 1000 Intermediate cold 81,000

Types of Light Fitting

The types of light fitting that we use in modern
buildings can be divided into five sections:

1. Decorative lighting

2. Commercial lighting

3. Industrial lighting

4. Outdoor lighting

5. Emergency lighting

Decorative lighting

This includes Downlights, Uplights, Spots and Wall lights.

Downlights
The above photo shows fixed position downlights in compact fluorescent or low
voltage tungsten halogen lamp versions.

• 2 x 13W, 1 x 18W or 2 x 18W 4-limb, 4-pin compact fluorescent options

• Maximum IOOW M28 tungsten halogen capsule lamp option

Specialised Downlights

The heat lamp shown below emits radiant heat and is used in Bathrooms and
shower areas to provide heat.

The infrared output which is unaffected by draughts, warms the body without
heating the surrounding air.

Adjustable Parabolic Downlight

The above Adjustable Parabolic Downlights are complete luminaires, the housing

has an inbuilt plug/socket for instant connection to transformers and extension

leads.

Uplights

Lamp Type: GLS, Tungsten Halogen or Compact Fluorescent.

These Plaster Uplighters can be supplied for the following lamps:

Incandescent Max.100W, Tungsten Halogen Max.200 or Compact Fluorescent

The atrium shown below demonstrates the use of Uplights.

Decorative Uplighter

Some uplighters emit a pleasing glow.

Floor Uplighters

Some offer a decorative feature in a room such as this Bedroom.

Control Spots

Control Spots are easily positioned in any direction to create incisive lighting for
special projects, or simply to light awkward corners and blind spots, providing the
most comprehensive solution to almost every lighting opportunity.

Wide selection of mains and low voltage tungsten halogen and high intensity
discharge lamps provides spectrum of effects from narrow beam to high intensity
spotlighting.

 dimmer enables lumen output to be varied

 transformer

Museum Lighting

Lighting the object with the correct quantity of light in the right place is the task
below.
Walls Lights

Some decorative spheres are shown for use with compact fluorescent lamps, with a
variety of mounting options.
Available in 18W and 26W 4 limb versions
Tungsten halogen and compact fluorescent lamps can be used in this wall light
shown below.
Fibre Optics

A range of fibre optic lighting solutions including interior and exterior

systems with focusable spotlights powered from a remote light
generator.

Suitable for a wide variety of applications including museum lighting,

lighting in confined spaces and spotlighting small objects.

• Uses a 50W MBI-T single ended metal halide lamp.

• up to 12 luminaires can be powered from one source.

Designer Lighting
Table Lamps

Commercial lighting.
This includes Fluorescent fittings as follows;

Fluorescent Fittings

Slimline Fluorescent

Slimline fluorescent luminaires are suitable for use in a very wide range of
applications, particularly those where there is limited mounting space available.

The most common applications are advertising and display lighting, concealed
lighting, under cupboard lighting etc.

Reflector Fluorescent

TYPICAL USES:

Offices, banks, conference areas, schools, shops: areas with VDTs; refurbishment’s.
18W, 36W, 58W standard T8 tubes.

Louvres: highly-specular aluminium.

* Profiled louvre version for effective lighting of shops and general areas.

Fluorescent Battens

TYPICAL USES
Factories, workshops, stores, offices, shops, concealed lighting etc.

Twin Batten

A twin batten luminaire specifically for the 26mm energy saving lamps.

APPLICATIONS:

Schools, offices, kitchens, workshops etc.

Recessed Fluorescent

TYPICAL USES

Offices, showrooms, libraries, schools, supermarkets; areas with VDTs.

Louvres or Prismatic controller

Louvres: highly-specular aluminium, chemically brightened and anodised.

MOUNTING
Recessed.

* For exposed ceilings grids – wide variety of applications ideal for areas where
VDTs are used.

Water Proof Fluorescent

TYPICAL USES

Food factories, dairies, car parks, loading bays, stations, garages.

* IP65 (dust-tight and jetproof): can be hosed down.

Circular Fitting

DESCRIPTION

A fully enclosed circular luminaire with opal diffuser.

APPLICATIONS

Ideal for shops, schools, corridors, hotels etc

VARIATIONS

Available from 27W to 60W with circular fluorescent lamps and in 16W, 28W and
38W 2D energy saving versions.

Fluorescent Square

APPLICATIONS

Offices, shops and other commercial environments

Fluorescent Prismatic Diffuser

for General Purpose commercial, Hospital General Areas, Hospital Wards and
Colleges -

• Clear acrylic prismatic diffuser gives good glare control

Louvred Fluorescent

Constructed from painted extruded aluminium sections and includes an aluminium

reflector.

Decorative Bulkhead

Used in environments where a wall or vertical light source is required but for a more
decorative situation.
Fittings: GLS, 2D and PL.

Industrial lighting

This includes High Bay, Low Bay and Industrial Reflectors

High Bay

High bay luminaires are suited to industrial areas

where mounting heights are sufficient to take
advantage of high intensity lamps.
They are for indoor use and give a variable distribution
particularly suited to factories, stores, warehouses and
sports centres.

The reflector is formed from high quality spun

aluminium and can easily be detached from the control
gear housing.

LAMPS: use elliptical discharge lamps.

Low Bay

APPLICATION

Low bay luminaires have been designed with a shallow profile to enable modern high intensity ligh

sources to be used in situations involving lower mounting heights or restricted head room due to

mobile cranes, gantries etc.

LOCATION:

Warehousing, shops, factories, offices, with mounting heights between 3 - 5 metres.

VARIATIONS

Available either with high pressure sodium, metal halide or mercury vapour lamps.
Industrial Reflector

FEATURES

Reflectors provide a broad light distribution, with

discharge lamps

of 150-400 watts.

Reflector is manufactured from spun aluminium,

brightened and anodised..

APPLICATIONS

The reflector gives a broad light distribution suitable for

indoor industrial use, e.g. factories, stores, warehouses
etc.

Outdoor lighting
This includes Bollards, Floodlights, column Mounted Lights and Lanterns

Bollards

The bollard posts shown below are manufactured from extruded aluminium finished
in textured black powder polyester coat.

Bollards can be set into concrete.

APPLICATION: Car parks, driveways.

Floodlights

Most floodlights offer a variety of lamp options to meet most area and site lighting
requirements.

These floodlights are particularly suited to small area and security lighting.
The floodlight shown below is for exterior use.

The floodlight shown above is for use with Discharge lamps up to 400 Watts.

APPLICATIONS

For outdoor use where general area floodlighting is required e.g.

Car parks, Forecourts, Sports Grounds, Security Areas, Buildings, Industrial Yards
and Goods Areas, Docks, Shipyards, Airports, Railway Complexes, Pedestrian
Shopping Precincts and other large areas.

High Pressure Sodium Floodlights

High pressure sodium floodlight for security applications, building facades and
perimeters, car parks, loading bays and precincts.

The floodlight shown above uses a 70W elliptical SON lamp with internal ignitor

* Especially suitable for local area lighting from low mounting heights of 3-5m for
close offset lighting of buildings
Floodlighting Buildings

The cathedral shown below is a good example of floodlighting for effect.

High pressure sodium floodlights are used for general lighting of car parks,
industrial storage and loading areas, building facades, security and sports lighting
(especially tennis courts).

* 150W and 250W SON-T lamps for economy and long life
* Low glare version available for tennis courts and similar applications

Wide Angle Floodlights

TYPICAL USES:

Exterior: Building facades, signs, sports areas, security lighting, car parks, area
floodlighting.

Interior: Swimming pools, churches, sports facilities.

LAMPS:

* Choice of Metal Halide or SON

• 50W and 70W tubular SON versions available

• 70W version with metal halide lamp

• Integral photocell option

Column Mounted Lights

The column mounted lights shown above have a hemispherical reflector,

eliminating any significant upward light.

Lamps that can be used include high pressure sodium and metal halide.

Lanterns

These are used for major traffic routes utilising a variety of light sources.

Suitable for high output SON lamps.

• Choice of 100W, 150W, 250W and 400W high pressure sodium lamps to meet the
majority of applications

The light shown below is used for city centres, pedestrian areas, parks and
residential thoroughfares.
Lamps used can be high pressure sodium, metal halide or mercury vapour.

The lantern shown below uses the same types as the above fitting.

Used in: corporate office parks, shopping malls and hotels.

 Emergency Lighting.

This includes exit signs and bulkhead fittings.

Exit Signs

The exit signs shown below are suspended from the ceiling.
They utilise 8W fluorescent lamps.

Applications include commercial and public transport facilities, schools, hospitals

and supermarkets.

Available in the following versions:

  for 3 hour non-maintained operation,
 for 3 hour maintained.
 3 hours sustained and mains only versions.

Sealed nickel cadmium batteries cut in automatically as power failure occurs.

Bulkhead

The bulkhead fitting is also used for emergency lighting.

Lighting Levels

The CIBSE (Chartered Institute of Building Services Engineers) produces a Code for
Interior Lighting which gives lighting requirements for areas.

This is also replicated in BS EN 12464-1:2002 Light and lighting - Lighting of work

places - Part 1: Indoor work places

A sample is shown below.

uminance
Activity Area
(lux)
100 Casual seeing Corridors, changing rooms, stores

150 Some perception of detail Loading bays, switch rooms, plant rooms
200 Continuously occupied Foyers, entrance halls, dining rooms

300 Visual tasks moderately easy Libraries, sports halls, lecture theatres.

500 Visual tasks moderately difficult General offices, kitchens, laboratories, retail shops.

750 Visual tasks difficult Drawing offices, meat inspection, chain stores.
General inspection, electronic assembly, paintwork,
1000 Visual tasks very difficult
supermarkets.
1500 Visual tasks extremely difficult Fine work and inspection, precision assembly.

2000 Visual tasks exceptionally difficult Assembly of minute items, finished fabric inspection.

Extracts from CIBSE Code for Lighting Part 2 (2002)

Educational

Illuminance Limiting Glare Minimum colour

Area
(lux) rating rendering (Ra)
Classrooms 300 19 80

TechnicaI drawing room 750 16 80

Computer practice rooms 300 19 80

Healthcare - Wards

Illuminance Limiting Glare Minimum colour

Area
(lux) rating rendering (Ra)
General lighting 100 19 80

Reading lighting 300 19 80

Simple examinations 300 19 80

Examination and treatment 1000 19 80

Hotels and Restaurants

Illuminance Limiting Glare Minimum colour

Area
(lux) rating rendering (Ra)
Kitchen 500 22 80
Restaurant, dining room,
- - 80
function room.
Self service restaurant 200 22 80

Conference rooms 500 19 80

Offices

Illuminance Limiting Glare Minimum colour

Area
(lux) rating rendering (Ra)
Filing, copying etc. 300 19 80
Writing, typing, reading,
500 19 80
data processing
TechnicaI drawing 750 16 80
CAD work stations 500 19 80
Conference and meeting
500 19 80
rooms
Reception desk 300 22 80
Archives 200 25 80
 Residential - Flats /Bedsits

Illuminance Limiting Glare Minimum colour

Area
(lux) rating rendering (Ra)
Lounge 100 - 300 19 80
Kitchens 150 - 300 - 80
Bathrooms 150 - 80
Toilets 100 - 80

Retail Premises

Illuminance Limiting Glare Minimum colour

Area
(lux) rating rendering (Ra)
Sales area 300 22 80
Till area 500 19 80
Wrapper table 500 19 80

Theatres, Concert Halls and Cinemas

Illuminance Limiting Glare Minimum colour

Area
(lux) rating rendering (Ra)
Practice rooms, dressing
300 22 80
rooms
Foyers 200 - -
Auditoria 100 - -
There are also some Lighting Guides from CIBSE that gives details for various
building types, for example;

Lighting Guide 7 (2005): Office lighting

The recommended design maintained illuminance over the task area in any room
where office work is carried out is generally in the range 300 to 500 lux.

Where the tasks are mainly screen based, such as data retrieval or telephone sales,
then illuminances at the lower end of this range should be used.

Where the tasks are mainly document based, such as writing or copy typing, then
500 lux will be required.

Where there are visually more onerous tasks, such as proof reading or technical
drawing, even higher levels should be considered.

The minimum level set by the Health and Safety Executive for any permanently
occupied area is 200 lux.

Lighting Guide 1 (1989): The Industrial Environment

For recommendations of illuminance, colour rendering and glare see Schedule in the
Code for Lighting a summary of key values are given below.

Illuminance
Area
(lux)
Lifts 100
Corridors and stairs 100
Toilets 100
Canteens 300
Mess rooms 150 - 300
Plant rooms 150 - 300
Store rooms 100
More illuminance values are given for a range of industrial buildings in the Guides.

Lumen Method

The quantity of light reaching a certain surface is usually the main

consideration in designing a lighting system.

This quantity of light is specified by illuminance measured in lux, and as

this level varies across the working plane, an average figure is used.

CIBSE Lighting Guides give values of illuminance that are suitable for
various areas.

The section - Lighting Levels in these notes also gives illuminance values.

The lumen method is used to determine the number of lamps that should
be installed for a given area or room.

Calculating for the Lumen Method

The method is a commonly used technique of lighting design, which is valid,

if the light fittings (luminaires) are to be mounted overhead in a regular
pattern.

The luminous flux output (lumens) of each lamp needs to be known as well
as details of the luminaires and the room surfaces.
Usually the illuminance is already specified e.g. office 500 lux, kitchen 300
lux, the designer chooses suitable luminaires and then wishes to know how
many are required.

The number of lamps is given by the formula:

E x A
N =
F x UF x MF

where,

N = number of lamps required.

E = illuminance level required (lux)

A = area at working plane height (m2)

F = average luminous flux from each lamp (lm)

UF= utilisation factor, an allowance for the light distribution of the

luminaire

and the room surfaces.

MF= maintenance factor, an allowance for reduced light

output because of deterioration and dirt.

Example 1

A production area in a factory measures 60 metres x 24 metres.

Find the number of lamps required if each lamp has a Lighting Design
Lumen (LDL) output of 18,000 lumens.

The illumination required for the factory area is 200 lux.

Utilisation factor = 0.4

Lamp Maintenance Factor = 0.75

PLAN

N = ( 200 lux x 60m x 24m ) / ( 18,000 lumens x 0.4 x 0.75 )

N = 53.33

N = 54 lamps.
Spacing

The aim of a good lighting design is to approach uniformity in illumination

over the working plane.

Complete uniformity is impossible in practice, but an acceptable standard is

for the minimum to be at least 70% of the maximum illumination level.

This means, for example, that for a room with an illumination level of 500
lux, if this is taken as the minimum level, then the maximum level in
another part of the room will be no higher than 714 lux as shown below.

500 / 0.7 = 714 lux

Data in manufacturer's catalogues gives the maximum ratio between the

spacing (centre to centre) of the fittings and their height ( to lamp centre)
above the working plane (0.85 metres above f.f.l.)
Example 2

Using data in the previous example show the lighting design layout below.

The spacing to mounting height ratio is 3 : 2.

Spacing distance Mounting
The mounting height (Hm) = 4 metres.
Height
The spacing between lamps is calculated from from Spacing/H m ratio of 3 :
2.
0.85 metres
If the mounting height is 4 m then the maximum spacing is:
Working plane f.f.l.

3/2 = Spacing / 4

Spacing = 1.5 x 4 = 6 metres

The number of rows of lamps is calculated by dividing the width of the

building (24 m) by the spacing:

24 / 6 = 4 rows of lamps

This can be shown below. Half the spacing is used for the ends of rows.

60 metres

Spacing between rows = 6 m

24 metres

Half spacing = 3 m

Scale 1 cm = 4 metres
Factory Plan
The number of lamps in each row can be calculated by dividing the total
number of lamps found in example 1 by the number of rows.

Total lamps 54 / 4 = 13.5 goes up to nearest whole number =

14 lamps in each row.

The longitudinal spacing between lamps can be calculated by dividing the

length of the building by the number of lamps per row.

Length of building 60 m / 14 = 4.28 metres.

There will be half the spacing at both ends = 4.28 / 2

= 2.14 metres

This can be shown below.

Half Spacing 2.14 metres

60 metres

4.28 metres
6m

24 metres

Factory Plan Scale 1 cm = 4 metres

The total array of fittings can be shown below.

4.28 m Light Fittings

60 metres

6m

24 metres

Factory Plan Scale 1 cm = 4 metres

For more even spacing the layout should be re-considered.

The spacing previously was 6 m between rows and 4.28 m between lamps.

If 5 rows of 11 lamps were used then the spacing would be:

Spacing between rows = 24 / 5 = 4.8 metres

Spacing between lamps = 60 / 11 = 5.45 metres

Installed Flux

Sometimes it is useful to know the total amount of light or flux, which has
to be put into a space.

Installed flux (lm) = Number of fittings (N) x Number of lamps per

fitting x L.D.L. output of each lamp (F)

Example 3

A factory measuring 50m x 10m has a lighting scheme consisting of 4 rows

of 25 lighting fittings each housing 2No. 65-Watt fluorescent lamps.

(a) Find the installed flux in total.

(b) What is the installed flux per m2 of floor area.

50m

2.0 m

2.5 m

Factory Plan
The output of the lamps in the above example may be found from
catalogues. For a 65-Watt fluorescent lamp the Lighting Design Lumens
(LDL) is 4400 lm.

(a)

Installed flux (lm) = N x no. lamps/fitting x F

= 4 x 25 x 2 x 4400

= 880,000 lumens

(b)

The floor area = 50 x 10 = 500 m2.

Installed flux per m2 = 880,000 / 500

= 1760 lm/m2.
Example 4

A room measures 15m x 7m x 3.6m high and the design illumination is 200
lux on the working plane (0.85 metres above the floor).

The Utilisation factor is 0.5 and the Maintenance factor is 0.8.

If the LDL output of each fitting is 2720 lumens, calculate;

(a) the number of fittings required.

(b) the fittings layout.

(c) If the spacing/mounting height ratio is 1 : 1 determine whether the

current design is acceptable.

(a) Number of fittings.

N = ( 200 x 15 x 7 ) / ( 2720 x 0.5 x 0.8 )

N = 19.3

N = 20 lamps

(b) Fittings layout

For shallow fittings, the mounting height (H m) may be taken as the distance
form the ceiling to the working plane.

Therefore Hm = 3.6 - 0.85

 Hm = 2.75 metres

If 3 rows of 7 fittings are considered then the spacing is;

(c) Spacing/ mounting height.

Spacing / Hm ratio:

2.33 / 2.75 = 0.847 Therefore ratio is 0.85 : 1.0

2.14 / 2.75 = 0.778 Therefore ratio is 0.78 : 1.0

15 metres

2.33 m
7 metr

2.142 m

Scale 1 cm = 1 metre
Room Plan
Example 5

A room, as shown below, has a design illumination is 500 lux on the working
plane (0.85 metres above the floor).

The Utilisation factor is 0.5 and the Maintenance factor is 0.8.

If the LDL output of each fitting is 2720 lumens, calculate;

(a) the number of fittings required.

(b) the fittings layout.

(c) If the spacing/mounting height ratio is 1 : 1 determine whether the

current design is acceptable.

12 metres
(a)

N = ( 500 x 10 x 12 ) / ( 2720 x 0.5 x 0.8 )

N = 55.15

N = 56 lamps.

(b)

Spacing, say 8 lamps x 7 rows.

Spacing along 12 m wall = 12 / 8 = 1.50 m

Spacing along 10 m wall = 10 / 7 = 1.43 m

(c)

Mounting height = 3.0 - 0.85 = 2.15 m

Desired Ratio = 1:1

Actual ratio = 1.5 / 2.15 = 0.69 Therefore ratio is 0.69 : 1.0

Actual ratio = 1.43 / 2.15 = 0.67 Therefore ratio is 0.67 : 1.0

Lighting Design

Quantity of light

The amount of light emitted from a light fitting is given in lumens (lm)

A lumen is the unit of luminous flux.

The catalogues of light fittings give outputs in lumens; a selection is shown in the
table below.

Light Fitting Watts Lumen Output (lm)

Light bulb (GLS Tungsten) 60 710

Fluorescent tube 58 4,600

Low pressure sodium (SOX) 180 3,300

High pressure sodium (SON) 150 16,000

High pressure mercury (MBF) 125 6,500

High pressure mercury (MBIF) 1000 81,000

The amount of light falling on a surface is measured in lux.

One lux is equal to 1 lumen per square metre …….. 1 lux = 1 lm/m2.

The CIBSE (Chartered Institute of Building Services Engineers) produces a Code for
Interior Lighting which gives lighting requirements for areas.

A sample is shown below.

Illuminance
Activity Area
(lux)
100 Casual seeing Corridors, changing rooms, stores
Loading bays, switch rooms, plant
150 Some perception of detail
rooms
200 Continuously occupied Foyers, entrance halls, dining rooms

300 Visual tasks moderately easy Libraries, sports halls, lecture theatres.
Visual tasks moderately General offices, kitchens, laboratories,
500
difficult retail shops.
Drawing offices, meat inspection, chain
750 Visual tasks difficult
stores.
General inspection, electronic
1000 Visual tasks very difficult
assembly, paintwork, supermarkets.
Fine work and inspection, precision
1500 Visual tasks extremely difficult
assembly.
Visual tasks exceptionally Assembly of minute items, finished
2000
difficult fabric inspection.

Quality of light

Artificial light from lamps can be emitted in various colour spectra and at different
angles fro emitter to receiver.

There are several aspects to be aware of for good design, for example; glare, colour
appearance and colour rendering.

Glare

Glare can render a lighting system less than satisfactory.

Discomfort glare may cause irritation if the occupier is under the effect of a badly
designed system.

Also disability glare can be dangerous if a task is to be carried out and glare has an
adverse effect on the operator.
 Limiting Glare Index

Limiting glare index Applications

16 Museums, art galleries, lecture theatres, control rooms, industrial inspection.

19 Classroom, libraries, laboratories, general offices, fine assembly work.

22 Supermarket, circulation areas, medium assembly work.

25 Boiler houses, rough assembly work.

28 Foundries, works store areas.

Colour Appearance

This is the apparent colour of the light emitted by the lamp and is quantified by its
correlated colour temperature (CCT).

Most lamps produce some form of white light from cool to warm.

This is their colour appearance.

A warmer appearance is suitable for relaxed situations whereas a cooler

appearance is used where high lighting levels are required and in work situations.

Colour Rendering

The CIE colour rendering index is used to compare lamps and quantify how good
they are at reproducing colour.

A set of test colours is reproduced by the lamp of interest relative to how they are
reproduced by an appropriate standard light source.

A perfect colour rendering lamp would give a value of 100.

Some lamps provide good colour rendering properties and this may be necessary in
areas where accurate colour appearance is important such as, car sales showrooms
and clothes retail outlets.
Most rooms have a minimum colour rendering of 80 in the CIE index.

Some rooms where colour is important such as Health Care, Product Colour
Inspection and Art Rooms have an Index of 90.

DAYLIGHT

Since the quality and quantity of daylight is a useful addition to artificial light in
buildings, the challenge to designers is to make use of daylight in an effective way.

For daylight calculations and design it is assumed that the sky is overcast and direct
sunlight is not used. The amount of illumination from a uniform overcast sky at
most is 35,000 lux in July at noon. However a standard figure of 5000 lux may be
used for calculations.

Window location, shape and size will determine the amount of light from outside
that enters a building and how far that light penetrates into the core of the building.
To assess the influence of window size, shape and position the daylight at a point in
a room is quantified by use of the daylight factor.

DAYLIGHT FACTOR

The daylight factor is the ratio of internal illuminance at a point in a room to the
external illuminance.

Internal Illuminance
Daylight factor = X 100%
External Illuminance
Like other light measurements the internal illuminance is normally taken at the
horizontal working plane level i.e. 0.85 metres above floor level.

The table below gives some daylight factor recommendations.

Average Minimum
daylight
Area
Daylight
factor factor
Commercial Buildings:
General office 5% 2%
Classroom 5% 2%
Dwellings:
Kitchen 2%
Living room 1%
Bedroom 0.5%

Example 1

Calculate the illuminance at a point in a room given the daylight factor of 5% if the
external illuminance is 9500 lux.

Internal Illuminance
X 100%
Daylight factor =
External Illuminance

Therefore:

Internal illuminance = ( Daylight factor x External illuminance ) / 100%

Internal illuminance = ( 5 x 9500 ) / 100%

Internal illuminance = 475 lux

Example 2

Calculate the illuminance at a point in a domestic kitchen if the average external

illuminance is 5000 lux.

From the above table the recommended daylight factor for a kitchen is 2%.

Internal illuminance = ( Daylight factor x External illuminance ) / 100%

Internal illuminance = ( 2 x 5000 ) / 100%

Internal illuminance = 100 lux

CONTOURS

Contours of equal amounts of daylight can be produced for rooms to give an

indication of where the illumination from outside falls and the effects of differing
window shapes, as shown below.

2%

5%

10%
15% 15%
20% 20%

Plan
Daylight factor contours
WINDOWS

Windows facing the direction of the sun (south in the northern hemisphere) will
receive more daylight than those facing in the opposite direction.

Tall windows will push the daylight factor contours back into a room while wide
windows give a better distribution across the width of a room but do not let the light
penetrate to the back.

To obtain an internal illuminance of 500 lux the daylight factor would need to be
about 10% in the U.K., this is higher than is normally expected, therefore artificial
light is added to daylight in most buildings. Artificial sources of light are needed at
night time anyway, but this does not mean that we should neglect window design.

One design process is used to ensure that the back of a room is not dull. It uses the
formula as follows:

( L / W + L / W ) shall not exceed 2 / ( 1 – R B)

Where;
L = depth of room from window to back wall (m)

W = room width (m)

H = height from window lintel to floor level (m)

RB = average reflectance of the half of the interior at the back of the room.

CONTROL VALVE SIZING

To obtain good control it is recommended that the valve size is selected so that
its authority is never less than 0.5.
The pressure drop through the valve should therefore be at least equal to the
pressure drop through that part of the system in which the flow is varying, as
shown below.
This requirement applies whether the valve is used in a mixing or diverting
application.
The following procedure should be adopted:
1. Calculate the flow rate of water through the valve in m3/h.

H = m x Cp x T.
Where:
H = Heat load in system (kW)
m = Mass flow rate of water (kg/s)
Cp = Specific heat capacity of water (4.187 kJ/kg degC)
T = Water temperature difference between flow and return
(10degC for L.T.H.W.)
Therefore: m = H / (Cp x T)

Q = ( m /  ) x 3600

Where:
Q = Flow rate in m3/hr
 = Density of water (1000 kg/m3)

2. Find the pressure drop across the valve in bars for a valve authority of 0.5
using the following formula:

Valve authority 0.5 =

It follows that if valve authority is 0.5 then Pvalve equals Pcircuit.

Pvalve = Pcircuit.
1 bar = 100,000
2
N/m
1 bar = 100
2
kN/m .
 NOTE: The pressure drop around the circuit refers to that part of the
circuit where the water flow varies.

3. Find the flow characteristic Kv.

Flow rate Q (m3/hr) = Kv ( Pressure drop across valve in

bars)0.5

Flow rate Q (m3/hr) = Kv (Pvalve )0.5

Therefore:

Flow characteristic Kv = Q / (Pvalve )0.5.

4. Select a valve from a catalogue with this value of Kv.

5. If the valve has a flow characteristic coefficient Kv which is not close to that
required, check the valve authority to see if it is in the range 0.3 to 0.8.

EXAMPLE 1.

A 3-port motorised valve is installed in a heating system as shown below. Size a

suitable valve using information in the Satchwell catalogue for MZX valves.
1. Calculate the flow rate of water through the valve in
m3/h.
m = H / (Cp x T)
Where:
H = Heat load in system (kW)
m = Mass flow rate of water (kg/s)
Cp = Specific heat capacity of water (4.187 kJ/kg degC)
T = Water temperature difference between flow and return
(10degC for L.T.H.W.)

m = 40 / (4.2 x 10)
m = 0.95 kg/s
Q = ( m /  ) x 3600
Where:
Q = Flow rate in m3/hr
 = Density of water (1000 kg/m3)

Q = (0.95 / 1000 ) x 3600

Q = 3.42 m3/h

2. Find the pressure drop across the valve in bars for a valve authority of 0.5
using the following formula:

It follows that if valve authority is 0.5 then Pvalve equals Pcircuit.

Pvalve = Pcircuit.

Pvalve = 20 kN/m2.

Pvalve = 20 / 100 bar = 0.2 bar

3. Find the flow characteristic Kv if:

Flow characteristic Kv = Q / (Pvalve )0.5.

Kv = 3.42 / ( 0.2) 0.5

Kv = 3.42 / 0.4472

Kv = 7.65
4. Select a valve from a catalogue with this value of Kv.

A 1” (25mm) valve has a flow characteristic Kv of 8.

5. Check the valve authority to see if it is in the range 0.3 to 0.8.

Flow characteristic Kv = Q / (Pvalve )0.5.

(Pvalve )0.5 = Q / Kv

Pvalve = (Q / Kv )2

Pvalve = ( 3.42 / 8 ) 2

Pvalve = 0.1828 bar

Pvalve = 18.28 kN/m2.

Pvalve

Pvalve + Pcircuit

Valve authority =

Valve authority =  /  + 20 (kN/m2)

Valve authority =  / 38.28 = 0.48

This valve authority is within the range therefore the valve

size 1” MZX is appropriate.

If a 11/4” valve had been chosen then the Kv from the catalogue
would be 12 and the valve authority would be:

Pvalve = (Q / Kv )2
 Pvalve = ( 3.42 / 12 ) 2
Pvalve = 0.08123 bar
Pvalve = 8.123 kN/m2.

Valve authority =

Valve authority = 8.123 / 8.123  + 20 (kN/m2)

Valve authority = 0.29
This value is too small and the valve would not be
suitable.

Valve and Pump positions

Some manufacturers recommend that MIXING valves are positioned in the flow
with the pump positioned in the return pipe. Also for DIVERTINGapplications
the valve is to be positioned in the return pipe with the pump in the return pipe as
shown below.

Satchwell Recommendations:
MIXING AND DIVERTING APPLICATIONS
These valves must always be installed with two inlet streams and
one outlet stream i.e. as mixers. Reversal of this direction will cause
vibration and water hammer which will damage both valve and
actuator.
For diverting applications the valve must therefore be fitted in the
return pipe.
The water will be diverted with respect to the load, but will mix in
the valve.